use strict;
use Benchmark qw(cmpthese);

my $foo = "abcdefghijklmnopqrstuvwxyz"x500;
my $re = "[Aa][Bb][Cc]";

cmpthese(1000000, {
  'i'       => sub { $foo =~ /abc/ig },
  'chars'   => sub { $foo =~ /[Aa][Bb][Cc]/og },
  'charvar' => sub { $foo =~ /$re/og },
});