If you want a list of all two letter patterns that appear at least twice somewhere in your string, you need to make three changes to your regex.
- you need to make (\w{2,}) non-greedy by adding a "?" to the end, e.g. (\w{2,}?).
- you need to wrap what comes after (\w{2,}?) with a zero width lookahead group. Otherwise you will miss all the matches between the first and second occurrence of "ab"
- you need to handle repetitions of your regex slightly differently. Instead of /( mumblefoo )+/ you need /mumblefoo/g. Using a + the way you did will only get you the last match found because each time the + causes the regex to repeat, it replaces the previous match.
Taken together these changes will make your regex will look like this: /(\w{2,}?)(?=.*?\1)/g:
print $x = "abcdefgxxabcdefgzzabcdsjfhkdfab", "\n";
print "<" . join('|',$x =~ /(\w{2,}?)(?=.*?\1)/g) , ">\n";
#outputs: <ab|cd|ef|ab|cd|ab>
You can more info on zerolength lookaheads via the Extended Patterns section of the perlre manpage on perldoc
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