With mod_perl, you can use Perl in Apache configuration files. What this means is that you can make your Apache configuration much more flexible by using conditionals.

Any Perl code in Apache configuration files should be placed between <Perl> and </Perl> directives. This code can define variables and lists used by mod_perl to assign the associated Apache configuration directives; for example, assigning the $ServerAdmin variable will redefine the ServerAdmin Apache configuration directive.

Suppose you share the same Apache configuration files across multiple servers, and you want to allow personal directories on only one of them. You can use Perl directives like this:

<Perl>
if ('hostname' =~ /public/) {
        $UserDir = "public.html";
} else {
        $UserDir = "DISABLED";
}
1;
</Perl>

Directive blocks (such as <Location>...</Location>) can be represented as a hash. For example:

<Perl>
$Location{"/design_dept/"} = {
        DefaultType   => 'image/gif',
        FancyIndexing => 'On'
}
</Perl>