'vanilla' => sub {
            if ($text =~ /gotcha/) {
                $pre = $`;
                $post = $';
                $match = $&;
            }
        },
    }

##</code><code>##

    print "vanilla\n";
    print "prematch  :", $`, "\n";
    print "match     :", $&, "\n";
    print "postmatch :", $', "\n";

##</code><code>##

Benchmark: timing 500000 iterations of substr, unpack, vanilla...
substr:  5 wallclock secs <snip> @ 106678.05/s
unpack:  8 wallclock secs <snip> @ 54241.70/s
vanilla: 0 wallclock secs <snip> @ 492125.98/s

##</code><code>##

my ($i, $j, $k);
for ('a' .. 'z', 'A' .. 'Z') {
  $i++ if $text2 =~ /$_/;
}
$j++ if $text3 =~ /quux/;
$k++ if $text4 =~ /H/;

##</code><code>##

substr: 25 wallclock secs ...
unpack: 26 wallclock secs ...
vanilla: 26 wallclock secs ...

##</code><code>##

use strict;
use warnings;
use Benchmark qw(timethese);

open OUT, '>', 'temp.txt' or die "can't open $!";
select OUT;

my $repeat = 10;
my $text = ('abc' x $repeat) . 'gotcha' . ('xyz' x $repeat);
my $text2 = 'Fork over rice before serving';
my $text3 = 'foo bar baz quux';
my $text4 = 'Just Another Perl hacker';

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);
      }
      my ($i, $j, $k);
      for ('a' .. 'z', 'A' .. 'Z') {
         $i++ if $text2 =~ /$_/;
      }
      $j++ if $text3 =~ /quux/;
      $k++ if $text4 =~ /H/;
   },
   'substr' => sub {
      if ($text =~ /gotcha/) {
         $pre = substr_prematch($text);
         $post = substr_postmatch($text);
         $match = substr_match($text);
      }
      my ($i, $j, $k);
      for ('a' .. 'z', 'A' .. 'Z') {
         $i++ if $text2 =~ /$_/;
      }
      $j++ if $text3 =~ /quux/;
      $k++ if $text4 =~ /H/;
   },
   'vanilla' => sub {
      if ($text =~ /gotcha/) {
         $pre = $`;
         $post = $';
         $match = $&;
      }
      my ($i, $j, $k);
      for ('a' .. 'z', 'A' .. 'Z') {
         $i++ if $text2 =~ /$_/;
      }
      $j++ if $text3 =~ /quux/;
      $k++ if $text4 =~ /H/;
   },
 }
);

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";

    print "vanilla\n";
    print "prematch  :", $`, "\n";
    print "match     :", $&, "\n";
    print "postmatch :", $', "\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] )
}