Padding a number in a filename to a fixed length

Question

I have a directory of files such as:

file.1.png
file.2.png
…
file.10.png
…
file.1000.png
file.1001.png
…

How can I pad the number to 4 digits? It should end up like this:

file.0001.png
file.0002.png
…
file.0010.png
…
file.1000.png
file.1001.png
…

Answer 1

This will also work:

for f in *.png; do
    int=`basename $f .png | cut -d '.' -f 2`
    new_name=`printf "file.%0.4i.png\n" $int`
    [ ! -f $new_name ] && mv $f $new_name
done

Answer 2

Try the following:

for f in *.png
do
   foo='0000'${f#file.} #remove "file." and prepend 0000
   foo=${foo:(-8)} #last eight characters
   echo mv $f file.$foo   
done

Remove the echo if you are happy with the output.

Answer 3

If you have the rename command from the Perl package (as opposed to the one from the util-linux package):

rename 's/(\d+)/sprintf"%04d",$1/ge' file.*.png

Alternative based on glenn jackman' comment, which suggests a portable solution involving Perl. As Perl has its own rename function, there is no more need for the external mv:

ls -1 file.*.png | perl -ne 'chomp;($n=$_)=~s/(\d+)/sprintf"%04d",$1/ge;rename$_,$n'

That code is easier to enhance to reproduce the extras added by the rename external command: skip if the new file name is identical with the old one and skip if there is already a file with the new name:

ls -1 | perl -ne 'chomp;($n=$_)=~s/(\d+)/sprintf"%04d",$1/ge;rename$_,$n if$_ ne$n&&!-f$n'

With some adaptation, a loop-less solution can be achieved even with Sed:

ls -1 file.*.png | sed -r '/[0-9]{4}/d;h;:p;/[0-9]{4}/!s/([0-9]{1,3})/0\1/;tp;G;s/(.+)\n(.+)/mv \2 \1/' | sh

Answer 4

A simple trick if you want a simple, portable script is to start counting at 10001 and strip the initial digit.

for x in file.*.png; do
  n=${x%.*}; n=${n##*.}
  n=$((n + 10000))
  mv "$x" "${x%.*.*}.${n#1}.${x##*.}"
done

With zsh, using zmv and the l parameter expansion flag:

setopt extended_glob
autoload zmv
zmv '(file).([0-9]##).(png)' '$1.${(l:4::0:)2}.$3'

Answer 5

There are already quite a few answers here, but I thought I'd throw up a simple one

rename 'file.' 'file.000' file.?.png
rename 'file.' 'file.00' file.??.png
rename 'file.' 'file.0' file.???.png

The rename utility comes standard on every distro I know of. Its not as fancy as some of the other solutions here, but simple is easy to remember.

The first line takes file.1.png and converts it to file.0001.png.
The second converts file.10.png to file.0010.png, and the third does file.100.png to file.0100.png.
The 4 digit ones are already done.