Revision: 375
http://www.exim.org/viewvc/pcre2?view=rev&revision=375
Author: ph10
Date: 2015-09-22 17:51:11 +0100 (Tue, 22 Sep 2015)
Log Message:
-----------
Documentation for offset limits.
Modified Paths:
--------------
code/trunk/Makefile.am
code/trunk/doc/html/index.html
code/trunk/doc/html/pcre2api.html
code/trunk/doc/html/pcre2test.html
code/trunk/doc/index.html.src
code/trunk/doc/pcre2.txt
code/trunk/doc/pcre2api.3
code/trunk/doc/pcre2test.1
code/trunk/doc/pcre2test.txt
Added Paths:
-----------
code/trunk/doc/html/pcre2_set_offset_limit.html
code/trunk/doc/pcre2_set_offset_limit.3
Modified: code/trunk/Makefile.am
===================================================================
--- code/trunk/Makefile.am 2015-09-22 16:41:25 UTC (rev 374)
+++ code/trunk/Makefile.am 2015-09-22 16:51:11 UTC (rev 375)
@@ -64,6 +64,7 @@
doc/html/pcre2_set_character_tables.html \
doc/html/pcre2_set_compile_recursion_guard.html \
doc/html/pcre2_set_match_limit.html \
+ doc/html/pcre2_set_offset_limit.html \
doc/html/pcre2_set_newline.html \
doc/html/pcre2_set_parens_nest_limit.html \
doc/html/pcre2_set_recursion_limit.html \
@@ -143,6 +144,7 @@
doc/pcre2_set_character_tables.3 \
doc/pcre2_set_compile_recursion_guard.3 \
doc/pcre2_set_match_limit.3 \
+ doc/pcre2_set_offset_limit.3 \
doc/pcre2_set_newline.3 \
doc/pcre2_set_parens_nest_limit.3 \
doc/pcre2_set_recursion_limit.3 \
Modified: code/trunk/doc/html/index.html
===================================================================
--- code/trunk/doc/html/index.html 2015-09-22 16:41:25 UTC (rev 374)
+++ code/trunk/doc/html/index.html 2015-09-22 16:51:11 UTC (rev 375)
@@ -210,6 +210,9 @@
<tr><td><a href="pcre2_set_match_limit.html">pcre2_set_match_limit</a></td>
<td> Set the match limit</td></tr>
+<tr><td><a href="pcre2_set_offset_limit.html">pcre2_set_offset_limit</a></td>
+ <td> Set the offset limit</td></tr>
+
<tr><td><a href="pcre2_set_newline.html">pcre2_set_newline</a></td>
<td> Set the newline convention</td></tr>
Added: code/trunk/doc/html/pcre2_set_offset_limit.html
===================================================================
--- code/trunk/doc/html/pcre2_set_offset_limit.html (rev 0)
+++ code/trunk/doc/html/pcre2_set_offset_limit.html 2015-09-22 16:51:11 UTC (rev 375)
@@ -0,0 +1,40 @@
+<html>
+<head>
+<title>pcre2_set_offset_limit specification</title>
+</head>
+<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
+<h1>pcre2_set_offset_limit man page</h1>
+<p>
+Return to the <a href="index.html">PCRE2 index page</a>.
+</p>
+<p>
+This page is part of the PCRE2 HTML documentation. It was generated
+automatically from the original man page. If there is any nonsense in it,
+please consult the man page, in case the conversion went wrong.
+<br>
+<br><b>
+SYNOPSIS
+</b><br>
+<P>
+<b>#include <pcre2.h></b>
+</P>
+<P>
+<b>int pcre2_set_offset_limit(pcre2_match_context *<i>mcontext</i>,</b>
+<b> PCRE2_SIZE <i>value</i>);</b>
+</P>
+<br><b>
+DESCRIPTION
+</b><br>
+<P>
+This function sets the offset limit field in a match context. The result is
+always zero.
+</P>
+<P>
+There is a complete description of the PCRE2 native API in the
+<a href="pcre2api.html"><b>pcre2api</b></a>
+page and a description of the POSIX API in the
+<a href="pcre2posix.html"><b>pcre2posix</b></a>
+page.
+<p>
+Return to the <a href="index.html">PCRE2 index page</a>.
+</p>
Modified: code/trunk/doc/html/pcre2api.html
===================================================================
--- code/trunk/doc/html/pcre2api.html 2015-09-22 16:41:25 UTC (rev 374)
+++ code/trunk/doc/html/pcre2api.html 2015-09-22 16:51:11 UTC (rev 375)
@@ -176,6 +176,10 @@
<b> uint32_t <i>value</i>);</b>
<br>
<br>
+<b>int pcre2_set_offset_limit(pcre2_match_context *<i>mcontext</i>,</b>
+<b> PCRE2_SIZE <i>value</i>);</b>
+<br>
+<br>
<b>int pcre2_set_recursion_limit(pcre2_match_context *<i>mcontext</i>,</b>
<b> uint32_t <i>value</i>);</b>
<br>
@@ -697,6 +701,7 @@
of the following match-time parameters:
<pre>
A callout function
+ The offset limit for matching an unanchored pattern
The limit for calling <i>match()</i>
The limit for calling <i>match()</i> recursively
</pre>
@@ -729,6 +734,30 @@
during a matching operation. Details are given in the
<a href="pcre2callout.html"><b>pcre2callout</b></a>
documentation.
+<b>int pcre2_set_offset_limit(pcre2_match_context *<i>mcontext</i>,</b>
+<b> PCRE2_SIZE <i>value</i>);</b>
+<br>
+<br>
+The <i>offset_limit</i> parameter limits how far an unanchored search can
+advance in the subject string. The default value is PCRE2_UNSET. The
+<b>pcre2_match()</b> and <b>pcre2_dfa_match()</b> functions return
+PCRE2_ERROR_NOMATCH if a match with a starting point before or at the given
+offset is not found. For example, if the pattern /abc/ is matched against
+"123abc" with an offset limit less than 3, the result is PCRE2_ERROR_NO_MATCH.
+A match can never be found if the <i>startoffset</i> argument of
+<b>pcre2_match()</b> or <b>pcre2_dfa_match()</b> is greater than the offset
+limit.
+</P>
+<P>
+When using this facility, you must set PCRE2_USE_OFFSET_LIMIT when calling
+<b>pcre2_compile()</b> so that when JIT is in use, different code can be
+compiled. If a match is started with a non-default match limit when
+PCRE2_USE_OFFSET_LIMIT is not set, an error is generated.
+</P>
+<P>
+The offset limit facility can be used to track progress when searching large
+subject strings. See also the PCRE2_FIRSTLINE option, which requires a match to
+start within the first line of the subject.
<b>int pcre2_set_match_limit(pcre2_match_context *<i>mcontext</i>,</b>
<b> uint32_t <i>value</i>);</b>
<br>
@@ -1168,7 +1197,8 @@
</pre>
If this option is set, an unanchored pattern is required to match before or at
the first newline in the subject string, though the matched text may continue
-over the newline.
+over the newline. See also PCRE2_USE_OFFSET_LIMIT, which provides a more
+general limiting facility.
<pre>
PCRE2_MATCH_UNSET_BACKREF
</pre>
@@ -1351,6 +1381,17 @@
greedy by default, but become greedy if followed by "?". It is not compatible
with Perl. It can also be set by a (?U) option setting within the pattern.
<pre>
+ PCRE2_USE_OFFSET_LIMIT
+</pre>
+This option must be set for <b>pcre2_compile()</b> if
+<b>pcre2_set_offset_limit()</b> is going to be used to set a non-default offset
+limit in a match context for matches that use this pattern. An error is
+generated if an offset limit is set without this option. For more details, see
+the description of <b>pcre2_set_offset_limit()</b> in the
+<a href="#matchcontext">section</a>
+that describes match contexts. See also the PCRE2_FIRSTLINE
+option above.
+<pre>
PCRE2_UTF
</pre>
This option causes PCRE2 to regard both the pattern and the subject strings
@@ -2912,7 +2953,7 @@
</P>
<br><a name="SEC40" href="#TOC1">REVISION</a><br>
<P>
-Last updated: 02 September 2015
+Last updated: 22 September 2015
<br>
Copyright © 1997-2015 University of Cambridge.
<br>
Modified: code/trunk/doc/html/pcre2test.html
===================================================================
--- code/trunk/doc/html/pcre2test.html 2015-09-22 16:41:25 UTC (rev 374)
+++ code/trunk/doc/html/pcre2test.html 2015-09-22 16:51:11 UTC (rev 375)
@@ -485,6 +485,12 @@
<pre>
abc\=notbol,notempty
</pre>
+If the subject string is empty and \= is followed by whitespace, the line is
+treated as a comment line, and is not used for matching. For example:
+<pre>
+ \= This is a comment.
+ abc\= This is an invalid modifier list.
+</pre>
A backslash followed by any other non-alphanumeric character just escapes that
character. A backslash followed by anything else causes an error. However, if
the very last character in the line is a backslash (and there is no modifier
@@ -691,9 +697,9 @@
to <b>pcre2_match()</b> with either the PCRE2_PARTIAL_SOFT or the
PCRE2_PARTIAL_HARD option set. Note that such a call may return a complete
match; the options enable the possibility of a partial match, but do not
-require it. Note also that if you request JIT compilation only for partial
-matching (for example, /jit=2) but do not set the <b>partial</b> modifier on a
-subject line, that match will not use JIT code because none was compiled for
+require it. Note also that if you request JIT compilation only for partial
+matching (for example, /jit=2) but do not set the <b>partial</b> modifier on a
+subject line, that match will not use JIT code because none was compiled for
non-partial matching.
</P>
<P>
@@ -1533,7 +1539,7 @@
</P>
<br><a name="SEC21" href="#TOC1">REVISION</a><br>
<P>
-Last updated: 12 September 2015
+Last updated: 14 September 2015
<br>
Copyright © 1997-2015 University of Cambridge.
<br>
Modified: code/trunk/doc/index.html.src
===================================================================
--- code/trunk/doc/index.html.src 2015-09-22 16:41:25 UTC (rev 374)
+++ code/trunk/doc/index.html.src 2015-09-22 16:51:11 UTC (rev 375)
@@ -210,6 +210,9 @@
<tr><td><a href="pcre2_set_match_limit.html">pcre2_set_match_limit</a></td>
<td> Set the match limit</td></tr>
+<tr><td><a href="pcre2_set_offset_limit.html">pcre2_set_offset_limit</a></td>
+ <td> Set the offset limit</td></tr>
+
<tr><td><a href="pcre2_set_newline.html">pcre2_set_newline</a></td>
<td> Set the newline convention</td></tr>
Modified: code/trunk/doc/pcre2.txt
===================================================================
--- code/trunk/doc/pcre2.txt 2015-09-22 16:41:25 UTC (rev 374)
+++ code/trunk/doc/pcre2.txt 2015-09-22 16:51:11 UTC (rev 375)
@@ -278,6 +278,9 @@
int pcre2_set_match_limit(pcre2_match_context *mcontext,
uint32_t value);
+ int pcre2_set_offset_limit(pcre2_match_context *mcontext,
+ PCRE2_SIZE value);
+
int pcre2_set_recursion_limit(pcre2_match_context *mcontext,
uint32_t value);
@@ -755,6 +758,7 @@
any of the following match-time parameters:
A callout function
+ The offset limit for matching an unanchored pattern
The limit for calling match()
The limit for calling match() recursively
@@ -785,40 +789,62 @@
points during a matching operation. Details are given in the pcre2call-
out documentation.
+ int pcre2_set_offset_limit(pcre2_match_context *mcontext,
+ PCRE2_SIZE value);
+
+ The offset_limit parameter limits how far an unanchored search can
+ advance in the subject string. The default value is PCRE2_UNSET. The
+ pcre2_match() and pcre2_dfa_match() functions return
+ PCRE2_ERROR_NOMATCH if a match with a starting point before or at the
+ given offset is not found. For example, if the pattern /abc/ is matched
+ against "123abc" with an offset limit less than 3, the result is
+ PCRE2_ERROR_NO_MATCH. A match can never be found if the startoffset
+ argument of pcre2_match() or pcre2_dfa_match() is greater than the off-
+ set limit.
+
+ When using this facility, you must set PCRE2_USE_OFFSET_LIMIT when
+ calling pcre2_compile() so that when JIT is in use, different code can
+ be compiled. If a match is started with a non-default match limit when
+ PCRE2_USE_OFFSET_LIMIT is not set, an error is generated.
+
+ The offset limit facility can be used to track progress when searching
+ large subject strings. See also the PCRE2_FIRSTLINE option, which
+ requires a match to start within the first line of the subject.
+
int pcre2_set_match_limit(pcre2_match_context *mcontext,
uint32_t value);
- The match_limit parameter provides a means of preventing PCRE2 from
+ The match_limit parameter provides a means of preventing PCRE2 from
using up too many resources when processing patterns that are not going
- to match, but which have a very large number of possibilities in their
- search trees. The classic example is a pattern that uses nested unlim-
+ to match, but which have a very large number of possibilities in their
+ search trees. The classic example is a pattern that uses nested unlim-
ited repeats.
- Internally, pcre2_match() uses a function called match(), which it
- calls repeatedly (sometimes recursively). The limit set by match_limit
- is imposed on the number of times this function is called during a
+ Internally, pcre2_match() uses a function called match(), which it
+ calls repeatedly (sometimes recursively). The limit set by match_limit
+ is imposed on the number of times this function is called during a
match, which has the effect of limiting the amount of backtracking that
- can take place. For patterns that are not anchored, the count restarts
- from zero for each position in the subject string. This limit is not
+ can take place. For patterns that are not anchored, the count restarts
+ from zero for each position in the subject string. This limit is not
relevant to pcre2_dfa_match(), which ignores it.
- When pcre2_match() is called with a pattern that was successfully pro-
+ When pcre2_match() is called with a pattern that was successfully pro-
cessed by pcre2_jit_compile(), the way in which matching is executed is
- entirely different. However, there is still the possibility of runaway
- matching that goes on for a very long time, and so the match_limit
- value is also used in this case (but in a different way) to limit how
+ entirely different. However, there is still the possibility of runaway
+ matching that goes on for a very long time, and so the match_limit
+ value is also used in this case (but in a different way) to limit how
long the matching can continue.
- The default value for the limit can be set when PCRE2 is built; the
- default default is 10 million, which handles all but the most extreme
- cases. If the limit is exceeded, pcre2_match() returns
- PCRE2_ERROR_MATCHLIMIT. A value for the match limit may also be sup-
+ The default value for the limit can be set when PCRE2 is built; the
+ default default is 10 million, which handles all but the most extreme
+ cases. If the limit is exceeded, pcre2_match() returns
+ PCRE2_ERROR_MATCHLIMIT. A value for the match limit may also be sup-
plied by an item at the start of a pattern of the form
(*LIMIT_MATCH=ddd)
- where ddd is a decimal number. However, such a setting is ignored
- unless ddd is less than the limit set by the caller of pcre2_match()
+ where ddd is a decimal number. However, such a setting is ignored
+ unless ddd is less than the limit set by the caller of pcre2_match()
or, if no such limit is set, less than the default.
int pcre2_set_recursion_limit(pcre2_match_context *mcontext,
@@ -825,27 +851,27 @@
uint32_t value);
The recursion_limit parameter is similar to match_limit, but instead of
- limiting the total number of times that match() is called, it limits
- the depth of recursion. The recursion depth is a smaller number than
- the total number of calls, because not all calls to match() are recur-
+ limiting the total number of times that match() is called, it limits
+ the depth of recursion. The recursion depth is a smaller number than
+ the total number of calls, because not all calls to match() are recur-
sive. This limit is of use only if it is set smaller than match_limit.
Limiting the recursion depth limits the amount of system stack that can
- be used, or, when PCRE2 has been compiled to use memory on the heap
- instead of the stack, the amount of heap memory that can be used. This
- limit is not relevant, and is ignored, when matching is done using JIT
+ be used, or, when PCRE2 has been compiled to use memory on the heap
+ instead of the stack, the amount of heap memory that can be used. This
+ limit is not relevant, and is ignored, when matching is done using JIT
compiled code or by the pcre2_dfa_match() function.
- The default value for recursion_limit can be set when PCRE2 is built;
- the default default is the same value as the default for match_limit.
- If the limit is exceeded, pcre2_match() returns PCRE2_ERROR_RECURSION-
- LIMIT. A value for the recursion limit may also be supplied by an item
+ The default value for recursion_limit can be set when PCRE2 is built;
+ the default default is the same value as the default for match_limit.
+ If the limit is exceeded, pcre2_match() returns PCRE2_ERROR_RECURSION-
+ LIMIT. A value for the recursion limit may also be supplied by an item
at the start of a pattern of the form
(*LIMIT_RECURSION=ddd)
- where ddd is a decimal number. However, such a setting is ignored
- unless ddd is less than the limit set by the caller of pcre2_match()
+ where ddd is a decimal number. However, such a setting is ignored
+ unless ddd is less than the limit set by the caller of pcre2_match()
or, if no such limit is set, less than the default.
int pcre2_set_recursion_memory_management(
@@ -854,21 +880,21 @@
void (*private_free)(void *, void *), void *memory_data);
This function sets up two additional custom memory management functions
- for use by pcre2_match() when PCRE2 is compiled to use the heap for
+ for use by pcre2_match() when PCRE2 is compiled to use the heap for
remembering backtracking data, instead of recursive function calls that
- use the system stack. There is a discussion about PCRE2's stack usage
- in the pcre2stack documentation. See the pcre2build documentation for
+ use the system stack. There is a discussion about PCRE2's stack usage
+ in the pcre2stack documentation. See the pcre2build documentation for
details of how to build PCRE2.
- Using the heap for recursion is a non-standard way of building PCRE2,
- for use in environments that have limited stacks. Because of the
+ Using the heap for recursion is a non-standard way of building PCRE2,
+ for use in environments that have limited stacks. Because of the
greater use of memory management, pcre2_match() runs more slowly. Func-
- tions that are different to the general custom memory functions are
- provided so that special-purpose external code can be used for this
- case, because the memory blocks are all the same size. The blocks are
+ tions that are different to the general custom memory functions are
+ provided so that special-purpose external code can be used for this
+ case, because the memory blocks are all the same size. The blocks are
retained by pcre2_match() until it is about to exit so that they can be
- re-used when possible during the match. In the absence of these func-
- tions, the normal custom memory management functions are used, if sup-
+ re-used when possible during the match. In the absence of these func-
+ tions, the normal custom memory management functions are used, if sup-
plied, otherwise the system functions.
@@ -876,75 +902,75 @@
int pcre2_config(uint32_t what, void *where);
- The function pcre2_config() makes it possible for a PCRE2 client to
- discover which optional features have been compiled into the PCRE2
- library. The pcre2build documentation has more details about these
+ The function pcre2_config() makes it possible for a PCRE2 client to
+ discover which optional features have been compiled into the PCRE2
+ library. The pcre2build documentation has more details about these
optional features.
- The first argument for pcre2_config() specifies which information is
- required. The second argument is a pointer to memory into which the
- information is placed. If NULL is passed, the function returns the
- amount of memory that is needed for the requested information. For
- calls that return numerical values, the value is in bytes; when
- requesting these values, where should point to appropriately aligned
- memory. For calls that return strings, the required length is given in
+ The first argument for pcre2_config() specifies which information is
+ required. The second argument is a pointer to memory into which the
+ information is placed. If NULL is passed, the function returns the
+ amount of memory that is needed for the requested information. For
+ calls that return numerical values, the value is in bytes; when
+ requesting these values, where should point to appropriately aligned
+ memory. For calls that return strings, the required length is given in
code units, not counting the terminating zero.
- When requesting information, the returned value from pcre2_config() is
- non-negative on success, or the negative error code PCRE2_ERROR_BADOP-
- TION if the value in the first argument is not recognized. The follow-
+ When requesting information, the returned value from pcre2_config() is
+ non-negative on success, or the negative error code PCRE2_ERROR_BADOP-
+ TION if the value in the first argument is not recognized. The follow-
ing information is available:
PCRE2_CONFIG_BSR
- The output is a uint32_t integer whose value indicates what character
- sequences the \R escape sequence matches by default. A value of
+ The output is a uint32_t integer whose value indicates what character
+ sequences the \R escape sequence matches by default. A value of
PCRE2_BSR_UNICODE means that \R matches any Unicode line ending
- sequence; a value of PCRE2_BSR_ANYCRLF means that \R matches only CR,
+ sequence; a value of PCRE2_BSR_ANYCRLF means that \R matches only CR,
LF, or CRLF. The default can be overridden when a pattern is compiled.
PCRE2_CONFIG_JIT
- The output is a uint32_t integer that is set to one if support for
+ The output is a uint32_t integer that is set to one if support for
just-in-time compiling is available; otherwise it is set to zero.
PCRE2_CONFIG_JITTARGET
- The where argument should point to a buffer that is at least 48 code
- units long. (The exact length required can be found by calling
- pcre2_config() with where set to NULL.) The buffer is filled with a
- string that contains the name of the architecture for which the JIT
- compiler is configured, for example "x86 32bit (little endian +
- unaligned)". If JIT support is not available, PCRE2_ERROR_BADOPTION is
- returned, otherwise the number of code units used is returned. This is
+ The where argument should point to a buffer that is at least 48 code
+ units long. (The exact length required can be found by calling
+ pcre2_config() with where set to NULL.) The buffer is filled with a
+ string that contains the name of the architecture for which the JIT
+ compiler is configured, for example "x86 32bit (little endian +
+ unaligned)". If JIT support is not available, PCRE2_ERROR_BADOPTION is
+ returned, otherwise the number of code units used is returned. This is
the length of the string, plus one unit for the terminating zero.
PCRE2_CONFIG_LINKSIZE
The output is a uint32_t integer that contains the number of bytes used
- for internal linkage in compiled regular expressions. When PCRE2 is
- configured, the value can be set to 2, 3, or 4, with the default being
- 2. This is the value that is returned by pcre2_config(). However, when
- the 16-bit library is compiled, a value of 3 is rounded up to 4, and
- when the 32-bit library is compiled, internal linkages always use 4
+ for internal linkage in compiled regular expressions. When PCRE2 is
+ configured, the value can be set to 2, 3, or 4, with the default being
+ 2. This is the value that is returned by pcre2_config(). However, when
+ the 16-bit library is compiled, a value of 3 is rounded up to 4, and
+ when the 32-bit library is compiled, internal linkages always use 4
bytes, so the configured value is not relevant.
The default value of 2 for the 8-bit and 16-bit libraries is sufficient
- for all but the most massive patterns, since it allows the size of the
+ for all but the most massive patterns, since it allows the size of the
compiled pattern to be up to 64K code units. Larger values allow larger
- regular expressions to be compiled by those two libraries, but at the
+ regular expressions to be compiled by those two libraries, but at the
expense of slower matching.
PCRE2_CONFIG_MATCHLIMIT
- The output is a uint32_t integer that gives the default limit for the
- number of internal matching function calls in a pcre2_match() execu-
+ The output is a uint32_t integer that gives the default limit for the
+ number of internal matching function calls in a pcre2_match() execu-
tion. Further details are given with pcre2_match() below.
PCRE2_CONFIG_NEWLINE
- The output is a uint32_t integer whose value specifies the default
- character sequence that is recognized as meaning "newline". The values
+ The output is a uint32_t integer whose value specifies the default
+ character sequence that is recognized as meaning "newline". The values
are:
PCRE2_NEWLINE_CR Carriage return (CR)
@@ -953,56 +979,56 @@
PCRE2_NEWLINE_ANY Any Unicode line ending
PCRE2_NEWLINE_ANYCRLF Any of CR, LF, or CRLF
- The default should normally correspond to the standard sequence for
+ The default should normally correspond to the standard sequence for
your operating system.
PCRE2_CONFIG_PARENSLIMIT
- The output is a uint32_t integer that gives the maximum depth of nest-
+ The output is a uint32_t integer that gives the maximum depth of nest-
ing of parentheses (of any kind) in a pattern. This limit is imposed to
- cap the amount of system stack used when a pattern is compiled. It is
- specified when PCRE2 is built; the default is 250. This limit does not
- take into account the stack that may already be used by the calling
- application. For finer control over compilation stack usage, see
+ cap the amount of system stack used when a pattern is compiled. It is
+ specified when PCRE2 is built; the default is 250. This limit does not
+ take into account the stack that may already be used by the calling
+ application. For finer control over compilation stack usage, see
pcre2_set_compile_recursion_guard().
PCRE2_CONFIG_RECURSIONLIMIT
- The output is a uint32_t integer that gives the default limit for the
- depth of recursion when calling the internal matching function in a
- pcre2_match() execution. Further details are given with pcre2_match()
+ The output is a uint32_t integer that gives the default limit for the
+ depth of recursion when calling the internal matching function in a
+ pcre2_match() execution. Further details are given with pcre2_match()
below.
PCRE2_CONFIG_STACKRECURSE
- The output is a uint32_t integer that is set to one if internal recur-
- sion when running pcre2_match() is implemented by recursive function
- calls that use the system stack to remember their state. This is the
- usual way that PCRE2 is compiled. The output is zero if PCRE2 was com-
- piled to use blocks of data on the heap instead of recursive function
+ The output is a uint32_t integer that is set to one if internal recur-
+ sion when running pcre2_match() is implemented by recursive function
+ calls that use the system stack to remember their state. This is the
+ usual way that PCRE2 is compiled. The output is zero if PCRE2 was com-
+ piled to use blocks of data on the heap instead of recursive function
calls.
PCRE2_CONFIG_UNICODE_VERSION
- The where argument should point to a buffer that is at least 24 code
- units long. (The exact length required can be found by calling
- pcre2_config() with where set to NULL.) If PCRE2 has been compiled
- without Unicode support, the buffer is filled with the text "Unicode
- not supported". Otherwise, the Unicode version string (for example,
- "8.0.0") is inserted. The number of code units used is returned. This
+ The where argument should point to a buffer that is at least 24 code
+ units long. (The exact length required can be found by calling
+ pcre2_config() with where set to NULL.) If PCRE2 has been compiled
+ without Unicode support, the buffer is filled with the text "Unicode
+ not supported". Otherwise, the Unicode version string (for example,
+ "8.0.0") is inserted. The number of code units used is returned. This
is the length of the string plus one unit for the terminating zero.
PCRE2_CONFIG_UNICODE
- The output is a uint32_t integer that is set to one if Unicode support
- is available; otherwise it is set to zero. Unicode support implies UTF
+ The output is a uint32_t integer that is set to one if Unicode support
+ is available; otherwise it is set to zero. Unicode support implies UTF
support.
PCRE2_CONFIG_VERSION
- The where argument should point to a buffer that is at least 12 code
- units long. (The exact length required can be found by calling
- pcre2_config() with where set to NULL.) The buffer is filled with the
+ The where argument should point to a buffer that is at least 12 code
+ units long. (The exact length required can be found by calling
+ pcre2_config() with where set to NULL.) The buffer is filled with the
PCRE2 version string, zero-terminated. The number of code units used is
returned. This is the length of the string plus one unit for the termi-
nating zero.
@@ -1016,58 +1042,58 @@
void pcre2_code_free(pcre2_code *code);
- The pcre2_compile() function compiles a pattern into an internal form.
- The pattern is defined by a pointer to a string of code units and a
- length, If the pattern is zero-terminated, the length can be specified
- as PCRE2_ZERO_TERMINATED. The function returns a pointer to a block of
- memory that contains the compiled pattern and related data. The caller
- must free the memory by calling pcre2_code_free() when it is no longer
+ The pcre2_compile() function compiles a pattern into an internal form.
+ The pattern is defined by a pointer to a string of code units and a
+ length, If the pattern is zero-terminated, the length can be specified
+ as PCRE2_ZERO_TERMINATED. The function returns a pointer to a block of
+ memory that contains the compiled pattern and related data. The caller
+ must free the memory by calling pcre2_code_free() when it is no longer
needed.
- NOTE: When one of the matching functions is called, pointers to the
+ NOTE: When one of the matching functions is called, pointers to the
compiled pattern and the subject string are set in the match data block
- so that they can be referenced by the extraction functions. After run-
- ning a match, you must not free a compiled pattern (or a subject
- string) until after all operations on the match data block have taken
+ so that they can be referenced by the extraction functions. After run-
+ ning a match, you must not free a compiled pattern (or a subject
+ string) until after all operations on the match data block have taken
place.
- If the compile context argument ccontext is NULL, memory for the com-
- piled pattern is obtained by calling malloc(). Otherwise, it is
- obtained from the same memory function that was used for the compile
+ If the compile context argument ccontext is NULL, memory for the com-
+ piled pattern is obtained by calling malloc(). Otherwise, it is
+ obtained from the same memory function that was used for the compile
context.
The options argument contains various bit settings that affect the com-
- pilation. It should be zero if no options are required. The available
- options are described below. Some of them (in particular, those that
- are compatible with Perl, but some others as well) can also be set and
- unset from within the pattern (see the detailed description in the
+ pilation. It should be zero if no options are required. The available
+ options are described below. Some of them (in particular, those that
+ are compatible with Perl, but some others as well) can also be set and
+ unset from within the pattern (see the detailed description in the
pcre2pattern documentation).
- For those options that can be different in different parts of the pat-
- tern, the contents of the options argument specifies their settings at
- the start of compilation. The PCRE2_ANCHORED and PCRE2_NO_UTF_CHECK
+ For those options that can be different in different parts of the pat-
+ tern, the contents of the options argument specifies their settings at
+ the start of compilation. The PCRE2_ANCHORED and PCRE2_NO_UTF_CHECK
options can be set at the time of matching as well as at compile time.
- Other, less frequently required compile-time parameters (for example,
+ Other, less frequently required compile-time parameters (for example,
the newline setting) can be provided in a compile context (as described
above).
If errorcode or erroroffset is NULL, pcre2_compile() returns NULL imme-
- diately. Otherwise, if compilation of a pattern fails, pcre2_compile()
+ diately. Otherwise, if compilation of a pattern fails, pcre2_compile()
returns NULL, having set these variables to an error code and an offset
- (number of code units) within the pattern, respectively. The
- pcre2_get_error_message() function provides a textual message for each
+ (number of code units) within the pattern, respectively. The
+ pcre2_get_error_message() function provides a textual message for each
error code. Compilation errors are positive numbers, but UTF formatting
errors are negative numbers. For an invalid UTF-8 or UTF-16 string, the
offset is that of the first code unit of the failing character.
- Some errors are not detected until the whole pattern has been scanned;
- in these cases, the offset passed back is the length of the pattern.
- Note that the offset is in code units, not characters, even in a UTF
+ Some errors are not detected until the whole pattern has been scanned;
+ in these cases, the offset passed back is the length of the pattern.
+ Note that the offset is in code units, not characters, even in a UTF
mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char-
acter.
- This code fragment shows a typical straightforward call to pcre2_com-
+ This code fragment shows a typical straightforward call to pcre2_com-
pile():
pcre2_code *re;
@@ -1081,28 +1107,28 @@
&erroffset, /* for error offset */
NULL); /* no compile context */
- The following names for option bits are defined in the pcre2.h header
+ The following names for option bits are defined in the pcre2.h header
file:
PCRE2_ANCHORED
If this bit is set, the pattern is forced to be "anchored", that is, it
- is constrained to match only at the first matching point in the string
- that is being searched (the "subject string"). This effect can also be
- achieved by appropriate constructs in the pattern itself, which is the
+ is constrained to match only at the first matching point in the string
+ that is being searched (the "subject string"). This effect can also be
+ achieved by appropriate constructs in the pattern itself, which is the
only way to do it in Perl.
PCRE2_ALLOW_EMPTY_CLASS
- By default, for compatibility with Perl, a closing square bracket that
- immediately follows an opening one is treated as a data character for
- the class. When PCRE2_ALLOW_EMPTY_CLASS is set, it terminates the
+ By default, for compatibility with Perl, a closing square bracket that
+ immediately follows an opening one is treated as a data character for
+ the class. When PCRE2_ALLOW_EMPTY_CLASS is set, it terminates the
class, which therefore contains no characters and so can never match.
PCRE2_ALT_BSUX
- This option request alternative handling of three escape sequences,
- which makes PCRE2's behaviour more like ECMAscript (aka JavaScript).
+ This option request alternative handling of three escape sequences,
+ which makes PCRE2's behaviour more like ECMAscript (aka JavaScript).
When it is set:
(1) \U matches an upper case "U" character; by default \U causes a com-
@@ -1109,13 +1135,13 @@
pile time error (Perl uses \U to upper case subsequent characters).
(2) \u matches a lower case "u" character unless it is followed by four
- hexadecimal digits, in which case the hexadecimal number defines the
- code point to match. By default, \u causes a compile time error (Perl
+ hexadecimal digits, in which case the hexadecimal number defines the
+ code point to match. By default, \u causes a compile time error (Perl
uses it to upper case the following character).
- (3) \x matches a lower case "x" character unless it is followed by two
- hexadecimal digits, in which case the hexadecimal number defines the
- code point to match. By default, as in Perl, a hexadecimal number is
+ (3) \x matches a lower case "x" character unless it is followed by two
+ hexadecimal digits, in which case the hexadecimal number defines the
+ code point to match. By default, as in Perl, a hexadecimal number is
always expected after \x, but it may have zero, one, or two digits (so,
for example, \xz matches a binary zero character followed by z).
@@ -1122,53 +1148,53 @@
PCRE2_ALT_CIRCUMFLEX
In multiline mode (when PCRE2_MULTILINE is set), the circumflex
- metacharacter matches at the start of the subject (unless PCRE2_NOTBOL
- is set), and also after any internal newline. However, it does not
+ metacharacter matches at the start of the subject (unless PCRE2_NOTBOL
+ is set), and also after any internal newline. However, it does not
match after a newline at the end of the subject, for compatibility with
- Perl. If you want a multiline circumflex also to match after a termi-
+ Perl. If you want a multiline circumflex also to match after a termi-
nating newline, you must set PCRE2_ALT_CIRCUMFLEX.
PCRE2_ALT_VERBNAMES
- By default, for compatibility with Perl, the name in any verb sequence
- such as (*MARK:NAME) is any sequence of characters that does not
- include a closing parenthesis. The name is not processed in any way,
- and it is not possible to include a closing parenthesis in the name.
- However, if the PCRE2_ALT_VERBNAMES option is set, normal backslash
- processing is applied to verb names and only an unescaped closing
- parenthesis terminates the name. A closing parenthesis can be included
- in a name either as \) or between \Q and \E. If the PCRE2_EXTENDED
+ By default, for compatibility with Perl, the name in any verb sequence
+ such as (*MARK:NAME) is any sequence of characters that does not
+ include a closing parenthesis. The name is not processed in any way,
+ and it is not possible to include a closing parenthesis in the name.
+ However, if the PCRE2_ALT_VERBNAMES option is set, normal backslash
+ processing is applied to verb names and only an unescaped closing
+ parenthesis terminates the name. A closing parenthesis can be included
+ in a name either as \) or between \Q and \E. If the PCRE2_EXTENDED
option is set, unescaped whitespace in verb names is skipped and #-com-
ments are recognized, exactly as in the rest of the pattern.
PCRE2_AUTO_CALLOUT
- If this bit is set, pcre2_compile() automatically inserts callout
+ If this bit is set, pcre2_compile() automatically inserts callout
items, all with number 255, before each pattern item. For discussion of
the callout facility, see the pcre2callout documentation.
PCRE2_CASELESS
- If this bit is set, letters in the pattern match both upper and lower
- case letters in the subject. It is equivalent to Perl's /i option, and
+ If this bit is set, letters in the pattern match both upper and lower
+ case letters in the subject. It is equivalent to Perl's /i option, and
it can be changed within a pattern by a (?i) option setting.
PCRE2_DOLLAR_ENDONLY
- If this bit is set, a dollar metacharacter in the pattern matches only
- at the end of the subject string. Without this option, a dollar also
- matches immediately before a newline at the end of the string (but not
- before any other newlines). The PCRE2_DOLLAR_ENDONLY option is ignored
- if PCRE2_MULTILINE is set. There is no equivalent to this option in
+ If this bit is set, a dollar metacharacter in the pattern matches only
+ at the end of the subject string. Without this option, a dollar also
+ matches immediately before a newline at the end of the string (but not
+ before any other newlines). The PCRE2_DOLLAR_ENDONLY option is ignored
+ if PCRE2_MULTILINE is set. There is no equivalent to this option in
Perl, and no way to set it within a pattern.
PCRE2_DOTALL
- If this bit is set, a dot metacharacter in the pattern matches any
- character, including one that indicates a newline. However, it only
+ If this bit is set, a dot metacharacter in the pattern matches any
+ character, including one that indicates a newline. However, it only
ever matches one character, even if newlines are coded as CRLF. Without
this option, a dot does not match when the current position in the sub-
- ject is at a newline. This option is equivalent to Perl's /s option,
+ ject is at a newline. This option is equivalent to Perl's /s option,
and it can be changed within a pattern by a (?s) option setting. A neg-
ative class such as [^a] always matches newline characters, independent
of the setting of this option.
@@ -1175,41 +1201,42 @@
PCRE2_DUPNAMES
- If this bit is set, names used to identify capturing subpatterns need
+ If this bit is set, names used to identify capturing subpatterns need
not be unique. This can be helpful for certain types of pattern when it
- is known that only one instance of the named subpattern can ever be
- matched. There are more details of named subpatterns below; see also
+ is known that only one instance of the named subpattern can ever be
+ matched. There are more details of named subpatterns below; see also
the pcre2pattern documentation.
PCRE2_EXTENDED
- If this bit is set, most white space characters in the pattern are
- totally ignored except when escaped or inside a character class. How-
- ever, white space is not allowed within sequences such as (?> that
+ If this bit is set, most white space characters in the pattern are
+ totally ignored except when escaped or inside a character class. How-
+ ever, white space is not allowed within sequences such as (?> that
introduce various parenthesized subpatterns, nor within numerical quan-
- tifiers such as {1,3}. Ignorable white space is permitted between an
- item and a following quantifier and between a quantifier and a follow-
+ tifiers such as {1,3}. Ignorable white space is permitted between an
+ item and a following quantifier and between a quantifier and a follow-
ing + that indicates possessiveness.
- PCRE2_EXTENDED also causes characters between an unescaped # outside a
- character class and the next newline, inclusive, to be ignored, which
+ PCRE2_EXTENDED also causes characters between an unescaped # outside a
+ character class and the next newline, inclusive, to be ignored, which
makes it possible to include comments inside complicated patterns. Note
- that the end of this type of comment is a literal newline sequence in
+ that the end of this type of comment is a literal newline sequence in
the pattern; escape sequences that happen to represent a newline do not
- count. PCRE2_EXTENDED is equivalent to Perl's /x option, and it can be
+ count. PCRE2_EXTENDED is equivalent to Perl's /x option, and it can be
changed within a pattern by a (?x) option setting.
Which characters are interpreted as newlines can be specified by a set-
- ting in the compile context that is passed to pcre2_compile() or by a
- special sequence at the start of the pattern, as described in the sec-
- tion entitled "Newline conventions" in the pcre2pattern documentation.
+ ting in the compile context that is passed to pcre2_compile() or by a
+ special sequence at the start of the pattern, as described in the sec-
+ tion entitled "Newline conventions" in the pcre2pattern documentation.
A default is defined when PCRE2 is built.
PCRE2_FIRSTLINE
- If this option is set, an unanchored pattern is required to match
- before or at the first newline in the subject string, though the
- matched text may continue over the newline.
+ If this option is set, an unanchored pattern is required to match
+ before or at the first newline in the subject string, though the
+ matched text may continue over the newline. See also PCRE2_USE_OFF-
+ SET_LIMIT, which provides a more general limiting facility.
PCRE2_MATCH_UNSET_BACKREF
@@ -1388,23 +1415,32 @@
not compatible with Perl. It can also be set by a (?U) option setting
within the pattern.
+ PCRE2_USE_OFFSET_LIMIT
+
+ This option must be set for pcre2_compile() if pcre2_set_offset_limit()
+ is going to be used to set a non-default offset limit in a match con-
+ text for matches that use this pattern. An error is generated if an
+ offset limit is set without this option. For more details, see the
+ description of pcre2_set_offset_limit() in the section that describes
+ match contexts. See also the PCRE2_FIRSTLINE option above.
+
PCRE2_UTF
- This option causes PCRE2 to regard both the pattern and the subject
- strings that are subsequently processed as strings of UTF characters
- instead of single-code-unit strings. It is available when PCRE2 is
- built to include Unicode support (which is the default). If Unicode
- support is not available, the use of this option provokes an error.
- Details of how this option changes the behaviour of PCRE2 are given in
+ This option causes PCRE2 to regard both the pattern and the subject
+ strings that are subsequently processed as strings of UTF characters
+ instead of single-code-unit strings. It is available when PCRE2 is
+ built to include Unicode support (which is the default). If Unicode
+ support is not available, the use of this option provokes an error.
+ Details of how this option changes the behaviour of PCRE2 are given in
the pcre2unicode page.
COMPILATION ERROR CODES
- There are over 80 positive error codes that pcre2_compile() may return
+ There are over 80 positive error codes that pcre2_compile() may return
if it finds an error in the pattern. There are also some negative error
- codes that are used for invalid UTF strings. These are the same as
- given by pcre2_match() and pcre2_dfa_match(), and are described in the
+ codes that are used for invalid UTF strings. These are the same as
+ given by pcre2_match() and pcre2_dfa_match(), and are described in the
pcre2unicode page. The pcre2_get_error_message() function can be called
to obtain a textual error message from any error code.
@@ -1428,53 +1464,53 @@
void pcre2_jit_stack_free(pcre2_jit_stack *jit_stack);
- These functions provide support for JIT compilation, which, if the
- just-in-time compiler is available, further processes a compiled pat-
+ These functions provide support for JIT compilation, which, if the
+ just-in-time compiler is available, further processes a compiled pat-
tern into machine code that executes much faster than the pcre2_match()
- interpretive matching function. Full details are given in the pcre2jit
+ interpretive matching function. Full details are given in the pcre2jit
documentation.
- JIT compilation is a heavyweight optimization. It can take some time
- for patterns to be analyzed, and for one-off matches and simple pat-
- terns the benefit of faster execution might be offset by a much slower
- compilation time. Most, but not all patterns can be optimized by the
+ JIT compilation is a heavyweight optimization. It can take some time
+ for patterns to be analyzed, and for one-off matches and simple pat-
+ terns the benefit of faster execution might be offset by a much slower
+ compilation time. Most, but not all patterns can be optimized by the
JIT compiler.
LOCALE SUPPORT
- PCRE2 handles caseless matching, and determines whether characters are
- letters, digits, or whatever, by reference to a set of tables, indexed
- by character code point. This applies only to characters whose code
- points are less than 256. By default, higher-valued code points never
- match escapes such as \w or \d. However, if PCRE2 is built with UTF
- support, all characters can be tested with \p and \P, or, alterna-
- tively, the PCRE2_UCP option can be set when a pattern is compiled;
- this causes \w and friends to use Unicode property support instead of
+ PCRE2 handles caseless matching, and determines whether characters are
+ letters, digits, or whatever, by reference to a set of tables, indexed
+ by character code point. This applies only to characters whose code
+ points are less than 256. By default, higher-valued code points never
+ match escapes such as \w or \d. However, if PCRE2 is built with UTF
+ support, all characters can be tested with \p and \P, or, alterna-
+ tively, the PCRE2_UCP option can be set when a pattern is compiled;
+ this causes \w and friends to use Unicode property support instead of
the built-in tables.
- The use of locales with Unicode is discouraged. If you are handling
- characters with code points greater than 128, you should either use
+ The use of locales with Unicode is discouraged. If you are handling
+ characters with code points greater than 128, you should either use
Unicode support, or use locales, but not try to mix the two.
- PCRE2 contains an internal set of character tables that are used by
- default. These are sufficient for many applications. Normally, the
+ PCRE2 contains an internal set of character tables that are used by
+ default. These are sufficient for many applications. Normally, the
internal tables recognize only ASCII characters. However, when PCRE2 is
built, it is possible to cause the internal tables to be rebuilt in the
default "C" locale of the local system, which may cause them to be dif-
ferent.
- The internal tables can be overridden by tables supplied by the appli-
- cation that calls PCRE2. These may be created in a different locale
- from the default. As more and more applications change to using Uni-
+ The internal tables can be overridden by tables supplied by the appli-
+ cation that calls PCRE2. These may be created in a different locale
+ from the default. As more and more applications change to using Uni-
code, the need for this locale support is expected to die away.
- External tables are built by calling the pcre2_maketables() function,
- in the relevant locale. The result can be passed to pcre2_compile() as
- often as necessary, by creating a compile context and calling
- pcre2_set_character_tables() to set the tables pointer therein. For
- example, to build and use tables that are appropriate for the French
- locale (where accented characters with values greater than 128 are
+ External tables are built by calling the pcre2_maketables() function,
+ in the relevant locale. The result can be passed to pcre2_compile() as
+ often as necessary, by creating a compile context and calling
+ pcre2_set_character_tables() to set the tables pointer therein. For
+ example, to build and use tables that are appropriate for the French
+ locale (where accented characters with values greater than 128 are
treated as letters), the following code could be used:
setlocale(LC_CTYPE, "fr_FR");
@@ -1483,15 +1519,15 @@
pcre2_set_character_tables(ccontext, tables);
re = pcre2_compile(..., ccontext);
- The locale name "fr_FR" is used on Linux and other Unix-like systems;
- if you are using Windows, the name for the French locale is "french".
- It is the caller's responsibility to ensure that the memory containing
+ The locale name "fr_FR" is used on Linux and other Unix-like systems;
+ if you are using Windows, the name for the French locale is "french".
+ It is the caller's responsibility to ensure that the memory containing
the tables remains available for as long as it is needed.
The pointer that is passed (via the compile context) to pcre2_compile()
- is saved with the compiled pattern, and the same tables are used by
- pcre2_match() and pcre_dfa_match(). Thus, for any single pattern, com-
- pilation, and matching all happen in the same locale, but different
+ is saved with the compiled pattern, and the same tables are used by
+ pcre2_match() and pcre_dfa_match(). Thus, for any single pattern, com-
+ pilation, and matching all happen in the same locale, but different
patterns can be processed in different locales.
@@ -1499,13 +1535,13 @@
int pcre2_pattern_info(const pcre2 *code, uint32_t what, void *where);
- The pcre2_pattern_info() function returns general information about a
+ The pcre2_pattern_info() function returns general information about a
compiled pattern. For information about callouts, see the next section.
- The first argument for pcre2_pattern_info() is a pointer to the com-
+ The first argument for pcre2_pattern_info() is a pointer to the com-
piled pattern. The second argument specifies which piece of information
- is required, and the third argument is a pointer to a variable to
- receive the data. If the third argument is NULL, the first argument is
- ignored, and the function returns the size in bytes of the variable
+ is required, and the third argument is a pointer to a variable to
+ receive the data. If the third argument is NULL, the first argument is
+ ignored, and the function returns the size in bytes of the variable
that is required for the information requested. Otherwise, The yield of
the function is zero for success, or one of the following negative num-
bers:
@@ -1515,9 +1551,9 @@
PCRE2_ERROR_BADOPTION the value of what was invalid
PCRE2_ERROR_UNSET the requested field is not set
- The "magic number" is placed at the start of each compiled pattern as
- an simple check against passing an arbitrary memory pointer. Here is a
- typical call of pcre2_pattern_info(), to obtain the length of the com-
+ The "magic number" is placed at the start of each compiled pattern as
+ an simple check against passing an arbitrary memory pointer. Here is a
+ typical call of pcre2_pattern_info(), to obtain the length of the com-
piled pattern:
int rc;
@@ -1534,16 +1570,16 @@
PCRE2_INFO_ARGOPTIONS
Return a copy of the pattern's options. The third argument should point
- to a uint32_t variable. PCRE2_INFO_ARGOPTIONS returns exactly the
- options that were passed to pcre2_compile(), whereas PCRE2_INFO_ALLOP-
- TIONS returns the compile options as modified by any top-level option
- settings at the start of the pattern itself. In other words, they are
+ to a uint32_t variable. PCRE2_INFO_ARGOPTIONS returns exactly the
+ options that were passed to pcre2_compile(), whereas PCRE2_INFO_ALLOP-
+ TIONS returns the compile options as modified by any top-level option
+ settings at the start of the pattern itself. In other words, they are
the options that will be in force when matching starts. For example, if
the pattern /(?im)abc(?-i)d/ is compiled with the PCRE2_EXTENDED
- option, the result is PCRE2_CASELESS, PCRE2_MULTILINE, and
+ option, the result is PCRE2_CASELESS, PCRE2_MULTILINE, and
PCRE2_EXTENDED.
- A pattern compiled without PCRE2_ANCHORED is automatically anchored by
+ A pattern compiled without PCRE2_ANCHORED is automatically anchored by
PCRE2 if the first significant item in every top-level branch is one of
the following:
@@ -1552,7 +1588,7 @@
\G always
.* sometimes - see below
- When .* is the first significant item, anchoring is possible only when
+ When .* is the first significant item, anchoring is possible only when
all the following are true:
.* is not in an atomic group
@@ -1562,18 +1598,18 @@
Neither (*PRUNE) nor (*SKIP) appears in the pattern.
PCRE2_NO_DOTSTAR_ANCHOR is not set.
- For patterns that are auto-anchored, the PCRE2_ANCHORED bit is set in
+ For patterns that are auto-anchored, the PCRE2_ANCHORED bit is set in
the options returned for PCRE2_INFO_ALLOPTIONS.
PCRE2_INFO_BACKREFMAX
- Return the number of the highest back reference in the pattern. The
- third argument should point to an uint32_t variable. Named subpatterns
- acquire numbers as well as names, and these count towards the highest
- back reference. Back references such as \4 or \g{12} match the cap-
- tured characters of the given group, but in addition, the check that a
+ Return the number of the highest back reference in the pattern. The
+ third argument should point to an uint32_t variable. Named subpatterns
+ acquire numbers as well as names, and these count towards the highest
+ back reference. Back references such as \4 or \g{12} match the cap-
+ tured characters of the given group, but in addition, the check that a
capturing group is set in a conditional subpattern such as (?(3)a|b) is
- also a back reference. Zero is returned if there are no back refer-
+ also a back reference. Zero is returned if there are no back refer-
ences.
PCRE2_INFO_BSR
@@ -1580,122 +1616,122 @@
The output is a uint32_t whose value indicates what character sequences
the \R escape sequence matches. A value of PCRE2_BSR_UNICODE means that
- \R matches any Unicode line ending sequence; a value of PCRE2_BSR_ANY-
+ \R matches any Unicode line ending sequence; a value of PCRE2_BSR_ANY-
CRLF means that \R matches only CR, LF, or CRLF.
PCRE2_INFO_CAPTURECOUNT
- Return the number of capturing subpatterns in the pattern. The third
+ Return the number of capturing subpatterns in the pattern. The third
argument should point to an uint32_t variable.
PCRE2_INFO_FIRSTCODETYPE
Return information about the first code unit of any matched string, for
- a non-anchored pattern. The third argument should point to an uint32_t
+ a non-anchored pattern. The third argument should point to an uint32_t
variable.
- If there is a fixed first value, for example, the letter "c" from a
- pattern such as (cat|cow|coyote), 1 is returned, and the character
- value can be retrieved using PCRE2_INFO_FIRSTCODEUNIT. If there is no
- fixed first value, but it is known that a match can occur only at the
- start of the subject or following a newline in the subject, 2 is
+ If there is a fixed first value, for example, the letter "c" from a
+ pattern such as (cat|cow|coyote), 1 is returned, and the character
+ value can be retrieved using PCRE2_INFO_FIRSTCODEUNIT. If there is no
+ fixed first value, but it is known that a match can occur only at the
+ start of the subject or following a newline in the subject, 2 is
returned. Otherwise, and for anchored patterns, 0 is returned.
PCRE2_INFO_FIRSTCODEUNIT
- Return the value of the first code unit of any matched string in the
+ Return the value of the first code unit of any matched string in the
situation where PCRE2_INFO_FIRSTCODETYPE returns 1; otherwise return 0.
- The third argument should point to an uint32_t variable. In the 8-bit
- library, the value is always less than 256. In the 16-bit library the
- value can be up to 0xffff. In the 32-bit library in UTF-32 mode the
+ The third argument should point to an uint32_t variable. In the 8-bit
+ library, the value is always less than 256. In the 16-bit library the
+ value can be up to 0xffff. In the 32-bit library in UTF-32 mode the
value can be up to 0x10ffff, and up to 0xffffffff when not using UTF-32
mode.
PCRE2_INFO_FIRSTBITMAP
- In the absence of a single first code unit for a non-anchored pattern,
- pcre2_compile() may construct a 256-bit table that defines a fixed set
- of values for the first code unit in any match. For example, a pattern
- that starts with [abc] results in a table with three bits set. When
- code unit values greater than 255 are supported, the flag bit for 255
- means "any code unit of value 255 or above". If such a table was con-
- structed, a pointer to it is returned. Otherwise NULL is returned. The
+ In the absence of a single first code unit for a non-anchored pattern,
+ pcre2_compile() may construct a 256-bit table that defines a fixed set
+ of values for the first code unit in any match. For example, a pattern
+ that starts with [abc] results in a table with three bits set. When
+ code unit values greater than 255 are supported, the flag bit for 255
+ means "any code unit of value 255 or above". If such a table was con-
+ structed, a pointer to it is returned. Otherwise NULL is returned. The
third argument should point to an const uint8_t * variable.
PCRE2_INFO_HASCRORLF
- Return 1 if the pattern contains any explicit matches for CR or LF
+ Return 1 if the pattern contains any explicit matches for CR or LF
characters, otherwise 0. The third argument should point to an uint32_t
- variable. An explicit match is either a literal CR or LF character, or
+ variable. An explicit match is either a literal CR or LF character, or
\r or \n.
PCRE2_INFO_JCHANGED
- Return 1 if the (?J) or (?-J) option setting is used in the pattern,
- otherwise 0. The third argument should point to an uint32_t variable.
- (?J) and (?-J) set and unset the local PCRE2_DUPNAMES option, respec-
+ Return 1 if the (?J) or (?-J) option setting is used in the pattern,
+ otherwise 0. The third argument should point to an uint32_t variable.
+ (?J) and (?-J) set and unset the local PCRE2_DUPNAMES option, respec-
tively.
PCRE2_INFO_JITSIZE
- If the compiled pattern was successfully processed by pcre2_jit_com-
- pile(), return the size of the JIT compiled code, otherwise return
+ If the compiled pattern was successfully processed by pcre2_jit_com-
+ pile(), return the size of the JIT compiled code, otherwise return
zero. The third argument should point to a size_t variable.
PCRE2_INFO_LASTCODETYPE
- Returns 1 if there is a rightmost literal code unit that must exist in
- any matched string, other than at its start. The third argument should
- point to an uint32_t variable. If there is no such value, 0 is
- returned. When 1 is returned, the code unit value itself can be
+ Returns 1 if there is a rightmost literal code unit that must exist in
+ any matched string, other than at its start. The third argument should
+ point to an uint32_t variable. If there is no such value, 0 is
+ returned. When 1 is returned, the code unit value itself can be
retrieved using PCRE2_INFO_LASTCODEUNIT.
For anchored patterns, a last literal value is recorded only if it fol-
- lows something of variable length. For example, for the pattern
- /^a\d+z\d+/ the returned value is 1 (with "z" returned from
+ lows something of variable length. For example, for the pattern
+ /^a\d+z\d+/ the returned value is 1 (with "z" returned from
PCRE2_INFO_LASTCODEUNIT), but for /^a\dz\d/ the returned value is 0.
PCRE2_INFO_LASTCODEUNIT
- Return the value of the rightmost literal data unit that must exist in
- any matched string, other than at its start, if such a value has been
- recorded. The third argument should point to an uint32_t variable. If
+ Return the value of the rightmost literal data unit that must exist in
+ any matched string, other than at its start, if such a value has been
+ recorded. The third argument should point to an uint32_t variable. If
there is no such value, 0 is returned.
PCRE2_INFO_MATCHEMPTY
- Return 1 if the pattern can match an empty string, otherwise 0. The
+ Return 1 if the pattern can match an empty string, otherwise 0. The
third argument should point to an uint32_t variable.
PCRE2_INFO_MATCHLIMIT
- If the pattern set a match limit by including an item of the form
- (*LIMIT_MATCH=nnnn) at the start, the value is returned. The third
- argument should point to an unsigned 32-bit integer. If no such value
- has been set, the call to pcre2_pattern_info() returns the error
+ If the pattern set a match limit by including an item of the form
+ (*LIMIT_MATCH=nnnn) at the start, the value is returned. The third
+ argument should point to an unsigned 32-bit integer. If no such value
+ has been set, the call to pcre2_pattern_info() returns the error
PCRE2_ERROR_UNSET.
PCRE2_INFO_MAXLOOKBEHIND
Return the number of characters (not code units) in the longest lookbe-
- hind assertion in the pattern. The third argument should point to an
- unsigned 32-bit integer. This information is useful when doing multi-
- segment matching using the partial matching facilities. Note that the
+ hind assertion in the pattern. The third argument should point to an
+ unsigned 32-bit integer. This information is useful when doing multi-
+ segment matching using the partial matching facilities. Note that the
simple assertions \b and \B require a one-character lookbehind. \A also
- registers a one-character lookbehind, though it does not actually
- inspect the previous character. This is to ensure that at least one
- character from the old segment is retained when a new segment is pro-
+ registers a one-character lookbehind, though it does not actually
+ inspect the previous character. This is to ensure that at least one
+ character from the old segment is retained when a new segment is pro-
cessed. Otherwise, if there are no lookbehinds in the pattern, \A might
match incorrectly at the start of a new segment.
PCRE2_INFO_MINLENGTH
- If a minimum length for matching subject strings was computed, its
- value is returned. Otherwise the returned value is 0. The value is a
- number of characters, which in UTF mode may be different from the num-
- ber of code units. The third argument should point to an uint32_t
- variable. The value is a lower bound to the length of any matching
- string. There may not be any strings of that length that do actually
+ If a minimum length for matching subject strings was computed, its
+ value is returned. Otherwise the returned value is 0. The value is a
+ number of characters, which in UTF mode may be different from the num-
+ ber of code units. The third argument should point to an uint32_t
+ variable. The value is a lower bound to the length of any matching
+ string. There may not be any strings of that length that do actually
match, but every string that does match is at least that long.
PCRE2_INFO_NAMECOUNT
@@ -1703,50 +1739,50 @@
PCRE2_INFO_NAMETABLE
PCRE2 supports the use of named as well as numbered capturing parenthe-
- ses. The names are just an additional way of identifying the parenthe-
+ ses. The names are just an additional way of identifying the parenthe-
ses, which still acquire numbers. Several convenience functions such as
- pcre2_substring_get_byname() are provided for extracting captured sub-
- strings by name. It is also possible to extract the data directly, by
- first converting the name to a number in order to access the correct
- pointers in the output vector (described with pcre2_match() below). To
- do the conversion, you need to use the name-to-number map, which is
+ pcre2_substring_get_byname() are provided for extracting captured sub-
+ strings by name. It is also possible to extract the data directly, by
+ first converting the name to a number in order to access the correct
+ pointers in the output vector (described with pcre2_match() below). To
+ do the conversion, you need to use the name-to-number map, which is
described by these three values.
- The map consists of a number of fixed-size entries. PCRE2_INFO_NAME-
- COUNT gives the number of entries, and PCRE2_INFO_NAMEENTRYSIZE gives
- the size of each entry in code units; both of these return a uint32_t
+ The map consists of a number of fixed-size entries. PCRE2_INFO_NAME-
+ COUNT gives the number of entries, and PCRE2_INFO_NAMEENTRYSIZE gives
+ the size of each entry in code units; both of these return a uint32_t
value. The entry size depends on the length of the longest name.
PCRE2_INFO_NAMETABLE returns a pointer to the first entry of the table.
- This is a PCRE2_SPTR pointer to a block of code units. In the 8-bit
- library, the first two bytes of each entry are the number of the cap-
+ This is a PCRE2_SPTR pointer to a block of code units. In the 8-bit
+ library, the first two bytes of each entry are the number of the cap-
turing parenthesis, most significant byte first. In the 16-bit library,
- the pointer points to 16-bit code units, the first of which contains
- the parenthesis number. In the 32-bit library, the pointer points to
- 32-bit code units, the first of which contains the parenthesis number.
+ the pointer points to 16-bit code units, the first of which contains
+ the parenthesis number. In the 32-bit library, the pointer points to
+ 32-bit code units, the first of which contains the parenthesis number.
The rest of the entry is the corresponding name, zero terminated.
- The names are in alphabetical order. If (?| is used to create multiple
- groups with the same number, as described in the section on duplicate
- subpattern numbers in the pcre2pattern page, the groups may be given
- the same name, but there is only one entry in the table. Different
+ The names are in alphabetical order. If (?| is used to create multiple
+ groups with the same number, as described in the section on duplicate
+ subpattern numbers in the pcre2pattern page, the groups may be given
+ the same name, but there is only one entry in the table. Different
names for groups of the same number are not permitted.
- Duplicate names for subpatterns with different numbers are permitted,
- but only if PCRE2_DUPNAMES is set. They appear in the table in the
- order in which they were found in the pattern. In the absence of (?|
- this is the order of increasing number; when (?| is used this is not
+ Duplicate names for subpatterns with different numbers are permitted,
+ but only if PCRE2_DUPNAMES is set. They appear in the table in the
+ order in which they were found in the pattern. In the absence of (?|
+ this is the order of increasing number; when (?| is used this is not
necessarily the case because later subpatterns may have lower numbers.
- As a simple example of the name/number table, consider the following
- pattern after compilation by the 8-bit library (assume PCRE2_EXTENDED
+ As a simple example of the name/number table, consider the following
+ pattern after compilation by the 8-bit library (assume PCRE2_EXTENDED
is set, so white space - including newlines - is ignored):
(?<date> (?<year>(\d\d)?\d\d) -
(?<month>\d\d) - (?<day>\d\d) )
- There are four named subpatterns, so the table has four entries, and
- each entry in the table is eight bytes long. The table is as follows,
+ There are four named subpatterns, so the table has four entries, and
+ each entry in the table is eight bytes long. The table is as follows,
with non-printing bytes shows in hexadecimal, and undefined bytes shown
as ??:
@@ -1755,8 +1791,8 @@
00 04 m o n t h 00
00 02 y e a r 00 ??
- When writing code to extract data from named subpatterns using the
- name-to-number map, remember that the length of the entries is likely
+ When writing code to extract data from named subpatterns using the
+ name-to-number map, remember that the length of the entries is likely
to be different for each compiled pattern.
PCRE2_INFO_NEWLINE
@@ -1769,27 +1805,27 @@
PCRE2_NEWLINE_ANY Any Unicode line ending
PCRE2_NEWLINE_ANYCRLF Any of CR, LF, or CRLF
- This specifies the default character sequence that will be recognized
+ This specifies the default character sequence that will be recognized
as meaning "newline" while matching.
PCRE2_INFO_RECURSIONLIMIT
- If the pattern set a recursion limit by including an item of the form
- (*LIMIT_RECURSION=nnnn) at the start, the value is returned. The third
- argument should point to an unsigned 32-bit integer. If no such value
- has been set, the call to pcre2_pattern_info() returns the error
+ If the pattern set a recursion limit by including an item of the form
+ (*LIMIT_RECURSION=nnnn) at the start, the value is returned. The third
+ argument should point to an unsigned 32-bit integer. If no such value
+ has been set, the call to pcre2_pattern_info() returns the error
PCRE2_ERROR_UNSET.
PCRE2_INFO_SIZE
- Return the size of the compiled pattern in bytes (for all three
- libraries). The third argument should point to a size_t variable. This
- value includes the size of the general data block that precedes the
- code units of the compiled pattern itself. The value that is used when
- pcre2_compile() is getting memory in which to place the compiled pat-
- tern may be slightly larger than the value returned by this option,
- because there are cases where the code that calculates the size has to
- over-estimate. Processing a pattern with the JIT compiler does not
+ Return the size of the compiled pattern in bytes (for all three
+ libraries). The third argument should point to a size_t variable. This
+ value includes the size of the general data block that precedes the
+ code units of the compiled pattern itself. The value that is used when
+ pcre2_compile() is getting memory in which to place the compiled pat-
+ tern may be slightly larger than the value returned by this option,
+ because there are cases where the code that calculates the size has to
+ over-estimate. Processing a pattern with the JIT compiler does not
alter the value returned by this option.
@@ -1800,22 +1836,22 @@
void *user_data);
A script language that supports the use of string arguments in callouts
- might like to scan all the callouts in a pattern before running the
+ might like to scan all the callouts in a pattern before running the
match. This can be done by calling pcre2_callout_enumerate(). The first
- argument is a pointer to a compiled pattern, the second points to a
- callback function, and the third is arbitrary user data. The callback
- function is called for every callout in the pattern in the order in
+ argument is a pointer to a compiled pattern, the second points to a
+ callback function, and the third is arbitrary user data. The callback
+ function is called for every callout in the pattern in the order in
which they appear. Its first argument is a pointer to a callout enumer-
- ation block, and its second argument is the user_data value that was
- passed to pcre2_callout_enumerate(). The contents of the callout enu-
- meration block are described in the pcre2callout documentation, which
+ ation block, and its second argument is the user_data value that was
+ passed to pcre2_callout_enumerate(). The contents of the callout enu-
+ meration block are described in the pcre2callout documentation, which
also gives further details about callouts.
SERIALIZATION AND PRECOMPILING
- It is possible to save compiled patterns on disc or elsewhere, and
- reload them later, subject to a number of restrictions. The functions
+ It is possible to save compiled patterns on disc or elsewhere, and
+ reload them later, subject to a number of restrictions. The functions
whose names begin with pcre2_serialize_ are used for this purpose. They
are described in the pcre2serialize documentation.
@@ -1830,56 +1866,56 @@
void pcre2_match_data_free(pcre2_match_data *match_data);
- Information about a successful or unsuccessful match is placed in a
- match data block, which is an opaque structure that is accessed by
- function calls. In particular, the match data block contains a vector
- of offsets into the subject string that define the matched part of the
- subject and any substrings that were captured. This is know as the
+ Information about a successful or unsuccessful match is placed in a
+ match data block, which is an opaque structure that is accessed by
+ function calls. In particular, the match data block contains a vector
+ of offsets into the subject string that define the matched part of the
+ subject and any substrings that were captured. This is know as the
ovector.
- Before calling pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match()
+ Before calling pcre2_match(), pcre2_dfa_match(), or pcre2_jit_match()
you must create a match data block by calling one of the creation func-
- tions above. For pcre2_match_data_create(), the first argument is the
- number of pairs of offsets in the ovector. One pair of offsets is
- required to identify the string that matched the whole pattern, with
- another pair for each captured substring. For example, a value of 4
- creates enough space to record the matched portion of the subject plus
- three captured substrings. A minimum of at least 1 pair is imposed by
+ tions above. For pcre2_match_data_create(), the first argument is the
+ number of pairs of offsets in the ovector. One pair of offsets is
+ required to identify the string that matched the whole pattern, with
+ another pair for each captured substring. For example, a value of 4
+ creates enough space to record the matched portion of the subject plus
+ three captured substrings. A minimum of at least 1 pair is imposed by
pcre2_match_data_create(), so it is always possible to return the over-
all matched string.
The second argument of pcre2_match_data_create() is a pointer to a gen-
- eral context, which can specify custom memory management for obtaining
+ eral context, which can specify custom memory management for obtaining
the memory for the match data block. If you are not using custom memory
management, pass NULL, which causes malloc() to be used.
- For pcre2_match_data_create_from_pattern(), the first argument is a
+ For pcre2_match_data_create_from_pattern(), the first argument is a
pointer to a compiled pattern. The ovector is created to be exactly the
right size to hold all the substrings a pattern might capture. The sec-
- ond argument is again a pointer to a general context, but in this case
+ ond argument is again a pointer to a general context, but in this case
if NULL is passed, the memory is obtained using the same allocator that
was used for the compiled pattern (custom or default).
- A match data block can be used many times, with the same or different
- compiled patterns. You can extract information from a match data block
+ A match data block can be used many times, with the same or different
+ compiled patterns. You can extract information from a match data block
after a match operation has finished, using functions that are
- described in the sections on matched strings and other match data
+ described in the sections on matched strings and other match data
below.
- When a call of pcre2_match() fails, valid data is available in the
- match block only when the error is PCRE2_ERROR_NOMATCH,
- PCRE2_ERROR_PARTIAL, or one of the error codes for an invalid UTF
+ When a call of pcre2_match() fails, valid data is available in the
+ match block only when the error is PCRE2_ERROR_NOMATCH,
+ PCRE2_ERROR_PARTIAL, or one of the error codes for an invalid UTF
string. Exactly what is available depends on the error, and is detailed
below.
- When one of the matching functions is called, pointers to the compiled
- pattern and the subject string are set in the match data block so that
- they can be referenced by the extraction functions. After running a
- match, you must not free a compiled pattern or a subject string until
- after all operations on the match data block (for that match) have
+ When one of the matching functions is called, pointers to the compiled
+ pattern and the subject string are set in the match data block so that
+ they can be referenced by the extraction functions. After running a
+ match, you must not free a compiled pattern or a subject string until
+ after all operations on the match data block (for that match) have
taken place.
- When a match data block itself is no longer needed, it should be freed
+ When a match data block itself is no longer needed, it should be freed
by calling pcre2_match_data_free().
@@ -1890,15 +1926,15 @@
uint32_t options, pcre2_match_data *match_data,
pcre2_match_context *mcontext);
- The function pcre2_match() is called to match a subject string against
- a compiled pattern, which is passed in the code argument. You can call
+ The function pcre2_match() is called to match a subject string against
+ a compiled pattern, which is passed in the code argument. You can call
pcre2_match() with the same code argument as many times as you like, in
- order to find multiple matches in the subject string or to match dif-
+ order to find multiple matches in the subject string or to match dif-
ferent subject strings with the same pattern.
- This function is the main matching facility of the library, and it
- operates in a Perl-like manner. For specialist use there is also an
- alternative matching function, which is described below in the section
+ This function is the main matching facility of the library, and it
+ operates in a Perl-like manner. For specialist use there is also an
+ alternative matching function, which is described below in the section
about the pcre2_dfa_match() function.
Here is an example of a simple call to pcre2_match():
@@ -1913,7 +1949,7 @@
match_data, /* the match data block */
NULL); /* a match context; NULL means use defaults */
- If the subject string is zero-terminated, the length can be given as
+ If the subject string is zero-terminated, the length can be given as
PCRE2_ZERO_TERMINATED. A match context must be provided if certain less
common matching parameters are to be changed. For details, see the sec-
tion on the match context above.
@@ -1920,67 +1956,67 @@
The string to be matched by pcre2_match()
- The subject string is passed to pcre2_match() as a pointer in subject,
- a length in length, and a starting offset in startoffset. The length
- and offset are in code units, not characters. That is, they are in
- bytes for the 8-bit library, 16-bit code units for the 16-bit library,
- and 32-bit code units for the 32-bit library, whether or not UTF pro-
+ The subject string is passed to pcre2_match() as a pointer in subject,
+ a length in length, and a starting offset in startoffset. The length
+ and offset are in code units, not characters. That is, they are in
+ bytes for the 8-bit library, 16-bit code units for the 16-bit library,
+ and 32-bit code units for the 32-bit library, whether or not UTF pro-
cessing is enabled.
If startoffset is greater than the length of the subject, pcre2_match()
- returns PCRE2_ERROR_BADOFFSET. When the starting offset is zero, the
- search for a match starts at the beginning of the subject, and this is
+ returns PCRE2_ERROR_BADOFFSET. When the starting offset is zero, the
+ search for a match starts at the beginning of the subject, and this is
by far the most common case. In UTF-8 or UTF-16 mode, the starting off-
- set must point to the start of a character, or to the end of the sub-
- ject (in UTF-32 mode, one code unit equals one character, so all off-
- sets are valid). Like the pattern string, the subject may contain
+ set must point to the start of a character, or to the end of the sub-
+ ject (in UTF-32 mode, one code unit equals one character, so all off-
+ sets are valid). Like the pattern string, the subject may contain
binary zeroes.
- A non-zero starting offset is useful when searching for another match
- in the same subject by calling pcre2_match() again after a previous
- success. Setting startoffset differs from passing over a shortened
- string and setting PCRE2_NOTBOL in the case of a pattern that begins
+ A non-zero starting offset is useful when searching for another match
+ in the same subject by calling pcre2_match() again after a previous
+ success. Setting startoffset differs from passing over a shortened
+ string and setting PCRE2_NOTBOL in the case of a pattern that begins
with any kind of lookbehind. For example, consider the pattern
\Biss\B
- which finds occurrences of "iss" in the middle of words. (\B matches
- only if the current position in the subject is not a word boundary.)
+ which finds occurrences of "iss" in the middle of words. (\B matches
+ only if the current position in the subject is not a word boundary.)
When applied to the string "Mississipi" the first call to pcre2_match()
- finds the first occurrence. If pcre2_match() is called again with just
- the remainder of the subject, namely "issipi", it does not match,
+ finds the first occurrence. If pcre2_match() is called again with just
+ the remainder of the subject, namely "issipi", it does not match,
because \B is always false at the start of the subject, which is deemed
- to be a word boundary. However, if pcre2_match() is passed the entire
+ to be a word boundary. However, if pcre2_match() is passed the entire
string again, but with startoffset set to 4, it finds the second occur-
- rence of "iss" because it is able to look behind the starting point to
+ rence of "iss" because it is able to look behind the starting point to
discover that it is preceded by a letter.
- Finding all the matches in a subject is tricky when the pattern can
+ Finding all the matches in a subject is tricky when the pattern can
match an empty string. It is possible to emulate Perl's /g behaviour by
- first trying the match again at the same offset, with the
- PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED options, and then if that
- fails, advancing the starting offset and trying an ordinary match
- again. There is some code that demonstrates how to do this in the
- pcre2demo sample program. In the most general case, you have to check
- to see if the newline convention recognizes CRLF as a newline, and if
- so, and the current character is CR followed by LF, advance the start-
+ first trying the match again at the same offset, with the
+ PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED options, and then if that
+ fails, advancing the starting offset and trying an ordinary match
+ again. There is some code that demonstrates how to do this in the
+ pcre2demo sample program. In the most general case, you have to check
+ to see if the newline convention recognizes CRLF as a newline, and if
+ so, and the current character is CR followed by LF, advance the start-
ing offset by two characters instead of one.
- If a non-zero starting offset is passed when the pattern is anchored,
+ If a non-zero starting offset is passed when the pattern is anchored,
one attempt to match at the given offset is made. This can only succeed
- if the pattern does not require the match to be at the start of the
+ if the pattern does not require the match to be at the start of the
subject.
Option bits for pcre2_match()
The unused bits of the options argument for pcre2_match() must be zero.
- The only bits that may be set are PCRE2_ANCHORED, PCRE2_NOTBOL,
+ The only bits that may be set are PCRE2_ANCHORED, PCRE2_NOTBOL,
PCRE2_NOTEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART,
- PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT. Their
+ PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, and PCRE2_PARTIAL_SOFT. Their
action is described below.
- Setting PCRE2_ANCHORED at match time is not supported by the just-in-
- time (JIT) compiler. If it is set, JIT matching is disabled and the
+ Setting PCRE2_ANCHORED at match time is not supported by the just-in-
+ time (JIT) compiler. If it is set, JIT matching is disabled and the
normal interpretive code in pcre2_match() is run. The remaining options
are supported for JIT matching.
@@ -1987,16 +2023,16 @@
PCRE2_ANCHORED
The PCRE2_ANCHORED option limits pcre2_match() to matching at the first
- matching position. If a pattern was compiled with PCRE2_ANCHORED, or
- turned out to be anchored by virtue of its contents, it cannot be made
- unachored at matching time. Note that setting the option at match time
+ matching position. If a pattern was compiled with PCRE2_ANCHORED, or
+ turned out to be anchored by virtue of its contents, it cannot be made
+ unachored at matching time. Note that setting the option at match time
disables JIT matching.
PCRE2_NOTBOL
This option specifies that first character of the subject string is not
- the beginning of a line, so the circumflex metacharacter should not
- match before it. Setting this without having set PCRE2_MULTILINE at
+ the beginning of a line, so the circumflex metacharacter should not
+ match before it. Setting this without having set PCRE2_MULTILINE at
compile time causes circumflex never to match. This option affects only
the behaviour of the circumflex metacharacter. It does not affect \A.
@@ -2003,9 +2039,9 @@
PCRE2_NOTEOL
This option specifies that the end of the subject string is not the end
- of a line, so the dollar metacharacter should not match it nor (except
- in multiline mode) a newline immediately before it. Setting this with-
- out having set PCRE2_MULTILINE at compile time causes dollar never to
+ of a line, so the dollar metacharacter should not match it nor (except
+ in multiline mode) a newline immediately before it. Setting this with-
+ out having set PCRE2_MULTILINE at compile time causes dollar never to
match. This option affects only the behaviour of the dollar metacharac-
ter. It does not affect \Z or \z.
@@ -2012,72 +2048,72 @@
PCRE2_NOTEMPTY
An empty string is not considered to be a valid match if this option is
- set. If there are alternatives in the pattern, they are tried. If all
- the alternatives match the empty string, the entire match fails. For
+ set. If there are alternatives in the pattern, they are tried. If all
+ the alternatives match the empty string, the entire match fails. For
example, if the pattern
a?b?
- is applied to a string not beginning with "a" or "b", it matches an
+ is applied to a string not beginning with "a" or "b", it matches an
empty string at the start of the subject. With PCRE2_NOTEMPTY set, this
- match is not valid, so pcre2_match() searches further into the string
+ match is not valid, so pcre2_match() searches further into the string
for occurrences of "a" or "b".
PCRE2_NOTEMPTY_ATSTART
- This is like PCRE2_NOTEMPTY, except that it locks out an empty string
+ This is like PCRE2_NOTEMPTY, except that it locks out an empty string
match only at the first matching position, that is, at the start of the
- subject plus the starting offset. An empty string match later in the
- subject is permitted. If the pattern is anchored, such a match can
+ subject plus the starting offset. An empty string match later in the
+ subject is permitted. If the pattern is anchored, such a match can
occur only if the pattern contains \K.
PCRE2_NO_UTF_CHECK
When PCRE2_UTF is set at compile time, the validity of the subject as a
- UTF string is checked by default when pcre2_match() is subsequently
- called. If a non-zero starting offset is given, the check is applied
- only to that part of the subject that could be inspected during match-
- ing, and there is a check that the starting offset points to the first
- code unit of a character or to the end of the subject. If there are no
- lookbehind assertions in the pattern, the check starts at the starting
- offset. Otherwise, it starts at the length of the longest lookbehind
+ UTF string is checked by default when pcre2_match() is subsequently
+ called. If a non-zero starting offset is given, the check is applied
+ only to that part of the subject that could be inspected during match-
+ ing, and there is a check that the starting offset points to the first
+ code unit of a character or to the end of the subject. If there are no
+ lookbehind assertions in the pattern, the check starts at the starting
+ offset. Otherwise, it starts at the length of the longest lookbehind
before the starting offset, or at the start of the subject if there are
- not that many characters before the starting offset. Note that the
+ not that many characters before the starting offset. Note that the
sequences \b and \B are one-character lookbehinds.
The check is carried out before any other processing takes place, and a
- negative error code is returned if the check fails. There are several
- UTF error codes for each code unit width, corresponding to different
- problems with the code unit sequence. There are discussions about the
- validity of UTF-8 strings, UTF-16 strings, and UTF-32 strings in the
+ negative error code is returned if the check fails. There are several
+ UTF error codes for each code unit width, corresponding to different
+ problems with the code unit sequence. There are discussions about the
+ validity of UTF-8 strings, UTF-16 strings, and UTF-32 strings in the
pcre2unicode page.
- If you know that your subject is valid, and you want to skip these
- checks for performance reasons, you can set the PCRE2_NO_UTF_CHECK
- option when calling pcre2_match(). You might want to do this for the
+ If you know that your subject is valid, and you want to skip these
+ checks for performance reasons, you can set the PCRE2_NO_UTF_CHECK
+ option when calling pcre2_match(). You might want to do this for the
second and subsequent calls to pcre2_match() if you are making repeated
calls to find all the matches in a single subject string.
- NOTE: When PCRE2_NO_UTF_CHECK is set, the effect of passing an invalid
- string as a subject, or an invalid value of startoffset, is undefined.
+ NOTE: When PCRE2_NO_UTF_CHECK is set, the effect of passing an invalid
+ string as a subject, or an invalid value of startoffset, is undefined.
Your program may crash or loop indefinitely.
PCRE2_PARTIAL_HARD
PCRE2_PARTIAL_SOFT
- These options turn on the partial matching feature. A partial match
- occurs if the end of the subject string is reached successfully, but
- there are not enough subject characters to complete the match. If this
- happens when PCRE2_PARTIAL_SOFT (but not PCRE2_PARTIAL_HARD) is set,
- matching continues by testing any remaining alternatives. Only if no
- complete match can be found is PCRE2_ERROR_PARTIAL returned instead of
- PCRE2_ERROR_NOMATCH. In other words, PCRE2_PARTIAL_SOFT specifies that
- the caller is prepared to handle a partial match, but only if no com-
+ These options turn on the partial matching feature. A partial match
+ occurs if the end of the subject string is reached successfully, but
+ there are not enough subject characters to complete the match. If this
+ happens when PCRE2_PARTIAL_SOFT (but not PCRE2_PARTIAL_HARD) is set,
+ matching continues by testing any remaining alternatives. Only if no
+ complete match can be found is PCRE2_ERROR_PARTIAL returned instead of
+ PCRE2_ERROR_NOMATCH. In other words, PCRE2_PARTIAL_SOFT specifies that
+ the caller is prepared to handle a partial match, but only if no com-
plete match can be found.
- If PCRE2_PARTIAL_HARD is set, it overrides PCRE2_PARTIAL_SOFT. In this
- case, if a partial match is found, pcre2_match() immediately returns
- PCRE2_ERROR_PARTIAL, without considering any other alternatives. In
+ If PCRE2_PARTIAL_HARD is set, it overrides PCRE2_PARTIAL_SOFT. In this
+ case, if a partial match is found, pcre2_match() immediately returns
+ PCRE2_ERROR_PARTIAL, without considering any other alternatives. In
other words, when PCRE2_PARTIAL_HARD is set, a partial match is consid-
ered to be more important that an alternative complete match.
@@ -2087,34 +2123,34 @@
NEWLINE HANDLING WHEN MATCHING
- When PCRE2 is built, a default newline convention is set; this is usu-
- ally the standard convention for the operating system. The default can
- be overridden in a compile context. During matching, the newline
- choice affects the behaviour of the dot, circumflex, and dollar
- metacharacters. It may also alter the way the match starting position
+ When PCRE2 is built, a default newline convention is set; this is usu-
+ ally the standard convention for the operating system. The default can
+ be overridden in a compile context. During matching, the newline
+ choice affects the behaviour of the dot, circumflex, and dollar
+ metacharacters. It may also alter the way the match starting position
is advanced after a match failure for an unanchored pattern.
When PCRE2_NEWLINE_CRLF, PCRE2_NEWLINE_ANYCRLF, or PCRE2_NEWLINE_ANY is
- set as the newline convention, and a match attempt for an unanchored
+ set as the newline convention, and a match attempt for an unanchored
pattern fails when the current starting position is at a CRLF sequence,
- and the pattern contains no explicit matches for CR or LF characters,
- the match position is advanced by two characters instead of one, in
+ and the pattern contains no explicit matches for CR or LF characters,
+ the match position is advanced by two characters instead of one, in
other words, to after the CRLF.
The above rule is a compromise that makes the most common cases work as
- expected. For example, if the pattern is .+A (and the PCRE2_DOTALL
+ expected. For example, if the pattern is .+A (and the PCRE2_DOTALL
option is not set), it does not match the string "\r\nA" because, after
- failing at the start, it skips both the CR and the LF before retrying.
- However, the pattern [\r\n]A does match that string, because it con-
+ failing at the start, it skips both the CR and the LF before retrying.
+ However, the pattern [\r\n]A does match that string, because it con-
tains an explicit CR or LF reference, and so advances only by one char-
acter after the first failure.
An explicit match for CR of LF is either a literal appearance of one of
- those characters in the pattern, or one of the \r or \n escape
- sequences. Implicit matches such as [^X] do not count, nor does \s,
+ those characters in the pattern, or one of the \r or \n escape
+ sequences. Implicit matches such as [^X] do not count, nor does \s,
even though it includes CR and LF in the characters that it matches.
- Notwithstanding the above, anomalous effects may still occur when CRLF
+ Notwithstanding the above, anomalous effects may still occur when CRLF
is a valid newline sequence and explicit \r or \n escapes appear in the
pattern.
@@ -2125,84 +2161,84 @@
PCRE2_SIZE *pcre2_get_ovector_pointer(pcre2_match_data *match_data);
- In general, a pattern matches a certain portion of the subject, and in
- addition, further substrings from the subject may be picked out by
- parenthesized parts of the pattern. Following the usage in Jeffrey
- Friedl's book, this is called "capturing" in what follows, and the
- phrase "capturing subpattern" or "capturing group" is used for a frag-
- ment of a pattern that picks out a substring. PCRE2 supports several
+ In general, a pattern matches a certain portion of the subject, and in
+ addition, further substrings from the subject may be picked out by
+ parenthesized parts of the pattern. Following the usage in Jeffrey
+ Friedl's book, this is called "capturing" in what follows, and the
+ phrase "capturing subpattern" or "capturing group" is used for a frag-
+ ment of a pattern that picks out a substring. PCRE2 supports several
other kinds of parenthesized subpattern that do not cause substrings to
- be captured. The pcre2_pattern_info() function can be used to find out
+ be captured. The pcre2_pattern_info() function can be used to find out
how many capturing subpatterns there are in a compiled pattern.
- A successful match returns the overall matched string and any captured
- substrings to the caller via a vector of PCRE2_SIZE values. This is
- called the ovector, and is contained within the match data block. You
- can obtain direct access to the ovector by calling pcre2_get_ovec-
- tor_pointer() to find its address, and pcre2_get_ovector_count() to
- find the number of pairs of values it contains. Alternatively, you can
+ A successful match returns the overall matched string and any captured
+ substrings to the caller via a vector of PCRE2_SIZE values. This is
+ called the ovector, and is contained within the match data block. You
+ can obtain direct access to the ovector by calling pcre2_get_ovec-
+ tor_pointer() to find its address, and pcre2_get_ovector_count() to
+ find the number of pairs of values it contains. Alternatively, you can
use the auxiliary functions for accessing captured substrings by number
or by name (see below).
Within the ovector, the first in each pair of values is set to the off-
set of the first code unit of a substring, and the second is set to the
- offset of the first code unit after the end of a substring. These val-
- ues are always code unit offsets, not character offsets. That is, they
- are byte offsets in the 8-bit library, 16-bit offsets in the 16-bit
+ offset of the first code unit after the end of a substring. These val-
+ ues are always code unit offsets, not character offsets. That is, they
+ are byte offsets in the 8-bit library, 16-bit offsets in the 16-bit
library, and 32-bit offsets in the 32-bit library.
- After a partial match (error return PCRE2_ERROR_PARTIAL), only the
- first pair of offsets (that is, ovector[0] and ovector[1]) are set.
- They identify the part of the subject that was partially matched. See
+ After a partial match (error return PCRE2_ERROR_PARTIAL), only the
+ first pair of offsets (that is, ovector[0] and ovector[1]) are set.
+ They identify the part of the subject that was partially matched. See
the pcre2partial documentation for details of partial matching.
After a successful match, the first pair of offsets identifies the por-
- tion of the subject string that was matched by the entire pattern. The
- next pair is used for the first capturing subpattern, and so on. The
- value returned by pcre2_match() is one more than the highest numbered
- pair that has been set. For example, if two substrings have been cap-
- tured, the returned value is 3. If there are no capturing subpatterns,
+ tion of the subject string that was matched by the entire pattern. The
+ next pair is used for the first capturing subpattern, and so on. The
+ value returned by pcre2_match() is one more than the highest numbered
+ pair that has been set. For example, if two substrings have been cap-
+ tured, the returned value is 3. If there are no capturing subpatterns,
the return value from a successful match is 1, indicating that just the
first pair of offsets has been set.
- If a pattern uses the \K escape sequence within a positive assertion,
+ If a pattern uses the \K escape sequence within a positive assertion,
the reported start of a successful match can be greater than the end of
- the match. For example, if the pattern (?=ab\K) is matched against
+ the match. For example, if the pattern (?=ab\K) is matched against
"ab", the start and end offset values for the match are 2 and 0.
- If a capturing subpattern group is matched repeatedly within a single
- match operation, it is the last portion of the subject that it matched
+ If a capturing subpattern group is matched repeatedly within a single
+ match operation, it is the last portion of the subject that it matched
that is returned.
If the ovector is too small to hold all the captured substring offsets,
- as much as possible is filled in, and the function returns a value of
- zero. If captured substrings are not of interest, pcre2_match() may be
+ as much as possible is filled in, and the function returns a value of
+ zero. If captured substrings are not of interest, pcre2_match() may be
called with a match data block whose ovector is of minimum length (that
is, one pair). However, if the pattern contains back references and the
ovector is not big enough to remember the related substrings, PCRE2 has
- to get additional memory for use during matching. Thus it is usually
+ to get additional memory for use during matching. Thus it is usually
advisable to set up a match data block containing an ovector of reason-
able size.
- It is possible for capturing subpattern number n+1 to match some part
+ It is possible for capturing subpattern number n+1 to match some part
of the subject when subpattern n has not been used at all. For example,
- if the string "abc" is matched against the pattern (a|(z))(bc) the
+ if the string "abc" is matched against the pattern (a|(z))(bc) the
return from the function is 4, and subpatterns 1 and 3 are matched, but
- 2 is not. When this happens, both values in the offset pairs corre-
+ 2 is not. When this happens, both values in the offset pairs corre-
sponding to unused subpatterns are set to PCRE2_UNSET.
- Offset values that correspond to unused subpatterns at the end of the
- expression are also set to PCRE2_UNSET. For example, if the string
+ Offset values that correspond to unused subpatterns at the end of the
+ expression are also set to PCRE2_UNSET. For example, if the string
"abc" is matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3
- are not matched. The return from the function is 2, because the high-
+ are not matched. The return from the function is 2, because the high-
est used capturing subpattern number is 1. The offsets for for the sec-
- ond and third capturing subpatterns (assuming the vector is large
+ ond and third capturing subpatterns (assuming the vector is large
enough, of course) are set to PCRE2_UNSET.
Elements in the ovector that do not correspond to capturing parentheses
in the pattern are never changed. That is, if a pattern contains n cap-
turing parentheses, no more than ovector[0] to ovector[2n+1] are set by
- pcre2_match(). The other elements retain whatever values they previ-
+ pcre2_match(). The other elements retain whatever values they previ-
ously had.
@@ -2212,37 +2248,37 @@
PCRE2_SIZE pcre2_get_startchar(pcre2_match_data *match_data);
- As well as the offsets in the ovector, other information about a match
- is retained in the match data block and can be retrieved by the above
- functions in appropriate circumstances. If they are called at other
+ As well as the offsets in the ovector, other information about a match
+ is retained in the match data block and can be retrieved by the above
+ functions in appropriate circumstances. If they are called at other
times, the result is undefined.
- After a successful match, a partial match (PCRE2_ERROR_PARTIAL), or a
- failure to match (PCRE2_ERROR_NOMATCH), a (*MARK) name may be avail-
- able, and pcre2_get_mark() can be called. It returns a pointer to the
- zero-terminated name, which is within the compiled pattern. Otherwise
- NULL is returned. After a successful match, the (*MARK) name that is
- returned is the last one encountered on the matching path through the
- pattern. After a "no match" or a partial match, the last encountered
+ After a successful match, a partial match (PCRE2_ERROR_PARTIAL), or a
+ failure to match (PCRE2_ERROR_NOMATCH), a (*MARK) name may be avail-
+ able, and pcre2_get_mark() can be called. It returns a pointer to the
+ zero-terminated name, which is within the compiled pattern. Otherwise
+ NULL is returned. After a successful match, the (*MARK) name that is
+ returned is the last one encountered on the matching path through the
+ pattern. After a "no match" or a partial match, the last encountered
(*MARK) name is returned. For example, consider this pattern:
^(*MARK:A)((*MARK:B)a|b)c
- When it matches "bc", the returned mark is A. The B mark is "seen" in
- the first branch of the group, but it is not on the matching path. On
- the other hand, when this pattern fails to match "bx", the returned
+ When it matches "bc", the returned mark is A. The B mark is "seen" in
+ the first branch of the group, but it is not on the matching path. On
+ the other hand, when this pattern fails to match "bx", the returned
mark is B.
- After a successful match, a partial match, or one of the invalid UTF
- errors (for example, PCRE2_ERROR_UTF8_ERR5), pcre2_get_startchar() can
+ After a successful match, a partial match, or one of the invalid UTF
+ errors (for example, PCRE2_ERROR_UTF8_ERR5), pcre2_get_startchar() can
be called. After a successful or partial match it returns the code unit
- offset of the character at which the match started. For a non-partial
- match, this can be different to the value of ovector[0] if the pattern
- contains the \K escape sequence. After a partial match, however, this
- value is always the same as ovector[0] because \K does not affect the
+ offset of the character at which the match started. For a non-partial
+ match, this can be different to the value of ovector[0] if the pattern
+ contains the \K escape sequence. After a partial match, however, this
+ value is always the same as ovector[0] because \K does not affect the
result of a partial match.
- After a UTF check failure, pcre2_get_startchar() can be used to obtain
+ After a UTF check failure, pcre2_get_startchar() can be used to obtain
the code unit offset of the invalid UTF character. Details are given in
the pcre2unicode page.
@@ -2249,12 +2285,12 @@
ERROR RETURNS FROM pcre2_match()
- If pcre2_match() fails, it returns a negative number. This can be con-
- verted to a text string by calling pcre2_get_error_message(). Negative
- error codes are also returned by other functions, and are documented
+ If pcre2_match() fails, it returns a negative number. This can be con-
+ verted to a text string by calling pcre2_get_error_message(). Negative
+ error codes are also returned by other functions, and are documented
with them. The codes are given names in the header file. If UTF check-
ing is in force and an invalid UTF subject string is detected, one of a
- number of UTF-specific negative error codes is returned. Details are
+ number of UTF-specific negative error codes is returned. Details are
given in the pcre2unicode page. The following are the other errors that
may be returned by pcre2_match():
@@ -2264,19 +2300,19 @@
PCRE2_ERROR_PARTIAL
- The subject string did not match, but it did match partially. See the
+ The subject string did not match, but it did match partially. See the
pcre2partial documentation for details of partial matching.
PCRE2_ERROR_BADMAGIC
PCRE2 stores a 4-byte "magic number" at the start of the compiled code,
- to catch the case when it is passed a junk pointer. This is the error
+ to catch the case when it is passed a junk pointer. This is the error
that is returned when the magic number is not present.
PCRE2_ERROR_BADMODE
- This error is given when a pattern that was compiled by the 8-bit
- library is passed to a 16-bit or 32-bit library function, or vice
+ This error is given when a pattern that was compiled by the 8-bit
+ library is passed to a 16-bit or 32-bit library function, or vice
versa.
PCRE2_ERROR_BADOFFSET
@@ -2290,35 +2326,35 @@
PCRE2_ERROR_BADUTFOFFSET
The UTF code unit sequence that was passed as a subject was checked and
- found to be valid (the PCRE2_NO_UTF_CHECK option was not set), but the
- value of startoffset did not point to the beginning of a UTF character
+ found to be valid (the PCRE2_NO_UTF_CHECK option was not set), but the
+ value of startoffset did not point to the beginning of a UTF character
or the end of the subject.
PCRE2_ERROR_CALLOUT
- This error is never generated by pcre2_match() itself. It is provided
- for use by callout functions that want to cause pcre2_match() or
- pcre2_callout_enumerate() to return a distinctive error code. See the
+ This error is never generated by pcre2_match() itself. It is provided
+ for use by callout functions that want to cause pcre2_match() or
+ pcre2_callout_enumerate() to return a distinctive error code. See the
pcre2callout documentation for details.
PCRE2_ERROR_INTERNAL
- An unexpected internal error has occurred. This error could be caused
+ An unexpected internal error has occurred. This error could be caused
by a bug in PCRE2 or by overwriting of the compiled pattern.
PCRE2_ERROR_JIT_BADOPTION
- This error is returned when a pattern that was successfully studied
- using JIT is being matched, but the matching mode (partial or complete
- match) does not correspond to any JIT compilation mode. When the JIT
- fast path function is used, this error may be also given for invalid
+ This error is returned when a pattern that was successfully studied
+ using JIT is being matched, but the matching mode (partial or complete
+ match) does not correspond to any JIT compilation mode. When the JIT
+ fast path function is used, this error may be also given for invalid
options. See the pcre2jit documentation for more details.
PCRE2_ERROR_JIT_STACKLIMIT
- This error is returned when a pattern that was successfully studied
- using JIT is being matched, but the memory available for the just-in-
- time processing stack is not large enough. See the pcre2jit documenta-
+ This error is returned when a pattern that was successfully studied
+ using JIT is being matched, but the memory available for the just-in-
+ time processing stack is not large enough. See the pcre2jit documenta-
tion for more details.
PCRE2_ERROR_MATCHLIMIT
@@ -2327,10 +2363,10 @@
PCRE2_ERROR_NOMEMORY
- If a pattern contains back references, but the ovector is not big
- enough to remember the referenced substrings, PCRE2 gets a block of
+ If a pattern contains back references, but the ovector is not big
+ enough to remember the referenced substrings, PCRE2 gets a block of
memory at the start of matching to use for this purpose. There are some
- other special cases where extra memory is needed during matching. This
+ other special cases where extra memory is needed during matching. This
error is given when memory cannot be obtained.
PCRE2_ERROR_NULL
@@ -2339,12 +2375,12 @@
PCRE2_ERROR_RECURSELOOP
- This error is returned when pcre2_match() detects a recursion loop
- within the pattern. Specifically, it means that either the whole pat-
+ This error is returned when pcre2_match() detects a recursion loop
+ within the pattern. Specifically, it means that either the whole pat-
tern or a subpattern has been called recursively for the second time at
- the same position in the subject string. Some simple patterns that
- might do this are detected and faulted at compile time, but more com-
- plicated cases, in particular mutual recursions between two different
+ the same position in the subject string. Some simple patterns that
+ might do this are detected and faulted at compile time, but more com-
+ plicated cases, in particular mutual recursions between two different
subpatterns, cannot be detected until matching is attempted.
PCRE2_ERROR_RECURSIONLIMIT
@@ -2367,39 +2403,39 @@
void pcre2_substring_free(PCRE2_UCHAR *buffer);
- Captured substrings can be accessed directly by using the ovector as
+ Captured substrings can be accessed directly by using the ovector as
described above. For convenience, auxiliary functions are provided for
- extracting captured substrings as new, separate, zero-terminated
+ extracting captured substrings as new, separate, zero-terminated
strings. A substring that contains a binary zero is correctly extracted
- and has a further zero added on the end, but the result is not, of
+ and has a further zero added on the end, but the result is not, of
course, a C string.
The functions in this section identify substrings by number. The number
zero refers to the entire matched substring, with higher numbers refer-
- ring to substrings captured by parenthesized groups. After a partial
- match, only substring zero is available. An attempt to extract any
- other substring gives the error PCRE2_ERROR_PARTIAL. The next section
+ ring to substrings captured by parenthesized groups. After a partial
+ match, only substring zero is available. An attempt to extract any
+ other substring gives the error PCRE2_ERROR_PARTIAL. The next section
describes similar functions for extracting captured substrings by name.
- If a pattern uses the \K escape sequence within a positive assertion,
+ If a pattern uses the \K escape sequence within a positive assertion,
the reported start of a successful match can be greater than the end of
- the match. For example, if the pattern (?=ab\K) is matched against
- "ab", the start and end offset values for the match are 2 and 0. In
- this situation, calling these functions with a zero substring number
+ the match. For example, if the pattern (?=ab\K) is matched against
+ "ab", the start and end offset values for the match are 2 and 0. In
+ this situation, calling these functions with a zero substring number
extracts a zero-length empty string.
- You can find the length in code units of a captured substring without
- extracting it by calling pcre2_substring_length_bynumber(). The first
- argument is a pointer to the match data block, the second is the group
- number, and the third is a pointer to a variable into which the length
- is placed. If you just want to know whether or not the substring has
+ You can find the length in code units of a captured substring without
+ extracting it by calling pcre2_substring_length_bynumber(). The first
+ argument is a pointer to the match data block, the second is the group
+ number, and the third is a pointer to a variable into which the length
+ is placed. If you just want to know whether or not the substring has
been captured, you can pass the third argument as NULL.
- The pcre2_substring_copy_bynumber() function copies a captured sub-
- string into a supplied buffer, whereas pcre2_substring_get_bynumber()
- copies it into new memory, obtained using the same memory allocation
- function that was used for the match data block. The first two argu-
- ments of these functions are a pointer to the match data block and a
+ The pcre2_substring_copy_bynumber() function copies a captured sub-
+ string into a supplied buffer, whereas pcre2_substring_get_bynumber()
+ copies it into new memory, obtained using the same memory allocation
+ function that was used for the match data block. The first two argu-
+ ments of these functions are a pointer to the match data block and a
capturing group number.
The final arguments of pcre2_substring_copy_bynumber() are a pointer to
@@ -2408,25 +2444,25 @@
for the extracted substring, excluding the terminating zero.
For pcre2_substring_get_bynumber() the third and fourth arguments point
- to variables that are updated with a pointer to the new memory and the
- number of code units that comprise the substring, again excluding the
- terminating zero. When the substring is no longer needed, the memory
+ to variables that are updated with a pointer to the new memory and the
+ number of code units that comprise the substring, again excluding the
+ terminating zero. When the substring is no longer needed, the memory
should be freed by calling pcre2_substring_free().
- The return value from all these functions is zero for success, or a
- negative error code. If the pattern match failed, the match failure
- code is returned. If a substring number greater than zero is used
- after a partial match, PCRE2_ERROR_PARTIAL is returned. Other possible
+ The return value from all these functions is zero for success, or a
+ negative error code. If the pattern match failed, the match failure
+ code is returned. If a substring number greater than zero is used
+ after a partial match, PCRE2_ERROR_PARTIAL is returned. Other possible
error codes are:
PCRE2_ERROR_NOMEMORY
- The buffer was too small for pcre2_substring_copy_bynumber(), or the
+ The buffer was too small for pcre2_substring_copy_bynumber(), or the
attempt to get memory failed for pcre2_substring_get_bynumber().
PCRE2_ERROR_NOSUBSTRING
- There is no substring with that number in the pattern, that is, the
+ There is no substring with that number in the pattern, that is, the
number is greater than the number of capturing parentheses.
PCRE2_ERROR_UNAVAILABLE
@@ -2437,8 +2473,8 @@
PCRE2_ERROR_UNSET
- The substring did not participate in the match. For example, if the
- pattern is (abc)|(def) and the subject is "def", and the ovector con-
+ The substring did not participate in the match. For example, if the
+ pattern is (abc)|(def) and the subject is "def", and the ovector con-
tains at least two capturing slots, substring number 1 is unset.
@@ -2449,32 +2485,32 @@
void pcre2_substring_list_free(PCRE2_SPTR *list);
- The pcre2_substring_list_get() function extracts all available sub-
- strings and builds a list of pointers to them. It also (optionally)
- builds a second list that contains their lengths (in code units),
+ The pcre2_substring_list_get() function extracts all available sub-
+ strings and builds a list of pointers to them. It also (optionally)
+ builds a second list that contains their lengths (in code units),
excluding a terminating zero that is added to each of them. All this is
done in a single block of memory that is obtained using the same memory
allocation function that was used to get the match data block.
- This function must be called only after a successful match. If called
+ This function must be called only after a successful match. If called
after a partial match, the error code PCRE2_ERROR_PARTIAL is returned.
- The address of the memory block is returned via listptr, which is also
+ The address of the memory block is returned via listptr, which is also
the start of the list of string pointers. The end of the list is marked
- by a NULL pointer. The address of the list of lengths is returned via
- lengthsptr. If your strings do not contain binary zeros and you do not
+ by a NULL pointer. The address of the list of lengths is returned via
+ lengthsptr. If your strings do not contain binary zeros and you do not
therefore need the lengths, you may supply NULL as the lengthsptr argu-
- ment to disable the creation of a list of lengths. The yield of the
- function is zero if all went well, or PCRE2_ERROR_NOMEMORY if the mem-
- ory block could not be obtained. When the list is no longer needed, it
+ ment to disable the creation of a list of lengths. The yield of the
+ function is zero if all went well, or PCRE2_ERROR_NOMEMORY if the mem-
+ ory block could not be obtained. When the list is no longer needed, it
should be freed by calling pcre2_substring_list_free().
If this function encounters a substring that is unset, which can happen
- when capturing subpattern number n+1 matches some part of the subject,
- but subpattern n has not been used at all, it returns an empty string.
- This can be distinguished from a genuine zero-length substring by
+ when capturing subpattern number n+1 matches some part of the subject,
+ but subpattern n has not been used at all, it returns an empty string.
+ This can be distinguished from a genuine zero-length substring by
inspecting the appropriate offset in the ovector, which contain
- PCRE2_UNSET for unset substrings, or by calling pcre2_sub-
+ PCRE2_UNSET for unset substrings, or by calling pcre2_sub-
string_length_bynumber().
@@ -2494,39 +2530,39 @@
void pcre2_substring_free(PCRE2_UCHAR *buffer);
- To extract a substring by name, you first have to find associated num-
+ To extract a substring by name, you first have to find associated num-
ber. For example, for this pattern:
(a+)b(?<xxx>\d+)...
the number of the subpattern called "xxx" is 2. If the name is known to
- be unique (PCRE2_DUPNAMES was not set), you can find the number from
+ be unique (PCRE2_DUPNAMES was not set), you can find the number from
the name by calling pcre2_substring_number_from_name(). The first argu-
- ment is the compiled pattern, and the second is the name. The yield of
+ ment is the compiled pattern, and the second is the name. The yield of
the function is the subpattern number, PCRE2_ERROR_NOSUBSTRING if there
- is no subpattern of that name, or PCRE2_ERROR_NOUNIQUESUBSTRING if
- there is more than one subpattern of that name. Given the number, you
- can extract the substring directly, or use one of the functions
+ is no subpattern of that name, or PCRE2_ERROR_NOUNIQUESUBSTRING if
+ there is more than one subpattern of that name. Given the number, you
+ can extract the substring directly, or use one of the functions
described above.
- For convenience, there are also "byname" functions that correspond to
- the "bynumber" functions, the only difference being that the second
- argument is a name instead of a number. If PCRE2_DUPNAMES is set and
+ For convenience, there are also "byname" functions that correspond to
+ the "bynumber" functions, the only difference being that the second
+ argument is a name instead of a number. If PCRE2_DUPNAMES is set and
there are duplicate names, these functions scan all the groups with the
given name, and return the first named string that is set.
- If there are no groups with the given name, PCRE2_ERROR_NOSUBSTRING is
- returned. If all groups with the name have numbers that are greater
- than the number of slots in the ovector, PCRE2_ERROR_UNAVAILABLE is
- returned. If there is at least one group with a slot in the ovector,
+ If there are no groups with the given name, PCRE2_ERROR_NOSUBSTRING is
+ returned. If all groups with the name have numbers that are greater
+ than the number of slots in the ovector, PCRE2_ERROR_UNAVAILABLE is
+ returned. If there is at least one group with a slot in the ovector,
but no group is found to be set, PCRE2_ERROR_UNSET is returned.
Warning: If the pattern uses the (?| feature to set up multiple subpat-
- terns with the same number, as described in the section on duplicate
- subpattern numbers in the pcre2pattern page, you cannot use names to
- distinguish the different subpatterns, because names are not included
- in the compiled code. The matching process uses only numbers. For this
- reason, the use of different names for subpatterns of the same number
+ terns with the same number, as described in the section on duplicate
+ subpattern numbers in the pcre2pattern page, you cannot use names to
+ distinguish the different subpatterns, because names are not included
+ in the compiled code. The matching process uses only numbers. For this
+ reason, the use of different names for subpatterns of the same number
causes an error at compile time.
@@ -2538,15 +2574,15 @@
pcre2_match_context *mcontext, PCRE2_SPTR replacementzfP,
PCRE2_SIZE rlength, PCRE2_UCHAR *outputbufferP,
PCRE2_SIZE *outlengthptr);
- This function calls pcre2_match() and then makes a copy of the subject
- string in outputbuffer, replacing the part that was matched with the
- replacement string, whose length is supplied in rlength. This can be
+ This function calls pcre2_match() and then makes a copy of the subject
+ string in outputbuffer, replacing the part that was matched with the
+ replacement string, whose length is supplied in rlength. This can be
given as PCRE2_ZERO_TERMINATED for a zero-terminated string.
- In the replacement string, which is interpreted as a UTF string in UTF
- mode, and is checked for UTF validity unless the PCRE2_NO_UTF_CHECK
+ In the replacement string, which is interpreted as a UTF string in UTF
+ mode, and is checked for UTF validity unless the PCRE2_NO_UTF_CHECK
option is set, a dollar character is an escape character that can spec-
- ify the insertion of characters from capturing groups or (*MARK) items
+ ify the insertion of characters from capturing groups or (*MARK) items
in the pattern. The following forms are recognized:
$$ insert a dollar character
@@ -2553,12 +2589,12 @@
$<n> or ${<n>} insert the contents of group <n>
$*MARK or ${*MARK} insert the name of the last (*MARK) encountered
- Either a group number or a group name can be given for <n>. Curly
- brackets are required only if the following character would be inter-
+ Either a group number or a group name can be given for <n>. Curly
+ brackets are required only if the following character would be inter-
preted as part of the number or name. The number may be zero to include
- the entire matched string. For example, if the pattern a(b)c is
- matched with "=abc=" and the replacement string "+$1$0$1+", the result
- is "=+babcb+=". Group insertion is done by calling pcre2_copy_byname()
+ the entire matched string. For example, if the pattern a(b)c is
+ matched with "=abc=" and the replacement string "+$1$0$1+", the result
+ is "=+babcb+=". Group insertion is done by calling pcre2_copy_byname()
or pcre2_copy_bynumber() as appropriate.
The facility for inserting a (*MARK) name can be used to perform simple
@@ -2568,30 +2604,30 @@
apple lemon
2: pear orange
- The first seven arguments of pcre2_substitute() are the same as for
+ The first seven arguments of pcre2_substitute() are the same as for
pcre2_match(), except that the partial matching options are not permit-
- ted, and match_data may be passed as NULL, in which case a match data
- block is obtained and freed within this function, using memory manage-
- ment functions from the match context, if provided, or else those that
+ ted, and match_data may be passed as NULL, in which case a match data
+ block is obtained and freed within this function, using memory manage-
+ ment functions from the match context, if provided, or else those that
were used to allocate memory for the compiled code.
- There is one additional option, PCRE2_SUBSTITUTE_GLOBAL, which causes
+ There is one additional option, PCRE2_SUBSTITUTE_GLOBAL, which causes
the function to iterate over the subject string, replacing every match-
ing substring. If this is not set, only the first matching substring is
replaced.
- The outlengthptr argument must point to a variable that contains the
- length, in code units, of the output buffer. It is updated to contain
+ The outlengthptr argument must point to a variable that contains the
+ length, in code units, of the output buffer. It is updated to contain
the length of the new string, excluding the trailing zero that is auto-
matically added.
- The function returns the number of replacements that were made. This
- may be zero if no matches were found, and is never greater than 1
+ The function returns the number of replacements that were made. This
+ may be zero if no matches were found, and is never greater than 1
unless PCRE2_SUBSTITUTE_GLOBAL is set. In the event of an error, a neg-
- ative error code is returned. Except for PCRE2_ERROR_NOMATCH (which is
+ ative error code is returned. Except for PCRE2_ERROR_NOMATCH (which is
never returned), any errors from pcre2_match() or the substring copying
functions are passed straight back. PCRE2_ERROR_BADREPLACEMENT is
- returned for an invalid replacement string (unrecognized sequence fol-
+ returned for an invalid replacement string (unrecognized sequence fol-
lowing a dollar sign), and PCRE2_ERROR_NOMEMORY is returned if the out-
put buffer is not big enough.
@@ -2601,38 +2637,38 @@
int pcre2_substring_nametable_scan(const pcre2_code *code,
PCRE2_SPTR name, PCRE2_SPTR *first, PCRE2_SPTR *last);
- When a pattern is compiled with the PCRE2_DUPNAMES option, names for
- subpatterns are not required to be unique. Duplicate names are always
- allowed for subpatterns with the same number, created by using the (?|
- feature. Indeed, if such subpatterns are named, they are required to
+ When a pattern is compiled with the PCRE2_DUPNAMES option, names for
+ subpatterns are not required to be unique. Duplicate names are always
+ allowed for subpatterns with the same number, created by using the (?|
+ feature. Indeed, if such subpatterns are named, they are required to
use the same names.
Normally, patterns with duplicate names are such that in any one match,
- only one of the named subpatterns participates. An example is shown in
+ only one of the named subpatterns participates. An example is shown in
the pcre2pattern documentation.
- When duplicates are present, pcre2_substring_copy_byname() and
- pcre2_substring_get_byname() return the first substring corresponding
- to the given name that is set. Only if none are set is
- PCRE2_ERROR_UNSET is returned. The pcre2_substring_number_from_name()
+ When duplicates are present, pcre2_substring_copy_byname() and
+ pcre2_substring_get_byname() return the first substring corresponding
+ to the given name that is set. Only if none are set is
+ PCRE2_ERROR_UNSET is returned. The pcre2_substring_number_from_name()
function returns the error PCRE2_ERROR_NOUNIQUESUBSTRING when there are
duplicate names.
- If you want to get full details of all captured substrings for a given
- name, you must use the pcre2_substring_nametable_scan() function. The
- first argument is the compiled pattern, and the second is the name. If
- the third and fourth arguments are NULL, the function returns a group
+ If you want to get full details of all captured substrings for a given
+ name, you must use the pcre2_substring_nametable_scan() function. The
+ first argument is the compiled pattern, and the second is the name. If
+ the third and fourth arguments are NULL, the function returns a group
number for a unique name, or PCRE2_ERROR_NOUNIQUESUBSTRING otherwise.
When the third and fourth arguments are not NULL, they must be pointers
- to variables that are updated by the function. After it has run, they
+ to variables that are updated by the function. After it has run, they
point to the first and last entries in the name-to-number table for the
- given name, and the function returns the length of each entry in code
- units. In both cases, PCRE2_ERROR_NOSUBSTRING is returned if there are
+ given name, and the function returns the length of each entry in code
+ units. In both cases, PCRE2_ERROR_NOSUBSTRING is returned if there are
no entries for the given name.
The format of the name table is described above in the section entitled
- Information about a pattern above. Given all the relevant entries for
+ Information about a pattern above. Given all the relevant entries for
the name, you can extract each of their numbers, and hence the captured
data.
@@ -2639,18 +2675,18 @@
FINDING ALL POSSIBLE MATCHES AT ONE POSITION
- The traditional matching function uses a similar algorithm to Perl,
- which stops when it finds the first match at a given point in the sub-
+ The traditional matching function uses a similar algorithm to Perl,
+ which stops when it finds the first match at a given point in the sub-
ject. If you want to find all possible matches, or the longest possible
- match at a given position, consider using the alternative matching
- function (see below) instead. If you cannot use the alternative func-
+ match at a given position, consider using the alternative matching
+ function (see below) instead. If you cannot use the alternative func-
tion, you can kludge it up by making use of the callout facility, which
is described in the pcre2callout documentation.
What you have to do is to insert a callout right at the end of the pat-
- tern. When your callout function is called, extract and save the cur-
- rent matched substring. Then return 1, which forces pcre2_match() to
- backtrack and try other alternatives. Ultimately, when it runs out of
+ tern. When your callout function is called, extract and save the cur-
+ rent matched substring. Then return 1, which forces pcre2_match() to
+ backtrack and try other alternatives. Ultimately, when it runs out of
matches, pcre2_match() will yield PCRE2_ERROR_NOMATCH.
@@ -2662,26 +2698,26 @@
pcre2_match_context *mcontext,
int *workspace, PCRE2_SIZE wscount);
- The function pcre2_dfa_match() is called to match a subject string
- against a compiled pattern, using a matching algorithm that scans the
- subject string just once, and does not backtrack. This has different
- characteristics to the normal algorithm, and is not compatible with
- Perl. Some of the features of PCRE2 patterns are not supported. Never-
- theless, there are times when this kind of matching can be useful. For
- a discussion of the two matching algorithms, and a list of features
+ The function pcre2_dfa_match() is called to match a subject string
+ against a compiled pattern, using a matching algorithm that scans the
+ subject string just once, and does not backtrack. This has different
+ characteristics to the normal algorithm, and is not compatible with
+ Perl. Some of the features of PCRE2 patterns are not supported. Never-
+ theless, there are times when this kind of matching can be useful. For
+ a discussion of the two matching algorithms, and a list of features
that pcre2_dfa_match() does not support, see the pcre2matching documen-
tation.
- The arguments for the pcre2_dfa_match() function are the same as for
+ The arguments for the pcre2_dfa_match() function are the same as for
pcre2_match(), plus two extras. The ovector within the match data block
is used in a different way, and this is described below. The other com-
- mon arguments are used in the same way as for pcre2_match(), so their
+ mon arguments are used in the same way as for pcre2_match(), so their
description is not repeated here.
- The two additional arguments provide workspace for the function. The
- workspace vector should contain at least 20 elements. It is used for
+ The two additional arguments provide workspace for the function. The
+ workspace vector should contain at least 20 elements. It is used for
keeping track of multiple paths through the pattern tree. More
- workspace is needed for patterns and subjects where there are a lot of
+ workspace is needed for patterns and subjects where there are a lot of
potential matches.
Here is an example of a simple call to pcre2_dfa_match():
@@ -2701,45 +2737,45 @@
Option bits for pcre_dfa_match()
- The unused bits of the options argument for pcre2_dfa_match() must be
- zero. The only bits that may be set are PCRE2_ANCHORED, PCRE2_NOTBOL,
+ The unused bits of the options argument for pcre2_dfa_match() must be
+ zero. The only bits that may be set are PCRE2_ANCHORED, PCRE2_NOTBOL,
PCRE2_NOTEOL, PCRE2_NOTEMPTY, PCRE2_NOTEMPTY_ATSTART,
PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, PCRE2_PARTIAL_SOFT,
- PCRE2_DFA_SHORTEST, and PCRE2_DFA_RESTART. All but the last four of
- these are exactly the same as for pcre2_match(), so their description
+ PCRE2_DFA_SHORTEST, and PCRE2_DFA_RESTART. All but the last four of
+ these are exactly the same as for pcre2_match(), so their description
is not repeated here.
PCRE2_PARTIAL_HARD
PCRE2_PARTIAL_SOFT
- These have the same general effect as they do for pcre2_match(), but
- the details are slightly different. When PCRE2_PARTIAL_HARD is set for
- pcre2_dfa_match(), it returns PCRE2_ERROR_PARTIAL if the end of the
+ These have the same general effect as they do for pcre2_match(), but
+ the details are slightly different. When PCRE2_PARTIAL_HARD is set for
+ pcre2_dfa_match(), it returns PCRE2_ERROR_PARTIAL if the end of the
subject is reached and there is still at least one matching possibility
that requires additional characters. This happens even if some complete
- matches have already been found. When PCRE2_PARTIAL_SOFT is set, the
- return code PCRE2_ERROR_NOMATCH is converted into PCRE2_ERROR_PARTIAL
- if the end of the subject is reached, there have been no complete
+ matches have already been found. When PCRE2_PARTIAL_SOFT is set, the
+ return code PCRE2_ERROR_NOMATCH is converted into PCRE2_ERROR_PARTIAL
+ if the end of the subject is reached, there have been no complete
matches, but there is still at least one matching possibility. The por-
- tion of the string that was inspected when the longest partial match
+ tion of the string that was inspected when the longest partial match
was found is set as the first matching string in both cases. There is a
- more detailed discussion of partial and multi-segment matching, with
+ more detailed discussion of partial and multi-segment matching, with
examples, in the pcre2partial documentation.
PCRE2_DFA_SHORTEST
- Setting the PCRE2_DFA_SHORTEST option causes the matching algorithm to
+ Setting the PCRE2_DFA_SHORTEST option causes the matching algorithm to
stop as soon as it has found one match. Because of the way the alterna-
- tive algorithm works, this is necessarily the shortest possible match
+ tive algorithm works, this is necessarily the shortest possible match
at the first possible matching point in the subject string.
PCRE2_DFA_RESTART
- When pcre2_dfa_match() returns a partial match, it is possible to call
+ When pcre2_dfa_match() returns a partial match, it is possible to call
it again, with additional subject characters, and have it continue with
the same match. The PCRE2_DFA_RESTART option requests this action; when
- it is set, the workspace and wscount options must reference the same
- vector as before because data about the match so far is left in them
+ it is set, the workspace and wscount options must reference the same
+ vector as before because data about the match so far is left in them
after a partial match. There is more discussion of this facility in the
pcre2partial documentation.
@@ -2747,8 +2783,8 @@
When pcre2_dfa_match() succeeds, it may have matched more than one sub-
string in the subject. Note, however, that all the matches from one run
- of the function start at the same point in the subject. The shorter
- matches are all initial substrings of the longer matches. For example,
+ of the function start at the same point in the subject. The shorter
+ matches are all initial substrings of the longer matches. For example,
if the pattern
<.*>
@@ -2763,17 +2799,17 @@
<something> <something else>
<something>
- On success, the yield of the function is a number greater than zero,
- which is the number of matched substrings. The offsets of the sub-
- strings are returned in the ovector, and can be extracted by number in
- the same way as for pcre2_match(), but the numbers bear no relation to
- any capturing groups that may exist in the pattern, because DFA match-
+ On success, the yield of the function is a number greater than zero,
+ which is the number of matched substrings. The offsets of the sub-
+ strings are returned in the ovector, and can be extracted by number in
+ the same way as for pcre2_match(), but the numbers bear no relation to
+ any capturing groups that may exist in the pattern, because DFA match-
ing does not support group capture.
- Calls to the convenience functions that extract substrings by name
- return the error PCRE2_ERROR_DFA_UFUNC (unsupported function) if used
+ Calls to the convenience functions that extract substrings by name
+ return the error PCRE2_ERROR_DFA_UFUNC (unsupported function) if used
after a DFA match. The convenience functions that extract substrings by
- number never return PCRE2_ERROR_NOSUBSTRING, and the meanings of some
+ number never return PCRE2_ERROR_NOSUBSTRING, and the meanings of some
other errors are slightly different:
PCRE2_ERROR_UNAVAILABLE
@@ -2783,64 +2819,64 @@
PCRE2_ERROR_UNSET
- There is a slot in the ovector for this substring, but there were
+ There is a slot in the ovector for this substring, but there were
insufficient matches to fill it.
- The matched strings are stored in the ovector in reverse order of
- length; that is, the longest matching string is first. If there were
- too many matches to fit into the ovector, the yield of the function is
+ The matched strings are stored in the ovector in reverse order of
+ length; that is, the longest matching string is first. If there were
+ too many matches to fit into the ovector, the yield of the function is
zero, and the vector is filled with the longest matches.
- NOTE: PCRE2's "auto-possessification" optimization usually applies to
- character repeats at the end of a pattern (as well as internally). For
- example, the pattern "a\d+" is compiled as if it were "a\d++". For DFA
- matching, this means that only one possible match is found. If you
- really do want multiple matches in such cases, either use an ungreedy
- repeat auch as "a\d+?" or set the PCRE2_NO_AUTO_POSSESS option when
+ NOTE: PCRE2's "auto-possessification" optimization usually applies to
+ character repeats at the end of a pattern (as well as internally). For
+ example, the pattern "a\d+" is compiled as if it were "a\d++". For DFA
+ matching, this means that only one possible match is found. If you
+ really do want multiple matches in such cases, either use an ungreedy
+ repeat auch as "a\d+?" or set the PCRE2_NO_AUTO_POSSESS option when
compiling.
Error returns from pcre2_dfa_match()
The pcre2_dfa_match() function returns a negative number when it fails.
- Many of the errors are the same as for pcre2_match(), as described
+ Many of the errors are the same as for pcre2_match(), as described
above. There are in addition the following errors that are specific to
pcre2_dfa_match():
PCRE2_ERROR_DFA_UITEM
- This return is given if pcre2_dfa_match() encounters an item in the
+ This return is given if pcre2_dfa_match() encounters an item in the
pattern that it does not support, for instance, the use of \C or a back
reference.
PCRE2_ERROR_DFA_UCOND
- This return is given if pcre2_dfa_match() encounters a condition item
- that uses a back reference for the condition, or a test for recursion
+ This return is given if pcre2_dfa_match() encounters a condition item
+ that uses a back reference for the condition, or a test for recursion
in a specific group. These are not supported.
PCRE2_ERROR_DFA_WSSIZE
- This return is given if pcre2_dfa_match() runs out of space in the
+ This return is given if pcre2_dfa_match() runs out of space in the
workspace vector.
PCRE2_ERROR_DFA_RECURSE
- When a recursive subpattern is processed, the matching function calls
+ When a recursive subpattern is processed, the matching function calls
itself recursively, using private memory for the ovector and workspace.
- This error is given if the internal ovector is not large enough. This
+ This error is given if the internal ovector is not large enough. This
should be extremely rare, as a vector of size 1000 is used.
PCRE2_ERROR_DFA_BADRESTART
- When pcre2_dfa_match() is called with the PCRE2_DFA_RESTART option,
- some plausibility checks are made on the contents of the workspace,
- which should contain data about the previous partial match. If any of
+ When pcre2_dfa_match() is called with the PCRE2_DFA_RESTART option,
+ some plausibility checks are made on the contents of the workspace,
+ which should contain data about the previous partial match. If any of
these checks fail, this error is given.
SEE ALSO
- pcre2build(3), pcre2callout(3), pcre2demo(3), pcre2matching(3),
+ pcre2build(3), pcre2callout(3), pcre2demo(3), pcre2matching(3),
pcre2partial(3), pcre2posix(3), pcre2sample(3), pcre2stack(3),
pcre2unicode(3).
@@ -2854,7 +2890,7 @@
REVISION
- Last updated: 02 September 2015
+ Last updated: 22 September 2015
Copyright (c) 1997-2015 University of Cambridge.
------------------------------------------------------------------------------
@@ -5002,6 +5038,4298 @@
------------------------------------------------------------------------------
+PCRE2PATTERN(3) Library Functions Manual PCRE2PATTERN(3)
+
+
+
+NAME
+ PCRE2 - Perl-compatible regular expressions (revised API)
+
+PCRE2 REGULAR EXPRESSION DETAILS
+
+ The syntax and semantics of the regular expressions that are supported
+ by PCRE2 are described in detail below. There is a quick-reference syn-
+ tax summary in the pcre2syntax page. PCRE2 tries to match Perl syntax
+ and semantics as closely as it can. PCRE2 also supports some alterna-
+ tive regular expression syntax (which does not conflict with the Perl
+ syntax) in order to provide some compatibility with regular expressions
+ in Python, .NET, and Oniguruma.
+
+ Perl's regular expressions are described in its own documentation, and
+ regular expressions in general are covered in a number of books, some
+ of which have copious examples. Jeffrey Friedl's "Mastering Regular
+ Expressions", published by O'Reilly, covers regular expressions in
+ great detail. This description of PCRE2's regular expressions is
+ intended as reference material.
+
+ This document discusses the patterns that are supported by PCRE2 when
+ its main matching function, pcre2_match(), is used. PCRE2 also has an
+ alternative matching function, pcre2_dfa_match(), which matches using a
+ different algorithm that is not Perl-compatible. Some of the features
+ discussed below are not available when DFA matching is used. The advan-
+ tages and disadvantages of the alternative function, and how it differs
+ from the normal function, are discussed in the pcre2matching page.
+
+
+SPECIAL START-OF-PATTERN ITEMS
+
+ A number of options that can be passed to pcre2_compile() can also be
+ set by special items at the start of a pattern. These are not Perl-com-
+ patible, but are provided to make these options accessible to pattern
+ writers who are not able to change the program that processes the pat-
+ tern. Any number of these items may appear, but they must all be
+ together right at the start of the pattern string, and the letters must
+ be in upper case.
+
+ UTF support
+
+ In the 8-bit and 16-bit PCRE2 libraries, characters may be coded either
+ as single code units, or as multiple UTF-8 or UTF-16 code units. UTF-32
+ can be specified for the 32-bit library, in which case it constrains
+ the character values to valid Unicode code points. To process UTF
+ strings, PCRE2 must be built to include Unicode support (which is the
+ default). When using UTF strings you must either call the compiling
+ function with the PCRE2_UTF option, or the pattern must start with the
+ special sequence (*UTF), which is equivalent to setting the relevant
+ option. How setting a UTF mode affects pattern matching is mentioned in
+ several places below. There is also a summary of features in the
+ pcre2unicode page.
+
+ Some applications that allow their users to supply patterns may wish to
+ restrict them to non-UTF data for security reasons. If the
+ PCRE2_NEVER_UTF option is passed to pcre2_compile(), (*UTF) is not
+ allowed, and its appearance in a pattern causes an error.
+
+ Unicode property support
+
+ Another special sequence that may appear at the start of a pattern is
+ (*UCP). This has the same effect as setting the PCRE2_UCP option: it
+ causes sequences such as \d and \w to use Unicode properties to deter-
+ mine character types, instead of recognizing only characters with codes
+ less than 256 via a lookup table.
+
+ Some applications that allow their users to supply patterns may wish to
+ restrict them for security reasons. If the PCRE2_NEVER_UCP option is
+ passed to pcre2_compile(), (*UCP) is not allowed, and its appearance in
+ a pattern causes an error.
+
+ Locking out empty string matching
+
+ Starting a pattern with (*NOTEMPTY) or (*NOTEMPTY_ATSTART) has the same
+ effect as passing the PCRE2_NOTEMPTY or PCRE2_NOTEMPTY_ATSTART option
+ to whichever matching function is subsequently called to match the pat-
+ tern. These options lock out the matching of empty strings, either
+ entirely, or only at the start of the subject.
+
+ Disabling auto-possessification
+
+ If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as
+ setting the PCRE2_NO_AUTO_POSSESS option. This stops PCRE2 from making
+ quantifiers possessive when what follows cannot match the repeated
+ item. For example, by default a+b is treated as a++b. For more details,
+ see the pcre2api documentation.
+
+ Disabling start-up optimizations
+
+ If a pattern starts with (*NO_START_OPT), it has the same effect as
+ setting the PCRE2_NO_START_OPTIMIZE option. This disables several opti-
+ mizations for quickly reaching "no match" results. For more details,
+ see the pcre2api documentation.
+
+ Disabling automatic anchoring
+
+ If a pattern starts with (*NO_DOTSTAR_ANCHOR), it has the same effect
+ as setting the PCRE2_NO_DOTSTAR_ANCHOR option. This disables optimiza-
+ tions that apply to patterns whose top-level branches all start with .*
+ (match any number of arbitrary characters). For more details, see the
+ pcre2api documentation.
+
+ Disabling JIT compilation
+
+ If a pattern that starts with (*NO_JIT) is successfully compiled, an
+ attempt by the application to apply the JIT optimization by calling
+ pcre2_jit_compile() is ignored.
+
+ Setting match and recursion limits
+
+ The caller of pcre2_match() can set a limit on the number of times the
+ internal match() function is called and on the maximum depth of recur-
+ sive calls. These facilities are provided to catch runaway matches that
+ are provoked by patterns with huge matching trees (a typical example is
+ a pattern with nested unlimited repeats) and to avoid running out of
+ system stack by too much recursion. When one of these limits is
+ reached, pcre2_match() gives an error return. The limits can also be
+ set by items at the start of the pattern of the form
+
+ (*LIMIT_MATCH=d)
+ (*LIMIT_RECURSION=d)
+
+ where d is any number of decimal digits. However, the value of the set-
+ ting must be less than the value set (or defaulted) by the caller of
+ pcre2_match() for it to have any effect. In other words, the pattern
+ writer can lower the limits set by the programmer, but not raise them.
+ If there is more than one setting of one of these limits, the lower
+ value is used.
+
+ Newline conventions
+
+ PCRE2 supports five different conventions for indicating line breaks in
+ strings: a single CR (carriage return) character, a single LF (line-
+ feed) character, the two-character sequence CRLF, any of the three pre-
+ ceding, or any Unicode newline sequence. The pcre2api page has further
+ discussion about newlines, and shows how to set the newline convention
+ when calling pcre2_compile().
+
+ It is also possible to specify a newline convention by starting a pat-
+ tern string with one of the following five sequences:
+
+ (*CR) carriage return
+ (*LF) linefeed
+ (*CRLF) carriage return, followed by linefeed
+ (*ANYCRLF) any of the three above
+ (*ANY) all Unicode newline sequences
+
+ These override the default and the options given to the compiling func-
+ tion. For example, on a Unix system where LF is the default newline
+ sequence, the pattern
+
+ (*CR)a.b
+
+ changes the convention to CR. That pattern matches "a\nb" because LF is
+ no longer a newline. If more than one of these settings is present, the
+ last one is used.
+
+ The newline convention affects where the circumflex and dollar asser-
+ tions are true. It also affects the interpretation of the dot metachar-
+ acter when PCRE2_DOTALL is not set, and the behaviour of \N. However,
+ it does not affect what the \R escape sequence matches. By default,
+ this is any Unicode newline sequence, for Perl compatibility. However,
+ this can be changed; see the description of \R in the section entitled
+ "Newline sequences" below. A change of \R setting can be combined with
+ a change of newline convention.
+
+ Specifying what \R matches
+
+ It is possible to restrict \R to match only CR, LF, or CRLF (instead of
+ the complete set of Unicode line endings) by setting the option
+ PCRE2_BSR_ANYCRLF at compile time. This effect can also be achieved by
+ starting a pattern with (*BSR_ANYCRLF). For completeness, (*BSR_UNI-
+ CODE) is also recognized, corresponding to PCRE2_BSR_UNICODE.
+
+
+EBCDIC CHARACTER CODES
+
+ PCRE2 can be compiled to run in an environment that uses EBCDIC as its
+ character code rather than ASCII or Unicode (typically a mainframe sys-
+ tem). In the sections below, character code values are ASCII or Uni-
+ code; in an EBCDIC environment these characters may have different code
+ values, and there are no code points greater than 255.
+
+
+CHARACTERS AND METACHARACTERS
+
+ A regular expression is a pattern that is matched against a subject
+ string from left to right. Most characters stand for themselves in a
+ pattern, and match the corresponding characters in the subject. As a
+ trivial example, the pattern
+
+ The quick brown fox
+
+ matches a portion of a subject string that is identical to itself. When
+ caseless matching is specified (the PCRE2_CASELESS option), letters are
+ matched independently of case.
+
+ The power of regular expressions comes from the ability to include
+ alternatives and repetitions in the pattern. These are encoded in the
+ pattern by the use of metacharacters, which do not stand for themselves
+ but instead are interpreted in some special way.
+
+ There are two different sets of metacharacters: those that are recog-
+ nized anywhere in the pattern except within square brackets, and those
+ that are recognized within square brackets. Outside square brackets,
+ the metacharacters are as follows:
+
+ \ general escape character with several uses
+ ^ assert start of string (or line, in multiline mode)
+ $ assert end of string (or line, in multiline mode)
+ . match any character except newline (by default)
+ [ start character class definition
+ | start of alternative branch
+ ( start subpattern
+ ) end subpattern
+ ? extends the meaning of (
+ also 0 or 1 quantifier
+ also quantifier minimizer
+ * 0 or more quantifier
+ + 1 or more quantifier
+ also "possessive quantifier"
+ { start min/max quantifier
+
+ Part of a pattern that is in square brackets is called a "character
+ class". In a character class the only metacharacters are:
+
+ \ general escape character
+ ^ negate the class, but only if the first character
+ - indicates character range
+ [ POSIX character class (only if followed by POSIX
+ syntax)
+ ] terminates the character class
+
+ The following sections describe the use of each of the metacharacters.
+
+
+BACKSLASH
+
+ The backslash character has several uses. Firstly, if it is followed by
+ a character that is not a number or a letter, it takes away any special
+ meaning that character may have. This use of backslash as an escape
+ character applies both inside and outside character classes.
+
+ For example, if you want to match a * character, you write \* in the
+ pattern. This escaping action applies whether or not the following
+ character would otherwise be interpreted as a metacharacter, so it is
+ always safe to precede a non-alphanumeric with backslash to specify
+ that it stands for itself. In particular, if you want to match a back-
+ slash, you write \\.
+
+ In a UTF mode, only ASCII numbers and letters have any special meaning
+ after a backslash. All other characters (in particular, those whose
+ codepoints are greater than 127) are treated as literals.
+
+ If a pattern is compiled with the PCRE2_EXTENDED option, most white
+ space in the pattern (other than in a character class), and characters
+ between a # outside a character class and the next newline, inclusive,
+ are ignored. An escaping backslash can be used to include a white space
+ or # character as part of the pattern.
+
+ If you want to remove the special meaning from a sequence of charac-
+ ters, you can do so by putting them between \Q and \E. This is differ-
+ ent from Perl in that $ and @ are handled as literals in \Q...\E
+ sequences in PCRE2, whereas in Perl, $ and @ cause variable interpola-
+ tion. Note the following examples:
+
+ Pattern PCRE2 matches Perl matches
+
+ \Qabc$xyz\E abc$xyz abc followed by the
+ contents of $xyz
+ \Qabc\$xyz\E abc\$xyz abc\$xyz
+ \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
+
+ The \Q...\E sequence is recognized both inside and outside character
+ classes. An isolated \E that is not preceded by \Q is ignored. If \Q
+ is not followed by \E later in the pattern, the literal interpretation
+ continues to the end of the pattern (that is, \E is assumed at the
+ end). If the isolated \Q is inside a character class, this causes an
+ error, because the character class is not terminated.
+
+ Non-printing characters
+
+ A second use of backslash provides a way of encoding non-printing char-
+ acters in patterns in a visible manner. There is no restriction on the
+ appearance of non-printing characters in a pattern, but when a pattern
+ is being prepared by text editing, it is often easier to use one of the
+ following escape sequences than the binary character it represents. In
+ an ASCII or Unicode environment, these escapes are as follows:
+
+ \a alarm, that is, the BEL character (hex 07)
+ \cx "control-x", where x is any printable ASCII character
+ \e escape (hex 1B)
+ \f form feed (hex 0C)
+ \n linefeed (hex 0A)
+ \r carriage return (hex 0D)
+ \t tab (hex 09)
+ \0dd character with octal code 0dd
+ \ddd character with octal code ddd, or back reference
+ \o{ddd..} character with octal code ddd..
+ \xhh character with hex code hh
+ \x{hhh..} character with hex code hhh.. (default mode)
+ \uhhhh character with hex code hhhh (when PCRE2_ALT_BSUX is set)
+
+ The precise effect of \cx on ASCII characters is as follows: if x is a
+ lower case letter, it is converted to upper case. Then bit 6 of the
+ character (hex 40) is inverted. Thus \cA to \cZ become hex 01 to hex 1A
+ (A is 41, Z is 5A), but \c{ becomes hex 3B ({ is 7B), and \c; becomes
+ hex 7B (; is 3B). If the code unit following \c has a value less than
+ 32 or greater than 126, a compile-time error occurs. This locks out
+ non-printable ASCII characters in all modes.
+
+ When PCRE2 is compiled in EBCDIC mode, \a, \e, \f, \n, \r, and \t gen-
+ erate the appropriate EBCDIC code values. The \c escape is processed as
+ specified for Perl in the perlebcdic document. The only characters that
+ are allowed after \c are A-Z, a-z, or one of @, [, \, ], ^, _, or ?.
+ Any other character provokes a compile-time error. The sequence \@
+ encodes character code 0; the letters (in either case) encode charac-
+ ters 1-26 (hex 01 to hex 1A); [, \, ], ^, and _ encode characters 27-31
+ (hex 1B to hex 1F), and \? becomes either 255 (hex FF) or 95 (hex 5F).
+
+ Thus, apart from \?, these escapes generate the same character code
+ values as they do in an ASCII environment, though the meanings of the
+ values mostly differ. For example, \G always generates code value 7,
+ which is BEL in ASCII but DEL in EBCDIC.
+
+ The sequence \? generates DEL (127, hex 7F) in an ASCII environment,
+ but because 127 is not a control character in EBCDIC, Perl makes it
+ generate the APC character. Unfortunately, there are several variants
+ of EBCDIC. In most of them the APC character has the value 255 (hex
+ FF), but in the one Perl calls POSIX-BC its value is 95 (hex 5F). If
+ certain other characters have POSIX-BC values, PCRE2 makes \? generate
+ 95; otherwise it generates 255.
+
+ After \0 up to two further octal digits are read. If there are fewer
+ than two digits, just those that are present are used. Thus the
+ sequence \0\x\015 specifies two binary zeros followed by a CR character
+ (code value 13). Make sure you supply two digits after the initial zero
+ if the pattern character that follows is itself an octal digit.
+
+ The escape \o must be followed by a sequence of octal digits, enclosed
+ in braces. An error occurs if this is not the case. This escape is a
+ recent addition to Perl; it provides way of specifying character code
+ points as octal numbers greater than 0777, and it also allows octal
+ numbers and back references to be unambiguously specified.
+
+ For greater clarity and unambiguity, it is best to avoid following \ by
+ a digit greater than zero. Instead, use \o{} or \x{} to specify charac-
+ ter numbers, and \g{} to specify back references. The following para-
+ graphs describe the old, ambiguous syntax.
+
+ The handling of a backslash followed by a digit other than 0 is compli-
+ cated, and Perl has changed over time, causing PCRE2 also to change.
+
+ Outside a character class, PCRE2 reads the digit and any following dig-
+ its as a decimal number. If the number is less than 10, begins with the
+ digit 8 or 9, or if there are at least that many previous capturing
+ left parentheses in the expression, the entire sequence is taken as a
+ back reference. A description of how this works is given later, follow-
+ ing the discussion of parenthesized subpatterns. Otherwise, up to
+ three octal digits are read to form a character code.
+
+ Inside a character class, PCRE2 handles \8 and \9 as the literal char-
+ acters "8" and "9", and otherwise reads up to three octal digits fol-
+ lowing the backslash, using them to generate a data character. Any sub-
+ sequent digits stand for themselves. For example, outside a character
+ class:
+
+ \040 is another way of writing an ASCII space
+ \40 is the same, provided there are fewer than 40
+ previous capturing subpatterns
+ \7 is always a back reference
+ \11 might be a back reference, or another way of
+ writing a tab
+ \011 is always a tab
+ \0113 is a tab followed by the character "3"
+ \113 might be a back reference, otherwise the
+ character with octal code 113
+ \377 might be a back reference, otherwise
+ the value 255 (decimal)
+ \81 is always a back reference
+
+ Note that octal values of 100 or greater that are specified using this
+ syntax must not be introduced by a leading zero, because no more than
+ three octal digits are ever read.
+
+ By default, after \x that is not followed by {, from zero to two hexa-
+ decimal digits are read (letters can be in upper or lower case). Any
+ number of hexadecimal digits may appear between \x{ and }. If a charac-
+ ter other than a hexadecimal digit appears between \x{ and }, or if
+ there is no terminating }, an error occurs.
+
+ If the PCRE2_ALT_BSUX option is set, the interpretation of \x is as
+ just described only when it is followed by two hexadecimal digits. Oth-
+ erwise, it matches a literal "x" character. In this mode mode, support
+ for code points greater than 256 is provided by \u, which must be fol-
+ lowed by four hexadecimal digits; otherwise it matches a literal "u"
+ character.
+
+ Characters whose value is less than 256 can be defined by either of the
+ two syntaxes for \x (or by \u in PCRE2_ALT_BSUX mode). There is no dif-
+ ference in the way they are handled. For example, \xdc is exactly the
+ same as \x{dc} (or \u00dc in PCRE2_ALT_BSUX mode).
+
+ Constraints on character values
+
+ Characters that are specified using octal or hexadecimal numbers are
+ limited to certain values, as follows:
+
+ 8-bit non-UTF mode less than 0x100
+ 8-bit UTF-8 mode less than 0x10ffff and a valid codepoint
+ 16-bit non-UTF mode less than 0x10000
+ 16-bit UTF-16 mode less than 0x10ffff and a valid codepoint
+ 32-bit non-UTF mode less than 0x100000000
+ 32-bit UTF-32 mode less than 0x10ffff and a valid codepoint
+
+ Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-
+ called "surrogate" codepoints), and 0xffef.
+
+ Escape sequences in character classes
+
+ All the sequences that define a single character value can be used both
+ inside and outside character classes. In addition, inside a character
+ class, \b is interpreted as the backspace character (hex 08).
+
+ \N is not allowed in a character class. \B, \R, and \X are not special
+ inside a character class. Like other unrecognized alphabetic escape
+ sequences, they cause an error. Outside a character class, these
+ sequences have different meanings.
+
+ Unsupported escape sequences
+
+ In Perl, the sequences \l, \L, \u, and \U are recognized by its string
+ handler and used to modify the case of following characters. By
+ default, PCRE2 does not support these escape sequences. However, if the
+ PCRE2_ALT_BSUX option is set, \U matches a "U" character, and \u can be
+ used to define a character by code point, as described in the previous
+ section.
+
+ Absolute and relative back references
+
+ The sequence \g followed by an unsigned or a negative number, option-
+ ally enclosed in braces, is an absolute or relative back reference. A
+ named back reference can be coded as \g{name}. Back references are dis-
+ cussed later, following the discussion of parenthesized subpatterns.
+
+ Absolute and relative subroutine calls
+
+ For compatibility with Oniguruma, the non-Perl syntax \g followed by a
+ name or a number enclosed either in angle brackets or single quotes, is
+ an alternative syntax for referencing a subpattern as a "subroutine".
+ Details are discussed later. Note that \g{...} (Perl syntax) and
+ \g<...> (Oniguruma syntax) are not synonymous. The former is a back
+ reference; the latter is a subroutine call.
+
+ Generic character types
+
+ Another use of backslash is for specifying generic character types:
+
+ \d any decimal digit
+ \D any character that is not a decimal digit
+ \h any horizontal white space character
+ \H any character that is not a horizontal white space character
+ \s any white space character
+ \S any character that is not a white space character
+ \v any vertical white space character
+ \V any character that is not a vertical white space character
+ \w any "word" character
+ \W any "non-word" character
+
+ There is also the single sequence \N, which matches a non-newline char-
+ acter. This is the same as the "." metacharacter when PCRE2_DOTALL is
+ not set. Perl also uses \N to match characters by name; PCRE2 does not
+ support this.
+
+ Each pair of lower and upper case escape sequences partitions the com-
+ plete set of characters into two disjoint sets. Any given character
+ matches one, and only one, of each pair. The sequences can appear both
+ inside and outside character classes. They each match one character of
+ the appropriate type. If the current matching point is at the end of
+ the subject string, all of them fail, because there is no character to
+ match.
+
+ The default \s characters are HT (9), LF (10), VT (11), FF (12), CR
+ (13), and space (32), which are defined as white space in the "C"
+ locale. This list may vary if locale-specific matching is taking place.
+ For example, in some locales the "non-breaking space" character (\xA0)
+ is recognized as white space, and in others the VT character is not.
+
+ A "word" character is an underscore or any character that is a letter
+ or digit. By default, the definition of letters and digits is con-
+ trolled by PCRE2's low-valued character tables, and may vary if locale-
+ specific matching is taking place (see "Locale support" in the pcre2api
+ page). For example, in a French locale such as "fr_FR" in Unix-like
+ systems, or "french" in Windows, some character codes greater than 127
+ are used for accented letters, and these are then matched by \w. The
+ use of locales with Unicode is discouraged.
+
+ By default, characters whose code points are greater than 127 never
+ match \d, \s, or \w, and always match \D, \S, and \W, although this may
+ be different for characters in the range 128-255 when locale-specific
+ matching is happening. These escape sequences retain their original
+ meanings from before Unicode support was available, mainly for effi-
+ ciency reasons. If the PCRE2_UCP option is set, the behaviour is
+ changed so that Unicode properties are used to determine character
+ types, as follows:
+
+ \d any character that matches \p{Nd} (decimal digit)
+ \s any character that matches \p{Z} or \h or \v
+ \w any character that matches \p{L} or \p{N}, plus underscore
+
+ The upper case escapes match the inverse sets of characters. Note that
+ \d matches only decimal digits, whereas \w matches any Unicode digit,
+ as well as any Unicode letter, and underscore. Note also that PCRE2_UCP
+ affects \b, and \B because they are defined in terms of \w and \W.
+ Matching these sequences is noticeably slower when PCRE2_UCP is set.
+
+ The sequences \h, \H, \v, and \V, in contrast to the other sequences,
+ which match only ASCII characters by default, always match a specific
+ list of code points, whether or not PCRE2_UCP is set. The horizontal
+ space characters are:
+
+ U+0009 Horizontal tab (HT)
+ U+0020 Space
+ U+00A0 Non-break space
+ U+1680 Ogham space mark
+ U+180E Mongolian vowel separator
+ U+2000 En quad
+ U+2001 Em quad
+ U+2002 En space
+ U+2003 Em space
+ U+2004 Three-per-em space
+ U+2005 Four-per-em space
+ U+2006 Six-per-em space
+ U+2007 Figure space
+ U+2008 Punctuation space
+ U+2009 Thin space
+ U+200A Hair space
+ U+202F Narrow no-break space
+ U+205F Medium mathematical space
+ U+3000 Ideographic space
+
+ The vertical space characters are:
+
+ U+000A Linefeed (LF)
+ U+000B Vertical tab (VT)
+ U+000C Form feed (FF)
+ U+000D Carriage return (CR)
+ U+0085 Next line (NEL)
+ U+2028 Line separator
+ U+2029 Paragraph separator
+
+ In 8-bit, non-UTF-8 mode, only the characters with code points less
+ than 256 are relevant.
+
+ Newline sequences
+
+ Outside a character class, by default, the escape sequence \R matches
+ any Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent
+ to the following:
+
+ (?>\r\n|\n|\x0b|\f|\r|\x85)
+
+ This is an example of an "atomic group", details of which are given
+ below. This particular group matches either the two-character sequence
+ CR followed by LF, or one of the single characters LF (linefeed,
+ U+000A), VT (vertical tab, U+000B), FF (form feed, U+000C), CR (car-
+ riage return, U+000D), or NEL (next line, U+0085). The two-character
+ sequence is treated as a single unit that cannot be split.
+
+ In other modes, two additional characters whose codepoints are greater
+ than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
+ rator, U+2029). Unicode support is not needed for these characters to
+ be recognized.
+
+ It is possible to restrict \R to match only CR, LF, or CRLF (instead of
+ the complete set of Unicode line endings) by setting the option
+ PCRE2_BSR_ANYCRLF at compile time. (BSR is an abbrevation for "back-
+ slash R".) This can be made the default when PCRE2 is built; if this is
+ the case, the other behaviour can be requested via the PCRE2_BSR_UNI-
+ CODE option. It is also possible to specify these settings by starting
+ a pattern string with one of the following sequences:
+
+ (*BSR_ANYCRLF) CR, LF, or CRLF only
+ (*BSR_UNICODE) any Unicode newline sequence
+
+ These override the default and the options given to the compiling func-
+ tion. Note that these special settings, which are not Perl-compatible,
+ are recognized only at the very start of a pattern, and that they must
+ be in upper case. If more than one of them is present, the last one is
+ used. They can be combined with a change of newline convention; for
+ example, a pattern can start with:
+
+ (*ANY)(*BSR_ANYCRLF)
+
+ They can also be combined with the (*UTF) or (*UCP) special sequences.
+ Inside a character class, \R is treated as an unrecognized escape
+ sequence, and causes an error.
+
+ Unicode character properties
+
+ When PCRE2 is built with Unicode support (the default), three addi-
+ tional escape sequences that match characters with specific properties
+ are available. In 8-bit non-UTF-8 mode, these sequences are of course
+ limited to testing characters whose codepoints are less than 256, but
+ they do work in this mode. The extra escape sequences are:
+
+ \p{xx} a character with the xx property
+ \P{xx} a character without the xx property
+ \X a Unicode extended grapheme cluster
+
+ The property names represented by xx above are limited to the Unicode
+ script names, the general category properties, "Any", which matches any
+ character (including newline), and some special PCRE2 properties
+ (described in the next section). Other Perl properties such as "InMu-
+ sicalSymbols" are not supported by PCRE2. Note that \P{Any} does not
+ match any characters, so always causes a match failure.
+
+ Sets of Unicode characters are defined as belonging to certain scripts.
+ A character from one of these sets can be matched using a script name.
+ For example:
+
+ \p{Greek}
+ \P{Han}
+
+ Those that are not part of an identified script are lumped together as
+ "Common". The current list of scripts is:
+
+ Ahom, Anatolian_Hieroglyphs, Arabic, Armenian, Avestan, Balinese,
+ Bamum, Bassa_Vah, Batak, Bengali, Bopomofo, Brahmi, Braille, Buginese,
+ Buhid, Canadian_Aboriginal, Carian, Caucasian_Albanian, Chakma, Cham,
+ Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret,
+ Devanagari, Duployan, Egyptian_Hieroglyphs, Elbasan, Ethiopic, Geor-
+ gian, Glagolitic, Gothic, Grantha, Greek, Gujarati, Gurmukhi, Han,
+ Hangul, Hanunoo, Hatran, Hebrew, Hiragana, Imperial_Aramaic, Inherited,
+ Inscriptional_Pahlavi, Inscriptional_Parthian, Javanese, Kaithi, Kan-
+ nada, Katakana, Kayah_Li, Kharoshthi, Khmer, Khojki, Khudawadi, Lao,
+ Latin, Lepcha, Limbu, Linear_A, Linear_B, Lisu, Lycian, Lydian, Maha-
+ jani, Malayalam, Mandaic, Manichaean, Meetei_Mayek, Mende_Kikakui,
+ Meroitic_Cursive, Meroitic_Hieroglyphs, Miao, Modi, Mongolian, Mro,
+ Multani, Myanmar, Nabataean, New_Tai_Lue, Nko, Ogham, Ol_Chiki,
+ Old_Hungarian, Old_Italic, Old_North_Arabian, Old_Permic, Old_Persian,
+ Old_South_Arabian, Old_Turkic, Oriya, Osmanya, Pahawh_Hmong, Palmyrene,
+ Pau_Cin_Hau, Phags_Pa, Phoenician, Psalter_Pahlavi, Rejang, Runic,
+ Samaritan, Saurashtra, Sharada, Shavian, Siddham, SignWriting, Sinhala,
+ Sora_Sompeng, Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa,
+ Tai_Le, Tai_Tham, Tai_Viet, Takri, Tamil, Telugu, Thaana, Thai,
+ Tibetan, Tifinagh, Tirhuta, Ugaritic, Vai, Warang_Citi, Yi.
+
+ Each character has exactly one Unicode general category property, spec-
+ ified by a two-letter abbreviation. For compatibility with Perl, nega-
+ tion can be specified by including a circumflex between the opening
+ brace and the property name. For example, \p{^Lu} is the same as
+ \P{Lu}.
+
+ If only one letter is specified with \p or \P, it includes all the gen-
+ eral category properties that start with that letter. In this case, in
+ the absence of negation, the curly brackets in the escape sequence are
+ optional; these two examples have the same effect:
+
+ \p{L}
+ \pL
+
+ The following general category property codes are supported:
+
+ C Other
+ Cc Control
+ Cf Format
+ Cn Unassigned
+ Co Private use
+ Cs Surrogate
+
+ L Letter
+ Ll Lower case letter
+ Lm Modifier letter
+ Lo Other letter
+ Lt Title case letter
+ Lu Upper case letter
+
+ M Mark
+ Mc Spacing mark
+ Me Enclosing mark
+ Mn Non-spacing mark
+
+ N Number
+ Nd Decimal number
+ Nl Letter number
+ No Other number
+
+ P Punctuation
+ Pc Connector punctuation
+ Pd Dash punctuation
+ Pe Close punctuation
+ Pf Final punctuation
+ Pi Initial punctuation
+ Po Other punctuation
+ Ps Open punctuation
+
+ S Symbol
+ Sc Currency symbol
+ Sk Modifier symbol
+ Sm Mathematical symbol
+ So Other symbol
+
+ Z Separator
+ Zl Line separator
+ Zp Paragraph separator
+ Zs Space separator
+
+ The special property L& is also supported: it matches a character that
+ has the Lu, Ll, or Lt property, in other words, a letter that is not
+ classified as a modifier or "other".
+
+ The Cs (Surrogate) property applies only to characters in the range
+ U+D800 to U+DFFF. Such characters are not valid in Unicode strings and
+ so cannot be tested by PCRE2, unless UTF validity checking has been
+ turned off (see the discussion of PCRE2_NO_UTF_CHECK in the pcre2api
+ page). Perl does not support the Cs property.
+
+ The long synonyms for property names that Perl supports (such as
+ \p{Letter}) are not supported by PCRE2, nor is it permitted to prefix
+ any of these properties with "Is".
+
+ No character that is in the Unicode table has the Cn (unassigned) prop-
+ erty. Instead, this property is assumed for any code point that is not
+ in the Unicode table.
+
+ Specifying caseless matching does not affect these escape sequences.
+ For example, \p{Lu} always matches only upper case letters. This is
+ different from the behaviour of current versions of Perl.
+
+ Matching characters by Unicode property is not fast, because PCRE2 has
+ to do a multistage table lookup in order to find a character's prop-
+ erty. That is why the traditional escape sequences such as \d and \w do
+ not use Unicode properties in PCRE2 by default, though you can make
+ them do so by setting the PCRE2_UCP option or by starting the pattern
+ with (*UCP).
+
+ Extended grapheme clusters
+
+ The \X escape matches any number of Unicode characters that form an
+ "extended grapheme cluster", and treats the sequence as an atomic group
+ (see below). Unicode supports various kinds of composite character by
+ giving each character a grapheme breaking property, and having rules
+ that use these properties to define the boundaries of extended grapheme
+ clusters. \X always matches at least one character. Then it decides
+ whether to add additional characters according to the following rules
+ for ending a cluster:
+
+ 1. End at the end of the subject string.
+
+ 2. Do not end between CR and LF; otherwise end after any control char-
+ acter.
+
+ 3. Do not break Hangul (a Korean script) syllable sequences. Hangul
+ characters are of five types: L, V, T, LV, and LVT. An L character may
+ be followed by an L, V, LV, or LVT character; an LV or V character may
+ be followed by a V or T character; an LVT or T character may be follwed
+ only by a T character.
+
+ 4. Do not end before extending characters or spacing marks. Characters
+ with the "mark" property always have the "extend" grapheme breaking
+ property.
+
+ 5. Do not end after prepend characters.
+
+ 6. Otherwise, end the cluster.
+
+ PCRE2's additional properties
+
+ As well as the standard Unicode properties described above, PCRE2 sup-
+ ports four more that make it possible to convert traditional escape
+ sequences such as \w and \s to use Unicode properties. PCRE2 uses these
+ non-standard, non-Perl properties internally when PCRE2_UCP is set.
+ However, they may also be used explicitly. These properties are:
+
+ Xan Any alphanumeric character
+ Xps Any POSIX space character
+ Xsp Any Perl space character
+ Xwd Any Perl "word" character
+
+ Xan matches characters that have either the L (letter) or the N (num-
+ ber) property. Xps matches the characters tab, linefeed, vertical tab,
+ form feed, or carriage return, and any other character that has the Z
+ (separator) property. Xsp is the same as Xps; in PCRE1 it used to
+ exclude vertical tab, for Perl compatibility, but Perl changed. Xwd
+ matches the same characters as Xan, plus underscore.
+
+ There is another non-standard property, Xuc, which matches any charac-
+ ter that can be represented by a Universal Character Name in C++ and
+ other programming languages. These are the characters $, @, ` (grave
+ accent), and all characters with Unicode code points greater than or
+ equal to U+00A0, except for the surrogates U+D800 to U+DFFF. Note that
+ most base (ASCII) characters are excluded. (Universal Character Names
+ are of the form \uHHHH or \UHHHHHHHH where H is a hexadecimal digit.
+ Note that the Xuc property does not match these sequences but the char-
+ acters that they represent.)
+
+ Resetting the match start
+
+ The escape sequence \K causes any previously matched characters not to
+ be included in the final matched sequence. For example, the pattern:
+
+ foo\Kbar
+
+ matches "foobar", but reports that it has matched "bar". This feature
+ is similar to a lookbehind assertion (described below). However, in
+ this case, the part of the subject before the real match does not have
+ to be of fixed length, as lookbehind assertions do. The use of \K does
+ not interfere with the setting of captured substrings. For example,
+ when the pattern
+
+ (foo)\Kbar
+
+ matches "foobar", the first substring is still set to "foo".
+
+ Perl documents that the use of \K within assertions is "not well
+ defined". In PCRE2, \K is acted upon when it occurs inside positive
+ assertions, but is ignored in negative assertions. Note that when a
+ pattern such as (?=ab\K) matches, the reported start of the match can
+ be greater than the end of the match.
+
+ Simple assertions
+
+ The final use of backslash is for certain simple assertions. An asser-
+ tion specifies a condition that has to be met at a particular point in
+ a match, without consuming any characters from the subject string. The
+ use of subpatterns for more complicated assertions is described below.
+ The backslashed assertions are:
+
+ \b matches at a word boundary
+ \B matches when not at a word boundary
+ \A matches at the start of the subject
+ \Z matches at the end of the subject
+ also matches before a newline at the end of the subject
+ \z matches only at the end of the subject
+ \G matches at the first matching position in the subject
+
+ Inside a character class, \b has a different meaning; it matches the
+ backspace character. If any other of these assertions appears in a
+ character class, an "invalid escape sequence" error is generated.
+
+ A word boundary is a position in the subject string where the current
+ character and the previous character do not both match \w or \W (i.e.
+ one matches \w and the other matches \W), or the start or end of the
+ string if the first or last character matches \w, respectively. In a
+ UTF mode, the meanings of \w and \W can be changed by setting the
+ PCRE2_UCP option. When this is done, it also affects \b and \B. Neither
+ PCRE2 nor Perl has a separate "start of word" or "end of word" metase-
+ quence. However, whatever follows \b normally determines which it is.
+ For example, the fragment \ba matches "a" at the start of a word.
+
+ The \A, \Z, and \z assertions differ from the traditional circumflex
+ and dollar (described in the next section) in that they only ever match
+ at the very start and end of the subject string, whatever options are
+ set. Thus, they are independent of multiline mode. These three asser-
+ tions are not affected by the PCRE2_NOTBOL or PCRE2_NOTEOL options,
+ which affect only the behaviour of the circumflex and dollar metachar-
+ acters. However, if the startoffset argument of pcre2_match() is non-
+ zero, indicating that matching is to start at a point other than the
+ beginning of the subject, \A can never match. The difference between
+ \Z and \z is that \Z matches before a newline at the end of the string
+ as well as at the very end, whereas \z matches only at the end.
+
+ The \G assertion is true only when the current matching position is at
+ the start point of the match, as specified by the startoffset argument
+ of pcre2_match(). It differs from \A when the value of startoffset is
+ non-zero. By calling pcre2_match() multiple times with appropriate
+ arguments, you can mimic Perl's /g option, and it is in this kind of
+ implementation where \G can be useful.
+
+ Note, however, that PCRE2's interpretation of \G, as the start of the
+ current match, is subtly different from Perl's, which defines it as the
+ end of the previous match. In Perl, these can be different when the
+ previously matched string was empty. Because PCRE2 does just one match
+ at a time, it cannot reproduce this behaviour.
+
+ If all the alternatives of a pattern begin with \G, the expression is
+ anchored to the starting match position, and the "anchored" flag is set
+ in the compiled regular expression.
+
+
+CIRCUMFLEX AND DOLLAR
+
+ The circumflex and dollar metacharacters are zero-width assertions.
+ That is, they test for a particular condition being true without con-
+ suming any characters from the subject string. These two metacharacters
+ are concerned with matching the starts and ends of lines. If the new-
+ line convention is set so that only the two-character sequence CRLF is
+ recognized as a newline, isolated CR and LF characters are treated as
+ ordinary data characters, and are not recognized as newlines.
+
+ Outside a character class, in the default matching mode, the circumflex
+ character is an assertion that is true only if the current matching
+ point is at the start of the subject string. If the startoffset argu-
+ ment of pcre2_match() is non-zero, or if PCRE2_NOTBOL is set, circum-
+ flex can never match if the PCRE2_MULTILINE option is unset. Inside a
+ character class, circumflex has an entirely different meaning (see
+ below).
+
+ Circumflex need not be the first character of the pattern if a number
+ of alternatives are involved, but it should be the first thing in each
+ alternative in which it appears if the pattern is ever to match that
+ branch. If all possible alternatives start with a circumflex, that is,
+ if the pattern is constrained to match only at the start of the sub-
+ ject, it is said to be an "anchored" pattern. (There are also other
+ constructs that can cause a pattern to be anchored.)
+
+ The dollar character is an assertion that is true only if the current
+ matching point is at the end of the subject string, or immediately
+ before a newline at the end of the string (by default), unless
+ PCRE2_NOTEOL is set. Note, however, that it does not actually match the
+ newline. Dollar need not be the last character of the pattern if a num-
+ ber of alternatives are involved, but it should be the last item in any
+ branch in which it appears. Dollar has no special meaning in a charac-
+ ter class.
+
+ The meaning of dollar can be changed so that it matches only at the
+ very end of the string, by setting the PCRE2_DOLLAR_ENDONLY option at
+ compile time. This does not affect the \Z assertion.
+
+ The meanings of the circumflex and dollar metacharacters are changed if
+ the PCRE2_MULTILINE option is set. When this is the case, a dollar
+ character matches before any newlines in the string, as well as at the
+ very end, and a circumflex matches immediately after internal newlines
+ as well as at the start of the subject string. It does not match after
+ a newline that ends the string, for compatibility with Perl. However,
+ this can be changed by setting the PCRE2_ALT_CIRCUMFLEX option.
+
+ For example, the pattern /^abc$/ matches the subject string "def\nabc"
+ (where \n represents a newline) in multiline mode, but not otherwise.
+ Consequently, patterns that are anchored in single line mode because
+ all branches start with ^ are not anchored in multiline mode, and a
+ match for circumflex is possible when the startoffset argument of
+ pcre2_match() is non-zero. The PCRE2_DOLLAR_ENDONLY option is ignored
+ if PCRE2_MULTILINE is set.
+
+ Note that the sequences \A, \Z, and \z can be used to match the start
+ and end of the subject in both modes, and if all branches of a pattern
+ start with \A it is always anchored, whether or not PCRE2_MULTILINE is
+ set.
+
+
+FULL STOP (PERIOD, DOT) AND \N
+
+ Outside a character class, a dot in the pattern matches any one charac-
+ ter in the subject string except (by default) a character that signi-
+ fies the end of a line.
+
+ When a line ending is defined as a single character, dot never matches
+ that character; when the two-character sequence CRLF is used, dot does
+ not match CR if it is immediately followed by LF, but otherwise it
+ matches all characters (including isolated CRs and LFs). When any Uni-
+ code line endings are being recognized, dot does not match CR or LF or
+ any of the other line ending characters.
+
+ The behaviour of dot with regard to newlines can be changed. If the
+ PCRE2_DOTALL option is set, a dot matches any one character, without
+ exception. If the two-character sequence CRLF is present in the sub-
+ ject string, it takes two dots to match it.
+
+ The handling of dot is entirely independent of the handling of circum-
+ flex and dollar, the only relationship being that they both involve
+ newlines. Dot has no special meaning in a character class.
+
+ The escape sequence \N behaves like a dot, except that it is not
+ affected by the PCRE2_DOTALL option. In other words, it matches any
+ character except one that signifies the end of a line. Perl also uses
+ \N to match characters by name; PCRE2 does not support this.
+
+
+MATCHING A SINGLE CODE UNIT
+
+ Outside a character class, the escape sequence \C matches any one code
+ unit, whether or not a UTF mode is set. In the 8-bit library, one code
+ unit is one byte; in the 16-bit library it is a 16-bit unit; in the
+ 32-bit library it is a 32-bit unit. Unlike a dot, \C always matches
+ line-ending characters. The feature is provided in Perl in order to
+ match individual bytes in UTF-8 mode, but it is unclear how it can use-
+ fully be used.
+
+ Because \C breaks up characters into individual code units, matching
+ one unit with \C in UTF-8 or UTF-16 mode means that the rest of the
+ string may start with a malformed UTF character. This has undefined
+ results, because PCRE2 assumes that it is matching character by charac-
+ ter in a valid UTF string (by default it checks the subject string's
+ validity at the start of processing unless the PCRE2_NO_UTF_CHECK
+ option is used). An application can lock out the use of \C by setting
+ the PCRE2_NEVER_BACKSLASH_C option.
+
+ PCRE2 does not allow \C to appear in lookbehind assertions (described
+ below) in a UTF mode, because this would make it impossible to calcu-
+ late the length of the lookbehind.
+
+ In general, the \C escape sequence is best avoided. However, one way of
+ using it that avoids the problem of malformed UTF characters is to use
+ a lookahead to check the length of the next character, as in this pat-
+ tern, which could be used with a UTF-8 string (ignore white space and
+ line breaks):
+
+ (?| (?=[\x00-\x7f])(\C) |
+ (?=[\x80-\x{7ff}])(\C)(\C) |
+ (?=[\x{800}-\x{ffff}])(\C)(\C)(\C) |
+ (?=[\x{10000}-\x{1fffff}])(\C)(\C)(\C)(\C))
+
+ In this example, a group that starts with (?| resets the capturing
+ parentheses numbers in each alternative (see "Duplicate Subpattern Num-
+ bers" below). The assertions at the start of each branch check the next
+ UTF-8 character for values whose encoding uses 1, 2, 3, or 4 bytes,
+ respectively. The character's individual bytes are then captured by the
+ appropriate number of \C groups.
+
+
+SQUARE BRACKETS AND CHARACTER CLASSES
+
+ An opening square bracket introduces a character class, terminated by a
+ closing square bracket. A closing square bracket on its own is not spe-
+ cial by default. If a closing square bracket is required as a member
+ of the class, it should be the first data character in the class (after
+ an initial circumflex, if present) or escaped with a backslash. This
+ means that, by default, an empty class cannot be defined. However, if
+ the PCRE2_ALLOW_EMPTY_CLASS option is set, a closing square bracket at
+ the start does end the (empty) class.
+
+ A character class matches a single character in the subject. A matched
+ character must be in the set of characters defined by the class, unless
+ the first character in the class definition is a circumflex, in which
+ case the subject character must not be in the set defined by the class.
+ If a circumflex is actually required as a member of the class, ensure
+ it is not the first character, or escape it with a backslash.
+
+ For example, the character class [aeiou] matches any lower case vowel,
+ while [^aeiou] matches any character that is not a lower case vowel.
+ Note that a circumflex is just a convenient notation for specifying the
+ characters that are in the class by enumerating those that are not. A
+ class that starts with a circumflex is not an assertion; it still con-
+ sumes a character from the subject string, and therefore it fails if
+ the current pointer is at the end of the string.
+
+ When caseless matching is set, any letters in a class represent both
+ their upper case and lower case versions, so for example, a caseless
+ [aeiou] matches "A" as well as "a", and a caseless [^aeiou] does not
+ match "A", whereas a caseful version would.
+
+ Characters that might indicate line breaks are never treated in any
+ special way when matching character classes, whatever line-ending
+ sequence is in use, and whatever setting of the PCRE2_DOTALL and
+ PCRE2_MULTILINE options is used. A class such as [^a] always matches
+ one of these characters.
+
+ The minus (hyphen) character can be used to specify a range of charac-
+ ters in a character class. For example, [d-m] matches any letter
+ between d and m, inclusive. If a minus character is required in a
+ class, it must be escaped with a backslash or appear in a position
+ where it cannot be interpreted as indicating a range, typically as the
+ first or last character in the class, or immediately after a range. For
+ example, [b-d-z] matches letters in the range b to d, a hyphen charac-
+ ter, or z.
+
+ It is not possible to have the literal character "]" as the end charac-
+ ter of a range. A pattern such as [W-]46] is interpreted as a class of
+ two characters ("W" and "-") followed by a literal string "46]", so it
+ would match "W46]" or "-46]". However, if the "]" is escaped with a
+ backslash it is interpreted as the end of range, so [W-\]46] is inter-
+ preted as a class containing a range followed by two other characters.
+ The octal or hexadecimal representation of "]" can also be used to end
+ a range.
+
+ An error is generated if a POSIX character class (see below) or an
+ escape sequence other than one that defines a single character appears
+ at a point where a range ending character is expected. For example,
+ [z-\xff] is valid, but [A-\d] and [A-[:digit:]] are not.
+
+ Ranges normally include all code points between the start and end char-
+ acters, inclusive. They can also be used for code points specified
+ numerically, for example [\000-\037]. Ranges can include any characters
+ that are valid for the current mode.
+
+ There is a special case in EBCDIC environments for ranges whose end
+ points are both specified as literal letters in the same case. For com-
+ patibility with Perl, EBCDIC code points within the range that are not
+ letters are omitted. For example, [h-k] matches only four characters,
+ even though the codes for h and k are 0x88 and 0x92, a range of 11 code
+ points. However, if the range is specified numerically, for example,
+ [\x88-\x92] or [h-\x92], all code points are included.
+
+ If a range that includes letters is used when caseless matching is set,
+ it matches the letters in either case. For example, [W-c] is equivalent
+ to [][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if
+ character tables for a French locale are in use, [\xc8-\xcb] matches
+ accented E characters in both cases.
+
+ The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v, \V,
+ \w, and \W may appear in a character class, and add the characters that
+ they match to the class. For example, [\dABCDEF] matches any hexadeci-
+ mal digit. In UTF modes, the PCRE2_UCP option affects the meanings of
+ \d, \s, \w and their upper case partners, just as it does when they
+ appear outside a character class, as described in the section entitled
+ "Generic character types" above. The escape sequence \b has a different
+ meaning inside a character class; it matches the backspace character.
+ The sequences \B, \N, \R, and \X are not special inside a character
+ class. Like any other unrecognized escape sequences, they cause an
+ error.
+
+ A circumflex can conveniently be used with the upper case character
+ types to specify a more restricted set of characters than the matching
+ lower case type. For example, the class [^\W_] matches any letter or
+ digit, but not underscore, whereas [\w] includes underscore. A positive
+ character class should be read as "something OR something OR ..." and a
+ negative class as "NOT something AND NOT something AND NOT ...".
+
+ The only metacharacters that are recognized in character classes are
+ backslash, hyphen (only where it can be interpreted as specifying a
+ range), circumflex (only at the start), opening square bracket (only
+ when it can be interpreted as introducing a POSIX class name, or for a
+ special compatibility feature - see the next two sections), and the
+ terminating closing square bracket. However, escaping other non-
+ alphanumeric characters does no harm.
+
+
+POSIX CHARACTER CLASSES
+
+ Perl supports the POSIX notation for character classes. This uses names
+ enclosed by [: and :] within the enclosing square brackets. PCRE2 also
+ supports this notation. For example,
+
+ [01[:alpha:]%]
+
+ matches "0", "1", any alphabetic character, or "%". The supported class
+ names are:
+
+ alnum letters and digits
+ alpha letters
+ ascii character codes 0 - 127
+ blank space or tab only
+ cntrl control characters
+ digit decimal digits (same as \d)
+ graph printing characters, excluding space
+ lower lower case letters
+ print printing characters, including space
+ punct printing characters, excluding letters and digits and space
+ space white space (the same as \s from PCRE2 8.34)
+ upper upper case letters
+ word "word" characters (same as \w)
+ xdigit hexadecimal digits
+
+ The default "space" characters are HT (9), LF (10), VT (11), FF (12),
+ CR (13), and space (32). If locale-specific matching is taking place,
+ the list of space characters may be different; there may be fewer or
+ more of them. "Space" and \s match the same set of characters.
+
+ The name "word" is a Perl extension, and "blank" is a GNU extension
+ from Perl 5.8. Another Perl extension is negation, which is indicated
+ by a ^ character after the colon. For example,
+
+ [12[:^digit:]]
+
+ matches "1", "2", or any non-digit. PCRE2 (and Perl) also recognize the
+ POSIX syntax [.ch.] and [=ch=] where "ch" is a "collating element", but
+ these are not supported, and an error is given if they are encountered.
+
+ By default, characters with values greater than 127 do not match any of
+ the POSIX character classes, although this may be different for charac-
+ ters in the range 128-255 when locale-specific matching is happening.
+ However, if the PCRE2_UCP option is passed to pcre2_compile(), some of
+ the classes are changed so that Unicode character properties are used.
+ This is achieved by replacing certain POSIX classes with other
+ sequences, as follows:
+
+ [:alnum:] becomes \p{Xan}
+ [:alpha:] becomes \p{L}
+ [:blank:] becomes \h
+ [:cntrl:] becomes \p{Cc}
+ [:digit:] becomes \p{Nd}
+ [:lower:] becomes \p{Ll}
+ [:space:] becomes \p{Xps}
+ [:upper:] becomes \p{Lu}
+ [:word:] becomes \p{Xwd}
+
+ Negated versions, such as [:^alpha:] use \P instead of \p. Three other
+ POSIX classes are handled specially in UCP mode:
+
+ [:graph:] This matches characters that have glyphs that mark the page
+ when printed. In Unicode property terms, it matches all char-
+ acters with the L, M, N, P, S, or Cf properties, except for:
+
+ U+061C Arabic Letter Mark
+ U+180E Mongolian Vowel Separator
+ U+2066 - U+2069 Various "isolate"s
+
+
+ [:print:] This matches the same characters as [:graph:] plus space
+ characters that are not controls, that is, characters with
+ the Zs property.
+
+ [:punct:] This matches all characters that have the Unicode P (punctua-
+ tion) property, plus those characters with code points less
+ than 256 that have the S (Symbol) property.
+
+ The other POSIX classes are unchanged, and match only characters with
+ code points less than 256.
+
+
+COMPATIBILITY FEATURE FOR WORD BOUNDARIES
+
+ In the POSIX.2 compliant library that was included in 4.4BSD Unix, the
+ ugly syntax [[:<:]] and [[:>:]] is used for matching "start of word"
+ and "end of word". PCRE2 treats these items as follows:
+
+ [[:<:]] is converted to \b(?=\w)
+ [[:>:]] is converted to \b(?<=\w)
+
+ Only these exact character sequences are recognized. A sequence such as
+ [a[:<:]b] provokes error for an unrecognized POSIX class name. This
+ support is not compatible with Perl. It is provided to help migrations
+ from other environments, and is best not used in any new patterns. Note
+ that \b matches at the start and the end of a word (see "Simple asser-
+ tions" above), and in a Perl-style pattern the preceding or following
+ character normally shows which is wanted, without the need for the
+ assertions that are used above in order to give exactly the POSIX be-
+ haviour.
+
+
+VERTICAL BAR
+
+ Vertical bar characters are used to separate alternative patterns. For
+ example, the pattern
+
+ gilbert|sullivan
+
+ matches either "gilbert" or "sullivan". Any number of alternatives may
+ appear, and an empty alternative is permitted (matching the empty
+ string). The matching process tries each alternative in turn, from left
+ to right, and the first one that succeeds is used. If the alternatives
+ are within a subpattern (defined below), "succeeds" means matching the
+ rest of the main pattern as well as the alternative in the subpattern.
+
+
+INTERNAL OPTION SETTING
+
+ The settings of the PCRE2_CASELESS, PCRE2_MULTILINE, PCRE2_DOTALL, and
+ PCRE2_EXTENDED options (which are Perl-compatible) can be changed from
+ within the pattern by a sequence of Perl option letters enclosed
+ between "(?" and ")". The option letters are
+
+ i for PCRE2_CASELESS
+ m for PCRE2_MULTILINE
+ s for PCRE2_DOTALL
+ x for PCRE2_EXTENDED
+
+ For example, (?im) sets caseless, multiline matching. It is also possi-
+ ble to unset these options by preceding the letter with a hyphen, and a
+ combined setting and unsetting such as (?im-sx), which sets PCRE2_CASE-
+ LESS and PCRE2_MULTILINE while unsetting PCRE2_DOTALL and
+ PCRE2_EXTENDED, is also permitted. If a letter appears both before and
+ after the hyphen, the option is unset. An empty options setting "(?)"
+ is allowed. Needless to say, it has no effect.
+
+ The PCRE2-specific options PCRE2_DUPNAMES and PCRE2_UNGREEDY can be
+ changed in the same way as the Perl-compatible options by using the
+ characters J and U respectively.
+
+ When one of these option changes occurs at top level (that is, not
+ inside subpattern parentheses), the change applies to the remainder of
+ the pattern that follows. If the change is placed right at the start of
+ a pattern, PCRE2 extracts it into the global options (and it will
+ therefore show up in data extracted by the pcre2_pattern_info() func-
+ tion).
+
+ An option change within a subpattern (see below for a description of
+ subpatterns) affects only that part of the subpattern that follows it,
+ so
+
+ (a(?i)b)c
+
+ matches abc and aBc and no other strings (assuming PCRE2_CASELESS is
+ not used). By this means, options can be made to have different set-
+ tings in different parts of the pattern. Any changes made in one alter-
+ native do carry on into subsequent branches within the same subpattern.
+ For example,
+
+ (a(?i)b|c)
+
+ matches "ab", "aB", "c", and "C", even though when matching "C" the
+ first branch is abandoned before the option setting. This is because
+ the effects of option settings happen at compile time. There would be
+ some very weird behaviour otherwise.
+
+ As a convenient shorthand, if any option settings are required at the
+ start of a non-capturing subpattern (see the next section), the option
+ letters may appear between the "?" and the ":". Thus the two patterns
+
+ (?i:saturday|sunday)
+ (?:(?i)saturday|sunday)
+
+ match exactly the same set of strings.
+
+ Note: There are other PCRE2-specific options that can be set by the
+ application when the compiling function is called. The pattern can con-
+ tain special leading sequences such as (*CRLF) to override what the
+ application has set or what has been defaulted. Details are given in
+ the section entitled "Newline sequences" above. There are also the
+ (*UTF) and (*UCP) leading sequences that can be used to set UTF and
+ Unicode property modes; they are equivalent to setting the PCRE2_UTF
+ and PCRE2_UCP options, respectively. However, the application can set
+ the PCRE2_NEVER_UTF and PCRE2_NEVER_UCP options, which lock out the use
+ of the (*UTF) and (*UCP) sequences.
+
+
+SUBPATTERNS
+
+ Subpatterns are delimited by parentheses (round brackets), which can be
+ nested. Turning part of a pattern into a subpattern does two things:
+
+ 1. It localizes a set of alternatives. For example, the pattern
+
+ cat(aract|erpillar|)
+
+ matches "cataract", "caterpillar", or "cat". Without the parentheses,
+ it would match "cataract", "erpillar" or an empty string.
+
+ 2. It sets up the subpattern as a capturing subpattern. This means
+ that, when the whole pattern matches, the portion of the subject string
+ that matched the subpattern is passed back to the caller, separately
+ from the portion that matched the whole pattern. (This applies only to
+ the traditional matching function; the DFA matching function does not
+ support capturing.)
+
+ Opening parentheses are counted from left to right (starting from 1) to
+ obtain numbers for the capturing subpatterns. For example, if the
+ string "the red king" is matched against the pattern
+
+ the ((red|white) (king|queen))
+
+ the captured substrings are "red king", "red", and "king", and are num-
+ bered 1, 2, and 3, respectively.
+
+ The fact that plain parentheses fulfil two functions is not always
+ helpful. There are often times when a grouping subpattern is required
+ without a capturing requirement. If an opening parenthesis is followed
+ by a question mark and a colon, the subpattern does not do any captur-
+ ing, and is not counted when computing the number of any subsequent
+ capturing subpatterns. For example, if the string "the white queen" is
+ matched against the pattern
+
+ the ((?:red|white) (king|queen))
+
+ the captured substrings are "white queen" and "queen", and are numbered
+ 1 and 2. The maximum number of capturing subpatterns is 65535.
+
+ As a convenient shorthand, if any option settings are required at the
+ start of a non-capturing subpattern, the option letters may appear
+ between the "?" and the ":". Thus the two patterns
+
+ (?i:saturday|sunday)
+ (?:(?i)saturday|sunday)
+
+ match exactly the same set of strings. Because alternative branches are
+ tried from left to right, and options are not reset until the end of
+ the subpattern is reached, an option setting in one branch does affect
+ subsequent branches, so the above patterns match "SUNDAY" as well as
+ "Saturday".
+
+
+DUPLICATE SUBPATTERN NUMBERS
+
+ Perl 5.10 introduced a feature whereby each alternative in a subpattern
+ uses the same numbers for its capturing parentheses. Such a subpattern
+ starts with (?| and is itself a non-capturing subpattern. For example,
+ consider this pattern:
+
+ (?|(Sat)ur|(Sun))day
+
+ Because the two alternatives are inside a (?| group, both sets of cap-
+ turing parentheses are numbered one. Thus, when the pattern matches,
+ you can look at captured substring number one, whichever alternative
+ matched. This construct is useful when you want to capture part, but
+ not all, of one of a number of alternatives. Inside a (?| group, paren-
+ theses are numbered as usual, but the number is reset at the start of
+ each branch. The numbers of any capturing parentheses that follow the
+ subpattern start after the highest number used in any branch. The fol-
+ lowing example is taken from the Perl documentation. The numbers under-
+ neath show in which buffer the captured content will be stored.
+
+ # before ---------------branch-reset----------- after
+ / ( a ) (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
+ # 1 2 2 3 2 3 4
+
+ A back reference to a numbered subpattern uses the most recent value
+ that is set for that number by any subpattern. The following pattern
+ matches "abcabc" or "defdef":
+
+ /(?|(abc)|(def))\1/
+
+ In contrast, a subroutine call to a numbered subpattern always refers
+ to the first one in the pattern with the given number. The following
+ pattern matches "abcabc" or "defabc":
+
+ /(?|(abc)|(def))(?1)/
+
+ If a condition test for a subpattern's having matched refers to a non-
+ unique number, the test is true if any of the subpatterns of that num-
+ ber have matched.
+
+ An alternative approach to using this "branch reset" feature is to use
+ duplicate named subpatterns, as described in the next section.
+
+
+NAMED SUBPATTERNS
+
+ Identifying capturing parentheses by number is simple, but it can be
+ very hard to keep track of the numbers in complicated regular expres-
+ sions. Furthermore, if an expression is modified, the numbers may
+ change. To help with this difficulty, PCRE2 supports the naming of sub-
+ patterns. This feature was not added to Perl until release 5.10. Python
+ had the feature earlier, and PCRE1 introduced it at release 4.0, using
+ the Python syntax. PCRE2 supports both the Perl and the Python syntax.
+ Perl allows identically numbered subpatterns to have different names,
+ but PCRE2 does not.
+
+ In PCRE2, a subpattern can be named in one of three ways: (?<name>...)
+ or (?'name'...) as in Perl, or (?P<name>...) as in Python. References
+ to capturing parentheses from other parts of the pattern, such as back
+ references, recursion, and conditions, can be made by name as well as
+ by number.
+
+ Names consist of up to 32 alphanumeric characters and underscores, but
+ must start with a non-digit. Named capturing parentheses are still
+ allocated numbers as well as names, exactly as if the names were not
+ present. The PCRE2 API provides function calls for extracting the name-
+ to-number translation table from a compiled pattern. There are also
+ convenience functions for extracting a captured substring by name.
+
+ By default, a name must be unique within a pattern, but it is possible
+ to relax this constraint by setting the PCRE2_DUPNAMES option at com-
+ pile time. (Duplicate names are also always permitted for subpatterns
+ with the same number, set up as described in the previous section.)
+ Duplicate names can be useful for patterns where only one instance of
+ the named parentheses can match. Suppose you want to match the name of
+ a weekday, either as a 3-letter abbreviation or as the full name, and
+ in both cases you want to extract the abbreviation. This pattern
+ (ignoring the line breaks) does the job:
+
+ (?<DN>Mon|Fri|Sun)(?:day)?|
+ (?<DN>Tue)(?:sday)?|
+ (?<DN>Wed)(?:nesday)?|
+ (?<DN>Thu)(?:rsday)?|
+ (?<DN>Sat)(?:urday)?
+
+ There are five capturing substrings, but only one is ever set after a
+ match. (An alternative way of solving this problem is to use a "branch
+ reset" subpattern, as described in the previous section.)
+
+ The convenience functions for extracting the data by name returns the
+ substring for the first (and in this example, the only) subpattern of
+ that name that matched. This saves searching to find which numbered
+ subpattern it was.
+
+ If you make a back reference to a non-unique named subpattern from
+ elsewhere in the pattern, the subpatterns to which the name refers are
+ checked in the order in which they appear in the overall pattern. The
+ first one that is set is used for the reference. For example, this pat-
+ tern matches both "foofoo" and "barbar" but not "foobar" or "barfoo":
+
+ (?:(?<n>foo)|(?<n>bar))\k<n>
+
+
+ If you make a subroutine call to a non-unique named subpattern, the one
+ that corresponds to the first occurrence of the name is used. In the
+ absence of duplicate numbers (see the previous section) this is the one
+ with the lowest number.
+
+ If you use a named reference in a condition test (see the section about
+ conditions below), either to check whether a subpattern has matched, or
+ to check for recursion, all subpatterns with the same name are tested.
+ If the condition is true for any one of them, the overall condition is
+ true. This is the same behaviour as testing by number. For further
+ details of the interfaces for handling named subpatterns, see the
+ pcre2api documentation.
+
+ Warning: You cannot use different names to distinguish between two sub-
+ patterns with the same number because PCRE2 uses only the numbers when
+ matching. For this reason, an error is given at compile time if differ-
+ ent names are given to subpatterns with the same number. However, you
+ can always give the same name to subpatterns with the same number, even
+ when PCRE2_DUPNAMES is not set.
+
+
+REPETITION
+
+ Repetition is specified by quantifiers, which can follow any of the
+ following items:
+
+ a literal data character
+ the dot metacharacter
+ the \C escape sequence
+ the \X escape sequence
+ the \R escape sequence
+ an escape such as \d or \pL that matches a single character
+ a character class
+ a back reference
+ a parenthesized subpattern (including most assertions)
+ a subroutine call to a subpattern (recursive or otherwise)
+
+ The general repetition quantifier specifies a minimum and maximum num-
+ ber of permitted matches, by giving the two numbers in curly brackets
+ (braces), separated by a comma. The numbers must be less than 65536,
+ and the first must be less than or equal to the second. For example:
+
+ z{2,4}
+
+ matches "zz", "zzz", or "zzzz". A closing brace on its own is not a
+ special character. If the second number is omitted, but the comma is
+ present, there is no upper limit; if the second number and the comma
+ are both omitted, the quantifier specifies an exact number of required
+ matches. Thus
+
+ [aeiou]{3,}
+
+ matches at least 3 successive vowels, but may match many more, whereas
+
+ \d{8}
+
+ matches exactly 8 digits. An opening curly bracket that appears in a
+ position where a quantifier is not allowed, or one that does not match
+ the syntax of a quantifier, is taken as a literal character. For exam-
+ ple, {,6} is not a quantifier, but a literal string of four characters.
+
+ In UTF modes, quantifiers apply to characters rather than to individual
+ code units. Thus, for example, \x{100}{2} matches two characters, each
+ of which is represented by a two-byte sequence in a UTF-8 string. Simi-
+ larly, \X{3} matches three Unicode extended grapheme clusters, each of
+ which may be several code units long (and they may be of different
+ lengths).
+
+ The quantifier {0} is permitted, causing the expression to behave as if
+ the previous item and the quantifier were not present. This may be use-
+ ful for subpatterns that are referenced as subroutines from elsewhere
+ in the pattern (but see also the section entitled "Defining subpatterns
+ for use by reference only" below). Items other than subpatterns that
+ have a {0} quantifier are omitted from the compiled pattern.
+
+ For convenience, the three most common quantifiers have single-charac-
+ ter abbreviations:
+
+ * is equivalent to {0,}
+ + is equivalent to {1,}
+ ? is equivalent to {0,1}
+
+ It is possible to construct infinite loops by following a subpattern
+ that can match no characters with a quantifier that has no upper limit,
+ for example:
+
+ (a?)*
+
+ Earlier versions of Perl and PCRE1 used to give an error at compile
+ time for such patterns. However, because there are cases where this can
+ be useful, such patterns are now accepted, but if any repetition of the
+ subpattern does in fact match no characters, the loop is forcibly bro-
+ ken.
+
+ By default, the quantifiers are "greedy", that is, they match as much
+ as possible (up to the maximum number of permitted times), without
+ causing the rest of the pattern to fail. The classic example of where
+ this gives problems is in trying to match comments in C programs. These
+ appear between /* and */ and within the comment, individual * and /
+ characters may appear. An attempt to match C comments by applying the
+ pattern
+
+ /\*.*\*/
+
+ to the string
+
+ /* first comment */ not comment /* second comment */
+
+ fails, because it matches the entire string owing to the greediness of
+ the .* item.
+
+ If a quantifier is followed by a question mark, it ceases to be greedy,
+ and instead matches the minimum number of times possible, so the pat-
+ tern
+
+ /\*.*?\*/
+
+ does the right thing with the C comments. The meaning of the various
+ quantifiers is not otherwise changed, just the preferred number of
+ matches. Do not confuse this use of question mark with its use as a
+ quantifier in its own right. Because it has two uses, it can sometimes
+ appear doubled, as in
+
+ \d??\d
+
+ which matches one digit by preference, but can match two if that is the
+ only way the rest of the pattern matches.
+
+ If the PCRE2_UNGREEDY option is set (an option that is not available in
+ Perl), the quantifiers are not greedy by default, but individual ones
+ can be made greedy by following them with a question mark. In other
+ words, it inverts the default behaviour.
+
+ When a parenthesized subpattern is quantified with a minimum repeat
+ count that is greater than 1 or with a limited maximum, more memory is
+ required for the compiled pattern, in proportion to the size of the
+ minimum or maximum.
+
+ If a pattern starts with .* or .{0,} and the PCRE2_DOTALL option
+ (equivalent to Perl's /s) is set, thus allowing the dot to match new-
+ lines, the pattern is implicitly anchored, because whatever follows
+ will be tried against every character position in the subject string,
+ so there is no point in retrying the overall match at any position
+ after the first. PCRE2 normally treats such a pattern as though it were
+ preceded by \A.
+
+ In cases where it is known that the subject string contains no new-
+ lines, it is worth setting PCRE2_DOTALL in order to obtain this opti-
+ mization, or alternatively, using ^ to indicate anchoring explicitly.
+
+ However, there are some cases where the optimization cannot be used.
+ When .* is inside capturing parentheses that are the subject of a back
+ reference elsewhere in the pattern, a match at the start may fail where
+ a later one succeeds. Consider, for example:
+
+ (.*)abc\1
+
+ If the subject is "xyz123abc123" the match point is the fourth charac-
+ ter. For this reason, such a pattern is not implicitly anchored.
+
+ Another case where implicit anchoring is not applied is when the lead-
+ ing .* is inside an atomic group. Once again, a match at the start may
+ fail where a later one succeeds. Consider this pattern:
+
+ (?>.*?a)b
+
+ It matches "ab" in the subject "aab". The use of the backtracking con-
+ trol verbs (*PRUNE) and (*SKIP) also disable this optimization, and
+ there is an option, PCRE2_NO_DOTSTAR_ANCHOR, to do so explicitly.
+
+ When a capturing subpattern is repeated, the value captured is the sub-
+ string that matched the final iteration. For example, after
+
+ (tweedle[dume]{3}\s*)+
+
+ has matched "tweedledum tweedledee" the value of the captured substring
+ is "tweedledee". However, if there are nested capturing subpatterns,
+ the corresponding captured values may have been set in previous itera-
+ tions. For example, after
+
+ (a|(b))+
+
+ matches "aba" the value of the second captured substring is "b".
+
+
+ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS
+
+ With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy")
+ repetition, failure of what follows normally causes the repeated item
+ to be re-evaluated to see if a different number of repeats allows the
+ rest of the pattern to match. Sometimes it is useful to prevent this,
+ either to change the nature of the match, or to cause it fail earlier
+ than it otherwise might, when the author of the pattern knows there is
+ no point in carrying on.
+
+ Consider, for example, the pattern \d+foo when applied to the subject
+ line
+
+ 123456bar
+
+ After matching all 6 digits and then failing to match "foo", the normal
+ action of the matcher is to try again with only 5 digits matching the
+ \d+ item, and then with 4, and so on, before ultimately failing.
+ "Atomic grouping" (a term taken from Jeffrey Friedl's book) provides
+ the means for specifying that once a subpattern has matched, it is not
+ to be re-evaluated in this way.
+
+ If we use atomic grouping for the previous example, the matcher gives
+ up immediately on failing to match "foo" the first time. The notation
+ is a kind of special parenthesis, starting with (?> as in this example:
+
+ (?>\d+)foo
+
+ This kind of parenthesis "locks up" the part of the pattern it con-
+ tains once it has matched, and a failure further into the pattern is
+ prevented from backtracking into it. Backtracking past it to previous
+ items, however, works as normal.
+
+ An alternative description is that a subpattern of this type matches
+ exactly the string of characters that an identical standalone pattern
+ would match, if anchored at the current point in the subject string.
+
+ Atomic grouping subpatterns are not capturing subpatterns. Simple cases
+ such as the above example can be thought of as a maximizing repeat that
+ must swallow everything it can. So, while both \d+ and \d+? are pre-
+ pared to adjust the number of digits they match in order to make the
+ rest of the pattern match, (?>\d+) can only match an entire sequence of
+ digits.
+
+ Atomic groups in general can of course contain arbitrarily complicated
+ subpatterns, and can be nested. However, when the subpattern for an
+ atomic group is just a single repeated item, as in the example above, a
+ simpler notation, called a "possessive quantifier" can be used. This
+ consists of an additional + character following a quantifier. Using
+ this notation, the previous example can be rewritten as
+
+ \d++foo
+
+ Note that a possessive quantifier can be used with an entire group, for
+ example:
+
+ (abc|xyz){2,3}+
+
+ Possessive quantifiers are always greedy; the setting of the
+ PCRE2_UNGREEDY option is ignored. They are a convenient notation for
+ the simpler forms of atomic group. However, there is no difference in
+ the meaning of a possessive quantifier and the equivalent atomic group,
+ though there may be a performance difference; possessive quantifiers
+ should be slightly faster.
+
+ The possessive quantifier syntax is an extension to the Perl 5.8 syn-
+ tax. Jeffrey Friedl originated the idea (and the name) in the first
+ edition of his book. Mike McCloskey liked it, so implemented it when he
+ built Sun's Java package, and PCRE1 copied it from there. It ultimately
+ found its way into Perl at release 5.10.
+
+ PCRE2 has an optimization that automatically "possessifies" certain
+ simple pattern constructs. For example, the sequence A+B is treated as
+ A++B because there is no point in backtracking into a sequence of A's
+ when B must follow. This feature can be disabled by the PCRE2_NO_AUTO-
+ POSSESS option, or starting the pattern with (*NO_AUTO_POSSESS).
+
+ When a pattern contains an unlimited repeat inside a subpattern that
+ can itself be repeated an unlimited number of times, the use of an
+ atomic group is the only way to avoid some failing matches taking a
+ very long time indeed. The pattern
+
+ (\D+|<\d+>)*[!?]
+
+ matches an unlimited number of substrings that either consist of non-
+ digits, or digits enclosed in <>, followed by either ! or ?. When it
+ matches, it runs quickly. However, if it is applied to
+
+ aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+
+ it takes a long time before reporting failure. This is because the
+ string can be divided between the internal \D+ repeat and the external
+ * repeat in a large number of ways, and all have to be tried. (The
+ example uses [!?] rather than a single character at the end, because
+ both PCRE2 and Perl have an optimization that allows for fast failure
+ when a single character is used. They remember the last single charac-
+ ter that is required for a match, and fail early if it is not present
+ in the string.) If the pattern is changed so that it uses an atomic
+ group, like this:
+
+ ((?>\D+)|<\d+>)*[!?]
+
+ sequences of non-digits cannot be broken, and failure happens quickly.
+
+
+BACK REFERENCES
+
+ Outside a character class, a backslash followed by a digit greater than
+ 0 (and possibly further digits) is a back reference to a capturing sub-
+ pattern earlier (that is, to its left) in the pattern, provided there
+ have been that many previous capturing left parentheses.
+
+ However, if the decimal number following the backslash is less than 8,
+ it is always taken as a back reference, and causes an error only if
+ there are not that many capturing left parentheses in the entire pat-
+ tern. In other words, the parentheses that are referenced need not be
+ to the left of the reference for numbers less than 8. A "forward back
+ reference" of this type can make sense when a repetition is involved
+ and the subpattern to the right has participated in an earlier itera-
+ tion.
+
+ It is not possible to have a numerical "forward back reference" to a
+ subpattern whose number is 8 or more using this syntax because a
+ sequence such as \50 is interpreted as a character defined in octal.
+ See the subsection entitled "Non-printing characters" above for further
+ details of the handling of digits following a backslash. There is no
+ such problem when named parentheses are used. A back reference to any
+ subpattern is possible using named parentheses (see below).
+
+ Another way of avoiding the ambiguity inherent in the use of digits
+ following a backslash is to use the \g escape sequence. This escape
+ must be followed by an unsigned number or a negative number, optionally
+ enclosed in braces. These examples are all identical:
+
+ (ring), \1
+ (ring), \g1
+ (ring), \g{1}
+
+ An unsigned number specifies an absolute reference without the ambigu-
+ ity that is present in the older syntax. It is also useful when literal
+ digits follow the reference. A negative number is a relative reference.
+ Consider this example:
+
+ (abc(def)ghi)\g{-1}
+
+ The sequence \g{-1} is a reference to the most recently started captur-
+ ing subpattern before \g, that is, is it equivalent to \2 in this exam-
+ ple. Similarly, \g{-2} would be equivalent to \1. The use of relative
+ references can be helpful in long patterns, and also in patterns that
+ are created by joining together fragments that contain references
+ within themselves.
+
+ A back reference matches whatever actually matched the capturing sub-
+ pattern in the current subject string, rather than anything matching
+ the subpattern itself (see "Subpatterns as subroutines" below for a way
+ of doing that). So the pattern
+
+ (sens|respons)e and \1ibility
+
+ matches "sense and sensibility" and "response and responsibility", but
+ not "sense and responsibility". If caseful matching is in force at the
+ time of the back reference, the case of letters is relevant. For exam-
+ ple,
+
+ ((?i)rah)\s+\1
+
+ matches "rah rah" and "RAH RAH", but not "RAH rah", even though the
+ original capturing subpattern is matched caselessly.
+
+ There are several different ways of writing back references to named
+ subpatterns. The .NET syntax \k{name} and the Perl syntax \k<name> or
+ \k'name' are supported, as is the Python syntax (?P=name). Perl 5.10's
+ unified back reference syntax, in which \g can be used for both numeric
+ and named references, is also supported. We could rewrite the above
+ example in any of the following ways:
+
+ (?<p1>(?i)rah)\s+\k<p1>
+ (?'p1'(?i)rah)\s+\k{p1}
+ (?P<p1>(?i)rah)\s+(?P=p1)
+ (?<p1>(?i)rah)\s+\g{p1}
+
+ A subpattern that is referenced by name may appear in the pattern
+ before or after the reference.
+
+ There may be more than one back reference to the same subpattern. If a
+ subpattern has not actually been used in a particular match, any back
+ references to it always fail by default. For example, the pattern
+
+ (a|(bc))\2
+
+ always fails if it starts to match "a" rather than "bc". However, if
+ the PCRE2_MATCH_UNSET_BACKREF option is set at compile time, a back
+ reference to an unset value matches an empty string.
+
+ Because there may be many capturing parentheses in a pattern, all dig-
+ its following a backslash are taken as part of a potential back refer-
+ ence number. If the pattern continues with a digit character, some
+ delimiter must be used to terminate the back reference. If the
+ PCRE2_EXTENDED option is set, this can be white space. Otherwise, the
+ \g{ syntax or an empty comment (see "Comments" below) can be used.
+
+ Recursive back references
+
+ A back reference that occurs inside the parentheses to which it refers
+ fails when the subpattern is first used, so, for example, (a\1) never
+ matches. However, such references can be useful inside repeated sub-
+ patterns. For example, the pattern
+
+ (a|b\1)+
+
+ matches any number of "a"s and also "aba", "ababbaa" etc. At each iter-
+ ation of the subpattern, the back reference matches the character
+ string corresponding to the previous iteration. In order for this to
+ work, the pattern must be such that the first iteration does not need
+ to match the back reference. This can be done using alternation, as in
+ the example above, or by a quantifier with a minimum of zero.
+
+ Back references of this type cause the group that they reference to be
+ treated as an atomic group. Once the whole group has been matched, a
+ subsequent matching failure cannot cause backtracking into the middle
+ of the group.
+
+
+ASSERTIONS
+
+ An assertion is a test on the characters following or preceding the
+ current matching point that does not consume any characters. The simple
+ assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are described
+ above.
+
+ More complicated assertions are coded as subpatterns. There are two
+ kinds: those that look ahead of the current position in the subject
+ string, and those that look behind it. An assertion subpattern is
+ matched in the normal way, except that it does not cause the current
+ matching position to be changed.
+
+ Assertion subpatterns are not capturing subpatterns. If such an asser-
+ tion contains capturing subpatterns within it, these are counted for
+ the purposes of numbering the capturing subpatterns in the whole pat-
+ tern. However, substring capturing is carried out only for positive
+ assertions. (Perl sometimes, but not always, does do capturing in nega-
+ tive assertions.)
+
+ For compatibility with Perl, most assertion subpatterns may be
+ repeated; though it makes no sense to assert the same thing several
+ times, the side effect of capturing parentheses may occasionally be
+ useful. However, an assertion that forms the condition for a condi-
+ tional subpattern may not be quantified. In practice, for other asser-
+ tions, there only three cases:
+
+ (1) If the quantifier is {0}, the assertion is never obeyed during
+ matching. However, it may contain internal capturing parenthesized
+ groups that are called from elsewhere via the subroutine mechanism.
+
+ (2) If quantifier is {0,n} where n is greater than zero, it is treated
+ as if it were {0,1}. At run time, the rest of the pattern match is
+ tried with and without the assertion, the order depending on the greed-
+ iness of the quantifier.
+
+ (3) If the minimum repetition is greater than zero, the quantifier is
+ ignored. The assertion is obeyed just once when encountered during
+ matching.
+
+ Lookahead assertions
+
+ Lookahead assertions start with (?= for positive assertions and (?! for
+ negative assertions. For example,
+
+ \w+(?=;)
+
+ matches a word followed by a semicolon, but does not include the semi-
+ colon in the match, and
+
+ foo(?!bar)
+
+ matches any occurrence of "foo" that is not followed by "bar". Note
+ that the apparently similar pattern
+
+ (?!foo)bar
+
+ does not find an occurrence of "bar" that is preceded by something
+ other than "foo"; it finds any occurrence of "bar" whatsoever, because
+ the assertion (?!foo) is always true when the next three characters are
+ "bar". A lookbehind assertion is needed to achieve the other effect.
+
+ If you want to force a matching failure at some point in a pattern, the
+ most convenient way to do it is with (?!) because an empty string
+ always matches, so an assertion that requires there not to be an empty
+ string must always fail. The backtracking control verb (*FAIL) or (*F)
+ is a synonym for (?!).
+
+ Lookbehind assertions
+
+ Lookbehind assertions start with (?<= for positive assertions and (?<!
+ for negative assertions. For example,
+
+ (?<!foo)bar
+
+ does find an occurrence of "bar" that is not preceded by "foo". The
+ contents of a lookbehind assertion are restricted such that all the
+ strings it matches must have a fixed length. However, if there are sev-
+ eral top-level alternatives, they do not all have to have the same
+ fixed length. Thus
+
+ (?<=bullock|donkey)
+
+ is permitted, but
+
+ (?<!dogs?|cats?)
+
+ causes an error at compile time. Branches that match different length
+ strings are permitted only at the top level of a lookbehind assertion.
+ This is an extension compared with Perl, which requires all branches to
+ match the same length of string. An assertion such as
+
+ (?<=ab(c|de))
+
+ is not permitted, because its single top-level branch can match two
+ different lengths, but it is acceptable to PCRE2 if rewritten to use
+ two top-level branches:
+
+ (?<=abc|abde)
+
+ In some cases, the escape sequence \K (see above) can be used instead
+ of a lookbehind assertion to get round the fixed-length restriction.
+
+ The implementation of lookbehind assertions is, for each alternative,
+ to temporarily move the current position back by the fixed length and
+ then try to match. If there are insufficient characters before the cur-
+ rent position, the assertion fails.
+
+ In a UTF mode, PCRE2 does not allow the \C escape (which matches a sin-
+ gle code unit even in a UTF mode) to appear in lookbehind assertions,
+ because it makes it impossible to calculate the length of the lookbe-
+ hind. The \X and \R escapes, which can match different numbers of code
+ units, are also not permitted.
+
+ "Subroutine" calls (see below) such as (?2) or (?&X) are permitted in
+ lookbehinds, as long as the subpattern matches a fixed-length string.
+ Recursion, however, is not supported.
+
+ Possessive quantifiers can be used in conjunction with lookbehind
+ assertions to specify efficient matching of fixed-length strings at the
+ end of subject strings. Consider a simple pattern such as
+
+ abcd$
+
+ when applied to a long string that does not match. Because matching
+ proceeds from left to right, PCRE2 will look for each "a" in the sub-
+ ject and then see if what follows matches the rest of the pattern. If
+ the pattern is specified as
+
+ ^.*abcd$
+
+ the initial .* matches the entire string at first, but when this fails
+ (because there is no following "a"), it backtracks to match all but the
+ last character, then all but the last two characters, and so on. Once
+ again the search for "a" covers the entire string, from right to left,
+ so we are no better off. However, if the pattern is written as
+
+ ^.*+(?<=abcd)
+
+ there can be no backtracking for the .*+ item because of the possessive
+ quantifier; it can match only the entire string. The subsequent lookbe-
+ hind assertion does a single test on the last four characters. If it
+ fails, the match fails immediately. For long strings, this approach
+ makes a significant difference to the processing time.
+
+ Using multiple assertions
+
+ Several assertions (of any sort) may occur in succession. For example,
+
+ (?<=\d{3})(?<!999)foo
+
+ matches "foo" preceded by three digits that are not "999". Notice that
+ each of the assertions is applied independently at the same point in
+ the subject string. First there is a check that the previous three
+ characters are all digits, and then there is a check that the same
+ three characters are not "999". This pattern does not match "foo" pre-
+ ceded by six characters, the first of which are digits and the last
+ three of which are not "999". For example, it doesn't match "123abc-
+ foo". A pattern to do that is
+
+ (?<=\d{3}...)(?<!999)foo
+
+ This time the first assertion looks at the preceding six characters,
+ checking that the first three are digits, and then the second assertion
+ checks that the preceding three characters are not "999".
+
+ Assertions can be nested in any combination. For example,
+
+ (?<=(?<!foo)bar)baz
+
+ matches an occurrence of "baz" that is preceded by "bar" which in turn
+ is not preceded by "foo", while
+
+ (?<=\d{3}(?!999)...)foo
+
+ is another pattern that matches "foo" preceded by three digits and any
+ three characters that are not "999".
+
+
+CONDITIONAL SUBPATTERNS
+
+ It is possible to cause the matching process to obey a subpattern con-
+ ditionally or to choose between two alternative subpatterns, depending
+ on the result of an assertion, or whether a specific capturing subpat-
+ tern has already been matched. The two possible forms of conditional
+ subpattern are:
+
+ (?(condition)yes-pattern)
+ (?(condition)yes-pattern|no-pattern)
+
+ If the condition is satisfied, the yes-pattern is used; otherwise the
+ no-pattern (if present) is used. If there are more than two alterna-
+ tives in the subpattern, a compile-time error occurs. Each of the two
+ alternatives may itself contain nested subpatterns of any form, includ-
+ ing conditional subpatterns; the restriction to two alternatives
+ applies only at the level of the condition. This pattern fragment is an
+ example where the alternatives are complex:
+
+ (?(1) (A|B|C) | (D | (?(2)E|F) | E) )
+
+
+ There are five kinds of condition: references to subpatterns, refer-
+ ences to recursion, two pseudo-conditions called DEFINE and VERSION,
+ and assertions.
+
+ Checking for a used subpattern by number
+
+ If the text between the parentheses consists of a sequence of digits,
+ the condition is true if a capturing subpattern of that number has pre-
+ viously matched. If there is more than one capturing subpattern with
+ the same number (see the earlier section about duplicate subpattern
+ numbers), the condition is true if any of them have matched. An alter-
+ native notation is to precede the digits with a plus or minus sign. In
+ this case, the subpattern number is relative rather than absolute. The
+ most recently opened parentheses can be referenced by (?(-1), the next
+ most recent by (?(-2), and so on. Inside loops it can also make sense
+ to refer to subsequent groups. The next parentheses to be opened can be
+ referenced as (?(+1), and so on. (The value zero in any of these forms
+ is not used; it provokes a compile-time error.)
+
+ Consider the following pattern, which contains non-significant white
+ space to make it more readable (assume the PCRE2_EXTENDED option) and
+ to divide it into three parts for ease of discussion:
+
+ ( \( )? [^()]+ (?(1) \) )
+
+ The first part matches an optional opening parenthesis, and if that
+ character is present, sets it as the first captured substring. The sec-
+ ond part matches one or more characters that are not parentheses. The
+ third part is a conditional subpattern that tests whether or not the
+ first set of parentheses matched. If they did, that is, if subject
+ started with an opening parenthesis, the condition is true, and so the
+ yes-pattern is executed and a closing parenthesis is required. Other-
+ wise, since no-pattern is not present, the subpattern matches nothing.
+ In other words, this pattern matches a sequence of non-parentheses,
+ optionally enclosed in parentheses.
+
+ If you were embedding this pattern in a larger one, you could use a
+ relative reference:
+
+ ...other stuff... ( \( )? [^()]+ (?(-1) \) ) ...
+
+ This makes the fragment independent of the parentheses in the larger
+ pattern.
+
+ Checking for a used subpattern by name
+
+ Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a
+ used subpattern by name. For compatibility with earlier versions of
+ PCRE1, which had this facility before Perl, the syntax (?(name)...) is
+ also recognized.
+
+ Rewriting the above example to use a named subpattern gives this:
+
+ (?<OPEN> \( )? [^()]+ (?(<OPEN>) \) )
+
+ If the name used in a condition of this kind is a duplicate, the test
+ is applied to all subpatterns of the same name, and is true if any one
+ of them has matched.
+
+ Checking for pattern recursion
+
+ If the condition is the string (R), and there is no subpattern with the
+ name R, the condition is true if a recursive call to the whole pattern
+ or any subpattern has been made. If digits or a name preceded by amper-
+ sand follow the letter R, for example:
+
+ (?(R3)...) or (?(R&name)...)
+
+ the condition is true if the most recent recursion is into a subpattern
+ whose number or name is given. This condition does not check the entire
+ recursion stack. If the name used in a condition of this kind is a
+ duplicate, the test is applied to all subpatterns of the same name, and
+ is true if any one of them is the most recent recursion.
+
+ At "top level", all these recursion test conditions are false. The
+ syntax for recursive patterns is described below.
+
+ Defining subpatterns for use by reference only
+
+ If the condition is the string (DEFINE), and there is no subpattern
+ with the name DEFINE, the condition is always false. In this case,
+ there may be only one alternative in the subpattern. It is always
+ skipped if control reaches this point in the pattern; the idea of
+ DEFINE is that it can be used to define subroutines that can be refer-
+ enced from elsewhere. (The use of subroutines is described below.) For
+ example, a pattern to match an IPv4 address such as "192.168.23.245"
+ could be written like this (ignore white space and line breaks):
+
+ (?(DEFINE) (?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d) )
+ \b (?&byte) (\.(?&byte)){3} \b
+
+ The first part of the pattern is a DEFINE group inside which a another
+ group named "byte" is defined. This matches an individual component of
+ an IPv4 address (a number less than 256). When matching takes place,
+ this part of the pattern is skipped because DEFINE acts like a false
+ condition. The rest of the pattern uses references to the named group
+ to match the four dot-separated components of an IPv4 address, insist-
+ ing on a word boundary at each end.
+
+ Checking the PCRE2 version
+
+ Programs that link with a PCRE2 library can check the version by call-
+ ing pcre2_config() with appropriate arguments. Users of applications
+ that do not have access to the underlying code cannot do this. A spe-
+ cial "condition" called VERSION exists to allow such users to discover
+ which version of PCRE2 they are dealing with by using this condition to
+ match a string such as "yesno". VERSION must be followed either by "="
+ or ">=" and a version number. For example:
+
+ (?(VERSION>=10.4)yes|no)
+
+ This pattern matches "yes" if the PCRE2 version is greater or equal to
+ 10.4, or "no" otherwise.
+
+ Assertion conditions
+
+ If the condition is not in any of the above formats, it must be an
+ assertion. This may be a positive or negative lookahead or lookbehind
+ assertion. Consider this pattern, again containing non-significant
+ white space, and with the two alternatives on the second line:
+
+ (?(?=[^a-z]*[a-z])
+ \d{2}-[a-z]{3}-\d{2} | \d{2}-\d{2}-\d{2} )
+
+ The condition is a positive lookahead assertion that matches an
+ optional sequence of non-letters followed by a letter. In other words,
+ it tests for the presence of at least one letter in the subject. If a
+ letter is found, the subject is matched against the first alternative;
+ otherwise it is matched against the second. This pattern matches
+ strings in one of the two forms dd-aaa-dd or dd-dd-dd, where aaa are
+ letters and dd are digits.
+
+
+COMMENTS
+
+ There are two ways of including comments in patterns that are processed
+ by PCRE2. In both cases, the start of the comment must not be in a
+ character class, nor in the middle of any other sequence of related
+ characters such as (?: or a subpattern name or number. The characters
+ that make up a comment play no part in the pattern matching.
+
+ The sequence (?# marks the start of a comment that continues up to the
+ next closing parenthesis. Nested parentheses are not permitted. If the
+ PCRE2_EXTENDED option is set, an unescaped # character also introduces
+ a comment, which in this case continues to immediately after the next
+ newline character or character sequence in the pattern. Which charac-
+ ters are interpreted as newlines is controlled by an option passed to
+ the compiling function or by a special sequence at the start of the
+ pattern, as described in the section entitled "Newline conventions"
+ above. Note that the end of this type of comment is a literal newline
+ sequence in the pattern; escape sequences that happen to represent a
+ newline do not count. For example, consider this pattern when
+ PCRE2_EXTENDED is set, and the default newline convention (a single
+ linefeed character) is in force:
+
+ abc #comment \n still comment
+
+ On encountering the # character, pcre2_compile() skips along, looking
+ for a newline in the pattern. The sequence \n is still literal at this
+ stage, so it does not terminate the comment. Only an actual character
+ with the code value 0x0a (the default newline) does so.
+
+
+RECURSIVE PATTERNS
+
+ Consider the problem of matching a string in parentheses, allowing for
+ unlimited nested parentheses. Without the use of recursion, the best
+ that can be done is to use a pattern that matches up to some fixed
+ depth of nesting. It is not possible to handle an arbitrary nesting
+ depth.
+
+ For some time, Perl has provided a facility that allows regular expres-
+ sions to recurse (amongst other things). It does this by interpolating
+ Perl code in the expression at run time, and the code can refer to the
+ expression itself. A Perl pattern using code interpolation to solve the
+ parentheses problem can be created like this:
+
+ $re = qr{\( (?: (?>[^()]+) | (?p{$re}) )* \)}x;
+
+ The (?p{...}) item interpolates Perl code at run time, and in this case
+ refers recursively to the pattern in which it appears.
+
+ Obviously, PCRE2 cannot support the interpolation of Perl code.
+ Instead, it supports special syntax for recursion of the entire pat-
+ tern, and also for individual subpattern recursion. After its introduc-
+ tion in PCRE1 and Python, this kind of recursion was subsequently
+ introduced into Perl at release 5.10.
+
+ A special item that consists of (? followed by a number greater than
+ zero and a closing parenthesis is a recursive subroutine call of the
+ subpattern of the given number, provided that it occurs inside that
+ subpattern. (If not, it is a non-recursive subroutine call, which is
+ described in the next section.) The special item (?R) or (?0) is a
+ recursive call of the entire regular expression.
+
+ This PCRE2 pattern solves the nested parentheses problem (assume the
+ PCRE2_EXTENDED option is set so that white space is ignored):
+
+ \( ( [^()]++ | (?R) )* \)
+
+ First it matches an opening parenthesis. Then it matches any number of
+ substrings which can either be a sequence of non-parentheses, or a
+ recursive match of the pattern itself (that is, a correctly parenthe-
+ sized substring). Finally there is a closing parenthesis. Note the use
+ of a possessive quantifier to avoid backtracking into sequences of non-
+ parentheses.
+
+ If this were part of a larger pattern, you would not want to recurse
+ the entire pattern, so instead you could use this:
+
+ ( \( ( [^()]++ | (?1) )* \) )
+
+ We have put the pattern into parentheses, and caused the recursion to
+ refer to them instead of the whole pattern.
+
+ In a larger pattern, keeping track of parenthesis numbers can be
+ tricky. This is made easier by the use of relative references. Instead
+ of (?1) in the pattern above you can write (?-2) to refer to the second
+ most recently opened parentheses preceding the recursion. In other
+ words, a negative number counts capturing parentheses leftwards from
+ the point at which it is encountered.
+
+ It is also possible to refer to subsequently opened parentheses, by
+ writing references such as (?+2). However, these cannot be recursive
+ because the reference is not inside the parentheses that are refer-
+ enced. They are always non-recursive subroutine calls, as described in
+ the next section.
+
+ An alternative approach is to use named parentheses. The Perl syntax
+ for this is (?&name); PCRE1's earlier syntax (?P>name) is also sup-
+ ported. We could rewrite the above example as follows:
+
+ (?<pn> \( ( [^()]++ | (?&pn) )* \) )
+
+ If there is more than one subpattern with the same name, the earliest
+ one is used.
+
+ The example pattern that we have been looking at contains nested unlim-
+ ited repeats, and so the use of a possessive quantifier for matching
+ strings of non-parentheses is important when applying the pattern to
+ strings that do not match. For example, when this pattern is applied to
+
+ (aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa()
+
+ it yields "no match" quickly. However, if a possessive quantifier is
+ not used, the match runs for a very long time indeed because there are
+ so many different ways the + and * repeats can carve up the subject,
+ and all have to be tested before failure can be reported.
+
+ At the end of a match, the values of capturing parentheses are those
+ from the outermost level. If you want to obtain intermediate values, a
+ callout function can be used (see below and the pcre2callout documenta-
+ tion). If the pattern above is matched against
+
+ (ab(cd)ef)
+
+ the value for the inner capturing parentheses (numbered 2) is "ef",
+ which is the last value taken on at the top level. If a capturing sub-
+ pattern is not matched at the top level, its final captured value is
+ unset, even if it was (temporarily) set at a deeper level during the
+ matching process.
+
+ If there are more than 15 capturing parentheses in a pattern, PCRE2 has
+ to obtain extra memory from the heap to store data during a recursion.
+ If no memory can be obtained, the match fails with the
+ PCRE2_ERROR_NOMEMORY error.
+
+ Do not confuse the (?R) item with the condition (R), which tests for
+ recursion. Consider this pattern, which matches text in angle brack-
+ ets, allowing for arbitrary nesting. Only digits are allowed in nested
+ brackets (that is, when recursing), whereas any characters are permit-
+ ted at the outer level.
+
+ < (?: (?(R) \d++ | [^<>]*+) | (?R)) * >
+
+ In this pattern, (?(R) is the start of a conditional subpattern, with
+ two different alternatives for the recursive and non-recursive cases.
+ The (?R) item is the actual recursive call.
+
+ Differences in recursion processing between PCRE2 and Perl
+
+ Recursion processing in PCRE2 differs from Perl in two important ways.
+ In PCRE2 (like Python, but unlike Perl), a recursive subpattern call is
+ always treated as an atomic group. That is, once it has matched some of
+ the subject string, it is never re-entered, even if it contains untried
+ alternatives and there is a subsequent matching failure. This can be
+ illustrated by the following pattern, which purports to match a palin-
+ dromic string that contains an odd number of characters (for example,
+ "a", "aba", "abcba", "abcdcba"):
+
+ ^(.|(.)(?1)\2)$
+
+ The idea is that it either matches a single character, or two identical
+ characters surrounding a sub-palindrome. In Perl, this pattern works;
+ in PCRE2 it does not if the pattern is longer than three characters.
+ Consider the subject string "abcba":
+
+ At the top level, the first character is matched, but as it is not at
+ the end of the string, the first alternative fails; the second alterna-
+ tive is taken and the recursion kicks in. The recursive call to subpat-
+ tern 1 successfully matches the next character ("b"). (Note that the
+ beginning and end of line tests are not part of the recursion).
+
+ Back at the top level, the next character ("c") is compared with what
+ subpattern 2 matched, which was "a". This fails. Because the recursion
+ is treated as an atomic group, there are now no backtracking points,
+ and so the entire match fails. (Perl is able, at this point, to re-
+ enter the recursion and try the second alternative.) However, if the
+ pattern is written with the alternatives in the other order, things are
+ different:
+
+ ^((.)(?1)\2|.)$
+
+ This time, the recursing alternative is tried first, and continues to
+ recurse until it runs out of characters, at which point the recursion
+ fails. But this time we do have another alternative to try at the
+ higher level. That is the big difference: in the previous case the
+ remaining alternative is at a deeper recursion level, which PCRE2 can-
+ not use.
+
+ To change the pattern so that it matches all palindromic strings, not
+ just those with an odd number of characters, it is tempting to change
+ the pattern to this:
+
+ ^((.)(?1)\2|.?)$
+
+ Again, this works in Perl, but not in PCRE2, and for the same reason.
+ When a deeper recursion has matched a single character, it cannot be
+ entered again in order to match an empty string. The solution is to
+ separate the two cases, and write out the odd and even cases as alter-
+ natives at the higher level:
+
+ ^(?:((.)(?1)\2|)|((.)(?3)\4|.))
+
+ If you want to match typical palindromic phrases, the pattern has to
+ ignore all non-word characters, which can be done like this:
+
+ ^\W*+(?:((.)\W*+(?1)\W*+\2|)|((.)\W*+(?3)\W*+\4|\W*+.\W*+))\W*+$
+
+ If run with the PCRE2_CASELESS option, this pattern matches phrases
+ such as "A man, a plan, a canal: Panama!" and it works in both PCRE2
+ and Perl. Note the use of the possessive quantifier *+ to avoid back-
+ tracking into sequences of non-word characters. Without this, PCRE2
+ takes a great deal longer (ten times or more) to match typical phrases,
+ and Perl takes so long that you think it has gone into a loop.
+
+ WARNING: The palindrome-matching patterns above work only if the sub-
+ ject string does not start with a palindrome that is shorter than the
+ entire string. For example, although "abcba" is correctly matched, if
+ the subject is "ababa", PCRE2 finds the palindrome "aba" at the start,
+ then fails at top level because the end of the string does not follow.
+ Once again, it cannot jump back into the recursion to try other alter-
+ natives, so the entire match fails.
+
+ The second way in which PCRE2 and Perl differ in their recursion pro-
+ cessing is in the handling of captured values. In Perl, when a subpat-
+ tern is called recursively or as a subpattern (see the next section),
+ it has no access to any values that were captured outside the recur-
+ sion, whereas in PCRE2 these values can be referenced. Consider this
+ pattern:
+
+ ^(.)(\1|a(?2))
+
+ In PCRE2, this pattern matches "bab". The first capturing parentheses
+ match "b", then in the second group, when the back reference \1 fails
+ to match "b", the second alternative matches "a" and then recurses. In
+ the recursion, \1 does now match "b" and so the whole match succeeds.
+ In Perl, the pattern fails to match because inside the recursive call
+ \1 cannot access the externally set value.
+
+
+SUBPATTERNS AS SUBROUTINES
+
+ If the syntax for a recursive subpattern call (either by number or by
+ name) is used outside the parentheses to which it refers, it operates
+ like a subroutine in a programming language. The called subpattern may
+ be defined before or after the reference. A numbered reference can be
+ absolute or relative, as in these examples:
+
+ (...(absolute)...)...(?2)...
+ (...(relative)...)...(?-1)...
+ (...(?+1)...(relative)...
+
+ An earlier example pointed out that the pattern
+
+ (sens|respons)e and \1ibility
+
+ matches "sense and sensibility" and "response and responsibility", but
+ not "sense and responsibility". If instead the pattern
+
+ (sens|respons)e and (?1)ibility
+
+ is used, it does match "sense and responsibility" as well as the other
+ two strings. Another example is given in the discussion of DEFINE
+ above.
+
+ All subroutine calls, whether recursive or not, are always treated as
+ atomic groups. That is, once a subroutine has matched some of the sub-
+ ject string, it is never re-entered, even if it contains untried alter-
+ natives and there is a subsequent matching failure. Any capturing
+ parentheses that are set during the subroutine call revert to their
+ previous values afterwards.
+
+ Processing options such as case-independence are fixed when a subpat-
+ tern is defined, so if it is used as a subroutine, such options cannot
+ be changed for different calls. For example, consider this pattern:
+
+ (abc)(?i:(?-1))
+
+ It matches "abcabc". It does not match "abcABC" because the change of
+ processing option does not affect the called subpattern.
+
+
+ONIGURUMA SUBROUTINE SYNTAX
+
+ For compatibility with Oniguruma, the non-Perl syntax \g followed by a
+ name or a number enclosed either in angle brackets or single quotes, is
+ an alternative syntax for referencing a subpattern as a subroutine,
+ possibly recursively. Here are two of the examples used above, rewrit-
+ ten using this syntax:
+
+ (?<pn> \( ( (?>[^()]+) | \g<pn> )* \) )
+ (sens|respons)e and \g'1'ibility
+
+ PCRE2 supports an extension to Oniguruma: if a number is preceded by a
+ plus or a minus sign it is taken as a relative reference. For example:
+
+ (abc)(?i:\g<-1>)
+
+ Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are not
+ synonymous. The former is a back reference; the latter is a subroutine
+ call.
+
+
+CALLOUTS
+
+ Perl has a feature whereby using the sequence (?{...}) causes arbitrary
+ Perl code to be obeyed in the middle of matching a regular expression.
+ This makes it possible, amongst other things, to extract different sub-
+ strings that match the same pair of parentheses when there is a repeti-
+ tion.
+
+ PCRE2 provides a similar feature, but of course it cannot obey arbi-
+ trary Perl code. The feature is called "callout". The caller of PCRE2
+ provides an external function by putting its entry point in a match
+ context using the function pcre2_set_callout(), and then passing that
+ context to pcre2_match() or pcre2_dfa_match(). If no match context is
+ passed, or if the callout entry point is set to NULL, callouts are dis-
+ abled.
+
+ Within a regular expression, (?C<arg>) indicates a point at which the
+ external function is to be called. There are two kinds of callout:
+ those with a numerical argument and those with a string argument. (?C)
+ on its own with no argument is treated as (?C0). A numerical argument
+ allows the application to distinguish between different callouts.
+ String arguments were added for release 10.20 to make it possible for
+ script languages that use PCRE2 to embed short scripts within patterns
+ in a similar way to Perl.
+
+ During matching, when PCRE2 reaches a callout point, the external func-
+ tion is called. It is provided with the number or string argument of
+ the callout, the position in the pattern, and one item of data that is
+ also set in the match block. The callout function may cause matching to
+ proceed, to backtrack, or to fail.
+
+ By default, PCRE2 implements a number of optimizations at matching
+ time, and one side-effect is that sometimes callouts are skipped. If
+ you need all possible callouts to happen, you need to set options that
+ disable the relevant optimizations. More details, including a complete
+ description of the programming interface to the callout function, are
+ given in the pcre2callout documentation.
+
+ Callouts with numerical arguments
+
+ If you just want to have a means of identifying different callout
+ points, put a number less than 256 after the letter C. For example,
+ this pattern has two callout points:
+
+ (?C1)abc(?C2)def
+
+ If the PCRE2_AUTO_CALLOUT flag is passed to pcre2_compile(), numerical
+ callouts are automatically installed before each item in the pattern.
+ They are all numbered 255. If there is a conditional group in the pat-
+ tern whose condition is an assertion, an additional callout is inserted
+ just before the condition. An explicit callout may also be set at this
+ position, as in this example:
+
+ (?(?C9)(?=a)abc|def)
+
+ Note that this applies only to assertion conditions, not to other types
+ of condition.
+
+ Callouts with string arguments
+
+ A delimited string may be used instead of a number as a callout argu-
+ ment. The starting delimiter must be one of ` ' " ^ % # $ { and the
+ ending delimiter is the same as the start, except for {, where the end-
+ ing delimiter is }. If the ending delimiter is needed within the
+ string, it must be doubled. For example:
+
+ (?C'ab ''c'' d')xyz(?C{any text})pqr
+
+ The doubling is removed before the string is passed to the callout
+ function.
+
+
+BACKTRACKING CONTROL
+
+ Perl 5.10 introduced a number of "Special Backtracking Control Verbs",
+ which are still described in the Perl documentation as "experimental
+ and subject to change or removal in a future version of Perl". It goes
+ on to say: "Their usage in production code should be noted to avoid
+ problems during upgrades." The same remarks apply to the PCRE2 features
+ described in this section.
+
+ The new verbs make use of what was previously invalid syntax: an open-
+ ing parenthesis followed by an asterisk. They are generally of the form
+ (*VERB) or (*VERB:NAME). Some verbs take either form, possibly behaving
+ differently depending on whether or not a name is present.
+
+ By default, for compatibility with Perl, a name is any sequence of
+ characters that does not include a closing parenthesis. The name is not
+ processed in any way, and it is not possible to include a closing
+ parenthesis in the name. However, if the PCRE2_ALT_VERBNAMES option is
+ set, normal backslash processing is applied to verb names and only an
+ unescaped closing parenthesis terminates the name. A closing parenthe-
+ sis can be included in a name either as \) or between \Q and \E. If the
+ PCRE2_EXTENDED option is set, unescaped whitespace in verb names is
+ skipped and #-comments are recognized, exactly as in the rest of the
+ pattern.
+
+ The maximum length of a name is 255 in the 8-bit library and 65535 in
+ the 16-bit and 32-bit libraries. If the name is empty, that is, if the
+ closing parenthesis immediately follows the colon, the effect is as if
+ the colon were not there. Any number of these verbs may occur in a pat-
+ tern.
+
+ Since these verbs are specifically related to backtracking, most of
+ them can be used only when the pattern is to be matched using the tra-
+ ditional matching function, because these use a backtracking algorithm.
+ With the exception of (*FAIL), which behaves like a failing negative
+ assertion, the backtracking control verbs cause an error if encountered
+ by the DFA matching function.
+
+ The behaviour of these verbs in repeated groups, assertions, and in
+ subpatterns called as subroutines (whether or not recursively) is docu-
+ mented below.
+
+ Optimizations that affect backtracking verbs
+
+ PCRE2 contains some optimizations that are used to speed up matching by
+ running some checks at the start of each match attempt. For example, it
+ may know the minimum length of matching subject, or that a particular
+ character must be present. When one of these optimizations bypasses the
+ running of a match, any included backtracking verbs will not, of
+ course, be processed. You can suppress the start-of-match optimizations
+ by setting the PCRE2_NO_START_OPTIMIZE option when calling pcre2_com-
+ pile(), or by starting the pattern with (*NO_START_OPT). There is more
+ discussion of this option in the section entitled "Compiling a pattern"
+ in the pcre2api documentation.
+
+ Experiments with Perl suggest that it too has similar optimizations,
+ sometimes leading to anomalous results.
+
+ Verbs that act immediately
+
+ The following verbs act as soon as they are encountered. They may not
+ be followed by a name.
+
+ (*ACCEPT)
+
+ This verb causes the match to end successfully, skipping the remainder
+ of the pattern. However, when it is inside a subpattern that is called
+ as a subroutine, only that subpattern is ended successfully. Matching
+ then continues at the outer level. If (*ACCEPT) in triggered in a posi-
+ tive assertion, the assertion succeeds; in a negative assertion, the
+ assertion fails.
+
+ If (*ACCEPT) is inside capturing parentheses, the data so far is cap-
+ tured. For example:
+
+ A((?:A|B(*ACCEPT)|C)D)
+
+ This matches "AB", "AAD", or "ACD"; when it matches "AB", "B" is cap-
+ tured by the outer parentheses.
+
+ (*FAIL) or (*F)
+
+ This verb causes a matching failure, forcing backtracking to occur. It
+ is equivalent to (?!) but easier to read. The Perl documentation notes
+ that it is probably useful only when combined with (?{}) or (??{}).
+ Those are, of course, Perl features that are not present in PCRE2. The
+ nearest equivalent is the callout feature, as for example in this pat-
+ tern:
+
+ a+(?C)(*FAIL)
+
+ A match with the string "aaaa" always fails, but the callout is taken
+ before each backtrack happens (in this example, 10 times).
+
+ Recording which path was taken
+
+ There is one verb whose main purpose is to track how a match was
+ arrived at, though it also has a secondary use in conjunction with
+ advancing the match starting point (see (*SKIP) below).
+
+ (*MARK:NAME) or (*:NAME)
+
+ A name is always required with this verb. There may be as many
+ instances of (*MARK) as you like in a pattern, and their names do not
+ have to be unique.
+
+ When a match succeeds, the name of the last-encountered (*MARK:NAME),
+ (*PRUNE:NAME), or (*THEN:NAME) on the matching path is passed back to
+ the caller as described in the section entitled "Other information
+ about the match" in the pcre2api documentation. Here is an example of
+ pcre2test output, where the "mark" modifier requests the retrieval and
+ outputting of (*MARK) data:
+
+ re> /X(*MARK:A)Y|X(*MARK:B)Z/mark
+ data> XY
+ 0: XY
+ MK: A
+ XZ
+ 0: XZ
+ MK: B
+
+ The (*MARK) name is tagged with "MK:" in this output, and in this exam-
+ ple it indicates which of the two alternatives matched. This is a more
+ efficient way of obtaining this information than putting each alterna-
+ tive in its own capturing parentheses.
+
+ If a verb with a name is encountered in a positive assertion that is
+ true, the name is recorded and passed back if it is the last-encoun-
+ tered. This does not happen for negative assertions or failing positive
+ assertions.
+
+ After a partial match or a failed match, the last encountered name in
+ the entire match process is returned. For example:
+
+ re> /X(*MARK:A)Y|X(*MARK:B)Z/mark
+ data> XP
+ No match, mark = B
+
+ Note that in this unanchored example the mark is retained from the
+ match attempt that started at the letter "X" in the subject. Subsequent
+ match attempts starting at "P" and then with an empty string do not get
+ as far as the (*MARK) item, but nevertheless do not reset it.
+
+ If you are interested in (*MARK) values after failed matches, you
+ should probably set the PCRE2_NO_START_OPTIMIZE option (see above) to
+ ensure that the match is always attempted.
+
+ Verbs that act after backtracking
+
+ The following verbs do nothing when they are encountered. Matching con-
+ tinues with what follows, but if there is no subsequent match, causing
+ a backtrack to the verb, a failure is forced. That is, backtracking
+ cannot pass to the left of the verb. However, when one of these verbs
+ appears inside an atomic group (which includes any group that is called
+ as a subroutine) or in an assertion that is true, its effect is con-
+ fined to that group, because once the group has been matched, there is
+ never any backtracking into it. In this situation, backtracking has to
+ jump to the left of the entire atomic group or assertion.
+
+ These verbs differ in exactly what kind of failure occurs when back-
+ tracking reaches them. The behaviour described below is what happens
+ when the verb is not in a subroutine or an assertion. Subsequent sec-
+ tions cover these special cases.
+
+ (*COMMIT)
+
+ This verb, which may not be followed by a name, causes the whole match
+ to fail outright if there is a later matching failure that causes back-
+ tracking to reach it. Even if the pattern is unanchored, no further
+ attempts to find a match by advancing the starting point take place. If
+ (*COMMIT) is the only backtracking verb that is encountered, once it
+ has been passed pcre2_match() is committed to finding a match at the
+ current starting point, or not at all. For example:
+
+ a+(*COMMIT)b
+
+ This matches "xxaab" but not "aacaab". It can be thought of as a kind
+ of dynamic anchor, or "I've started, so I must finish." The name of the
+ most recently passed (*MARK) in the path is passed back when (*COMMIT)
+ forces a match failure.
+
+ If there is more than one backtracking verb in a pattern, a different
+ one that follows (*COMMIT) may be triggered first, so merely passing
+ (*COMMIT) during a match does not always guarantee that a match must be
+ at this starting point.
+
+ Note that (*COMMIT) at the start of a pattern is not the same as an
+ anchor, unless PCRE2's start-of-match optimizations are turned off, as
+ shown in this output from pcre2test:
+
+ re> /(*COMMIT)abc/
+ data> xyzabc
+ 0: abc
+ data>
+ re> /(*COMMIT)abc/no_start_optimize
+ data> xyzabc
+ No match
+
+ For the first pattern, PCRE2 knows that any match must start with "a",
+ so the optimization skips along the subject to "a" before applying the
+ pattern to the first set of data. The match attempt then succeeds. The
+ second pattern disables the optimization that skips along to the first
+ character. The pattern is now applied starting at "x", and so the
+ (*COMMIT) causes the match to fail without trying any other starting
+ points.
+
+ (*PRUNE) or (*PRUNE:NAME)
+
+ This verb causes the match to fail at the current starting position in
+ the subject if there is a later matching failure that causes backtrack-
+ ing to reach it. If the pattern is unanchored, the normal "bumpalong"
+ advance to the next starting character then happens. Backtracking can
+ occur as usual to the left of (*PRUNE), before it is reached, or when
+ matching to the right of (*PRUNE), but if there is no match to the
+ right, backtracking cannot cross (*PRUNE). In simple cases, the use of
+ (*PRUNE) is just an alternative to an atomic group or possessive quan-
+ tifier, but there are some uses of (*PRUNE) that cannot be expressed in
+ any other way. In an anchored pattern (*PRUNE) has the same effect as
+ (*COMMIT).
+
+ The behaviour of (*PRUNE:NAME) is the not the same as
+ (*MARK:NAME)(*PRUNE). It is like (*MARK:NAME) in that the name is
+ remembered for passing back to the caller. However, (*SKIP:NAME)
+ searches only for names set with (*MARK), ignoring those set by
+ (*PRUNE) or (*THEN).
+
+ (*SKIP)
+
+ This verb, when given without a name, is like (*PRUNE), except that if
+ the pattern is unanchored, the "bumpalong" advance is not to the next
+ character, but to the position in the subject where (*SKIP) was encoun-
+ tered. (*SKIP) signifies that whatever text was matched leading up to
+ it cannot be part of a successful match. Consider:
+
+ a+(*SKIP)b
+
+ If the subject is "aaaac...", after the first match attempt fails
+ (starting at the first character in the string), the starting point
+ skips on to start the next attempt at "c". Note that a possessive quan-
+ tifer does not have the same effect as this example; although it would
+ suppress backtracking during the first match attempt, the second
+ attempt would start at the second character instead of skipping on to
+ "c".
+
+ (*SKIP:NAME)
+
+ When (*SKIP) has an associated name, its behaviour is modified. When it
+ is triggered, the previous path through the pattern is searched for the
+ most recent (*MARK) that has the same name. If one is found, the
+ "bumpalong" advance is to the subject position that corresponds to that
+ (*MARK) instead of to where (*SKIP) was encountered. If no (*MARK) with
+ a matching name is found, the (*SKIP) is ignored.
+
+ Note that (*SKIP:NAME) searches only for names set by (*MARK:NAME). It
+ ignores names that are set by (*PRUNE:NAME) or (*THEN:NAME).
+
+ (*THEN) or (*THEN:NAME)
+
+ This verb causes a skip to the next innermost alternative when back-
+ tracking reaches it. That is, it cancels any further backtracking
+ within the current alternative. Its name comes from the observation
+ that it can be used for a pattern-based if-then-else block:
+
+ ( COND1 (*THEN) FOO | COND2 (*THEN) BAR | COND3 (*THEN) BAZ ) ...
+
+ If the COND1 pattern matches, FOO is tried (and possibly further items
+ after the end of the group if FOO succeeds); on failure, the matcher
+ skips to the second alternative and tries COND2, without backtracking
+ into COND1. If that succeeds and BAR fails, COND3 is tried. If subse-
+ quently BAZ fails, there are no more alternatives, so there is a back-
+ track to whatever came before the entire group. If (*THEN) is not
+ inside an alternation, it acts like (*PRUNE).
+
+ The behaviour of (*THEN:NAME) is the not the same as
+ (*MARK:NAME)(*THEN). It is like (*MARK:NAME) in that the name is
+ remembered for passing back to the caller. However, (*SKIP:NAME)
+ searches only for names set with (*MARK), ignoring those set by
+ (*PRUNE) and (*THEN).
+
+ A subpattern that does not contain a | character is just a part of the
+ enclosing alternative; it is not a nested alternation with only one
+ alternative. The effect of (*THEN) extends beyond such a subpattern to
+ the enclosing alternative. Consider this pattern, where A, B, etc. are
+ complex pattern fragments that do not contain any | characters at this
+ level:
+
+ A (B(*THEN)C) | D
+
+ If A and B are matched, but there is a failure in C, matching does not
+ backtrack into A; instead it moves to the next alternative, that is, D.
+ However, if the subpattern containing (*THEN) is given an alternative,
+ it behaves differently:
+
+ A (B(*THEN)C | (*FAIL)) | D
+
+ The effect of (*THEN) is now confined to the inner subpattern. After a
+ failure in C, matching moves to (*FAIL), which causes the whole subpat-
+ tern to fail because there are no more alternatives to try. In this
+ case, matching does now backtrack into A.
+
+ Note that a conditional subpattern is not considered as having two
+ alternatives, because only one is ever used. In other words, the |
+ character in a conditional subpattern has a different meaning. Ignoring
+ white space, consider:
+
+ ^.*? (?(?=a) a | b(*THEN)c )
+
+ If the subject is "ba", this pattern does not match. Because .*? is
+ ungreedy, it initially matches zero characters. The condition (?=a)
+ then fails, the character "b" is matched, but "c" is not. At this
+ point, matching does not backtrack to .*? as might perhaps be expected
+ from the presence of the | character. The conditional subpattern is
+ part of the single alternative that comprises the whole pattern, and so
+ the match fails. (If there was a backtrack into .*?, allowing it to
+ match "b", the match would succeed.)
+
+ The verbs just described provide four different "strengths" of control
+ when subsequent matching fails. (*THEN) is the weakest, carrying on the
+ match at the next alternative. (*PRUNE) comes next, failing the match
+ at the current starting position, but allowing an advance to the next
+ character (for an unanchored pattern). (*SKIP) is similar, except that
+ the advance may be more than one character. (*COMMIT) is the strongest,
+ causing the entire match to fail.
+
+ More than one backtracking verb
+
+ If more than one backtracking verb is present in a pattern, the one
+ that is backtracked onto first acts. For example, consider this pat-
+ tern, where A, B, etc. are complex pattern fragments:
+
+ (A(*COMMIT)B(*THEN)C|ABD)
+
+ If A matches but B fails, the backtrack to (*COMMIT) causes the entire
+ match to fail. However, if A and B match, but C fails, the backtrack to
+ (*THEN) causes the next alternative (ABD) to be tried. This behaviour
+ is consistent, but is not always the same as Perl's. It means that if
+ two or more backtracking verbs appear in succession, all the the last
+ of them has no effect. Consider this example:
+
+ ...(*COMMIT)(*PRUNE)...
+
+ If there is a matching failure to the right, backtracking onto (*PRUNE)
+ causes it to be triggered, and its action is taken. There can never be
+ a backtrack onto (*COMMIT).
+
+ Backtracking verbs in repeated groups
+
+ PCRE2 differs from Perl in its handling of backtracking verbs in
+ repeated groups. For example, consider:
+
+ /(a(*COMMIT)b)+ac/
+
+ If the subject is "abac", Perl matches, but PCRE2 fails because the
+ (*COMMIT) in the second repeat of the group acts.
+
+ Backtracking verbs in assertions
+
+ (*FAIL) in an assertion has its normal effect: it forces an immediate
+ backtrack.
+
+ (*ACCEPT) in a positive assertion causes the assertion to succeed with-
+ out any further processing. In a negative assertion, (*ACCEPT) causes
+ the assertion to fail without any further processing.
+
+ The other backtracking verbs are not treated specially if they appear
+ in a positive assertion. In particular, (*THEN) skips to the next
+ alternative in the innermost enclosing group that has alternations,
+ whether or not this is within the assertion.
+
+ Negative assertions are, however, different, in order to ensure that
+ changing a positive assertion into a negative assertion changes its
+ result. Backtracking into (*COMMIT), (*SKIP), or (*PRUNE) causes a neg-
+ ative assertion to be true, without considering any further alternative
+ branches in the assertion. Backtracking into (*THEN) causes it to skip
+ to the next enclosing alternative within the assertion (the normal be-
+ haviour), but if the assertion does not have such an alternative,
+ (*THEN) behaves like (*PRUNE).
+
+ Backtracking verbs in subroutines
+
+ These behaviours occur whether or not the subpattern is called recur-
+ sively. Perl's treatment of subroutines is different in some cases.
+
+ (*FAIL) in a subpattern called as a subroutine has its normal effect:
+ it forces an immediate backtrack.
+
+ (*ACCEPT) in a subpattern called as a subroutine causes the subroutine
+ match to succeed without any further processing. Matching then contin-
+ ues after the subroutine call.
+
+ (*COMMIT), (*SKIP), and (*PRUNE) in a subpattern called as a subroutine
+ cause the subroutine match to fail.
+
+ (*THEN) skips to the next alternative in the innermost enclosing group
+ within the subpattern that has alternatives. If there is no such group
+ within the subpattern, (*THEN) causes the subroutine match to fail.
+
+
+SEE ALSO
+
+ pcre2api(3), pcre2callout(3), pcre2matching(3), pcre2syntax(3),
+ pcre2(3).
+
+
+AUTHOR
+
+ Philip Hazel
+ University Computing Service
+ Cambridge, England.
+
+
+REVISION
+
+ Last updated: 01 September 2015
+ Copyright (c) 1997-2015 University of Cambridge.
+------------------------------------------------------------------------------
+
+
+PCRE2PERFORM(3) Library Functions Manual PCRE2PERFORM(3)
+
+
+
+NAME
+ PCRE2 - Perl-compatible regular expressions (revised API)
+
+PCRE2 PERFORMANCE
+
+ Two aspects of performance are discussed below: memory usage and pro-
+ cessing time. The way you express your pattern as a regular expression
+ can affect both of them.
+
+
+COMPILED PATTERN MEMORY USAGE
+
+ Patterns are compiled by PCRE2 into a reasonably efficient interpretive
+ code, so that most simple patterns do not use much memory. However,
+ there is one case where the memory usage of a compiled pattern can be
+ unexpectedly large. If a parenthesized subpattern has a quantifier with
+ a minimum greater than 1 and/or a limited maximum, the whole subpattern
+ is repeated in the compiled code. For example, the pattern
+
+ (abc|def){2,4}
+
+ is compiled as if it were
+
+ (abc|def)(abc|def)((abc|def)(abc|def)?)?
+
+ (Technical aside: It is done this way so that backtrack points within
+ each of the repetitions can be independently maintained.)
+
+ For regular expressions whose quantifiers use only small numbers, this
+ is not usually a problem. However, if the numbers are large, and par-
+ ticularly if such repetitions are nested, the memory usage can become
+ an embarrassment. For example, the very simple pattern
+
+ ((ab){1,1000}c){1,3}
+
+ uses 51K bytes when compiled using the 8-bit library. When PCRE2 is
+ compiled with its default internal pointer size of two bytes, the size
+ limit on a compiled pattern is 64K code units in the 8-bit and 16-bit
+ libraries, and this is reached with the above pattern if the outer rep-
+ etition is increased from 3 to 4. PCRE2 can be compiled to use larger
+ internal pointers and thus handle larger compiled patterns, but it is
+ better to try to rewrite your pattern to use less memory if you can.
+
+ One way of reducing the memory usage for such patterns is to make use
+ of PCRE2's "subroutine" facility. Re-writing the above pattern as
+
+ ((ab)(?2){0,999}c)(?1){0,2}
+
+ reduces the memory requirements to 18K, and indeed it remains under 20K
+ even with the outer repetition increased to 100. However, this pattern
+ is not exactly equivalent, because the "subroutine" calls are treated
+ as atomic groups into which there can be no backtracking if there is a
+ subsequent matching failure. Therefore, PCRE2 cannot do this kind of
+ rewriting automatically. Furthermore, there is a noticeable loss of
+ speed when executing the modified pattern. Nevertheless, if the atomic
+ grouping is not a problem and the loss of speed is acceptable, this
+ kind of rewriting will allow you to process patterns that PCRE2 cannot
+ otherwise handle.
+
+
+STACK USAGE AT RUN TIME
+
+ When pcre2_match() is used for matching, certain kinds of pattern can
+ cause it to use large amounts of the process stack. In some environ-
+ ments the default process stack is quite small, and if it runs out the
+ result is often SIGSEGV. Rewriting your pattern can often help. The
+ pcre2stack documentation discusses this issue in detail.
+
+
+PROCESSING TIME
+
+ Certain items in regular expression patterns are processed more effi-
+ ciently than others. It is more efficient to use a character class like
+ [aeiou] than a set of single-character alternatives such as
+ (a|e|i|o|u). In general, the simplest construction that provides the
+ required behaviour is usually the most efficient. Jeffrey Friedl's book
+ contains a lot of useful general discussion about optimizing regular
+ expressions for efficient performance. This document contains a few
+ observations about PCRE2.
+
+ Using Unicode character properties (the \p, \P, and \X escapes) is
+ slow, because PCRE2 has to use a multi-stage table lookup whenever it
+ needs a character's property. If you can find an alternative pattern
+ that does not use character properties, it will probably be faster.
+
+ By default, the escape sequences \b, \d, \s, and \w, and the POSIX
+ character classes such as [:alpha:] do not use Unicode properties,
+ partly for backwards compatibility, and partly for performance reasons.
+ However, you can set the PCRE2_UCP option or start the pattern with
+ (*UCP) if you want Unicode character properties to be used. This can
+ double the matching time for items such as \d, when matched with
+ pcre2_match(); the performance loss is less with a DFA matching func-
+ tion, and in both cases there is not much difference for \b.
+
+ When a pattern begins with .* not in atomic parentheses, nor in paren-
+ theses that are the subject of a backreference, and the PCRE2_DOTALL
+ option is set, the pattern is implicitly anchored by PCRE2, since it
+ can match only at the start of a subject string. If the pattern has
+ multiple top-level branches, they must all be anchorable. The optimiza-
+ tion can be disabled by the PCRE2_NO_DOTSTAR_ANCHOR option, and is
+ automatically disabled if the pattern contains (*PRUNE) or (*SKIP).
+
+ If PCRE2_DOTALL is not set, PCRE2 cannot make this optimization,
+ because the dot metacharacter does not then match a newline, and if the
+ subject string contains newlines, the pattern may match from the char-
+ acter immediately following one of them instead of from the very start.
+ For example, the pattern
+
+ .*second
+
+ matches the subject "first\nand second" (where \n stands for a newline
+ character), with the match starting at the seventh character. In order
+ to do this, PCRE2 has to retry the match starting after every newline
+ in the subject.
+
+ If you are using such a pattern with subject strings that do not con-
+ tain newlines, the best performance is obtained by setting
+ PCRE2_DOTALL, or starting the pattern with ^.* or ^.*? to indicate
+ explicit anchoring. That saves PCRE2 from having to scan along the sub-
+ ject looking for a newline to restart at.
+
+ Beware of patterns that contain nested indefinite repeats. These can
+ take a long time to run when applied to a string that does not match.
+ Consider the pattern fragment
+
+ ^(a+)*
+
+ This can match "aaaa" in 16 different ways, and this number increases
+ very rapidly as the string gets longer. (The * repeat can match 0, 1,
+ 2, 3, or 4 times, and for each of those cases other than 0 or 4, the +
+ repeats can match different numbers of times.) When the remainder of
+ the pattern is such that the entire match is going to fail, PCRE2 has
+ in principle to try every possible variation, and this can take an
+ extremely long time, even for relatively short strings.
+
+ An optimization catches some of the more simple cases such as
+
+ (a+)*b
+
+ where a literal character follows. Before embarking on the standard
+ matching procedure, PCRE2 checks that there is a "b" later in the sub-
+ ject string, and if there is not, it fails the match immediately. How-
+ ever, when there is no following literal this optimization cannot be
+ used. You can see the difference by comparing the behaviour of
+
+ (a+)*\d
+
+ with the pattern above. The former gives a failure almost instantly
+ when applied to a whole line of "a" characters, whereas the latter
+ takes an appreciable time with strings longer than about 20 characters.
+
+ In many cases, the solution to this kind of performance issue is to use
+ an atomic group or a possessive quantifier.
+
+
+AUTHOR
+
+ Philip Hazel
+ University Computing Service
+ Cambridge, England.
+
+
+REVISION
+
+ Last updated: 02 January 2015
+ Copyright (c) 1997-2015 University of Cambridge.
+------------------------------------------------------------------------------
+
+
+PCRE2POSIX(3) Library Functions Manual PCRE2POSIX(3)
+
+
+
+NAME
+ PCRE2 - Perl-compatible regular expressions (revised API)
+
+SYNOPSIS
+
+ #include <pcre2posix.h>
+
+ int regcomp(regex_t *preg, const char *pattern,
+ int cflags);
+
+ int regexec(const regex_t *preg, const char *string,
+ size_t nmatch, regmatch_t pmatch[], int eflags);
+
+ size_t regerror(int errcode, const regex_t *preg,
+ char *errbuf, size_t errbuf_size);
+
+ void regfree(regex_t *preg);
+
+
+DESCRIPTION
+
+ This set of functions provides a POSIX-style API for the PCRE2 regular
+ expression 8-bit library. See the pcre2api documentation for a descrip-
+ tion of PCRE2's native API, which contains much additional functional-
+ ity. There is no POSIX-style wrapper for PCRE2's 16-bit and 32-bit
+ libraries.
+
+ The functions described here are just wrapper functions that ultimately
+ call the PCRE2 native API. Their prototypes are defined in the
+ pcre2posix.h header file, and on Unix systems the library itself is
+ called libpcre2-posix.a, so can be accessed by adding -lpcre2-posix to
+ the command for linking an application that uses them. Because the
+ POSIX functions call the native ones, it is also necessary to add
+ -lpcre2-8.
+
+ Those POSIX option bits that can reasonably be mapped to PCRE2 native
+ options have been implemented. In addition, the option REG_EXTENDED is
+ defined with the value zero. This has no effect, but since programs
+ that are written to the POSIX interface often use it, this makes it
+ easier to slot in PCRE2 as a replacement library. Other POSIX options
+ are not even defined.
+
+ There are also some other options that are not defined by POSIX. These
+ have been added at the request of users who want to make use of certain
+ PCRE2-specific features via the POSIX calling interface.
+
+ When PCRE2 is called via these functions, it is only the API that is
+ POSIX-like in style. The syntax and semantics of the regular expres-
+ sions themselves are still those of Perl, subject to the setting of
+ various PCRE2 options, as described below. "POSIX-like in style" means
+ that the API approximates to the POSIX definition; it is not fully
+ POSIX-compatible, and in multi-unit encoding domains it is probably
+ even less compatible.
+
+ The header for these functions is supplied as pcre2posix.h to avoid any
+ potential clash with other POSIX libraries. It can, of course, be
+ renamed or aliased as regex.h, which is the "correct" name. It provides
+ two structure types, regex_t for compiled internal forms, and reg-
+ match_t for returning captured substrings. It also defines some con-
+ stants whose names start with "REG_"; these are used for setting
+ options and identifying error codes.
+
+
+COMPILING A PATTERN
+
+ The function regcomp() is called to compile a pattern into an internal
+ form. The pattern is a C string terminated by a binary zero, and is
+ passed in the argument pattern. The preg argument is a pointer to a
+ regex_t structure that is used as a base for storing information about
+ the compiled regular expression.
+
+ The argument cflags is either zero, or contains one or more of the bits
+ defined by the following macros:
+
+ REG_DOTALL
+
+ The PCRE2_DOTALL option is set when the regular expression is passed
+ for compilation to the native function. Note that REG_DOTALL is not
+ part of the POSIX standard.
+
+ REG_ICASE
+
+ The PCRE2_CASELESS option is set when the regular expression is passed
+ for compilation to the native function.
+
+ REG_NEWLINE
+
+ The PCRE2_MULTILINE option is set when the regular expression is passed
+ for compilation to the native function. Note that this does not mimic
+ the defined POSIX behaviour for REG_NEWLINE (see the following sec-
+ tion).
+
+ REG_NOSUB
+
+ The PCRE2_NO_AUTO_CAPTURE option is set when the regular expression is
+ passed for compilation to the native function. In addition, when a pat-
+ tern that is compiled with this flag is passed to regexec() for match-
+ ing, the nmatch and pmatch arguments are ignored, and no captured
+ strings are returned.
+
+ REG_UCP
+
+ The PCRE2_UCP option is set when the regular expression is passed for
+ compilation to the native function. This causes PCRE2 to use Unicode
+ properties when matchine \d, \w, etc., instead of just recognizing
+ ASCII values. Note that REG_UCP is not part of the POSIX standard.
+
+ REG_UNGREEDY
+
+ The PCRE2_UNGREEDY option is set when the regular expression is passed
+ for compilation to the native function. Note that REG_UNGREEDY is not
+ part of the POSIX standard.
+
+ REG_UTF
+
+ The PCRE2_UTF option is set when the regular expression is passed for
+ compilation to the native function. This causes the pattern itself and
+ all data strings used for matching it to be treated as UTF-8 strings.
+ Note that REG_UTF is not part of the POSIX standard.
+
+ In the absence of these flags, no options are passed to the native
+ function. This means the the regex is compiled with PCRE2 default
+ semantics. In particular, the way it handles newline characters in the
+ subject string is the Perl way, not the POSIX way. Note that setting
+ PCRE2_MULTILINE has only some of the effects specified for REG_NEWLINE.
+ It does not affect the way newlines are matched by the dot metacharac-
+ ter (they are not) or by a negative class such as [^a] (they are).
+
+ The yield of regcomp() is zero on success, and non-zero otherwise. The
+ preg structure is filled in on success, and one member of the structure
+ is public: re_nsub contains the number of capturing subpatterns in the
+ regular expression. Various error codes are defined in the header file.
+
+ NOTE: If the yield of regcomp() is non-zero, you must not attempt to
+ use the contents of the preg structure. If, for example, you pass it to
+ regexec(), the result is undefined and your program is likely to crash.
+
+
+MATCHING NEWLINE CHARACTERS
+
+ This area is not simple, because POSIX and Perl take different views of
+ things. It is not possible to get PCRE2 to obey POSIX semantics, but
+ then PCRE2 was never intended to be a POSIX engine. The following table
+ lists the different possibilities for matching newline characters in
+ Perl and PCRE2:
+
+ Default Change with
+
+ . matches newline no PCRE2_DOTALL
+ newline matches [^a] yes not changeable
+ $ matches \n at end yes PCRE2_DOLLAR_ENDONLY
+ $ matches \n in middle no PCRE2_MULTILINE
+ ^ matches \n in middle no PCRE2_MULTILINE
+
+ This is the equivalent table for a POSIX-compatible pattern matcher:
+
+ Default Change with
+
+ . matches newline yes REG_NEWLINE
+ newline matches [^a] yes REG_NEWLINE
+ $ matches \n at end no REG_NEWLINE
+ $ matches \n in middle no REG_NEWLINE
+ ^ matches \n in middle no REG_NEWLINE
+
+ This behaviour is not what happens when PCRE2 is called via its POSIX
+ API. By default, PCRE2's behaviour is the same as Perl's, except that
+ there is no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2
+ and Perl, there is no way to stop newline from matching [^a].
+
+ Default POSIX newline handling can be obtained by setting PCRE2_DOTALL
+ and PCRE2_DOLLAR_ENDONLY when calling pcre2_compile() directly, but
+ there is no way to make PCRE2 behave exactly as for the REG_NEWLINE
+ action. When using the POSIX API, passing REG_NEWLINE to PCRE2's reg-
+ comp() function causes PCRE2_MULTILINE to be passed to pcre2_compile(),
+ and REG_DOTALL passes PCRE2_DOTALL. There is no way to pass PCRE2_DOL-
+ LAR_ENDONLY.
+
+
+MATCHING A PATTERN
+
+ The function regexec() is called to match a compiled pattern preg
+ against a given string, which is by default terminated by a zero byte
+ (but see REG_STARTEND below), subject to the options in eflags. These
+ can be:
+
+ REG_NOTBOL
+
+ The PCRE2_NOTBOL option is set when calling the underlying PCRE2 match-
+ ing function.
+
+ REG_NOTEMPTY
+
+ The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2
+ matching function. Note that REG_NOTEMPTY is not part of the POSIX
+ standard. However, setting this option can give more POSIX-like behav-
+ iour in some situations.
+
+ REG_NOTEOL
+
+ The PCRE2_NOTEOL option is set when calling the underlying PCRE2 match-
+ ing function.
+
+ REG_STARTEND
+
+ The string is considered to start at string + pmatch[0].rm_so and to
+ have a terminating NUL located at string + pmatch[0].rm_eo (there need
+ not actually be a NUL at that location), regardless of the value of
+ nmatch. This is a BSD extension, compatible with but not specified by
+ IEEE Standard 1003.2 (POSIX.2), and should be used with caution in
+ software intended to be portable to other systems. Note that a non-zero
+ rm_so does not imply REG_NOTBOL; REG_STARTEND affects only the location
+ of the string, not how it is matched.
+
+ If the pattern was compiled with the REG_NOSUB flag, no data about any
+ matched strings is returned. The nmatch and pmatch arguments of
+ regexec() are ignored.
+
+ If the value of nmatch is zero, or if the value pmatch is NULL, no data
+ about any matched strings is returned.
+
+ Otherwise,the portion of the string that was matched, and also any cap-
+ tured substrings, are returned via the pmatch argument, which points to
+ an array of nmatch structures of type regmatch_t, containing the mem-
+ bers rm_so and rm_eo. These contain the byte offset to the first char-
+ acter of each substring and the offset to the first character after the
+ end of each substring, respectively. The 0th element of the vector
+ relates to the entire portion of string that was matched; subsequent
+ elements relate to the capturing subpatterns of the regular expression.
+ Unused entries in the array have both structure members set to -1.
+
+ A successful match yields a zero return; various error codes are
+ defined in the header file, of which REG_NOMATCH is the "expected"
+ failure code.
+
+
+ERROR MESSAGES
+
+ The regerror() function maps a non-zero errorcode from either regcomp()
+ or regexec() to a printable message. If preg is not NULL, the error
+ should have arisen from the use of that structure. A message terminated
+ by a binary zero is placed in errbuf. The length of the message,
+ including the zero, is limited to errbuf_size. The yield of the func-
+ tion is the size of buffer needed to hold the whole message.
+
+
+MEMORY USAGE
+
+ Compiling a regular expression causes memory to be allocated and asso-
+ ciated with the preg structure. The function regfree() frees all such
+ memory, after which preg may no longer be used as a compiled expres-
+ sion.
+
+
+AUTHOR
+
+ Philip Hazel
+ University Computing Service
+ Cambridge, England.
+
+
+REVISION
+
+ Last updated: 03 September 2015
+ Copyright (c) 1997-2015 University of Cambridge.
+------------------------------------------------------------------------------
+
+
+PCRE2SAMPLE(3) Library Functions Manual PCRE2SAMPLE(3)
+
+
+
+NAME
+ PCRE2 - Perl-compatible regular expressions (revised API)
+
+PCRE2 SAMPLE PROGRAM
+
+ A simple, complete demonstration program to get you started with using
+ PCRE2 is supplied in the file pcre2demo.c in the src directory in the
+ PCRE2 distribution. A listing of this program is given in the pcre2demo
+ documentation. If you do not have a copy of the PCRE2 distribution, you
+ can save this listing to re-create the contents of pcre2demo.c.
+
+ The demonstration program, which uses the PCRE2 8-bit library, compiles
+ the regular expression that is its first argument, and matches it
+ against the subject string in its second argument. No PCRE2 options are
+ set, and default character tables are used. If matching succeeds, the
+ program outputs the portion of the subject that matched, together with
+ the contents of any captured substrings.
+
+ If the -g option is given on the command line, the program then goes on
+ to check for further matches of the same regular expression in the same
+ subject string. The logic is a little bit tricky because of the possi-
+ bility of matching an empty string. Comments in the code explain what
+ is going on.
+
+ If PCRE2 is installed in the standard include and library directories
+ for your operating system, you should be able to compile the demonstra-
+ tion program using this command:
+
+ gcc -o pcre2demo pcre2demo.c -lpcre2-8
+
+ If PCRE2 is installed elsewhere, you may need to add additional options
+ to the command line. For example, on a Unix-like system that has PCRE2
+ installed in /usr/local, you can compile the demonstration program
+ using a command like this:
+
+ gcc -o pcre2demo -I/usr/local/include pcre2demo.c \
+ -L/usr/local/lib -lpcre2-8
+
+
+ Once you have compiled and linked the demonstration program, you can
+ run simple tests like this:
+
+ ./pcre2demo 'cat|dog' 'the cat sat on the mat'
+ ./pcre2demo -g 'cat|dog' 'the dog sat on the cat'
+
+ Note that there is a much more comprehensive test program, called
+ pcre2test, which supports many more facilities for testing regular
+ expressions using the PCRE2 libraries. The pcre2demo program is pro-
+ vided as a simple coding example.
+
+ If you try to run pcre2demo when PCRE2 is not installed in the standard
+ library directory, you may get an error like this on some operating
+ systems (e.g. Solaris):
+
+ ld.so.1: a.out: fatal: libpcre2.so.0: open failed: No such file or
+ directory
+
+ This is caused by the way shared library support works on those sys-
+ tems. You need to add
+
+ -R/usr/local/lib
+
+ (for example) to the compile command to get round this problem.
+
+
+AUTHOR
+
+ Philip Hazel
+ University Computing Service
+ Cambridge, England.
+
+
+REVISION
+
+ Last updated: 20 October 2014
+ Copyright (c) 1997-2014 University of Cambridge.
+------------------------------------------------------------------------------
+PCRE2SERIALIZE(3) Library Functions Manual PCRE2SERIALIZE(3)
+
+
+
+NAME
+ PCRE2 - Perl-compatible regular expressions (revised API)
+
+SAVING AND RE-USING PRECOMPILED PCRE2 PATTERNS
+
+ int32_t pcre2_serialize_decode(pcre2_code **codes,
+ int32_t number_of_codes, const uint32_t *bytes,
+ pcre2_general_context *gcontext);
+
+ int32_t pcre2_serialize_encode(pcre2_code **codes,
+ int32_t number_of_codes, uint32_t **serialized_bytes,
+ PCRE2_SIZE *serialized_size, pcre2_general_context *gcontext);
+
+ void pcre2_serialize_free(uint8_t *bytes);
+
+ int32_t pcre2_serialize_get_number_of_codes(const uint8_t *bytes);
+
+ If you are running an application that uses a large number of regular
+ expression patterns, it may be useful to store them in a precompiled
+ form instead of having to compile them every time the application is
+ run. However, if you are using the just-in-time optimization feature,
+ it is not possible to save and reload the JIT data, because it is posi-
+ tion-dependent. In addition, the host on which the patterns are
+ reloaded must be running the same version of PCRE2, with the same code
+ unit width, and must also have the same endianness, pointer width and
+ PCRE2_SIZE type. For example, patterns compiled on a 32-bit system
+ using PCRE2's 16-bit library cannot be reloaded on a 64-bit system, nor
+ can they be reloaded using the 8-bit library.
+
+
+SAVING COMPILED PATTERNS
+
+ Before compiled patterns can be saved they must be serialized, that is,
+ converted to a stream of bytes. A single byte stream may contain any
+ number of compiled patterns, but they must all use the same character
+ tables. A single copy of the tables is included in the byte stream (its
+ size is 1088 bytes). For more details of character tables, see the sec-
+ tion on locale support in the pcre2api documentation.
+
+ The function pcre2_serialize_encode() creates a serialized byte stream
+ from a list of compiled patterns. Its first two arguments specify the
+ list, being a pointer to a vector of pointers to compiled patterns, and
+ the length of the vector. The third and fourth arguments point to vari-
+ ables which are set to point to the created byte stream and its length,
+ respectively. The final argument is a pointer to a general context,
+ which can be used to specify custom memory mangagement functions. If
+ this argument is NULL, malloc() is used to obtain memory for the byte
+ stream. The yield of the function is the number of serialized patterns,
+ or one of the following negative error codes:
+
+ PCRE2_ERROR_BADDATA the number of patterns is zero or less
+ PCRE2_ERROR_BADMAGIC mismatch of id bytes in one of the patterns
+ PCRE2_ERROR_MEMORY memory allocation failed
+ PCRE2_ERROR_MIXEDTABLES the patterns do not all use the same tables
+ PCRE2_ERROR_NULL the 1st, 3rd, or 4th argument is NULL
+
+ PCRE2_ERROR_BADMAGIC means either that a pattern's code has been cor-
+ rupted, or that a slot in the vector does not point to a compiled pat-
+ tern.
+
+ Once a set of patterns has been serialized you can save the data in any
+ appropriate manner. Here is sample code that compiles two patterns and
+ writes them to a file. It assumes that the variable fd refers to a file
+ that is open for output. The error checking that should be present in a
+ real application has been omitted for simplicity.
+
+ int errorcode;
+ uint8_t *bytes;
+ PCRE2_SIZE erroroffset;
+ PCRE2_SIZE bytescount;
+ pcre2_code *list_of_codes[2];
+ list_of_codes[0] = pcre2_compile("first pattern",
+ PCRE2_ZERO_TERMINATED, 0, &errorcode, &erroroffset, NULL);
+ list_of_codes[1] = pcre2_compile("second pattern",
+ PCRE2_ZERO_TERMINATED, 0, &errorcode, &erroroffset, NULL);
+ errorcode = pcre2_serialize_encode(list_of_codes, 2, &bytes,
+ &bytescount, NULL);
+ errorcode = fwrite(bytes, 1, bytescount, fd);
+
+ Note that the serialized data is binary data that may contain any of
+ the 256 possible byte values. On systems that make a distinction
+ between binary and non-binary data, be sure that the file is opened for
+ binary output.
+
+ Serializing a set of patterns leaves the original data untouched, so
+ they can still be used for matching. Their memory must eventually be
+ freed in the usual way by calling pcre2_code_free(). When you have fin-
+ ished with the byte stream, it too must be freed by calling pcre2_seri-
+ alize_free().
+
+
+RE-USING PRECOMPILED PATTERNS
+
+ In order to re-use a set of saved patterns you must first make the
+ serialized byte stream available in main memory (for example, by read-
+ ing from a file). The management of this memory block is up to the
+ application. You can use the pcre2_serialize_get_number_of_codes()
+ function to find out how many compiled patterns are in the serialized
+ data without actually decoding the patterns:
+
+ uint8_t *bytes = <serialized data>;
+ int32_t number_of_codes = pcre2_serialize_get_number_of_codes(bytes);
+
+ The pcre2_serialize_decode() function reads a byte stream and recreates
+ the compiled patterns in new memory blocks, setting pointers to them in
+ a vector. The first two arguments are a pointer to a suitable vector
+ and its length, and the third argument points to a byte stream. The
+ final argument is a pointer to a general context, which can be used to
+ specify custom memory mangagement functions for the decoded patterns.
+ If this argument is NULL, malloc() and free() are used. After deserial-
+ ization, the byte stream is no longer needed and can be discarded.
+
+ int32_t number_of_codes;
+ pcre2_code *list_of_codes[2];
+ uint8_t *bytes = <serialized data>;
+ int32_t number_of_codes =
+ pcre2_serialize_decode(list_of_codes, 2, bytes, NULL);
+
+ If the vector is not large enough for all the patterns in the byte
+ stream, it is filled with those that fit, and the remainder are
+ ignored. The yield of the function is the number of decoded patterns,
+ or one of the following negative error codes:
+
+ PCRE2_ERROR_BADDATA second argument is zero or less
+ PCRE2_ERROR_BADMAGIC mismatch of id bytes in the data
+ PCRE2_ERROR_BADMODE mismatch of variable unit size or PCRE2 version
+ PCRE2_ERROR_MEMORY memory allocation failed
+ PCRE2_ERROR_NULL first or third argument is NULL
+
+ PCRE2_ERROR_BADMAGIC may mean that the data is corrupt, or that it was
+ compiled on a system with different endianness.
+
+ Decoded patterns can be used for matching in the usual way, and must be
+ freed by calling pcre2_code_free() as normal. A single copy of the
+ character tables is used by all the decoded patterns. A reference count
+ is used to arrange for its memory to be automatically freed when the
+ last pattern is freed.
+
+ If a pattern was processed by pcre2_jit_compile() before being serial-
+ ized, the JIT data is discarded and so is no longer available after a
+ save/restore cycle. You can, however, process a restored pattern with
+ pcre2_jit_compile() if you wish.
+
+
+AUTHOR
+
+ Philip Hazel
+ University Computing Service
+ Cambridge, England.
+
+
+REVISION
+
+ Last updated: 20 January 2015
+ Copyright (c) 1997-2015 University of Cambridge.
+------------------------------------------------------------------------------
+
+
+PCRE2STACK(3) Library Functions Manual PCRE2STACK(3)
+
+
+
+NAME
+ PCRE2 - Perl-compatible regular expressions (revised API)
+
+PCRE2 DISCUSSION OF STACK USAGE
+
+ When you call pcre2_match(), it makes use of an internal function
+ called match(). This calls itself recursively at branch points in the
+ pattern, in order to remember the state of the match so that it can
+ back up and try a different alternative after a failure. As matching
+ proceeds deeper and deeper into the tree of possibilities, the recur-
+ sion depth increases. The match() function is also called in other cir-
+ cumstances, for example, whenever a parenthesized sub-pattern is
+ entered, and in certain cases of repetition.
+
+ Not all calls of match() increase the recursion depth; for an item such
+ as a* it may be called several times at the same level, after matching
+ different numbers of a's. Furthermore, in a number of cases where the
+ result of the recursive call would immediately be passed back as the
+ result of the current call (a "tail recursion"), the function is just
+ restarted instead.
+
+ Each time the internal match() function is called recursively, it uses
+ memory from the process stack. For certain kinds of pattern and data,
+ very large amounts of stack may be needed, despite the recognition of
+ "tail recursion". Note that if PCRE2 is compiled with the -fsani-
+ tize=address option of the GCC compiler, the stack requirements are
+ greatly increased.
+
+ The above comments apply when pcre2_match() is run in its normal inter-
+ pretive manner. If the compiled pattern was processed by pcre2_jit_com-
+ pile(), and just-in-time compiling was successful, and the options
+ passed to pcre2_match() were not incompatible, the matching process
+ uses the JIT-compiled code instead of the match() function. In this
+ case, the memory requirements are handled entirely differently. See the
+ pcre2jit documentation for details.
+
+ The pcre2_dfa_match() function operates in a different way to
+ pcre2_match(), and uses recursion only when there is a regular expres-
+ sion recursion or subroutine call in the pattern. This includes the
+ processing of assertion and "once-only" subpatterns, which are handled
+ like subroutine calls. Normally, these are never very deep, and the
+ limit on the complexity of pcre2_dfa_match() is controlled by the
+ amount of workspace it is given. However, it is possible to write pat-
+ terns with runaway infinite recursions; such patterns will cause
+ pcre2_dfa_match() to run out of stack. At present, there is no protec-
+ tion against this.
+
+ The comments that follow do NOT apply to pcre2_dfa_match(); they are
+ relevant only for pcre2_match() without the JIT optimization.
+
+ Reducing pcre2_match()'s stack usage
+
+ You can often reduce the amount of recursion, and therefore the amount
+ of stack used, by modifying the pattern that is being matched. Con-
+ sider, for example, this pattern:
+
+ ([^<]|<(?!inet))+
+
+ It matches from wherever it starts until it encounters "<inet" or the
+ end of the data, and is the kind of pattern that might be used when
+ processing an XML file. Each iteration of the outer parentheses matches
+ either one character that is not "<" or a "<" that is not followed by
+ "inet". However, each time a parenthesis is processed, a recursion
+ occurs, so this formulation uses a stack frame for each matched charac-
+ ter. For a long string, a lot of stack is required. Consider now this
+ rewritten pattern, which matches exactly the same strings:
+
+ ([^<]++|<(?!inet))+
+
+ This uses very much less stack, because runs of characters that do not
+ contain "<" are "swallowed" in one item inside the parentheses. Recur-
+ sion happens only when a "<" character that is not followed by "inet"
+ is encountered (and we assume this is relatively rare). A possessive
+ quantifier is used to stop any backtracking into the runs of non-"<"
+ characters, but that is not related to stack usage.
+
+ This example shows that one way of avoiding stack problems when match-
+ ing long subject strings is to write repeated parenthesized subpatterns
+ to match more than one character whenever possible.
+
+ Compiling PCRE2 to use heap instead of stack for pcre2_match()
+
+ In environments where stack memory is constrained, you might want to
+ compile PCRE2 to use heap memory instead of stack for remembering back-
+ up points when pcre2_match() is running. This makes it run more slowly,
+ however. Details of how to do this are given in the pcre2build documen-
+ tation. When built in this way, instead of using the stack, PCRE2 gets
+ memory for remembering backup points from the heap. By default, the
+ memory is obtained by calling the system malloc() function, but you can
+ arrange to supply your own memory management function. For details, see
+ the section entitled "The match context" in the pcre2api documentation.
+ Since the block sizes are always the same, it may be possible to imple-
+ ment customized a memory handler that is more efficient than the stan-
+ dard function. The memory blocks obtained for this purpose are retained
+ and re-used if possible while pcre2_match() is running. They are all
+ freed just before it exits.
+
+ Limiting pcre2_match()'s stack usage
+
+ You can set limits on the number of times the internal match() function
+ is called, both in total and recursively. If a limit is exceeded,
+ pcre2_match() returns an error code. Setting suitable limits should
+ prevent it from running out of stack. The default values of the limits
+ are very large, and unlikely ever to operate. They can be changed when
+ PCRE2 is built, and they can also be set when pcre2_match() is called.
+ For details of these interfaces, see the pcre2build documentation and
+ the section entitled "The match context" in the pcre2api documentation.
+
+ As a very rough rule of thumb, you should reckon on about 500 bytes per
+ recursion. Thus, if you want to limit your stack usage to 8Mb, you
+ should set the limit at 16000 recursions. A 64Mb stack, on the other
+ hand, can support around 128000 recursions.
+
+ The pcre2test test program has a modifier called "find_limits" which,
+ if applied to a subject line, causes it to find the smallest limits
+ that allow a a pattern to match. This is done by calling pcre2_match()
+ repeatedly with different limits.
+
+ Changing stack size in Unix-like systems
+
+ In Unix-like environments, there is not often a problem with the stack
+ unless very long strings are involved, though the default limit on
+ stack size varies from system to system. Values from 8Mb to 64Mb are
+ common. You can find your default limit by running the command:
+
+ ulimit -s
+
+ Unfortunately, the effect of running out of stack is often SIGSEGV,
+ though sometimes a more explicit error message is given. You can nor-
+ mally increase the limit on stack size by code such as this:
+
+ struct rlimit rlim;
+ getrlimit(RLIMIT_STACK, &rlim);
+ rlim.rlim_cur = 100*1024*1024;
+ setrlimit(RLIMIT_STACK, &rlim);
+
+ This reads the current limits (soft and hard) using getrlimit(), then
+ attempts to increase the soft limit to 100Mb using setrlimit(). You
+ must do this before calling pcre2_match().
+
+ Changing stack size in Mac OS X
+
+ Using setrlimit(), as described above, should also work on Mac OS X. It
+ is also possible to set a stack size when linking a program. There is a
+ discussion about stack sizes in Mac OS X at this web site:
+ http://developer.apple.com/qa/qa2005/qa1419.html.
+
+
+AUTHOR
+
+ Philip Hazel
+ University Computing Service
+ Cambridge, England.
+
+
+REVISION
+
+ Last updated: 21 November 2014
+ Copyright (c) 1997-2014 University of Cambridge.
+------------------------------------------------------------------------------
+
+
+PCRE2SYNTAX(3) Library Functions Manual PCRE2SYNTAX(3)
+
+
+
+NAME
+ PCRE2 - Perl-compatible regular expressions (revised API)
+
+PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY
+
+ The full syntax and semantics of the regular expressions that are sup-
+ ported by PCRE2 are described in the pcre2pattern documentation. This
+ document contains a quick-reference summary of the syntax.
+
+
+QUOTING
+
+ \x where x is non-alphanumeric is a literal x
+ \Q...\E treat enclosed characters as literal
+
+
+ESCAPED CHARACTERS
+
+ This table applies to ASCII and Unicode environments.
+
+ \a alarm, that is, the BEL character (hex 07)
+ \cx "control-x", where x is any ASCII printing character
+ \e escape (hex 1B)
+ \f form feed (hex 0C)
+ \n newline (hex 0A)
+ \r carriage return (hex 0D)
+ \t tab (hex 09)
+ \0dd character with octal code 0dd
+ \ddd character with octal code ddd, or backreference
+ \o{ddd..} character with octal code ddd..
+ \U "U" if PCRE2_ALT_BSUX is set (otherwise is an error)
+ \uhhhh character with hex code hhhh (if PCRE2_ALT_BSUX is set)
+ \xhh character with hex code hh
+ \x{hhh..} character with hex code hhh..
+
+ Note that \0dd is always an octal code. The treatment of backslash fol-
+ lowed by a non-zero digit is complicated; for details see the section
+ "Non-printing characters" in the pcre2pattern documentation, where
+ details of escape processing in EBCDIC environments are also given.
+
+ When \x is not followed by {, from zero to two hexadecimal digits are
+ read, but if PCRE2_ALT_BSUX is set, \x must be followed by two hexadec-
+ imal digits to be recognized as a hexadecimal escape; otherwise it
+ matches a literal "x". Likewise, if \u (in ALT_BSUX mode) is not fol-
+ lowed by four hexadecimal digits, it matches a literal "u".
+
+
+CHARACTER TYPES
+
+ . any character except newline;
+ in dotall mode, any character whatsoever
+ \C one code unit, even in UTF mode (best avoided)
+ \d a decimal digit
+ \D a character that is not a decimal digit
+ \h a horizontal white space character
+ \H a character that is not a horizontal white space character
+ \N a character that is not a newline
+ \p{xx} a character with the xx property
+ \P{xx} a character without the xx property
+ \R a newline sequence
+ \s a white space character
+ \S a character that is not a white space character
+ \v a vertical white space character
+ \V a character that is not a vertical white space character
+ \w a "word" character
+ \W a "non-word" character
+ \X a Unicode extended grapheme cluster
+
+ The application can lock out the use of \C by setting the
+ PCRE2_NEVER_BACKSLASH_C option. It is dangerous because it may leave
+ the current matching point in the middle of a UTF-8 or UTF-16 charac-
+ ter.
+
+ By default, \d, \s, and \w match only ASCII characters, even in UTF-8
+ mode or in the 16-bit and 32-bit libraries. However, if locale-specific
+ matching is happening, \s and \w may also match characters with code
+ points in the range 128-255. If the PCRE2_UCP option is set, the behav-
+ iour of these escape sequences is changed to use Unicode properties and
+ they match many more characters.
+
+
+GENERAL CATEGORY PROPERTIES FOR \p and \P
+
+ C Other
+ Cc Control
+ Cf Format
+ Cn Unassigned
+ Co Private use
+ Cs Surrogate
+
+ L Letter
+ Ll Lower case letter
+ Lm Modifier letter
+ Lo Other letter
+ Lt Title case letter
+ Lu Upper case letter
+ L& Ll, Lu, or Lt
+
+ M Mark
+ Mc Spacing mark
+ Me Enclosing mark
+ Mn Non-spacing mark
+
+ N Number
+ Nd Decimal number
+ Nl Letter number
+ No Other number
+
+ P Punctuation
+ Pc Connector punctuation
+ Pd Dash punctuation
+ Pe Close punctuation
+ Pf Final punctuation
+ Pi Initial punctuation
+ Po Other punctuation
+ Ps Open punctuation
+
+ S Symbol
+ Sc Currency symbol
+ Sk Modifier symbol
+ Sm Mathematical symbol
+ So Other symbol
+
+ Z Separator
+ Zl Line separator
+ Zp Paragraph separator
+ Zs Space separator
+
+
+PCRE2 SPECIAL CATEGORY PROPERTIES FOR \p and \P
+
+ Xan Alphanumeric: union of properties L and N
+ Xps POSIX space: property Z or tab, NL, VT, FF, CR
+ Xsp Perl space: property Z or tab, NL, VT, FF, CR
+ Xuc Univerally-named character: one that can be
+ represented by a Universal Character Name
+ Xwd Perl word: property Xan or underscore
+
+ Perl and POSIX space are now the same. Perl added VT to its space char-
+ acter set at release 5.18.
+
+
+SCRIPT NAMES FOR \p AND \P
+
+ Ahom, Anatolian_Hieroglyphs, Arabic, Armenian, Avestan, Balinese,
+ Bamum, Bassa_Vah, Batak, Bengali, Bopomofo, Brahmi, Braille, Buginese,
+ Buhid, Canadian_Aboriginal, Carian, Caucasian_Albanian, Chakma, Cham,
+ Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret,
+ Devanagari, Duployan, Egyptian_Hieroglyphs, Elbasan, Ethiopic, Geor-
+ gian, Glagolitic, Gothic, Grantha, Greek, Gujarati, Gurmukhi, Han,
+ Hangul, Hanunoo, Hatran, Hebrew, Hiragana, Imperial_Aramaic, Inherited,
+ Inscriptional_Pahlavi, Inscriptional_Parthian, Javanese, Kaithi, Kan-
+ nada, Katakana, Kayah_Li, Kharoshthi, Khmer, Khojki, Khudawadi, Lao,
+ Latin, Lepcha, Limbu, Linear_A, Linear_B, Lisu, Lycian, Lydian, Maha-
+ jani, Malayalam, Mandaic, Manichaean, Meetei_Mayek, Mende_Kikakui,
+ Meroitic_Cursive, Meroitic_Hieroglyphs, Miao, Modi, Mongolian, Mro,
+ Multani, Myanmar, Nabataean, New_Tai_Lue, Nko, Ogham, Ol_Chiki,
+ Old_Hungarian, Old_Italic, Old_North_Arabian, Old_Permic, Old_Persian,
+ Old_South_Arabian, Old_Turkic, Oriya, Osmanya, Pahawh_Hmong, Palmyrene,
+ Pau_Cin_Hau, Phags_Pa, Phoenician, Psalter_Pahlavi, Rejang, Runic,
+ Samaritan, Saurashtra, Sharada, Shavian, Siddham, SignWriting, Sinhala,
+ Sora_Sompeng, Sundanese, Syloti_Nagri, Syriac, Tagalog, Tagbanwa,
+ Tai_Le, Tai_Tham, Tai_Viet, Takri, Tamil, Telugu, Thaana, Thai,
+ Tibetan, Tifinagh, Tirhuta, Ugaritic, Vai, Warang_Citi, Yi.
+
+
+CHARACTER CLASSES
+
+ [...] positive character class
+ [^...] negative character class
+ [x-y] range (can be used for hex characters)
+ [[:xxx:]] positive POSIX named set
+ [[:^xxx:]] negative POSIX named set
+
+ alnum alphanumeric
+ alpha alphabetic
+ ascii 0-127
+ blank space or tab
+ cntrl control character
+ digit decimal digit
+ graph printing, excluding space
+ lower lower case letter
+ print printing, including space
+ punct printing, excluding alphanumeric
+ space white space
+ upper upper case letter
+ word same as \w
+ xdigit hexadecimal digit
+
+ In PCRE2, POSIX character set names recognize only ASCII characters by
+ default, but some of them use Unicode properties if PCRE2_UCP is set.
+ You can use \Q...\E inside a character class.
+
+
+QUANTIFIERS
+
+ ? 0 or 1, greedy
+ ?+ 0 or 1, possessive
+ ?? 0 or 1, lazy
+ * 0 or more, greedy
+ *+ 0 or more, possessive
+ *? 0 or more, lazy
+ + 1 or more, greedy
+ ++ 1 or more, possessive
+ +? 1 or more, lazy
+ {n} exactly n
+ {n,m} at least n, no more than m, greedy
+ {n,m}+ at least n, no more than m, possessive
+ {n,m}? at least n, no more than m, lazy
+ {n,} n or more, greedy
+ {n,}+ n or more, possessive
+ {n,}? n or more, lazy
+
+
+ANCHORS AND SIMPLE ASSERTIONS
+
+ \b word boundary
+ \B not a word boundary
+ ^ start of subject
+ also after an internal newline in multiline mode
+ (after any newline if PCRE2_ALT_CIRCUMFLEX is set)
+ \A start of subject
+ $ end of subject
+ also before newline at end of subject
+ also before internal newline in multiline mode
+ \Z end of subject
+ also before newline at end of subject
+ \z end of subject
+ \G first matching position in subject
+
+
+MATCH POINT RESET
+
+ \K reset start of match
+
+ \K is honoured in positive assertions, but ignored in negative ones.
+
+
+ALTERNATION
+
+ expr|expr|expr...
+
+
+CAPTURING
+
+ (...) capturing group
+ (?<name>...) named capturing group (Perl)
+ (?'name'...) named capturing group (Perl)
+ (?P<name>...) named capturing group (Python)
+ (?:...) non-capturing group
+ (?|...) non-capturing group; reset group numbers for
+ capturing groups in each alternative
+
+
+ATOMIC GROUPS
+
+ (?>...) atomic, non-capturing group
+
+
+COMMENT
+
+ (?#....) comment (not nestable)
+
+
+OPTION SETTING
+
+ (?i) caseless
+ (?J) allow duplicate names
+ (?m) multiline
+ (?s) single line (dotall)
+ (?U) default ungreedy (lazy)
+ (?x) extended (ignore white space)
+ (?-...) unset option(s)
+
+ The following are recognized only at the very start of a pattern or
+ after one of the newline or \R options with similar syntax. More than
+ one of them may appear.
+
+ (*LIMIT_MATCH=d) set the match limit to d (decimal number)
+ (*LIMIT_RECURSION=d) set the recursion limit to d (decimal number)
+ (*NOTEMPTY) set PCRE2_NOTEMPTY when matching
+ (*NOTEMPTY_ATSTART) set PCRE2_NOTEMPTY_ATSTART when matching
+ (*NO_AUTO_POSSESS) no auto-possessification (PCRE2_NO_AUTO_POSSESS)
+ (*NO_DOTSTAR_ANCHOR) no .* anchoring (PCRE2_NO_DOTSTAR_ANCHOR)
+ (*NO_JIT) disable JIT optimization
+ (*NO_START_OPT) no start-match optimization (PCRE2_NO_START_OPTIMIZE)
+ (*UTF) set appropriate UTF mode for the library in use
+ (*UCP) set PCRE2_UCP (use Unicode properties for \d etc)
+
+ Note that LIMIT_MATCH and LIMIT_RECURSION can only reduce the value of
+ the limits set by the caller of pcre2_match(), not increase them. The
+ application can lock out the use of (*UTF) and (*UCP) by setting the
+ PCRE2_NEVER_UTF or PCRE2_NEVER_UCP options, respectively, at compile
+ time.
+
+
+NEWLINE CONVENTION
+
+ These are recognized only at the very start of the pattern or after
+ option settings with a similar syntax.
+
+ (*CR) carriage return only
+ (*LF) linefeed only
+ (*CRLF) carriage return followed by linefeed
+ (*ANYCRLF) all three of the above
+ (*ANY) any Unicode newline sequence
+
+
+WHAT \R MATCHES
+
+ These are recognized only at the very start of the pattern or after
+ option setting with a similar syntax.
+
+ (*BSR_ANYCRLF) CR, LF, or CRLF
+ (*BSR_UNICODE) any Unicode newline sequence
+
+
+LOOKAHEAD AND LOOKBEHIND ASSERTIONS
+
+ (?=...) positive look ahead
+ (?!...) negative look ahead
+ (?<=...) positive look behind
+ (?<!...) negative look behind
+
+ Each top-level branch of a look behind must be of a fixed length.
+
+
+BACKREFERENCES
+
+ \n reference by number (can be ambiguous)
+ \gn reference by number
+ \g{n} reference by number
+ \g{-n} relative reference by number
+ \k<name> reference by name (Perl)
+ \k'name' reference by name (Perl)
+ \g{name} reference by name (Perl)
+ \k{name} reference by name (.NET)
+ (?P=name) reference by name (Python)
+
+
+SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)
+
+ (?R) recurse whole pattern
+ (?n) call subpattern by absolute number
+ (?+n) call subpattern by relative number
+ (?-n) call subpattern by relative number
+ (?&name) call subpattern by name (Perl)
+ (?P>name) call subpattern by name (Python)
+ \g<name> call subpattern by name (Oniguruma)
+ \g'name' call subpattern by name (Oniguruma)
+ \g<n> call subpattern by absolute number (Oniguruma)
+ \g'n' call subpattern by absolute number (Oniguruma)
+ \g<+n> call subpattern by relative number (PCRE2 extension)
+ \g'+n' call subpattern by relative number (PCRE2 extension)
+ \g<-n> call subpattern by relative number (PCRE2 extension)
+ \g'-n' call subpattern by relative number (PCRE2 extension)
+
+
+CONDITIONAL PATTERNS
+
+ (?(condition)yes-pattern)
+ (?(condition)yes-pattern|no-pattern)
+
+ (?(n) absolute reference condition
+ (?(+n) relative reference condition
+ (?(-n) relative reference condition
+ (?(<name>) named reference condition (Perl)
+ (?('name') named reference condition (Perl)
+ (?(name) named reference condition (PCRE2)
+ (?(R) overall recursion condition
+ (?(Rn) specific group recursion condition
+ (?(R&name) specific recursion condition
+ (?(DEFINE) define subpattern for reference
+ (?(VERSION[>]=n.m) test PCRE2 version
+ (?(assert) assertion condition
+
+
+BACKTRACKING CONTROL
+
+ The following act immediately they are reached:
+
+ (*ACCEPT) force successful match
+ (*FAIL) force backtrack; synonym (*F)
+ (*MARK:NAME) set name to be passed back; synonym (*:NAME)
+
+ The following act only when a subsequent match failure causes a back-
+ track to reach them. They all force a match failure, but they differ in
+ what happens afterwards. Those that advance the start-of-match point do
+ so only if the pattern is not anchored.
+
+ (*COMMIT) overall failure, no advance of starting point
+ (*PRUNE) advance to next starting character
+ (*PRUNE:NAME) equivalent to (*MARK:NAME)(*PRUNE)
+ (*SKIP) advance to current matching position
+ (*SKIP:NAME) advance to position corresponding to an earlier
+ (*MARK:NAME); if not found, the (*SKIP) is ignored
+ (*THEN) local failure, backtrack to next alternation
+ (*THEN:NAME) equivalent to (*MARK:NAME)(*THEN)
+
+
+CALLOUTS
+
+ (?C) callout (assumed number 0)
+ (?Cn) callout with numerical data n
+ (?C"text") callout with string data
+
+ The allowed string delimiters are ` ' " ^ % # $ (which are the same for
+ the start and the end), and the starting delimiter { matched with the
+ ending delimiter }. To encode the ending delimiter within the string,
+ double it.
+
+
+SEE ALSO
+
+ pcre2pattern(3), pcre2api(3), pcre2callout(3), pcre2matching(3),
+ pcre2(3).
+
+
+AUTHOR
+
+ Philip Hazel
+ University Computing Service
+ Cambridge, England.
+
+
+REVISION
+
+ Last updated: 17 July 2015
+ Copyright (c) 1997-2015 University of Cambridge.
+------------------------------------------------------------------------------
+
+
PCRE2UNICODE(3) Library Functions Manual PCRE2UNICODE(3)
Added: code/trunk/doc/pcre2_set_offset_limit.3
===================================================================
--- code/trunk/doc/pcre2_set_offset_limit.3 (rev 0)
+++ code/trunk/doc/pcre2_set_offset_limit.3 2015-09-22 16:51:11 UTC (rev 375)
@@ -0,0 +1,28 @@
+.TH PCRE2_SET_OFFSET_LIMIT 3 "22 September 2015" "PCRE2 10.21"
+.SH NAME
+PCRE2 - Perl-compatible regular expressions (revised API)
+.SH SYNOPSIS
+.rs
+.sp
+.B #include <pcre2.h>
+.PP
+.nf
+.B int pcre2_set_offset_limit(pcre2_match_context *\fImcontext\fP,
+.B " PCRE2_SIZE \fIvalue\fP);"
+.fi
+.
+.SH DESCRIPTION
+.rs
+.sp
+This function sets the offset limit field in a match context. The result is
+always zero.
+.P
+There is a complete description of the PCRE2 native API in the
+.\" HREF
+\fBpcre2api\fP
+.\"
+page and a description of the POSIX API in the
+.\" HREF
+\fBpcre2posix\fP
+.\"
+page.
Modified: code/trunk/doc/pcre2api.3
===================================================================
--- code/trunk/doc/pcre2api.3 2015-09-22 16:41:25 UTC (rev 374)
+++ code/trunk/doc/pcre2api.3 2015-09-22 16:51:11 UTC (rev 375)
@@ -1,4 +1,4 @@
-.TH PCRE2API 3 "02 September 2015" "PCRE2 10.21"
+.TH PCRE2API 3 "22 September 2015" "PCRE2 10.21"
.SH NAME
PCRE2 - Perl-compatible regular expressions (revised API)
.sp
@@ -120,6 +120,9 @@
.B int pcre2_set_match_limit(pcre2_match_context *\fImcontext\fP,
.B " uint32_t \fIvalue\fP);"
.sp
+.B int pcre2_set_offset_limit(pcre2_match_context *\fImcontext\fP,
+.B " PCRE2_SIZE \fIvalue\fP);"
+.sp
.B int pcre2_set_recursion_limit(pcre2_match_context *\fImcontext\fP,
.B " uint32_t \fIvalue\fP);"
.sp
@@ -659,6 +662,7 @@
of the following match-time parameters:
.sp
A callout function
+ The offset limit for matching an unanchored pattern
The limit for calling \fImatch()\fP
The limit for calling \fImatch()\fP recursively
.sp
@@ -696,6 +700,30 @@
documentation.
.sp
.nf
+.B int pcre2_set_offset_limit(pcre2_match_context *\fImcontext\fP,
+.B " PCRE2_SIZE \fIvalue\fP);"
+.fi
+.sp
+The \fIoffset_limit\fP parameter limits how far an unanchored search can
+advance in the subject string. The default value is PCRE2_UNSET. The
+\fBpcre2_match()\fP and \fBpcre2_dfa_match()\fP functions return
+PCRE2_ERROR_NOMATCH if a match with a starting point before or at the given
+offset is not found. For example, if the pattern /abc/ is matched against
+"123abc" with an offset limit less than 3, the result is PCRE2_ERROR_NO_MATCH.
+A match can never be found if the \fIstartoffset\fP argument of
+\fBpcre2_match()\fP or \fBpcre2_dfa_match()\fP is greater than the offset
+limit.
+.P
+When using this facility, you must set PCRE2_USE_OFFSET_LIMIT when calling
+\fBpcre2_compile()\fP so that when JIT is in use, different code can be
+compiled. If a match is started with a non-default match limit when
+PCRE2_USE_OFFSET_LIMIT is not set, an error is generated.
+.P
+The offset limit facility can be used to track progress when searching large
+subject strings. See also the PCRE2_FIRSTLINE option, which requires a match to
+start within the first line of the subject.
+.sp
+.nf
.B int pcre2_set_match_limit(pcre2_match_context *\fImcontext\fP,
.B " uint32_t \fIvalue\fP);"
.fi
@@ -1142,7 +1170,8 @@
.sp
If this option is set, an unanchored pattern is required to match before or at
the first newline in the subject string, though the matched text may continue
-over the newline.
+over the newline. See also PCRE2_USE_OFFSET_LIMIT, which provides a more
+general limiting facility.
.sp
PCRE2_MATCH_UNSET_BACKREF
.sp
@@ -1336,6 +1365,20 @@
greedy by default, but become greedy if followed by "?". It is not compatible
with Perl. It can also be set by a (?U) option setting within the pattern.
.sp
+ PCRE2_USE_OFFSET_LIMIT
+.sp
+This option must be set for \fBpcre2_compile()\fP if
+\fBpcre2_set_offset_limit()\fP is going to be used to set a non-default offset
+limit in a match context for matches that use this pattern. An error is
+generated if an offset limit is set without this option. For more details, see
+the description of \fBpcre2_set_offset_limit()\fP in the
+.\" HTML <a href="#matchcontext">
+.\" </a>
+section
+.\"
+that describes match contexts. See also the PCRE2_FIRSTLINE
+option above.
+.sp
PCRE2_UTF
.sp
This option causes PCRE2 to regard both the pattern and the subject strings
@@ -2965,6 +3008,6 @@
.rs
.sp
.nf
-Last updated: 02 September 2015
+Last updated: 22 September 2015
Copyright (c) 1997-2015 University of Cambridge.
.fi
Modified: code/trunk/doc/pcre2test.1
===================================================================
--- code/trunk/doc/pcre2test.1 2015-09-22 16:41:25 UTC (rev 374)
+++ code/trunk/doc/pcre2test.1 2015-09-22 16:51:11 UTC (rev 375)
@@ -1,4 +1,4 @@
-.TH PCRE2TEST 1 "14 September 2015" "PCRE 10.21"
+.TH PCRE2TEST 1 "22 September 2015" "PCRE 10.21"
.SH NAME
pcre2test - a program for testing Perl-compatible regular expressions.
.SH SYNOPSIS
@@ -472,7 +472,7 @@
The following modifiers set options for \fBpcre2_compile()\fP. The most common
ones have single-letter abbreviations. See
.\" HREF
-\fBpcreapi\fP
+\fBpcre2api\fP
.\"
for a description of their effects.
.sp
@@ -500,6 +500,7 @@
no_utf_check set PCRE2_NO_UTF_CHECK
ucp set PCRE2_UCP
ungreedy set PCRE2_UNGREEDY
+ use_offset_limit set PCRE2_USE_OFFSET_LIMIT
utf set PCRE2_UTF
.sp
As well as turning on the PCRE2_UTF option, the \fButf\fP modifier causes all
@@ -892,9 +893,10 @@
/g global global matching
jitstack=<n> set size of JIT stack
mark show mark values
- match_limit=>n> set a match limit
+ match_limit=<n> set a match limit
memory show memory usage
offset=<n> set starting offset
+ offset_limit=<n> set offset limit
ovector=<n> set size of output vector
recursion_limit=<n> set a recursion limit
replace=<string> specify a replacement string
@@ -1133,6 +1135,16 @@
matching starts. Its value is a number of code units, not characters.
.
.
+.SS "Setting an offset limit"
+.rs
+.sp
+The \fBoffset_limit\fP modifier sets a limit for unanchored matches. If a match
+cannot be found starting at or before this offset in the subject, a "no match"
+return is given. The data value is a number of code units, not characters. When
+this modifier is used, the \fBuse_offset_limit\fP modifier must have been set
+for the pattern; if not, an error is generated.
+.
+.
.SS "Setting the size of the output vector"
.rs
.sp
@@ -1525,6 +1537,6 @@
.rs
.sp
.nf
-Last updated: 14 September 2015
+Last updated: 22 September 2015
Copyright (c) 1997-2015 University of Cambridge.
.fi
Modified: code/trunk/doc/pcre2test.txt
===================================================================
--- code/trunk/doc/pcre2test.txt 2015-09-22 16:41:25 UTC (rev 374)
+++ code/trunk/doc/pcre2test.txt 2015-09-22 16:51:11 UTC (rev 375)
@@ -432,6 +432,13 @@
abc\=notbol,notempty
+ If the subject string is empty and \= is followed by whitespace, the
+ line is treated as a comment line, and is not used for matching. For
+ example:
+
+ \= This is a comment.
+ abc\= This is an invalid modifier list.
+
A backslash followed by any other non-alphanumeric character just
escapes that character. A backslash followed by anything else causes an
error. However, if the very last character in the line is a backslash
@@ -1391,5 +1398,5 @@
REVISION
- Last updated: 12 September 2015
+ Last updated: 14 September 2015
Copyright (c) 1997-2015 University of Cambridge.
