use Regexp::MatchContext -vars;

    $str = m/(?p) \d+ /;

    print "Before:  $PREMATCH\n";
    print "Matched: $MATCH\n";
    print "After:   $POSTMATCH\n";

    $MATCH = 2 * $MATCH;    # substitute into original $str

##</code><code>##

              Rate     regex   context  at_minus matchvars
regex      17271/s        --      -22%      -66%      -84%
context    22239/s       29%        --      -56%      -79%
at_minus   50420/s      192%      127%        --      -53%
matchvars 107527/s      523%      384%      113%        --

##</code><code>##

            Rate    regex  context at_minus
regex    17544/s       --     -24%     -69%
context  23112/s      32%       --     -60%
at_minus 57361/s     227%     148%       --

##</code><code>##

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

my $count   = 300000;
# to test that all solutions produce the same output
my $VERBOSE = 0;
$count = 2 if $VERBOSE;

my $seq
    = 'GGGTTGAAGTTTAGACCGCTCACAGTAGTTCTACCTATAGAAAAGATCATGAAAGAGGCGATCAGAATGGTACTCGAATCCATTTACGATCCCGAGTTTCCAGACACATCGCATTTCCGCTCGGGTCAAGGCTGCCACTCGGTCCTAAGACGGATCAAAGAAGAGTGGGGAATCTCTCGCTGGTTTTTAGAATTCGACATCAGGAAGTGTTTTCACACCATCGACCGACATCGACTCATCCAAATTTTGAAGGAAGAGATCGACGATCCCAAGTTCTTTTACTCCATTCAGAAAGTATTTTCCGCCGGACGACTCGTAGGAGTTGAGAGGGGCCCTTACTCCGTCCCACACAGTGTACTACTATCGGCCCTACCAGGCAACATCTACCTACACAAGCTCGATCAGGAGATAGGGAGGATCCGACAGAAGTACGAAATTCCGATTGTTCAGAGAGTCAGATCGGTTCTATTAAGGACAGGTCGTCGTATTGATGACCAAGAAAACCCTGGAGAAGAAGCAAGCTTCAACGCTCCCCAAGACAACAGAGCCATCATTGTGGGGAGCGTTAAGAGCATGCAACGCAAAGCGGCCTTTCATTCCCTTGTTTCGTCGTGGCACACCCCCCCCACAAGCACCCTCCGGCTCAGGGGGGACCAGAAAAGGCCTTTCGTTTTCCCCCCTTCGTCGGCCCTTGCCGTCTTCCTTAACAAGCCCTCGAGCCTTCTTTGCGCCGCCTTCCTCATAGAAGCCGCCGGGTTGACCCCGAAGGCTGAATTCTATGGTGGAGAACGCTGTAATAATAATTGGGCCATGAGAGACCTTCTTAAGTATTGCAAAAGAAAGGGCCTGCTGATAGAGCTGGGCGGGGAGGCGATACTAGTTATCAGGTCAGAGAGAGGCCTGGCCCGTAAGCAGGCCCCCTTAAAAACCCATTACTTAATAAGGATTTGTTACGCGCGATATGCCGACGACTTACTACTGGGAATCGTGGGTGCCGTAGAGCTTCTCATAGAAATACAAAAACGTATCGCCCATTTCCTACAATCTGGCCTGAACCTTTGGGTAGGCTCCGCAGGATCAACAACAATAGCTGCACGGAGTACGGTAGAATTCCTTGGTACGGTCATTCGGGAAGTCCCTCCGAGGACGACTCCCATACAATTTTTGCGAGAGCTGGAAAAGCGTCTACGGGTAAAGCACCGTATCCATATAACTGCTTGCCACCTACGCTCCGCCATCCATTCAAAGTTTAGGAACCTAGGTGATAGTATCCCGATCAAACAGCTGACGAAGGGGATGAGCAAAACAGGGAGTCTACAGGACGGGGTTCAACTAGCGGAGACTCTTGGAACAGCTGGAGTCAGAAGTCCCCAAGTTAGCGTATTATGGGGGACCGTCAAGCACATCCGGCAAGGATCAAGGGGGATCTCGTTCTTGCATAGCTCAGGTCGGAGCAACGCGTCATCGGACGTTCAACAGGTAGTCTCACGATCGGGCACTCATGCCCGTAAGTTGTCATTGTATACTCCCCCGGGTCGGAAGGCGGCGGGGGAGGGAGGAGGACACTGGGCGGGATCTATCAGCAGCGAATTCCCCATAAAGATAGAGGCACCTATAAAAAAGATACTCCGAAGGCTTCGGGATCGAGGTATCATTAGCCGAAGAAGACCCTGGCCAATCCACGTGGCCTGTTTGACGAACGTCAGCGACGAAGACATCGTAAATTGGTCCGCGGGCATCGCGATAAGTCCTCTGTCCTACTACAGGTGCCGCGACAACCTTTATCAAGTCCGAACGATTGTCGACCACCAGATTCGCTGGTCTGCAATATTCACCCTAGCCCACAAGCACAAATCCTCGGCGCCGAATATAATCCTCAAGTACTCCAAAGACTCAAATATTGTAAATCAAGAAGGTGGCAAGATCCTTGCAGAGTTCCCCAACAGCATAGAGCTTGGGAAGCTCGGACCCGGTCAAGACCTGAACAAGAAGGAACACTCAACTACTAGTCTAGTCTAG';

cmpthese(
    $count,
    {   'regex' => sub {
            my ( $prematch, $match, $postmatch )
                = $seq =~ m{(\A .*?) (CTGGCCCGTAA) (.*\z) }xms;
            warn "$prematch   $match   $postmatch" if $VERBOSE;
        },
        'matchvars' => sub {
            $seq =~ m{CTGGCCCGTAA}xms;
            my ($prematch, $match, $postmatch) = ($`, $&, $');
            warn "$prematch   $match   $postmatch" if $VERBOSE;
        },
        'context' => sub {
            $seq =~ m{(?p)CTGGCCCGTAA}xms;
            my ( $prematch, $match, $postmatch )
                = ( PREMATCH(), MATCH(), POSTMATCH() );
            warn "$prematch   $match   $postmatch" if $VERBOSE;
        },
        'at_minus' => sub {
            $seq =~ m{CTGGCCCGTAA}xms;
            my $prematch = substr( $seq, 0, $-[0] );
            my $match = substr( $seq, $-[$#-], $+[$#-] - $-[$#-] );
            my $postmatch = substr( $seq, $+[$#+] );
            warn "$prematch   $match   $postmatch" if $VERBOSE;
        },
    }
);