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

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

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

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

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

use strict;
use warnings;
use Benchmark qw(timethese);
...
sub substr_postmatch {
    substr( $_[0],  $+[0] )
}