sed - Unix: Search and replace in file names

Using sed, I can search and replace text in a file. Is there a way I can do search and replace of filenames? For example if I have a bunch of files in a folder with names like these:

• foo01


• foo02


• bar001


• bar002

I would like to quickly rename all of the ones starting with foo so that they have 3 digits instead of 2.

Answer

#!/bin/bash
shopt -s nullglob
for file in foo*
do
  filename=${file%%[0-9]*}
  num=${file##*[^0-9]}
  newnum=$(printf "%03d" $num)
  newfile=${filename}${newnum}
  mv "$file" "$newfile"
done