DUH! I started by looking for perl5db.pl when I was running under Devel::ptkdb, forgetting that any other debugger is loaded INSTEAD of perl5db.pl, not of ON TOP OF perl5db.pl.

I had also thought that I could use the current value of $DB::single to determine if I was in the debugger; that way I could get a value for the function no matter what debugger you are running. For some reason, however, I only see its value as zero, even under -d.

Anyway, here is what I am using for now:

sub am_i_debugging {
    print "$DB::single\n";
    return (the_debugger_is()) ? 1 : 0;
}

sub the_debugger_is {
    return '-d:ptkdb'
      if(exists $INC{'Devel/ptkdb.pm'});
    return '-d'
      if(exists $INC{'perl5db.pl'});
    return '';
}

print( join("\n",
            am_i_debugging(),
            the_debugger_is(),
            ''));
[download]