my $c = qr/(?>\s|--[^\n]*(?:\n|\z))/; # one whitespace or one comment

    # later on, when parsing...

    pos($str) = 0;

    if ($str =~ m/a/gc)
      { print "found a\n" } else { print "missing a\n" }

    $str =~ m/$c*/gc; # skip any comments, whitespaces

    if ($str =~ m/x/gc)
      { print "found x\n" } else { print "missing x\n" }