mod_perl Version 1.25 introduced Apache::MyConfig, which provides access to the various hooks and features set when mod_perl was built. This circumvents the need to set up a live server just to find out if a certain callback hook is available.

To see whether some feature was built in or not, check the %Apache::MyConfig::Setup hash. For example, suppose we install mod_perl with the following options:

panic% perl Makefile.PL EVERYTHING=1

but the next day we can't remember which callback hooks were enabled. We want to know whether the PERL_LOG callback hook is available. One of the ways to find an answer is to run the following code:

panic% perl -MApache::MyConfig -e 'print $Apache::MyConfig::Setup{PERL_LOG}'

If it prints 1, that means the PERL_LOG callback hook is enabled (which it should be, as EVERYTHING=1 enables them all).

Another approach is to configure Apache::Status (see Chapter 9) and run http://localhost/perl-status?hooks to check for enabled hooks.

If you want to check for the existence of various hooks within your handlers, you can use the script shown in Example 3-1.

Example 3-1.

use mod_perl_hooks;

for my $hook (mod_perl::hooks( )) {
    if (mod_perl::hook($hook)) {
        print "$hook is enabled\n";
    else {
        print "$hook is not enabled\n";

You can also try to look at the symbols inside the httpd executable with the help of nm(1) or a similar utility. For example, if you want to see whether you enabled PERL_LOG=1 while building mod_perl, you can search for a symbol with the same name but in lowercase:

panic% nm httpd | grep perl_log
08071724 T perl_logger

This shows that PERL_LOG=1 was enabled. But this approach will work only if you have an unstripped httpd binary. By default, make install strips the binary before installing it, thus removing the symbol names to save space. Use the —without-execstrip ./configure option to prevent stripping during the make install phase. [19]

[19]You might need the unstripped version for debugging reasons too.

Yet another approach that will work in most cases is to try to use the feature in question. If it wasn't configured, Apache will give an error message.