use Benchmark qw( cmpthese );

$_ = '
          df asdf sadf s f
          df asdf sadf s f
          df asdf sadf s f
          df asdf sadf s f
          df asdf sadf s f
          df asdf sadf s f
          df asdf sadf s f
          df asdf sadf s f
';
our $KEY="df";

cmpthese(-3, {
   caret => '/^ \s* $KEY /mx',
   cr => '/\n \s* $KEY /mx',
});