#!/usr/bin/perl 
use strict;
use warnings;
use Benchmark qw( cmpthese );

my $line = ('a' x 500) . 'b!' . ('a' x 20);


cmpthese -10, {
    literal     => sub {$line =~    /a.{1,10}b!/ },
    literal_exp => sub {$line =~    /a(?>.{1,10})b!/ },
    literal_look => sub {$line =~   /a(?>.{1,10})(?<=b!)/ },
    class       => sub {$line =~  / [a]    .{1,10}  [b] [!] /x},
    class_exp   => sub {$line =~   / a     .{1,10}   b  [!] /x},
    class_back  => sub {$line =~   / a (?> .{1,10} ) b  [!] /x},
    class_back_look  => sub {$line =~  /  a (?> .{1,10} ) (?<=b[!]) /x},
    class_b  => sub {$line =~          /  a     .{1,10}   (?<=b[!]) /x},
};