I have a folder with a lot of files that need to have their names edited. The original format is ABC%20DEF%20GHI%20JKL.xyz. What I need to do is to replace each "%20" with "_". I would rather run a script than download a program if possible. Unfortunately I have very little experience when it comes to using the command line, but would like to learn. Any good recommendation on where to start(website, books etc)?