$ cat bench
#!/usr/bin/perl

use strict;
use warnings;

use Benchmark 'cmpthese';

sub regex_subst {
  $_ = 'this/is/a/string';
  s|/|\\|g;
}

sub tr_subst {
  $_ = 'this/is/a/string';
  tr|/|\\|;
}

cmpthese(1_000_000, {
          s  => \&regex_subst,
          tr => \&tr_subst,
         });
$ ./bench
        Rate    s   tr
s   287356/s   -- -75%
tr 1162791/s 305%   --
$