Re: [exim] Remove header lines matching a specific pattern?

On 2009-07-13 at 22:54 +0200, Karl Fischer wrote:
> I followed this thread with interest and I'm still a little puzzled with the
> specific exim syntax, but in terms of regex and just extracting the header
> names, this perl regex should be more efficient: s/:.*?\n(\s+.*?\n)*/:/g
>
> This saves looping through map/extract by getting rid of the unwanted 1st.

Good point.

However, you're also not stripping out space between the header name and
the following colon, which is valid. This email could validly be
constructed with:
----------------------------8< cut here >8------------------------------
From: Phil ....
To : Karl ...
Cc : exim-users ....
----------------------------8< cut here >8------------------------------

With a little further optimisation, we get:

s/(?>\s*:.*?\n)(?>\s+.*?\n)*/:/g

although actually I'm not sure there would be any backtracking needed
for your s///g and it's probably only the \s*: that benefits from the
protection. (I can't be bothered to benchmark it).

> In exim syntax I'd assume this to be (not tested yet):
>
> MESSAGE_HEADERS = ${lc:${sg {$message_headers_raw}{\N:.*?\n(\s+.*?\n)*\N}{:}}}

${lc:${sg{$message_headers_raw}{\N(?>\s*:.*?\n)(?>\s+.*?\n)*\N}{:}}}