in reply to one liner to rename multiple files in a directory?

I don't know how to do it with a Perl one-liner, but I have been using this script for years: ren-regexp

It uses Perl regular expression syntax. This will work for your 1st example (to get rid of arbitrary leading crap): 

ren-regexp 's/^.*(Episode.*\.avi)/$1/' *Episode*.avi

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In Section Seekers of Perl Wisdom