although the \G in your version isn't doing anything in this case. I believe (but am open to correction) that \G doesn't have any effect unless you also use the /c modifier and even then, it only has an effect once a failure has occurred in which case, a subsequent match on the same target string will start from the point of the previous failure.

then let me correct ;-)

The '\G' forces the next match to start where the last ended. When the regex is executed the first time, '\G' is thus equivalent to '\A' (beginning of string). The next matches (due to the /g modifier) have to start where the previous one ended, so no part of the string can be skipped. This sure makes a difference, see the examples below.

sub test_regex {
    local $_ = shift;
    local $\ = "\n";

    print 'string:     ', $_, ;
    print 'with \G:    ', join(':', m/\G ( [0-9A-Z]{1,2} ) (?: :|$ ) /
+igx);
    print 'without \G: ', join(':', m/   ( [0-9A-Z]{1,2} ) (?: :|$ ) /
+igx), "\n";
}

test_regex('0:0A:0C:B:B8:F');
test_regex('#0:0A:0C:B:B8:F');
test_regex('0: 0A:0C:B:B8:F');
test_regex('0:0Aa:0C:B:B8:F');
[download]

-- Hofmator