#!/usr/bin/perl -w
use strict;
use Benchmark qw(timethese);

my $repeat = 10;
my $text = ('abc' x $repeat) . 'gotcha' . ('xyz' x $repeat);

my ($pre,$match,$post);

print "OS: $^O - Perl: $]\n";

timethese( 100000, {
    'unpack' => sub {
            if ($text =~ /gotcha/) {
                $pre = prematch($text);
                $post = postmatch($text);
                $match = match($text);
            }
        },
    'substr' => sub {
            if ($text =~ /gotcha/) {
                $pre = substr_prematch($text);
                $post = substr_postmatch($text);
                $match = substr_match($text);
            }
        },
    }
);

if ($text =~ /gotcha/) {
    print "unpack\n";
    print "prematch  :", prematch($text), "\n";
    print "match     :", match($text), "\n";
    print "postmatch :", postmatch($text), "\n";

    print "substring\n";
    print "prematch  :", substr_prematch($text), "\n";
    print "match     :", substr_match($text), "\n";
    print "postmatch :", substr_postmatch($text), "\n";
}

sub prematch {
    return unpack "a$-[0]", $_[0];
}

sub postmatch {
    return unpack "x$+[0] a*", $_[0];
}

sub match {
    my $len = $+[0] - $-[0];
    unpack "x$-[0] a$len", $_[0];
}

sub substr_match {
    substr( $_[0], $-[0], $+[0] - $-[0] )
}

sub substr_prematch {
    substr( $_[0], 0, $-[0] )
}

sub substr_postmatch {
    substr( $_[0],  $+[0] )
}
__END__
(output edited to fit the page better)

OS: cygwin - Perl: 5.008
Benchmark: timing 100000 iterations of substr, unpack...
    substr:  2 wallclock secs ( 1.92 usr +  0.00 sys =  1.92 CPU)
    unpack: 11 wallclock secs (11.89 usr +  0.00 sys = 11.89 CPU)
unpack
prematch  :abcabcabcabcabcabcabcabcabcabc
match     :gotcha
postmatch :xyzxyzxyzxyzxyzxyzxyzxyzxyzxyz
substring
prematch  :abcabcabcabcabcabcabcabcabcabc
match     :gotcha
postmatch :xyzxyzxyzxyzxyzxyzxyzxyzxyzxyz

OS: MSWin32 - Perl: 5.006001
Benchmark: timing 100000 iterations of substr, unpack...
    substr:  3 wallclock secs ( 1.93 usr +  0.00 sys =  1.93 CPU)
    unpack:  4 wallclock secs ( 3.87 usr +  0.00 sys =  3.87 CPU)
unpack

OS: linux - Perl: 5.006001
Benchmark: timing 100000 iterations of substr, unpack...
    substr:  2 wallclock secs ( 2.26 usr +  0.00 sys =  2.26 CPU)
    unpack:  4 wallclock secs ( 3.90 usr +  0.00 sys =  3.90 CPU)
unpack

##</code><code>##

sub prematch {
    unpack sprintf("a%d",$-[0]), $_[0];
}

sub postmatch {
    unpack sprintf( "x%d a*", $+[0]) , $_[0];
}

sub match {
    unpack sprintf ("x%d a%d", $-[0], $+[0] - $-[0] ), $_[0];
}