$string = "...foo\nbar...";
if ($string =~ /foo$bar/m) {
  # ...
}

##</code><code>##

$string = "...foo\nbar...";
if ($string =~ /foo$^bar/m) {
  # ...
}

##</code><code>##

$string = "...foo\nbar...";
if ($string =~ / foo$ ^bar /mx) {
  # ...
}