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<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN"
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<title>Postfix PCRE Support</title>
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<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix PCRE Support</h1>
<hr>
<h2>PCRE (Perl Compatible Regular Expressions) map support</h2>
<p> The optional "pcre" map type allows you to specify regular
expressions with the PERL style notation such as \s for space and
\S for non-space. The main benefit, however, is that pcre lookups
are often faster than regexp lookups. This is because the pcre
implementation is often more efficient than the POSIX regular
expression implementation that you find on many systems. </p>
<p> A description of how to use pcre tables, including examples,
is given in the pcre_table(5) manual page. Information about PCRE
itself can be found at http://www.pcre.org/. </p>
<h2>Building Postfix with PCRE support</h2>
<p> These instructions assume that you build Postfix from source
code as described in the INSTALL document. Some modification may
be required if you build Postfix from a vendor-specific source
package. </p>
<p> Note: to use pcre with Debian GNU/Linux's Postfix, all you
need is to install the postfix-pcre package and you're done. There
is no need to recompile Postfix. </p>
<p> In some future, Postfix will have a plug-in interface for adding
map types. Until then, you need to compile PCRE support into Postfix.
</p>
<p> First of all, you need the PCRE library (Perl Compatible Regular
Expressions), which can be obtained from: </p>
<blockquote>
ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/.
</blockquote>
<p> NOTE: pcre versions prior to 2.06 cannot be used. </p>
<p> In order to build Postfix with PCRE support you need to add
-DHAS_PCRE and a -I option for the PCRE include file to CCARGS, and
add the path to the PCRE library to AUXLIBS_PCRE, for example: </p>
<blockquote>
<pre>
make -f Makefile.init makefiles \
"CCARGS=-DHAS_PCRE `pcre-config --cflags`" \
"AUXLIBS_PCRE=`pcre-config --libs`"
</pre>
</blockquote>
<p> Postfix versions before 3.0 use AUXLIBS instead of AUXLIBS_PCRE.
With Postfix 3.0 and later, the old AUXLIBS variable still supports
building a statically-loaded PCRE database client, but only the new
AUXLIBS_PCRE variable supports building a dynamically-loaded or
statically-loaded PCRE database client. </p>
<blockquote>
<p> Failure to use the AUXLIBS_PCRE variable will defeat the purpose
of dynamic database client loading. Every Postfix executable file
will have PCRE library dependencies. And that was exactly
what dynamic database client loading was meant to avoid. </p>
</blockquote>
<h2>Things to know</h2>
<ul>
<li> <p> When Postfix searches a pcre: or regexp: lookup table,
each pattern is applied to the entire input string. Depending on
the application, that string is an entire client hostname, an entire
client IP address, or an entire mail address. Thus, no parent domain
or parent network search is done, "user@domain" mail addresses are
not broken up into their user and domain constituent parts, and
"user+foo" is not broken up into user and foo. </p>
<li> <p> Regular expression tables such as pcre: or regexp: are
not allowed to do $number substitution in lookup results that can
be security sensitive: currently, that restriction applies to the
local aliases(5) database or the virtual(8) delivery agent tables.
</p>
</ul>
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