for ("ab", "cd") {
  if ($str =~ /$_/) { ... }
}

##</code><code>##

($x, $y) = ("ab", "c");
for (1, 2) {
  if ($str =~ /$x$y/) { ... }
  ($x, $y) = ("a", "bc");
}

##</code><code>##

my @strings = make_10_strings();
for (@strings) {
  for my $p ('x+', 'yz?y', 'xz+y') {
    if ($_ =~ $p) { handle($_) }
  }
}

##</code><code>##

my @strings = make_10_strings();
for (@strings) {
  for my $p (qr/x+/, qr/yz?y/, qr/xz+y/) {
    if ($_ =~ $p) { handle($_) }
  }
}