Revision: 406
http://vcs.pcre.org/viewvc?view=rev&revision=406
Author: ph10
Date: 2009-03-23 12:05:43 +0000 (Mon, 23 Mar 2009)
Log Message:
-----------
Trailing space tidies
Modified Paths:
--------------
code/trunk/NON-UNIX-USE
code/trunk/README
code/trunk/doc/html/pcre.html
code/trunk/doc/html/pcrepattern.html
code/trunk/doc/pcre.3
code/trunk/doc/pcre.txt
code/trunk/doc/pcrepattern.3
code/trunk/pcre_compile.c
code/trunk/pcre_dfa_exec.c
code/trunk/pcre_exec.c
code/trunk/pcre_internal.h
Modified: code/trunk/NON-UNIX-USE
===================================================================
--- code/trunk/NON-UNIX-USE 2009-03-23 12:05:20 UTC (rev 405)
+++ code/trunk/NON-UNIX-USE 2009-03-23 12:05:43 UTC (rev 406)
@@ -23,7 +23,7 @@
libraries work. The items in the PCRE distribution and Makefile that relate to
anything other than Unix-like systems are untested by me.
-There are some other comments and files (including some documentation in CHM
+There are some other comments and files (including some documentation in CHM
format) in the Contrib directory on the FTP site:
ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/Contrib
Modified: code/trunk/README
===================================================================
--- code/trunk/README 2009-03-23 12:05:20 UTC (rev 405)
+++ code/trunk/README 2009-03-23 12:05:43 UTC (rev 406)
@@ -84,7 +84,7 @@
2. A set of files containing all the documentation in HTML form, hyperlinked
in various ways, and rooted in a file called index.html, is distributed in
doc/html and installed in <prefix>/share/doc/pcre/html.
-
+
Users of PCRE have contributed files containing the documentation for various
releases in CHM format. These can be found in the Contrib directory of the FTP
site (see next section).
Modified: code/trunk/doc/html/pcre.html
===================================================================
--- code/trunk/doc/html/pcre.html 2009-03-23 12:05:20 UTC (rev 405)
+++ code/trunk/doc/html/pcre.html 2009-03-23 12:05:43 UTC (rev 406)
@@ -258,7 +258,8 @@
values less than 256. This remains true even when PCRE includes Unicode
property support, because to do otherwise would slow down PCRE in many common
cases. If you really want to test for a wider sense of, say, "digit", you
-must use Unicode property tests such as \p{Nd}.
+must use Unicode property tests such as \p{Nd}. Note that this also applies to
+\b, because it is defined in terms of \w and \W.
</P>
<P>
7. Similarly, characters that match the POSIX named character classes are all
@@ -295,9 +296,9 @@
</P>
<br><a name="SEC6" href="#TOC1">REVISION</a><br>
<P>
-Last updated: 12 April 2008
+Last updated: 18 March 2009
<br>
-Copyright © 1997-2008 University of Cambridge.
+Copyright © 1997-2009 University of Cambridge.
<br>
<p>
Return to the <a href="index.html">PCRE index page</a>.
Modified: code/trunk/doc/html/pcrepattern.html
===================================================================
--- code/trunk/doc/html/pcrepattern.html 2009-03-23 12:05:20 UTC (rev 405)
+++ code/trunk/doc/html/pcrepattern.html 2009-03-23 12:05:43 UTC (rev 406)
@@ -368,7 +368,8 @@
\w, and always match \D, \S, and \W. This is true even when Unicode
character property support is available. These sequences retain their original
meanings from before UTF-8 support was available, mainly for efficiency
-reasons.
+reasons. Note that this also affects \b, because it is defined in terms of \w
+and \W.
</P>
<P>
The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to the
@@ -2243,7 +2244,7 @@
</P>
<br><a name="SEC28" href="#TOC1">REVISION</a><br>
<P>
-Last updated: 08 March 2009
+Last updated: 18 March 2009
<br>
Copyright © 1997-2009 University of Cambridge.
<br>
Modified: code/trunk/doc/pcre.3
===================================================================
--- code/trunk/doc/pcre.3 2009-03-23 12:05:20 UTC (rev 405)
+++ code/trunk/doc/pcre.3 2009-03-23 12:05:43 UTC (rev 406)
@@ -252,7 +252,7 @@
values less than 256. This remains true even when PCRE includes Unicode
property support, because to do otherwise would slow down PCRE in many common
cases. If you really want to test for a wider sense of, say, "digit", you
-must use Unicode property tests such as \ep{Nd}. Note that this also applies to
+must use Unicode property tests such as \ep{Nd}. Note that this also applies to
\eb, because it is defined in terms of \ew and \eW.
.P
7. Similarly, characters that match the POSIX named character classes are all
Modified: code/trunk/doc/pcre.txt
===================================================================
--- code/trunk/doc/pcre.txt 2009-03-23 12:05:20 UTC (rev 405)
+++ code/trunk/doc/pcre.txt 2009-03-23 12:05:43 UTC (rev 406)
@@ -224,24 +224,25 @@
includes Unicode property support, because to do otherwise would slow
down PCRE in many common cases. If you really want to test for a wider
sense of, say, "digit", you must use Unicode property tests such as
- \p{Nd}.
+ \p{Nd}. Note that this also applies to \b, because it is defined in
+ terms of \w and \W.
- 7. Similarly, characters that match the POSIX named character classes
+ 7. Similarly, characters that match the POSIX named character classes
are all low-valued characters.
- 8. However, the Perl 5.10 horizontal and vertical whitespace matching
+ 8. However, the Perl 5.10 horizontal and vertical whitespace matching
escapes (\h, \H, \v, and \V) do match all the appropriate Unicode char-
acters.
- 9. Case-insensitive matching applies only to characters whose values
- are less than 128, unless PCRE is built with Unicode property support.
- Even when Unicode property support is available, PCRE still uses its
- own character tables when checking the case of low-valued characters,
- so as not to degrade performance. The Unicode property information is
+ 9. Case-insensitive matching applies only to characters whose values
+ are less than 128, unless PCRE is built with Unicode property support.
+ Even when Unicode property support is available, PCRE still uses its
+ own character tables when checking the case of low-valued characters,
+ so as not to degrade performance. The Unicode property information is
used only for characters with higher values. Even when Unicode property
support is available, PCRE supports case-insensitive matching only when
- there is a one-to-one mapping between a letter's cases. There are a
- small number of many-to-one mappings in Unicode; these are not sup-
+ there is a one-to-one mapping between a letter's cases. There are a
+ small number of many-to-one mappings in Unicode; these are not sup-
ported by PCRE.
@@ -251,15 +252,15 @@
University Computing Service
Cambridge CB2 3QH, England.
- Putting an actual email address here seems to have been a spam magnet,
- so I've taken it away. If you want to email me, use my two initials,
+ Putting an actual email address here seems to have been a spam magnet,
+ so I've taken it away. If you want to email me, use my two initials,
followed by the two digits 10, at the domain cam.ac.uk.
REVISION
- Last updated: 12 April 2008
- Copyright (c) 1997-2008 University of Cambridge.
+ Last updated: 18 March 2009
+ Copyright (c) 1997-2009 University of Cambridge.
------------------------------------------------------------------------------
@@ -3268,10 +3269,11 @@
\s, or \w, and always match \D, \S, and \W. This is true even when Uni-
code character property support is available. These sequences retain
their original meanings from before UTF-8 support was available, mainly
- for efficiency reasons.
+ for efficiency reasons. Note that this also affects \b, because it is
+ defined in terms of \w and \W.
The sequences \h, \H, \v, and \V are Perl 5.10 features. In contrast to
- the other sequences, these do match certain high-valued codepoints in
+ the other sequences, these do match certain high-valued codepoints in
UTF-8 mode. The horizontal space characters are:
U+0009 Horizontal tab
@@ -3305,41 +3307,41 @@
U+2029 Paragraph separator
A "word" character is an underscore or any character less than 256 that
- is a letter or digit. The definition of letters and digits is con-
- trolled by PCRE's low-valued character tables, and may vary if locale-
- specific matching is taking place (see "Locale support" in the pcreapi
- page). For example, in a French locale such as "fr_FR" in Unix-like
- systems, or "french" in Windows, some character codes greater than 128
- are used for accented letters, and these are matched by \w. The use of
+ is a letter or digit. The definition of letters and digits is con-
+ trolled by PCRE's low-valued character tables, and may vary if locale-
+ specific matching is taking place (see "Locale support" in the pcreapi
+ page). For example, in a French locale such as "fr_FR" in Unix-like
+ systems, or "french" in Windows, some character codes greater than 128
+ are used for accented letters, and these are matched by \w. The use of
locales with Unicode is discouraged.
Newline sequences
- Outside a character class, by default, the escape sequence \R matches
+ Outside a character class, by default, the escape sequence \R matches
any Unicode newline sequence. This is a Perl 5.10 feature. In 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
+ 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,
+ CR followed by LF, or one of the single characters LF (linefeed,
U+000A), VT (vertical tab, U+000B), FF (formfeed, U+000C), CR (carriage
return, U+000D), or NEL (next line, U+0085). The two-character sequence
is treated as a single unit that cannot be split.
- In UTF-8 mode, two additional characters whose codepoints are greater
+ In UTF-8 mode, two additional characters whose codepoints are greater
than 255 are added: LS (line separator, U+2028) and PS (paragraph sepa-
- rator, U+2029). Unicode character property support is not needed for
+ rator, U+2029). Unicode character property 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
+ the complete set of Unicode line endings) by setting the option
PCRE_BSR_ANYCRLF either at compile time or when the pattern is matched.
(BSR is an abbrevation for "backslash R".) This can be made the default
- when PCRE is built; if this is the case, the other behaviour can be
- requested via the PCRE_BSR_UNICODE option. It is also possible to
- specify these settings by starting a pattern string with one of the
+ when PCRE is built; if this is the case, the other behaviour can be
+ requested via the PCRE_BSR_UNICODE 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
@@ -3348,9 +3350,9 @@
These override the default and the options given to pcre_compile(), but
they can be overridden by options given to pcre_exec(). 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
+ 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)
@@ -3360,49 +3362,49 @@
Unicode character properties
When PCRE is built with Unicode character property support, three addi-
- tional escape sequences that match characters with specific properties
- are available. When not in UTF-8 mode, these sequences are of course
- limited to testing characters whose codepoints are less than 256, but
+ tional escape sequences that match characters with specific properties
+ are available. When not in 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 an extended Unicode sequence
- The property names represented by xx above are limited to the Unicode
+ The property names represented by xx above are limited to the Unicode
script names, the general category properties, and "Any", which matches
any character (including newline). Other properties such as "InMusical-
- Symbols" are not currently supported by PCRE. Note that \P{Any} does
+ Symbols" are not currently supported by PCRE. 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.
+ 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
+ Those that are not part of an identified script are lumped together as
"Common". The current list of scripts is:
Arabic, Armenian, Balinese, Bengali, Bopomofo, Braille, Buginese,
- Buhid, Canadian_Aboriginal, Cherokee, Common, Coptic, Cuneiform,
+ Buhid, Canadian_Aboriginal, Cherokee, Common, Coptic, Cuneiform,
Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic,
- Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
- gana, Inherited, Kannada, Katakana, Kharoshthi, Khmer, Lao, Latin,
+ Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hira-
+ gana, Inherited, Kannada, Katakana, Kharoshthi, Khmer, Lao, Latin,
Limbu, Linear_B, Malayalam, Mongolian, Myanmar, New_Tai_Lue, Nko,
- Ogham, Old_Italic, Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
+ Ogham, Old_Italic, Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician,
Runic, Shavian, Sinhala, Syloti_Nagri, Syriac, Tagalog, Tagbanwa,
Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.
- Each character has exactly one general category property, specified by
+ Each character has exactly one general category property, specified by
a two-letter abbreviation. For compatibility with Perl, negation can be
- specified by including a circumflex between the opening brace and the
+ 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
+ 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}
@@ -3454,57 +3456,57 @@
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
+ 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 UTF-8 strings (see
+ The Cs (Surrogate) property applies only to characters in the range
+ U+D800 to U+DFFF. Such characters are not valid in UTF-8 strings (see
RFC 3629) and so cannot be tested by PCRE, unless UTF-8 validity check-
- ing has been turned off (see the discussion of PCRE_NO_UTF8_CHECK in
+ ing has been turned off (see the discussion of PCRE_NO_UTF8_CHECK in
the pcreapi page).
- The long synonyms for these properties that Perl supports (such as
- \p{Letter}) are not supported by PCRE, nor is it permitted to prefix
+ The long synonyms for these properties that Perl supports (such as
+ \p{Letter}) are not supported by PCRE, 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.
+ Specifying caseless matching does not affect these escape sequences.
For example, \p{Lu} always matches only upper case letters.
- The \X escape matches any number of Unicode characters that form an
+ The \X escape matches any number of Unicode characters that form an
extended Unicode sequence. \X is equivalent to
(?>\PM\pM*)
- That is, it matches a character without the "mark" property, followed
- by zero or more characters with the "mark" property, and treats the
- sequence as an atomic group (see below). Characters with the "mark"
- property are typically accents that affect the preceding character.
- None of them have codepoints less than 256, so in non-UTF-8 mode \X
+ That is, it matches a character without the "mark" property, followed
+ by zero or more characters with the "mark" property, and treats the
+ sequence as an atomic group (see below). Characters with the "mark"
+ property are typically accents that affect the preceding character.
+ None of them have codepoints less than 256, so in non-UTF-8 mode \X
matches any one character.
- Matching characters by Unicode property is not fast, because PCRE has
- to search a structure that contains data for over fifteen thousand
+ Matching characters by Unicode property is not fast, because PCRE has
+ to search a structure that contains data for over fifteen thousand
characters. That is why the traditional escape sequences such as \d and
\w do not use Unicode properties in PCRE.
Resetting the match start
The escape sequence \K, which is a Perl 5.10 feature, causes any previ-
- ously matched characters not to be included in the final matched
+ ously 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,
+ 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
@@ -3513,10 +3515,10 @@
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 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
@@ -3527,41 +3529,41 @@
\z matches only at the end of the subject
\G matches at the first matching position in the subject
- These assertions may not appear in character classes (but note that \b
+ These assertions may not appear in character classes (but note that \b
has a different meaning, namely the backspace character, inside a char-
acter class).
- 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
+ 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.
- The \A, \Z, and \z assertions differ from the traditional circumflex
+ 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-
+ 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 PCRE_NOTBOL or PCRE_NOTEOL options, which
- affect only the behaviour of the circumflex and dollar metacharacters.
- However, if the startoffset argument of pcre_exec() is non-zero, indi-
+ affect only the behaviour of the circumflex and dollar metacharacters.
+ However, if the startoffset argument of pcre_exec() is non-zero, indi-
cating 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
+ 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 pcre_exec(). It differs from \A when the value of startoffset is
- non-zero. By calling pcre_exec() multiple times with appropriate argu-
+ 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 pcre_exec(). It differs from \A when the value of startoffset is
+ non-zero. By calling pcre_exec() multiple times with appropriate argu-
ments, you can mimic Perl's /g option, and it is in this kind of imple-
mentation where \G can be useful.
- Note, however, that PCRE's interpretation of \G, as the start of the
+ Note, however, that PCRE'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 PCRE does just one match
+ end of the previous match. In Perl, these can be different when the
+ previously matched string was empty. Because PCRE 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
+ 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.
@@ -3569,90 +3571,90 @@
CIRCUMFLEX AND DOLLAR
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 pcre_exec() is non-zero, circumflex can never match if the
- PCRE_MULTILINE option is unset. Inside a character class, 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 pcre_exec() is non-zero, circumflex can never match if the
+ PCRE_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
+ 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.)
- A dollar character is an assertion that is true only if the current
- matching point is at the end of the subject string, or immediately
+ A 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). Dollar need not
- be the last character of the pattern if a number of alternatives are
- involved, but it should be the last item in any branch in which it
+ be the last character of the pattern if a number 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 character class.
- The meaning of dollar can be changed so that it matches only at the
- very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at
+ The meaning of dollar can be changed so that it matches only at the
+ very end of the string, by setting the PCRE_DOLLAR_ENDONLY option at
compile time. This does not affect the \Z assertion.
The meanings of the circumflex and dollar characters are changed if the
- PCRE_MULTILINE option is set. When this is the case, 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. A dollar matches before any newlines in the string, as well as
- at the very end, when PCRE_MULTILINE is set. When newline is specified
- as the two-character sequence CRLF, isolated CR and LF characters do
+ PCRE_MULTILINE option is set. When this is the case, 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. A dollar matches before any newlines in the string, as well as
+ at the very end, when PCRE_MULTILINE is set. When newline is specified
+ as the two-character sequence CRLF, isolated CR and LF characters do
not indicate newlines.
- For example, the pattern /^abc$/ matches the subject string "def\nabc"
- (where \n represents a newline) in multiline mode, but not otherwise.
- Consequently, patterns that are anchored in single line mode because
- all branches start with ^ are not anchored in multiline mode, and a
- match for circumflex is possible when the startoffset argument of
- pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
+ For example, the pattern /^abc$/ 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
+ pcre_exec() is non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
PCRE_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 PCRE_MULTILINE is
+ 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 PCRE_MULTILINE is
set.
FULL STOP (PERIOD, DOT)
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. In UTF-8 mode, the matched character may be
+ ter in the subject string except (by default) a character that signi-
+ fies the end of a line. In UTF-8 mode, the matched character may be
more than one byte long.
- 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
+ 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
- PCRE_DOTALL option is set, a dot matches any one character, without
+ The behaviour of dot with regard to newlines can be changed. If the
+ PCRE_DOTALL option is set, a dot matches any one character, without
exception. If the two-character sequence CRLF is present in the subject
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
+ 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.
MATCHING A SINGLE BYTE
Outside a character class, the escape sequence \C matches any one byte,
- both in and out of UTF-8 mode. Unlike a dot, it always matches any
- line-ending characters. The feature is provided in Perl in order to
- match individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-
- acters into individual bytes, what remains in the string may be a mal-
- formed UTF-8 string. For this reason, the \C escape sequence is best
+ both in and out of UTF-8 mode. Unlike a dot, it always matches any
+ line-ending characters. The feature is provided in Perl in order to
+ match individual bytes in UTF-8 mode. Because it breaks up UTF-8 char-
+ acters into individual bytes, what remains in the string may be a mal-
+ formed UTF-8 string. For this reason, the \C escape sequence is best
avoided.
- PCRE does not allow \C to appear in lookbehind assertions (described
- below), because in UTF-8 mode this would make it impossible to calcu-
+ PCRE does not allow \C to appear in lookbehind assertions (described
+ below), because in UTF-8 mode this would make it impossible to calcu-
late the length of the lookbehind.
@@ -3661,96 +3663,96 @@
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. 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
+ it should be the first data character in the class (after an initial
circumflex, if present) or escaped with a backslash.
- A character class matches a single character in the subject. In UTF-8
- mode, the character may occupy more than one byte. A matched character
+ A character class matches a single character in the subject. In UTF-8
+ mode, the character may occupy more than one byte. 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
+ 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.
+ 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
+ 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.
- In UTF-8 mode, characters with values greater than 255 can be included
- in a class as a literal string of bytes, or by using the \x{ escaping
+ In UTF-8 mode, characters with values greater than 255 can be included
+ in a class as a literal string of bytes, or by using the \x{ escaping
mechanism.
- 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. In UTF-8 mode, PCRE always
- understands the concept of case for characters whose values are less
- than 128, so caseless matching is always possible. For characters with
- higher values, the concept of case is supported if PCRE is compiled
- with Unicode property support, but not otherwise. If you want to use
- caseless matching for characters 128 and above, you must ensure that
- PCRE is compiled with Unicode property support as well as with UTF-8
+ 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. In UTF-8 mode, PCRE always
+ understands the concept of case for characters whose values are less
+ than 128, so caseless matching is always possible. For characters with
+ higher values, the concept of case is supported if PCRE is compiled
+ with Unicode property support, but not otherwise. If you want to use
+ caseless matching for characters 128 and above, you must ensure that
+ PCRE is compiled with Unicode property support as well as with UTF-8
support.
- 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 PCRE_DOTALL and
+ 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 PCRE_DOTALL and
PCRE_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
+ 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.
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
+ 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.
- Ranges operate in the collating sequence of character values. They can
- also be used for characters specified numerically, for example
- [\000-\037]. In UTF-8 mode, ranges can include characters whose values
+ Ranges operate in the collating sequence of character values. They can
+ also be used for characters specified numerically, for example
+ [\000-\037]. In UTF-8 mode, ranges can include characters whose values
are greater than 255, for example [\x{100}-\x{2ff}].
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 non-UTF-8 mode, if
- character tables for a French locale are in use, [\xc8-\xcb] matches
- accented E characters in both cases. In UTF-8 mode, PCRE supports the
- concept of case for characters with values greater than 128 only when
+ to [][\\^_`wxyzabc], matched caselessly, and in non-UTF-8 mode, if
+ character tables for a French locale are in use, [\xc8-\xcb] matches
+ accented E characters in both cases. In UTF-8 mode, PCRE supports the
+ concept of case for characters with values greater than 128 only when
it is compiled with Unicode property support.
- The character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear
- in a character class, and add the characters that they match to the
+ The character types \d, \D, \p, \P, \s, \S, \w, and \W may also appear
+ in a character class, and add the characters that they match to the
class. For example, [\dABCDEF] matches any hexadecimal digit. A circum-
- flex 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,
+ flex 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.
- 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 - see the
- next section), and the terminating closing square bracket. However,
+ 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 - see the
+ next section), 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. PCRE also
+ enclosed by [: and :] within the enclosing square brackets. PCRE also
supports this notation. For example,
[01[:alpha:]%]
@@ -3773,18 +3775,18 @@
word "word" characters (same as \w)
xdigit hexadecimal digits
- The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),
- and space (32). Notice that this list includes the VT character (code
+ The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),
+ and space (32). Notice that this list includes the VT character (code
11). This makes "space" different to \s, which does not include VT (for
Perl compatibility).
- 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
+ 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. PCRE (and Perl) also recognize the
+ matches "1", "2", or any non-digit. PCRE (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.
@@ -3794,24 +3796,24 @@
VERTICAL BAR
- Vertical bar characters are used to separate alternative patterns. For
+ 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
+ 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
+ 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 PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
- PCRE_EXTENDED options (which are Perl-compatible) can be changed from
- within the pattern by a sequence of Perl option letters enclosed
+ The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
+ PCRE_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 PCRE_CASELESS
@@ -3821,44 +3823,44 @@
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 PCRE_CASE-
- LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
- is also permitted. If a letter appears both before and after the
+ combined setting and unsetting such as (?im-sx), which sets PCRE_CASE-
+ LESS and PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED,
+ is also permitted. If a letter appears both before and after the
hyphen, the option is unset.
- The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
- can be changed in the same way as the Perl-compatible options by using
+ The PCRE-specific options PCRE_DUPNAMES, PCRE_UNGREEDY, and PCRE_EXTRA
+ can be changed in the same way as the Perl-compatible options by using
the characters J, U and X respectively.
- When an option change occurs at top level (that is, not inside subpat-
- tern parentheses), the change applies to the remainder of the pattern
+ When an option change occurs at top level (that is, not inside subpat-
+ tern parentheses), the change applies to the remainder of the pattern
that follows. If the change is placed right at the start of a pattern,
PCRE extracts it into the global options (and it will therefore show up
in data extracted by the pcre_fullinfo() function).
- An option change within a subpattern (see below for a description of
+ An option change within a subpattern (see below for a description of
subpatterns) affects only that part of the current pattern that follows
it, so
(a(?i)b)c
matches abc and aBc and no other strings (assuming PCRE_CASELESS is not
- used). By this means, options can be made to have different settings
- in different parts of the pattern. Any changes made in one alternative
- do carry on into subsequent branches within the same subpattern. For
+ used). By this means, options can be made to have different settings
+ in different parts of the pattern. Any changes made in one alternative
+ 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
+ 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.
- Note: There are other PCRE-specific options that can be set by the
- application when the compile or match functions are called. In some
- cases the pattern can contain special leading sequences to override
- what the application has set or what has been defaulted. Details are
+ Note: There are other PCRE-specific options that can be set by the
+ application when the compile or match functions are called. In some
+ cases the pattern can contain special leading sequences to override
+ what the application has set or what has been defaulted. Details are
given in the section entitled "Newline sequences" above.
@@ -3871,18 +3873,18 @@
cat(aract|erpillar|)
- matches one of the words "cat", "cataract", or "caterpillar". Without
- the parentheses, it would match "cataract", "erpillar" or an empty
+ matches one of the words "cat", "cataract", or "caterpillar". 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, that portion of the subject
+ 2. It sets up the subpattern as a capturing subpattern. This means
+ that, when the whole pattern matches, that portion of the subject
string that matched the subpattern is passed back to the caller via the
- ovector argument of pcre_exec(). Opening parentheses are counted from
- left to right (starting from 1) to obtain numbers for the capturing
+ ovector argument of pcre_exec(). 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 pat-
+ For example, if the string "the red king" is matched against the pat-
tern
the ((red|white) (king|queen))
@@ -3890,12 +3892,12 @@
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
+ 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))
@@ -3903,80 +3905,80 @@
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
+ 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
+ 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,
+ 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
+ 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 buffers that follow the sub-
- pattern start after the highest number used in any branch. The follow-
- ing example is taken from the Perl documentation. The numbers under-
+ theses are numbered as usual, but the number is reset at the start of
+ each branch. The numbers of any capturing buffers that follow the sub-
+ pattern start after the highest number used in any branch. The follow-
+ ing 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 backreference or a recursive call to a numbered subpattern always
+ A backreference or a recursive call to a numbered subpattern always
refers to the first one in the pattern with the given number.
- An alternative approach to using this "branch reset" feature is to use
+ 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, PCRE supports the naming of sub-
+ 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, PCRE supports the naming of sub-
patterns. This feature was not added to Perl until release 5.10. Python
- had the feature earlier, and PCRE introduced it at release 4.0, using
- the Python syntax. PCRE now supports both the Perl and the Python syn-
+ had the feature earlier, and PCRE introduced it at release 4.0, using
+ the Python syntax. PCRE now supports both the Perl and the Python syn-
tax.
- In PCRE, a subpattern can be named in one of three ways: (?<name>...)
- or (?'name'...) as in Perl, or (?P<name>...) as in Python. References
+ In PCRE, 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
+ references, recursion, and conditions, can be made by name as well as
by number.
- Names consist of up to 32 alphanumeric characters and underscores.
- Named capturing parentheses are still allocated numbers as well as
- names, exactly as if the names were not present. The PCRE API provides
+ Names consist of up to 32 alphanumeric characters and underscores.
+ Named capturing parentheses are still allocated numbers as well as
+ names, exactly as if the names were not present. The PCRE API provides
function calls for extracting the name-to-number translation table from
a compiled pattern. There is also a convenience function for extracting
a captured substring by name.
- By default, a name must be unique within a pattern, but it is possible
+ By default, a name must be unique within a pattern, but it is possible
to relax this constraint by setting the PCRE_DUPNAMES option at compile
- time. This 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
+ time. This 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:
@@ -3986,26 +3988,26 @@
(?<DN>Thu)(?:rsday)?|
(?<DN>Sat)(?:urday)?
- There are five capturing substrings, but only one is ever set after a
+ 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 function 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 reference to a non-unique named sub-
- pattern from elsewhere in the pattern, the one that corresponds to the
- lowest number is used. For further details of the interfaces for han-
+ The convenience function 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 reference to a non-unique named sub-
+ pattern from elsewhere in the pattern, the one that corresponds to the
+ lowest number is used. For further details of the interfaces for han-
dling named subpatterns, see the pcreapi documentation.
Warning: You cannot use different names to distinguish between two sub-
- patterns with the same number (see the previous section) because PCRE
+ patterns with the same number (see the previous section) because PCRE
uses only the numbers when matching.
REPETITION
- Repetition is specified by quantifiers, which can follow any of the
+ Repetition is specified by quantifiers, which can follow any of the
following items:
a literal data character
@@ -4018,17 +4020,17 @@
a back reference (see next section)
a parenthesized subpattern (unless it is an assertion)
- 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,
+ 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 "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,}
@@ -4037,49 +4039,49 @@
\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-
+ 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-8 mode, quantifiers apply to UTF-8 characters rather than to
+ In UTF-8 mode, quantifiers apply to UTF-8 characters rather than to
individual bytes. Thus, for example, \x{100}{2} matches two UTF-8 char-
acters, each of which is represented by a two-byte sequence. Similarly,
when Unicode property support is available, \X{3} matches three Unicode
- extended sequences, each of which may be several bytes long (and they
+ extended sequences, each of which may be several bytes 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
+ ful for subpatterns that are referenced as subroutines from elsewhere
in the pattern. 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-
+ 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
+ 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 PCRE 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-
+ 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
+ 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
+ appear between /* and */ and within the comment, individual * and /
+ characters may appear. An attempt to match C comments by applying the
pattern
/\*.*\*/
@@ -4088,19 +4090,19 @@
/* first comment */ not comment /* second comment */
- fails, because it matches the entire string owing to the greediness of
+ fails, because it matches the entire string owing to the greediness of
the .* item.
- However, if a quantifier is followed by a question mark, it ceases to
+ However, 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 pattern
/\*.*?\*/
- 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
+ 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
@@ -4108,36 +4110,36 @@
which matches one digit by preference, but can match two if that is the
only way the rest of the pattern matches.
- If the PCRE_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
+ If the PCRE_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
+ 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 PCRE_DOTALL option (equiv-
- alent to Perl's /s) is set, thus allowing the dot to match newlines,
- 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. PCRE normally treats such a pattern as though it were preceded
+ alent to Perl's /s) is set, thus allowing the dot to match newlines,
+ 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. PCRE 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 PCRE_DOTALL in order to obtain this opti-
+ In cases where it is known that the subject string contains no new-
+ lines, it is worth setting PCRE_DOTALL in order to obtain this opti-
mization, or alternatively using ^ to indicate anchoring explicitly.
- However, there is one situation where the optimization cannot be used.
- When .* is inside capturing parentheses that are the subject of a
- backreference elsewhere in the pattern, a match at the start may fail
+ However, there is one situation where the optimization cannot be used.
+ When .* is inside capturing parentheses that are the subject of a
+ backreference 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-
+ If the subject is "xyz123abc123" the match point is the fourth charac-
ter. For this reason, such a pattern is not implicitly anchored.
When a capturing subpattern is repeated, the value captured is the sub-
@@ -4146,8 +4148,8 @@
(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-
+ 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))+/
@@ -4157,53 +4159,53 @@
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
+ 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
+ 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
+ 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
+ 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
+ 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
- the string of characters that an identical standalone pattern would
+ An alternative description is that a subpattern of this type matches
+ 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
+ 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 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
+ 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
@@ -4213,45 +4215,45 @@
(abc|xyz){2,3}+
- Possessive quantifiers are always greedy; the setting of the
+ Possessive quantifiers are always greedy; the setting of the
PCRE_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
+ 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
+ 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 PCRE copied it from there. It ultimately
+ built Sun's Java package, and PCRE copied it from there. It ultimately
found its way into Perl at release 5.10.
PCRE has an optimization that automatically "possessifies" certain sim-
- ple 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
+ ple 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.
- 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
+ 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 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 PCRE 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
+ 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 PCRE 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+>)*[!?]
@@ -4263,37 +4265,37 @@
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
+ 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 10,
- 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 10. 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-
+ 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 10. 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 10 or more using this syntax because a
- sequence such as \50 is interpreted as a character defined in octal.
+ It is not possible to have a numerical "forward back reference" to a
+ subpattern whose number is 10 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
+ 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
+ Another way of avoiding the ambiguity inherent in the use of digits
following a backslash is to use the \g escape sequence, which is a fea-
- ture introduced in Perl 5.10. This escape must be followed by an
- unsigned number or a negative number, optionally enclosed in braces.
+ ture introduced in Perl 5.10. 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-
+ 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:
@@ -4301,33 +4303,33 @@
(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. Similarly,
+ ing subpattern before \g, that is, is it equivalent to \2. 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
+ 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
+ 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-
+ 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
+ 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
+ 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
+ and named references, is also supported. We could rewrite the above
example in any of the following ways:
(?<p1>(?i)rah)\s+\k<p1>
@@ -4335,57 +4337,57 @@
(?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
+ 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
+ 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. For example, the pattern
(a|(bc))\2
- always fails if it starts to match "a" rather than "bc". Because there
- may be many capturing parentheses in a pattern, all digits following
- the backslash are taken as part of a potential back reference number.
+ always fails if it starts to match "a" rather than "bc". Because there
+ may be many capturing parentheses in a pattern, all digits following
+ the backslash are taken as part of a potential back reference number.
If the pattern continues with a digit character, some delimiter must be
- used to terminate the back reference. If the PCRE_EXTENDED option is
- set, this can be whitespace. Otherwise an empty comment (see "Com-
+ used to terminate the back reference. If the PCRE_EXTENDED option is
+ set, this can be whitespace. Otherwise an empty comment (see "Com-
ments" below) can be used.
- 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-
+ 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
+ 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.
ASSERTIONS
- An assertion is a test on the characters following or preceding the
- current matching point that does not actually consume any characters.
- The simple assertions coded as \b, \B, \A, \G, \Z, \z, ^ and $ are
+ An assertion is a test on the characters following or preceding the
+ current matching point that does not actually 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
+ 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, and may not be
- repeated, because it makes no sense to assert the same thing several
- times. If any kind of assertion contains capturing subpatterns within
- it, these are counted for the purposes of numbering the capturing sub-
+ Assertion subpatterns are not capturing subpatterns, and may not be
+ repeated, because it makes no sense to assert the same thing several
+ times. If any kind of assertion contains capturing subpatterns within
+ it, these are counted for the purposes of numbering the capturing sub-
patterns in the whole pattern. However, substring capturing is carried
- out only for positive assertions, because it does not make sense for
+ out only for positive assertions, because it does not make sense for
negative assertions.
Lookahead assertions
@@ -4395,37 +4397,37 @@
\w+(?=;)
- matches a word followed by a semicolon, but does not include the semi-
+ 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
+ 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
+ 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
+ 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.
Lookbehind assertions
- Lookbehind assertions start with (?<= for positive assertions and (?<!
+ 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
+ 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
+ eral top-level alternatives, they do not all have to have the same
fixed length. Thus
(?<=bullock|donkey)
@@ -4434,59 +4436,59 @@
(?<!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 (at least for 5.8), which
- requires all branches to match the same length of string. An assertion
+ 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 (at least for 5.8), 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 if rewritten to use two top-
+ is not permitted, because its single top-level branch can match two
+ different lengths, but it is acceptable if rewritten to use two top-
level branches:
(?<=abc|abde)
In some cases, the Perl 5.10 escape sequence \K (see above) can be used
- instead of a lookbehind assertion; this is not restricted to a fixed-
+ instead of a lookbehind assertion; this is not restricted to a fixed-
length.
- The implementation of lookbehind assertions is, for each alternative,
- to temporarily move the current position back by the fixed length and
+ 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.
PCRE does not allow the \C escape (which matches a single byte in UTF-8
- mode) to appear in lookbehind assertions, because it makes it impossi-
- ble to calculate the length of the lookbehind. The \X and \R escapes,
+ mode) to appear in lookbehind assertions, because it makes it impossi-
+ ble to calculate the length of the lookbehind. The \X and \R escapes,
which can match different numbers of bytes, are also not permitted.
- Possessive quantifiers can be used in conjunction with lookbehind
- assertions to specify efficient matching at the end of the subject
+ Possessive quantifiers can be used in conjunction with lookbehind
+ assertions to specify efficient matching at the end of the subject
string. Consider a simple pattern such as
abcd$
- when applied to a long string that does not match. Because matching
+ when applied to a long string that does not match. Because matching
proceeds from left to right, PCRE will look for each "a" in the subject
- and then see if what follows matches the rest of the pattern. If the
+ 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
+ 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,
+ 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; it can match only the
- entire string. The subsequent lookbehind 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
+ there can be no backtracking for the .*+ item; it can match only the
+ entire string. The subsequent lookbehind 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
@@ -4495,18 +4497,18 @@
(?<=\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
+ 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-
+ 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,
+ 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".
@@ -4514,79 +4516,79 @@
(?<=(?<!foo)bar)baz
- matches an occurrence of "baz" that is preceded by "bar" which in turn
+ 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
+ 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 previous capturing subpat-
- tern matched or not. The two possible forms of conditional subpattern
+ 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 previous capturing subpat-
+ tern matched or not. 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-
+ 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.
- There are four kinds of condition: references to subpatterns, refer-
+ There are four kinds of condition: references to subpatterns, refer-
ences to recursion, a pseudo-condition called DEFINE, 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 the capturing subpattern of that number has
- previously matched. An alternative notation is to precede the digits
+ If the text between the parentheses consists of a sequence of digits,
+ the condition is true if the capturing subpattern of that number has
+ previously matched. An alternative notation is to precede the digits
with a plus or minus sign. In this case, the subpattern number is rela-
tive rather than absolute. The most recently opened parentheses can be
- referenced by (?(-1), the next most recent by (?(-2), and so on. In
+ referenced by (?(-1), the next most recent by (?(-2), and so on. In
looping constructs it can also make sense to refer to subsequent groups
with constructs such as (?(+2).
- Consider the following pattern, which contains non-significant white
+ Consider the following pattern, which contains non-significant white
space to make it more readable (assume the PCRE_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
+ 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
+ ond part matches one or more characters that are not parentheses. The
third part is a conditional subpattern that tests whether the first set
of parentheses matched or not. If they did, that is, if subject started
with an opening parenthesis, the condition is true, and so the yes-pat-
- tern is executed and a closing parenthesis is required. Otherwise,
- since no-pattern is not present, the subpattern matches nothing. In
- other words, this pattern matches a sequence of non-parentheses,
+ tern is executed and a closing parenthesis is required. Otherwise,
+ 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
+ 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
+ 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
- PCRE, which had this facility before Perl, the syntax (?(name)...) is
- also recognized. However, there is a possible ambiguity with this syn-
- tax, because subpattern names may consist entirely of digits. PCRE
- looks first for a named subpattern; if it cannot find one and the name
- consists entirely of digits, PCRE looks for a subpattern of that num-
- ber, which must be greater than zero. Using subpattern names that con-
+ Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a
+ used subpattern by name. For compatibility with earlier versions of
+ PCRE, which had this facility before Perl, the syntax (?(name)...) is
+ also recognized. However, there is a possible ambiguity with this syn-
+ tax, because subpattern names may consist entirely of digits. PCRE
+ looks first for a named subpattern; if it cannot find one and the name
+ consists entirely of digits, PCRE looks for a subpattern of that num-
+ ber, which must be greater than zero. Using subpattern names that con-
sist entirely of digits is not recommended.
Rewriting the above example to use a named subpattern gives this:
@@ -4597,85 +4599,85 @@
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
+ 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 the subpat-
- tern whose number or name is given. This condition does not check the
+ the condition is true if the most recent recursion is into the subpat-
+ tern whose number or name is given. This condition does not check the
entire recursion stack.
- At "top level", all these recursion test conditions are false. Recur-
+ At "top level", all these recursion test conditions are false. Recur-
sive patterns are 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 ref-
- erenced from elsewhere. (The use of "subroutines" is described below.)
- For example, a pattern to match an IPv4 address could be written like
+ 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 ref-
+ erenced from elsewhere. (The use of "subroutines" is described below.)
+ For example, a pattern to match an IPv4 address could be written like
this (ignore whitespace 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
+ 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, insisting on a word
+ four dot-separated components of an IPv4 address, insisting on a word
boundary at each end.
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
+ 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
+ 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
- The sequence (?# marks the start of a comment that continues up to the
- next closing parenthesis. Nested parentheses are not permitted. 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. The
+ characters that make up a comment play no part in the pattern matching
at all.
- If the PCRE_EXTENDED option is set, an unescaped # character outside a
- character class introduces a comment that continues to immediately
+ If the PCRE_EXTENDED option is set, an unescaped # character outside a
+ character class introduces a comment that continues to immediately
after the next newline in the pattern.
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
+ 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
+ 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:
@@ -4685,117 +4687,117 @@
refers recursively to the pattern in which it appears.
Obviously, PCRE cannot support the interpolation of Perl code. Instead,
- it supports special syntax for recursion of the entire pattern, and
- also for individual subpattern recursion. After its introduction in
- PCRE and Python, this kind of recursion was introduced into Perl at
+ it supports special syntax for recursion of the entire pattern, and
+ also for individual subpattern recursion. After its introduction in
+ PCRE and Python, this kind of recursion was introduced into Perl at
release 5.10.
- A special item that consists of (? followed by a number greater than
+ A special item that consists of (? followed by a number greater than
zero and a closing parenthesis is a recursive call of the subpattern of
- the given number, provided that it occurs inside that subpattern. (If
- not, it is a "subroutine" call, which is described in the next sec-
- tion.) The special item (?R) or (?0) is a recursive call of the entire
+ the given number, provided that it occurs inside that subpattern. (If
+ not, it is a "subroutine" call, which is described in the next sec-
+ tion.) The special item (?R) or (?0) is a recursive call of the entire
regular expression.
- In PCRE (like Python, but unlike Perl), a recursive subpattern call is
+ In PCRE (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 PCRE pattern solves the nested parentheses problem (assume the
+ This PCRE pattern solves the nested parentheses problem (assume the
PCRE_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-
+ 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.
- If this were part of a larger pattern, you would not want to recurse
+ 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
+ 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. (A Perl
- 5.10 feature.) Instead of (?1) in the pattern above you can write
+ In a larger pattern, keeping track of parenthesis numbers can be
+ tricky. This is made easier by the use of relative references. (A Perl
+ 5.10 feature.) 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
+ 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 "subroutine" calls, as described in the next
+ 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 "subroutine" calls, as described in the next
section.
- An alternative approach is to use named parentheses instead. The Perl
- syntax for this is (?&name); PCRE's earlier syntax (?P>name) is also
+ An alternative approach is to use named parentheses instead. The Perl
+ syntax for this is (?&name); PCRE's earlier syntax (?P>name) is also
supported. We could rewrite the above example as follows:
(?<pn> \( ( (?>[^()]+) | (?&pn) )* \) )
- If there is more than one subpattern with the same name, the earliest
+ If there is more than one subpattern with the same name, the earliest
one is used.
- This particular example pattern that we have been looking at contains
- nested unlimited repeats, and so the use of atomic grouping for match-
- ing strings of non-parentheses is important when applying the pattern
+ This particular example pattern that we have been looking at contains
+ nested unlimited repeats, and so the use of atomic grouping for match-
+ ing 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 atomic grouping 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
+ it yields "no match" quickly. However, if atomic grouping 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 set for any capturing subpatterns are
those from the outermost level of the recursion at which the subpattern
- value is set. If you want to obtain intermediate values, a callout
- function can be used (see below and the pcrecallout documentation). If
+ value is set. If you want to obtain intermediate values, a callout
+ function can be used (see below and the pcrecallout documentation). If
the pattern above is matched against
(ab(cd)ef)
- the value for the capturing parentheses is "ef", which is the last
- value taken on at the top level. If additional parentheses are added,
+ the value for the capturing parentheses is "ef", which is the last
+ value taken on at the top level. If additional parentheses are added,
giving
\( ( ( (?>[^()]+) | (?R) )* ) \)
^ ^
^ ^
- the string they capture is "ab(cd)ef", the contents of the top level
- parentheses. If there are more than 15 capturing parentheses in a pat-
+ the string they capture is "ab(cd)ef", the contents of the top level
+ parentheses. If there are more than 15 capturing parentheses in a pat-
tern, PCRE has to obtain extra memory to store data during a recursion,
- which it does by using pcre_malloc, freeing it via pcre_free after-
- wards. If no memory can be obtained, the match fails with the
+ which it does by using pcre_malloc, freeing it via pcre_free after-
+ wards. If no memory can be obtained, the match fails with the
PCRE_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-
+ 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.
+ 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.
SUBPATTERNS AS SUBROUTINES
If the syntax for a recursive subpattern reference (either by number or
- by name) is used outside the parentheses to which it refers, it oper-
- ates like a subroutine in a programming language. The "called" subpat-
+ by name) is used outside the parentheses to which it refers, it oper-
+ ates like a subroutine in a programming language. The "called" subpat-
tern may be defined before or after the reference. A numbered reference
can be absolute or relative, as in these examples:
@@ -4807,105 +4809,105 @@
(sens|respons)e and \1ibility
- matches "sense and sensibility" and "response and responsibility", but
+ 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
+ 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.
Like recursive subpatterns, a "subroutine" 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
+ 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.
- When a subpattern is used as a subroutine, processing options such as
+ When a subpattern is used as a subroutine, processing options such as
case-independence are fixed when the subpattern is defined. They 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
+ 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
+ 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-
+ 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
- PCRE supports an extension to Oniguruma: if a number is preceded by a
+ PCRE 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
+ 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.
+ 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.
PCRE provides a similar feature, but of course it cannot obey arbitrary
Perl code. The feature is called "callout". The caller of PCRE provides
- an external function by putting its entry point in the global variable
- pcre_callout. By default, this variable contains NULL, which disables
+ an external function by putting its entry point in the global variable
+ pcre_callout. By default, this variable contains NULL, which disables
all calling out.
- Within a regular expression, (?C) indicates the points at which the
- external function is to be called. If you want to identify different
- callout points, you can put a number less than 256 after the letter C.
- The default value is zero. For example, this pattern has two callout
+ Within a regular expression, (?C) indicates the points at which the
+ external function is to be called. If you want to identify different
+ callout points, you can put a number less than 256 after the letter C.
+ The default value is zero. For example, this pattern has two callout
points:
(?C1)abc(?C2)def
If the PCRE_AUTO_CALLOUT flag is passed to pcre_compile(), callouts are
- automatically installed before each item in the pattern. They are all
+ automatically installed before each item in the pattern. They are all
numbered 255.
During matching, when PCRE reaches a callout point (and pcre_callout is
- set), the external function is called. It is provided with the number
- of the callout, the position in the pattern, and, optionally, one item
- of data originally supplied by the caller of pcre_exec(). The callout
- function may cause matching to proceed, to backtrack, or to fail alto-
+ set), the external function is called. It is provided with the number
+ of the callout, the position in the pattern, and, optionally, one item
+ of data originally supplied by the caller of pcre_exec(). The callout
+ function may cause matching to proceed, to backtrack, or to fail alto-
gether. A complete description of the interface to the callout function
is given in the pcrecallout documentation.
BACKTRACKING CONTROL
- Perl 5.10 introduced a number of "Special Backtracking Control Verbs",
+ Perl 5.10 introduced a number of "Special Backtracking Control Verbs",
which are described in the Perl documentation as "experimental and sub-
- ject 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
+ ject 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 PCRE features described
in this section.
- Since these verbs are specifically related to backtracking, most of
- them can be used only when the pattern is to be matched using
+ Since these verbs are specifically related to backtracking, most of
+ them can be used only when the pattern is to be matched using
pcre_exec(), which uses a backtracking algorithm. With the exception of
(*FAIL), which behaves like a failing negative assertion, they cause an
error if encountered by pcre_dfa_exec().
- The new verbs make use of what was previously invalid syntax: an open-
+ The new verbs make use of what was previously invalid syntax: an open-
ing parenthesis followed by an asterisk. In Perl, they are generally of
the form (*VERB:ARG) but PCRE does not support the use of arguments, so
- its general form is just (*VERB). Any number of these verbs may occur
+ its general form is just (*VERB). Any number of these verbs may occur
in a pattern. There are two kinds:
Verbs that act immediately
@@ -4914,94 +4916,94 @@
(*ACCEPT)
- This verb causes the match to end successfully, skipping the remainder
- of the pattern. When inside a recursion, only the innermost pattern is
- ended immediately. PCRE differs from Perl in what happens if the
- (*ACCEPT) is inside capturing parentheses. In Perl, the data so far is
+ This verb causes the match to end successfully, skipping the remainder
+ of the pattern. When inside a recursion, only the innermost pattern is
+ ended immediately. PCRE differs from Perl in what happens if the
+ (*ACCEPT) is inside capturing parentheses. In Perl, the data so far is
captured: in PCRE no data is captured. For example:
A(A|B(*ACCEPT)|C)D
- This matches "AB", "AAD", or "ACD", but when it matches "AB", no data
+ This matches "AB", "AAD", or "ACD", but when it matches "AB", no data
is captured.
(*FAIL) or (*F)
- This verb causes the match to fail, 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 PCRE. The
- nearest equivalent is the callout feature, as for example in this pat-
+ This verb causes the match to fail, 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 PCRE. 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
+ A match with the string "aaaa" always fails, but the callout is taken
before each backtrack happens (in this example, 10 times).
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, a fail-
- ure is forced. The verbs differ in exactly what kind of failure
+ tinues with what follows, but if there is no subsequent match, a fail-
+ ure is forced. The verbs differ in exactly what kind of failure
occurs.
(*COMMIT)
- This verb causes the whole match to fail outright if the rest of the
- pattern does not match. Even if the pattern is unanchored, no further
- attempts to find a match by advancing the start point take place. Once
- (*COMMIT) has been passed, pcre_exec() is committed to finding a match
+ This verb causes the whole match to fail outright if the rest of the
+ pattern does not match. Even if the pattern is unanchored, no further
+ attempts to find a match by advancing the start point take place. Once
+ (*COMMIT) has been passed, pcre_exec() 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
+ 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."
(*PRUNE)
- This verb causes the match to fail at the current position if the rest
+ This verb causes the match to fail at the current position if the rest
of the pattern does not match. If the pattern is unanchored, the normal
- "bumpalong" advance to the next starting character then happens. Back-
- tracking can occur as usual to the left of (*PRUNE), or when matching
- to the right of (*PRUNE), but if there is no match to the right, back-
- tracking cannot cross (*PRUNE). In simple cases, the use of (*PRUNE)
+ "bumpalong" advance to the next starting character then happens. Back-
+ tracking can occur as usual to the left of (*PRUNE), or when matching
+ to the right of (*PRUNE), but if there is no match to the right, back-
+ tracking cannot cross (*PRUNE). In simple cases, the use of (*PRUNE)
is just an alternative to an atomic group or possessive quantifier, but
- there are some uses of (*PRUNE) that cannot be expressed in any other
+ there are some uses of (*PRUNE) that cannot be expressed in any other
way.
(*SKIP)
- This verb is like (*PRUNE), except that if the pattern is unanchored,
- the "bumpalong" advance is not to the next character, but to the posi-
- tion in the subject where (*SKIP) was encountered. (*SKIP) signifies
- that whatever text was matched leading up to it cannot be part of a
+ This verb is like (*PRUNE), except that if the pattern is unanchored,
+ the "bumpalong" advance is not to the next character, but to the posi-
+ tion in the subject where (*SKIP) was encountered. (*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
+ 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 in 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
+ tifer does not have the same effect in 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".
(*THEN)
This verb causes a skip to the next alternation if the rest of the pat-
tern does not match. That is, it cancels pending backtracking, but only
- within the current alternation. Its name comes from the observation
+ within the current alternation. 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 (*THEN) is used outside of any alternation, it acts
+ 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 (*THEN) is used outside of any alternation, it acts
exactly like (*PRUNE).
@@ -5019,7 +5021,7 @@
REVISION
- Last updated: 08 March 2009
+ Last updated: 18 March 2009
Copyright (c) 1997-2009 University of Cambridge.
------------------------------------------------------------------------------
Modified: code/trunk/doc/pcrepattern.3
===================================================================
--- code/trunk/doc/pcrepattern.3 2009-03-23 12:05:20 UTC (rev 405)
+++ code/trunk/doc/pcrepattern.3 2009-03-23 12:05:43 UTC (rev 406)
@@ -364,7 +364,7 @@
\ew, and always match \eD, \eS, and \eW. This is true even when Unicode
character property support is available. These sequences retain their original
meanings from before UTF-8 support was available, mainly for efficiency
-reasons. Note that this also affects \eb, because it is defined in terms of \ew
+reasons. Note that this also affects \eb, because it is defined in terms of \ew
and \eW.
.P
The sequences \eh, \eH, \ev, and \eV are Perl 5.10 features. In contrast to the
Modified: code/trunk/pcre_compile.c
===================================================================
--- code/trunk/pcre_compile.c 2009-03-23 12:05:20 UTC (rev 405)
+++ code/trunk/pcre_compile.c 2009-03-23 12:05:43 UTC (rev 406)
@@ -1663,15 +1663,15 @@
{
BOOL empty_branch;
if (GET(code, 1) == 0) return TRUE; /* Hit unclosed bracket */
-
- /* If a conditional group has only one branch, there is a second, implied,
+
+ /* If a conditional group has only one branch, there is a second, implied,
empty branch, so just skip over the conditional, because it could be empty.
Otherwise, scan the individual branches of the group. */
-
+
if (c == OP_COND && code[GET(code, 1)] != OP_ALT)
code += GET(code, 1);
else
- {
+ {
empty_branch = FALSE;
do
{
@@ -1682,7 +1682,7 @@
while (*code == OP_ALT);
if (!empty_branch) return FALSE; /* All branches are non-empty */
}
-
+
c = *code;
continue;
}
Modified: code/trunk/pcre_dfa_exec.c
===================================================================
--- code/trunk/pcre_dfa_exec.c 2009-03-23 12:05:20 UTC (rev 405)
+++ code/trunk/pcre_dfa_exec.c 2009-03-23 12:05:43 UTC (rev 406)
@@ -2200,16 +2200,16 @@
{
int local_offsets[1000];
int local_workspace[1000];
- int codelink = GET(code, 1);
+ int codelink = GET(code, 1);
int condcode;
-
+
/* Because of the way auto-callout works during compile, a callout item
- is inserted between OP_COND and an assertion condition. This does not
+ is inserted between OP_COND and an assertion condition. This does not
happen for the other conditions. */
if (code[LINK_SIZE+1] == OP_CALLOUT)
- {
- rrc = 0;
+ {
+ rrc = 0;
if (pcre_callout != NULL)
{
pcre_callout_block cb;
@@ -2229,10 +2229,10 @@
}
if (rrc > 0) break; /* Fail this thread */
code += _pcre_OP_lengths[OP_CALLOUT]; /* Skip callout data */
- }
+ }
condcode = code[LINK_SIZE+1];
-
+
/* Back reference conditions are not supported */
if (condcode == OP_CREF) return PCRE_ERROR_DFA_UCOND;
@@ -2250,7 +2250,7 @@
{
int value = GET2(code, LINK_SIZE+2);
if (value != RREF_ANY) return PCRE_ERROR_DFA_UCOND;
- if (recursing > 0)
+ if (recursing > 0)
{ ADD_ACTIVE(state_offset + LINK_SIZE + 4, 0); }
else { ADD_ACTIVE(state_offset + codelink + LINK_SIZE + 1, 0); }
}
@@ -2434,7 +2434,7 @@
/* Handle callouts */
case OP_CALLOUT:
- rrc = 0;
+ rrc = 0;
if (pcre_callout != NULL)
{
pcre_callout_block cb;
@@ -2451,9 +2451,9 @@
cb.capture_last = -1;
cb.callout_data = md->callout_data;
if ((rrc = (*pcre_callout)(&cb)) < 0) return rrc; /* Abandon */
- }
- if (rrc == 0)
- { ADD_ACTIVE(state_offset + _pcre_OP_lengths[OP_CALLOUT], 0); }
+ }
+ if (rrc == 0)
+ { ADD_ACTIVE(state_offset + _pcre_OP_lengths[OP_CALLOUT], 0); }
break;
Modified: code/trunk/pcre_exec.c
===================================================================
--- code/trunk/pcre_exec.c 2009-03-23 12:05:20 UTC (rev 405)
+++ code/trunk/pcre_exec.c 2009-03-23 12:05:43 UTC (rev 406)
@@ -334,9 +334,9 @@
/* Function local variables */
const uschar *Xcallpat;
-#ifdef SUPPORT_UTF8
+#ifdef SUPPORT_UTF8
const uschar *Xcharptr;
-#endif
+#endif
const uschar *Xdata;
const uschar *Xnext;
const uschar *Xpp;
@@ -641,7 +641,7 @@
{
minimize = possessive = FALSE;
op = *ecode;
-
+
/* For partial matching, remember if we ever hit the end of the subject after
matching at least one subject character. */
@@ -794,7 +794,7 @@
case OP_COND:
case OP_SCOND:
codelink= GET(ecode, 1);
-
+
/* Because of the way auto-callout works during compile, a callout item is
inserted between OP_COND and an assertion condition. */
@@ -822,7 +822,7 @@
}
condcode = ecode[LINK_SIZE+1];
-
+
/* Now see what the actual condition is */
if (condcode == OP_RREF) /* Recursion test */
Modified: code/trunk/pcre_internal.h
===================================================================
--- code/trunk/pcre_internal.h 2009-03-23 12:05:20 UTC (rev 405)
+++ code/trunk/pcre_internal.h 2009-03-23 12:05:43 UTC (rev 406)
@@ -58,7 +58,7 @@
#error The use of both EBCDIC and SUPPORT_UTF8 is not supported.
#endif
-/* If SUPPORT_UCP is defined, SUPPORT_UTF8 must also be defined. The
+/* If SUPPORT_UCP is defined, SUPPORT_UTF8 must also be defined. The
"configure" script ensures this, but not everybody uses "configure". */
#if defined SUPPORT_UCP && !defined SUPPORT_UTF8
