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<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix PCRE Support</h1>

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<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 <a href="pcre_table.5.html">pcre_table(5)</a> manual page. Information about PCRE
itself can be found at <a href="https://www.pcre.org/">https://www.pcre.org/</a>. </p>

<h2>Using Postfix packages with PCRE support</h2>

<p> To use pcre with Debian GNU/Linux's Postfix, or with Fedora or
RHEL Postfix, all you
need is to install the postfix-pcre package and you're done.  There
is no need to recompile Postfix. </p>

<h2>Building Postfix from source with PCRE support</h2>

<p> These instructions assume that you build Postfix from source
code as described in the <a href="INSTALL.html">INSTALL</a> document. </p>

<p> To build Postfix from source with pcre support, you need a pcre
library. Install a vendor package, or download the source code from
locations in <a href="https://www.pcre.org/">https://www.pcre.org/</a> and build that yourself.

<p> Postfix can build with the pcre2 library or the legacy pcre
library. It's probably easiest to let the Postfix build procedure
pick one. The following commands will first discover if the pcre2
library is installed, and if that is not available, will discover
if the legacy pcre library is installed. </p>

<blockquote>
<pre>
$ make -f Makefile.init makefiles
$ make
</pre>
</blockquote>

<p> To build Postfix explicitly with a pcre2 library (Postfix 3.7
and later): </p>

<blockquote>
<pre>
$ make -f Makefile.init makefiles \
    "CCARGS=-DHAS_PCRE=2 `pcre2-config --cflags`" \
    "<a href="PCRE_README.html">AUXLIBS_PCRE</a>=`pcre2-config --libs8`"
$ make
</pre>
</blockquote>

<p> To build Postfix explicitly with a legacy pcre library (all
Postfix versions): </p>

<blockquote>
<pre>
$ make -f Makefile.init makefiles \
    "CCARGS=-DHAS_PCRE=1 `pcre-config --cflags`" \
    "<a href="PCRE_README.html">AUXLIBS_PCRE</a>=`pcre-config --libs`"
$ make
</pre>
</blockquote>

<p> Postfix versions before 3.0 use AUXLIBS instead of <a href="PCRE_README.html">AUXLIBS_PCRE</a>.
With Postfix 3.0 and later, the old AUXLIBS variable still supports
building a statically-loaded PCRE database client, but only the new
<a href="PCRE_README.html">AUXLIBS_PCRE</a> variable supports building a dynamically-loaded or
statically-loaded PCRE database client.  </p>

<blockquote>

<p> Failure to use the <a href="PCRE_README.html">AUXLIBS_PCRE</a> 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 <a href="pcre_table.5.html">pcre</a>: or <a href="regexp_table.5.html">regexp</a>: 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 <a href="pcre_table.5.html">pcre</a>: or <a href="regexp_table.5.html">regexp</a>: are
not allowed to do $number substitution in lookup results that can
be security sensitive: currently, that restriction applies to the
local <a href="aliases.5.html">aliases(5)</a> database or the <a href="virtual.8.html">virtual(8)</a> delivery agent tables.
</p>

</ul>

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