Apache: The Definitive Guide, 3rd Edition

Chapter 17. mod_perl

Perl does some very useful things and provides such huge resources in the CPAN library (http://cpan.org) that it will clearly be with us for a long time yet as a way of writing scripts to run behind Apache. While Perl is powerful, CGI is not a particularly efficient means of connecting Perl to Apache. CGI’s big disadvantage is that each time a script is invoked, Apache has to load the Perl interpreter and then it has to load the script. This is a heavy and pointless overhead on a busy site, and it would obviously be much easier if Perl stayed loaded in memory, together with the scripts, to be invoked each time they were needed. This is what mod_perl does by modifying Apache.

This modification is definitely popular: according to Netcraft surveys in mid-2000, mod_perl was the third most popular add-on to Apache (after FrontPage and PHP), serving more than a million URLs on over 120,000 different IP numbers (http://perl.apache.org/outstanding/stats/netcraft.html).

The reason that this chapter is more than a couple of pages long is that Perl does not sit easily in a web server. It was originally designed as a better shell script to run standalone under Unix. It developed, over time, into a full-blown programming language. However, because the original Perl was not designed for this kind of work, various things have to happen. To illustrate them, we will start with a simple Perl script that runs under Apache’s mod_cgi and then modify it to run under mod_perl. (We ...