How to zero pad numbers in file names in Bash?

In case N is not a priori fixed:

for f in foo[0-9]*; do
  mv "$f" "$(printf 'foo%05d' "${f#foo}")"
done

Pure Bash, no external processes other than 'mv':

for file in foo*; do
  newnumber='00000'${file#foo}      # get number, pack with zeros
  newnumber=${newnumber:(-5)}       # the last five characters
  mv $file foo$newnumber            # rename
done

It's not pure bash, but much easier with the Perl version of rename:

rename 's/\d+/sprintf("%05d",$&)/e' foo*

Where 's/\d+/sprintf("%05d",$&)/e' is the Perl replace regular expression.

• \d+ will match the first set of numbers (at least one number)
• sprintf("%05d",$&) will pass the matched numbers to Perl's sprintf, and %05d will pad to five digits

I had a more complex case where the file names had a postfix as well as a prefix. I also needed to perform a subtraction on the number from the filename.

For example, I wanted foo56.png to become foo00000055.png.

I hope this helps if you're doing something more complex.

#!/bin/bash

prefix="foo"
postfix=".png"
targetDir="../newframes"
paddingLength=8

for file in ${prefix}[0-9]*${postfix}; do
  # strip the prefix off the file name
  postfile=${file#$prefix}
  # strip the postfix off the file name
  number=${postfile%$postfix}
  # subtract 1 from the resulting number
  i=$((number-1))
  # copy to a new name with padded zeros in a new folder
  cp ${file} "$targetDir"/$(printf $prefix%0${paddingLength}d$postfix $i)
done