Actually, what might serve the OP's purpose is Named backreferences, a new feature of 5.10. For example, to primitively rearrange a date:

$date = '8/1/2008';
$date =~ s!(?<month>\d{1,2})/(?<day>\d{1,2})/(?<year>\d{4})!$+{year}-$
++{month}-$+{day}!;
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This allows you to attach a name to a backreference like (?<name>pattern) that can be used within the match as \g{name} and anywhere else (in the replace or outside of the regex) as part of the hash %+. Keep in mind though, just because its a shiny new feature doesn't mean you have to use it. First figure out if its the best tool for the job :)

Disclaimer: Of course, the example above is a quick and dirty example, and as such should never be used. It was only meant to illustrate the feature noted.

Update: Ah, perhaps I did misunderstand the original question after all.