You might want to look at the CPAN module Devel::Trace. It prints out program lines as they're executed. See http://www.plover.com/~mjd/perl/Trace for details. Might be easier than using the standard debugger.

More interestingly, there's the Devel::TraceFuncs module, which does this:

Devel::TraceFuncs lets you instrument your programs, so you can see
what subroutines get called when, and by whom.  This is particularly
useful if you have a timing problem that doesn't show up if you use
the debugger (a "heisenbug").

The following program:

   use Devel::TraceFuncs qw(trace debug);
 
   sub foo {
     trace(my $f);

     debug "hi";
   }

   trace(my $f);

   foo(1, 2);
   debug "there";

produces this output:

   +-> global
   |  +-> main::foo(1, 2) (in t.pm:10)
   |  |  hi (in t.pm:6)
   |  +-< main::foo(1, 2) (in t.pm:10)
   |  there (in t.pm:11)
   +-< global
[download]

I haven't tried these, so your mileage may vary.

Also, read Refactoring by Martin Fowler. Great advice in there about how to cope with legacy pasta.

stephen