$text = 'ab';
if ($text =~ /(a*)((?:ab)*|b*)/) {
	print "'$1', '$2' \n";
}
if ($text =~ /(a*)(b*|(?:ab)*)/) {
	print "'$1', '$2' \n";
}

##</code><code>##

'a', ''
'a', 'b'