How can I easily bulk rename files with Perl?

Question

I have a lot of files I\'m trying to rename, I tried to make a regular expression to match them, but even that I got stuck on the files are named like:

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Answer 1

find . -type d -print0 | xargs -0 rename 's/(\d+)/sprintf "%03d", $1/e' 

or something like that, provided

1. You have GNU find and GNU xargs (for -print0 and -0)
2. You have the 'rename' utility that comes with perl
3. There's only one group of digits in the filename. If there's more than one, then you need to do something with the regex to make it only match the number you want to reformat.