#!/usr/bin/env perl

use 5.010;
use strict;
use warnings;

say "Perl Version: $^V";

my $test_string = 'www xxx-A-B-C-D yyy zzz-E-F-G-H';
my $re = qr< \S+ (?: [A-Z]- ){2,} [A-Z] \b >x;

say '=' x 60, "\n*** NO look-ahead ***\n", '=' x 60;
my $no_look_ahead_test_string = $test_string;

while ($no_look_ahead_test_string =~ /($re)/gp) {
    say "Prematch:  '${^PREMATCH}'";
    say "Match:     '${^MATCH}'";
    say "Postmatch: '${^POSTMATCH}'";
    say '-' x 60;
}

say '=' x 60, "\n*** USING look-ahead ***\n", '=' x 60;
my $look_ahead_test_string = $test_string;

while ($look_ahead_test_string =~ /(?=$re)/gp) {
    say "Prematch:  '${^PREMATCH}'";
    say "Match:     '${^MATCH}'";
    say "Postmatch: '${^POSTMATCH}'";
    say '-' x 60;
}

##</code><code>##

Perl Version: v5.12.3
============================================================
*** NO look-ahead ***
============================================================
Prematch:  'www '
Match:     'xxx-A-B-C-D'
Postmatch: ' yyy zzz-E-F-G-H'
------------------------------------------------------------
Prematch:  'www xxx-A-B-C-D yyy '
Match:     'zzz-E-F-G-H'
Postmatch: ''
------------------------------------------------------------
============================================================
*** USING look-ahead ***
============================================================
Prematch:  'www '
Match:     ''
Postmatch: 'xxx-A-B-C-D yyy zzz-E-F-G-H'
------------------------------------------------------------
Prematch:  'www xxx-A-B-C-D yyy '
Match:     ''
Postmatch: 'zzz-E-F-G-H'
------------------------------------------------------------

##</code><code>##

Perl Version: v5.14.2
============================================================
*** NO look-ahead ***
============================================================
Prematch:  'www '
Match:     'xxx-A-B-C-D'
Postmatch: ' yyy zzz-E-F-G-H'
------------------------------------------------------------
Prematch:  'www xxx-A-B-C-D yyy '
Match:     'zzz-E-F-G-H'
Postmatch: ''
------------------------------------------------------------
============================================================
*** USING look-ahead ***
============================================================
Prematch:  'www '
Match:     ''
Postmatch: 'xxx-A-B-C-D yyy zzz-E-F-G-H'
------------------------------------------------------------
Prematch:  'www x'
Match:     ''
Postmatch: 'xx-A-B-C-D yyy zzz-E-F-G-H'
------------------------------------------------------------
Prematch:  'www xx'
Match:     ''
Postmatch: 'x-A-B-C-D yyy zzz-E-F-G-H'
------------------------------------------------------------
Prematch:  'www xxx'
Match:     ''
Postmatch: '-A-B-C-D yyy zzz-E-F-G-H'
------------------------------------------------------------
Prematch:  'www xxx-'
Match:     ''
Postmatch: 'A-B-C-D yyy zzz-E-F-G-H'
------------------------------------------------------------
Prematch:  'www xxx-A'
Match:     ''
Postmatch: '-B-C-D yyy zzz-E-F-G-H'
------------------------------------------------------------
Prematch:  'www xxx-A-B-C-D yyy '
Match:     ''
Postmatch: 'zzz-E-F-G-H'
------------------------------------------------------------
Prematch:  'www xxx-A-B-C-D yyy z'
Match:     ''
Postmatch: 'zz-E-F-G-H'
------------------------------------------------------------
Prematch:  'www xxx-A-B-C-D yyy zz'
Match:     ''
Postmatch: 'z-E-F-G-H'
------------------------------------------------------------
Prematch:  'www xxx-A-B-C-D yyy zzz'
Match:     ''
Postmatch: '-E-F-G-H'
------------------------------------------------------------
Prematch:  'www xxx-A-B-C-D yyy zzz-'
Match:     ''
Postmatch: 'E-F-G-H'
------------------------------------------------------------
Prematch:  'www xxx-A-B-C-D yyy zzz-E'
Match:     ''
Postmatch: '-F-G-H'
------------------------------------------------------------