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11.4. Running CGI Scripts with mod_perl

What most people want to do with mod_perl is improve CGI performance. The mod_perl installation assumes this request by enabling the PerlHandler callback hook by default and by installing the Apache::Registry module. PerlHandler is the handler used for the content retrieval stage of the server transaction. Apache::Registry is the Perl module that emulates the CGI environment so you can use "standard" Perl CGI scripts with mod_perl without having to rewrite them (much). This is by far the cheapest way to get improved CGI performance.

With Apache::Registry, each individual CGI program is compiled and cached the first time it is called (or whenever it is changed) and remains available for all subsequent instances of that CGI script. This process avoids the costs of startup time.

Whereas most CGI scripts are kept in cgi-bin, scripts that use Apache::Registry are placed in a separate directory, e.g., perl-bin. The access.conf Apache configuration file needs to point to this directory by setting an alias and defining a handler for this new location:

Alias /perl-bin/ /usr/local/apache/perl-bin/

<Location /perl-bin>
SetHandler perl-script
PerlHandler Apache::Registry
PerlSendHeader On
Options ExecCGI

Instead of using the cgi-script handler, we use the perl-script handler to give control to mod_perl. Next, the PerlHandler directive tells mod_perl that the Apache::Registry module should be used for serving all files in that directory.PerlSendHeader is another mod_perl-specific directive; in this case, it tells mod_perl to send response lines and common headers—by default, none are sent. (For NPH scripts, you'll want to turn this feature off again.) Options ExecCGI is a standard Apache header that is needed to tell Apache to treat the script as a CGI script.

If you want to load Perl modules in addition to Apache::Registry, you can use the PerlModule directive:

PerlModule CGI

If you include this line, you shouldn't need to explicitly use CGI in each Perl CGI script anymore, since CGI.pm will be loaded directly from the Apache server. Up to ten modules can be listed with the PerlModule directive.

CGI scripts in the new directory should work now. However, if you have problems, the mod_perl manpage offers some words of wisdom:

In addition, it is recommended that you should use recent versions of Perl and CGI.pm. You should scan the mod_perl documentation for the latest compatibility news.

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