Oh, extracted numbers! Sure. I never use -e on sed, just pile the lines on the command line, but with pretty spacing, sed on sed lines and shell on shell lines. You, too, deserve readable code and a lower error rate!

Still a lot of mv fork() and exec(), so PERL might have an advantage, assuming it knows how to rewrite directories internally. In C or PERL, you link() the file to the new name and unlink() it from the old name.

BTW, directories never shrink, so making new directories is not a bad idea. Big directories can waste a lot of time.