Without checking environment variables

What's wrong with checking environment variables? If mod_perl is enabled, $ENV{ MOD_PERL } will be set to "mod_perl/VERSION" (in my case "mod_perl/1.29").

is there any other way that the function can be aware that it is running under apache?

If you want to know whether you're running under mod_perl you can check for $ENV{MOD_PERL} being set (see the mod_perl documentation for details).

Just a general comment on asking questions here. If you know that the standard way of checking for mod_perl is to test for an environment variable ($ENV{MOD_PERL}), and then you specifically state that you do not want to look at environment variables, then at least give a reason why you don't want to use environment variables. This is more a suggestion for future questions, then a critisism.

Otherwise you will just get a bunch of responses that (correctly so) ask you why you don't want to do things the standard way.

This of course assumes that you know about checking for $ENV{MOD_PERL}, but since you specifically mentioned environment variables, I guess that you do.

As for checking the apache request object to see if mod_perl is being used, I guess you could use eval and check for a failure.

my $r = eval { Apache->instance };
if ($@) {
  # mod_perl probably not available
}
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But checking the environment variable is much much cleaner.

if (!$ENV{MOD_PERL}) {
  # mod_perl is not available
}
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