perlvar:

               $` is the same as "substr($var, 0, $-[0])"
               $& is the same as "substr($var, $-[0], $+[0] - $-[0])"
               $' is the same as "substr($var, $+[0])"
[download]

So:

sub  prematch (;$) { substr((@_ ? $_[0] : $_), 0, $-[0]) }
sub     match (;$) { substr((@_ ? $_[0] : $_), $-[0], $+[0] - $-[0]) }
sub postmatch (;$) { substr((@_ ? $_[0] : $_), $+[0]) }

my $foo = 'Hello, world!';
$foo =~ /o, w../;

$\ = "\n";
print  prematch($foo);
print     match($foo);
print postmatch($foo);

=head2 C<prematch>, C<match>, C<postmatch>

Like C<$`>, C<$&> and C<$'>, but not slowing down, and 
needing a single argument: the string on which the 
most recent regex was performed. Uses C<$_> when no
argument is given.

=cut
[download]

Update: s/the variable on which/the string on which/

- Yes, I reinvent wheels.
- Spam: Visit eurotraQ.