use warnings;
use strict;
use Benchmark qw/:all/;

my $code = q{this is_++ meant to 0_be some_sample program $__code
             for testing whether the regex is(__0K__) ._._._};

cmpthese(-1, {
    'split' => q{ grep { /_/ } split /[^\w_]/, $code        },
    'grep'  => q{ grep { /_/ } $code =~ /[a-zA-Z_][\w_]*/g  },
    'regex' => q{ $code =~ /_[\w_]* | [a-zA-Z]\w*_\w*/gx    },
});

my @words = $code =~ /_[\w_]* | [a-zA-Z]\w*_\w*/gx;
print "\nWords: ", join(', ', @words);