Write code like this, create subs that take arguments , subs that don't work on global variables, its good practice everywhere and especially for registry , see CGI to mod_perl Porting. mod_perl Coding guidelines, see sub DebugCGI in UTF-8

Main( @ARGV );
exit( 0 );
sub Main {
    my $lig = 4;
    my $q = CGI->new;
    DoSomething( $lig, $q );
}
sub DoSomething {
    my( $lig, $q ) = @_;
    ...
}
[download]

Also, Basic debugging checklist , brian's Guide to Solving Any Perl Problem, CGI Help Guide , Troubleshooting Perl CGI scripts, CGI to mod_perl Porting. mod_perl Coding guidelines

Tutorials: Variable Scoping in Perl: the basics,
Coping with Scoping , Mini-Tutorial: Perl's Memory Management,
Lexical scoping like a fox,
Read this if you want to cut your development time in half!,
Closure on Closures , perlref#Circular References,
Memory leaks and circular references,
Circular references and Garbage collection.,
make perl release memory,
about memory management , Re^3: Scope of lexical variables in the main script , Re: What's the weaken here for?,
Devel::Cycle,
Devel::NYTProf,
Devel::Leak Devel::LeakTrace,
WeakRef

Basic debugging checklist and brian's Guide to Solving Any Perl Problem ) ... On debugging, verify everything, talk to teddybear ... checklists and more, Re^3: A Beginner Needs Homework help