my $str = 'xbaaaaaa' . ('_' x 20) . 'bcccccccccc';
my $start = $str =~ /a+/ ? $+[0] : 0;
my $end = $str =~ /b/ ? $-[0] : 0;

my $ext = substr $str, $start, $end - $start;
$, = " | "; $\ = "\n";
print $start, $end, $ext;

##</code><code>##

my $str = 'xbaaaaaa' . ('_' x 20) . 'bcccccccccc';
$str =~ /(?!)/g;   # A match that always fails, resetting pos()
my $start = $str =~ /a+/g ? $+[0] : 0;
my $end = $str =~ /b/g ? $-[0] : 0;

my $ext = substr $str, $start, $end - $start;
$, = " | "; $\ = "\n";
print $start, $end, $ext;