use strict;
use warnings;
use Carp;

package main;


sub debug {
   my ($pkg) = caller;

   {
      no strict 'refs';
      return unless ${ "${pkg}::DEBUG_FLAG" };
   }

   carp "@_";
}


package My_First; 

our $DEBUG_FLAG = 1;
::debug( "Print " . __PACKAGE__ );        # prints


package My_Second;

our $DEBUG_FLAG = 0;
::debug( "Print " . __PACKAGE__ );        # doesn't print
[download]

Print My_First at d:/Users/RolfLangsdorf/pm/pm_debug_caller.pl line 23
+.
[download]

Update

improved code with Carp to report file and line from callers perspective.