- make all files lower case in a directory tree (remove -type f to rename dirs as well)
for file in `find . -type f`; do mv $file `echo $file | tr [A-Z] [a-z]`; done;
- bulk rename file extension - there might be a simpler way to do this but this one is quite general
ls *.gif.bak|perl -ne 'm/((.*)\.bak)/;rename$1,"$2"'