If I understand your question, I think you are looking for information available in caller. You don't want to know who called you, but who called something that called you.

use strict;
use Carp;

trace('foo');
trace('bar');

func();


sub func
{
  trace('in func');
}

sub trace
{
  my $string = shift;
  my  ($package, $filename, $line, $subroutine, $hasargs,
       $wantarray, $evaltext, $is_require, $hints, $bitmask) = caller(
+1);
  
  if($subroutine)
  {
    print "[$subroutine]: $string\n";
  }
  else
  {
    print "[**IN MAIN**]: $string\n";
  }
}
__END__
[**IN MAIN**]: foo
[**IN MAIN**]: bar
[main::func]: in func
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