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

In my debian it works well with rename, tested with 300 files.

 perl -e 'map `touch door$_.txt`, 1..300;'
 rename 's/(\d+)\.txt/sprintf("%03d.txt", $1)/e' *.txt