So, a lot of people like to say that. And indeed, sometimes index is ten times faster. But sometimes it's more than three times slower!

use Benchmark qw(:all);

$text = <<EOF;
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaa
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaa
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaa
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaa
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaa
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaa
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaa
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+aaaaaaaaaa
EOF
$pattern = "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb";

cmpthese($count, {
  'regex' => sub {       $text =~ $pattern },
  'index' => sub { index $text,   $pattern },
});
__DATA__
           Rate index regex
index  630601/s    --  -67%
regex 1914815/s  204%    --
[download]

Moreover, increasing the lengths of the text and pattern, I can make the regex be 40 times faster*. See Re^8: "advanced" Perl functions and maintainability for reasons why people use regexes instead of index. Personally, I still don't understand why there even is a difference in speed -- shouldn't the regex engine be optimized to notice that this is a search for a constant string and then call the same function as index?

*: No, I'm not kidding. The output follows. Moreover, for this example, adding a single study $text is an extra 10 times faster, completely obliterating index.

         Rate  index  regex  study
index   178/s     --   -98%  -100%
regex  7538/s  4124%     --   -92%
study 98871/s 55311%  1212%     --
[download]