mv oldname newname.
But what about when you have 200 *.JPEG files and you need to rename them to be *.jpg? In the past I've written throwaway PHP scripts to do just this. Well, it turns out linux has a command called
rename, that can use regexes. To rename those jpegs:
rename 's/JPEG/jpg/' *.JPEG
What about a few thousand log files, and I want to remove the datestamp portion from the filename (because I'm going to keep each day's logs in their own subdirectory)? How about this:
mkdir 20110203 mv *.20110203.log 20110203/ rename 's/.20110203//' 20110203/*
(See here for how to then use a bash loop to loop through all the datestamps you have to deal with.)