#!/usr/bin/perl 
use strict;
use warnings;
use File::Find;
use Benchmark qw(:all) ;

sub sub1 {
    my %addresses;

    open my $fh, '<test.eml' or die;
    while (<$fh>) {
        last if $_ eq "\n"; # only scan headers
        $_ = lc $_;

        if (/\b(johnqp\@mailserver\.com)/xms) {
            my $addr = $1;
            $addresses{$addr}++;
        }

    }
    close $fh;
}


sub sub2 {
    my %addresses;

    open my $fh, '<test.eml' or die;
    while (<$fh>) {
        last if $_ eq "\n"; # only scan headers
        $_ = lc $_;

        if (/\b(johnqp\@mailserver\.com)/) {
            my $addr = $1;
            $addresses{$addr}++;
        }

    }
    close $fh;
}

sub sub3 {
    my %addresses;

    open my $fh, '<test.eml' or die;
    local $/ = '';
    $_ = <$fh>;
        if (/^(?:To|Cc):.+(johnqp\@mailserver\.com)/mi) {
        my $addr = $1;
        $addresses{$addr}++;
    }
    close $fh;
}


sub sub4 {
    my %addresses;

    open my $fh, '<test.eml' or die;
    local $/ = '';
    $_ = <$fh>;
        if (/^(?:To|Cc):.+(johnqp\@mailserver\.com)/xsmi) {
        my $addr = $1;
        $addresses{$addr}++;
    }
    close $fh;
}


cmpthese(100000, {
    'Linewise'  => \&sub1,
    'Line no /xms'  => \&sub2,
    'Blockwise' => \&sub3,
    'Block /xms' => \&sub4,
});

<STDIN>;

__END__

               Rate Line no /xms     Linewise   Block /xms    Blockwise
Linewise     3256/s          11%           --         -22%         -24%
Line no /xms 2946/s           --         -10%         -30%         -31%
Blockwise    4282/s          45%          32%           2%           --
Block /xms   4198/s          43%          29%           --          -2%