Getting back to capturing what matched and where, but use Not a Number's way of constructing the inner match:

    my  $s2 = '$endcod = index($s2eq, $end1 || $end2 || $end3, $s2tart
+cod);';

    while( $s2 =~ m/(end|dex|art)/g ) {
        printf "  Found '%s' at %d\n", $1, pos($s2);
    }
[download]

Outputs:

  Found 'end' at 4
  Found 'dex' at 15
  Found 'end' at 27
  Found 'end' at 36
  Found 'end' at 45
  Found 'art' at 55