I've tried a bunch of examples of the rename command but I can't figure out the syntax to do what I want.

I have a bunch of files labeled something like


I want to change only some of them by inserting a 0 so that the file names have the same number of characters.

So I want File_Ex_1.jpg to go to File_Ex_01.jpg, File_Ex_2.jpg to File_Ex_02.jpg

How do you do this with the rename command?

This rename command was installed via home-brew on a Mac. Output of rename -v:

rename -v
    rename [switches|transforms] [files]


    -0/--null (when reading from STDIN)
    -f/--force or -i/--interactive (proceed or prompt when overwriting)
Wide character in print at /System/Library/Perl/5.18/Pod/Text.pm line 286.

    -g/--glob (expand "*" etc. in filenames, useful in Windows™ CMD.EXE)
    -l/--symlink or -L/--hardlink

    Transforms, applied sequentially:

    -s/--subst *from* *to*
    -S/--subst-all *from* *to*
    --camelcase --urlesc --nows --rews --noctrl --nometa --trim (see manual)

Try with this:

rename -e 's/\d+/sprintf("%02d",$&)/e' -- *.jpg


$ ls
Device_Ex_10.jpg  Device_Ex_1.jpg  Device_Ex_4.jpg  Device_Ex_7.jpg
Device_Ex_11.jpg  Device_Ex_2.jpg  Device_Ex_5.jpg  Device_Ex_8.jpg
Device_Ex_12.jpg  Device_Ex_3.jpg  Device_Ex_6.jpg  Device_Ex_9.jpg
$ rename -e 's/\d+/sprintf("%02d",$&)/e' -- *.jpg
$ ls
Device_Ex_01.jpg  Device_Ex_04.jpg  Device_Ex_07.jpg  Device_Ex_10.jpg
Device_Ex_02.jpg  Device_Ex_05.jpg  Device_Ex_08.jpg  Device_Ex_11.jpg
Device_Ex_03.jpg  Device_Ex_06.jpg  Device_Ex_09.jpg  Device_Ex_12.jpg

I took the reference from here: https://stackoverflow.com/questions/5417979/batch-rename-sequential-files-by-padding-with-zeroes

Here adapted to your particular rename implementation.

  • This looks like a proper call for the Perl-based version of rename, which the asker doesn't appear to have. – dhag Feb 22 '17 at 21:20
  • Is there a good reference to explain what these commands mean? Like what the + sign does. This is close, except I guess the real format for my filenames is Device1_Ex_1.jpg Where this syntax would turn that into Device01_Ex_1.jpg and not Device1_Ex_01.jpg – toombzie Feb 22 '17 at 21:21
  • 1
    @dhag The asker definitely has a Perl-based version, both because they aren't running Linux so they don't have the util-linux rename, and because the output of rename -v explicitly mentions Perl. – Gilles Feb 22 '17 at 22:24
  • 1
    Yes, OK, my wording was terrible. I should have said "the version that accepts a Perl expression as one of its parameters". This still looks like a wrong answer, doesn't it? – dhag Feb 22 '17 at 22:44
  • Interestingly, while this appears to contradict the help text which, if I understand correctly, requires -e before the Perl code, this call actually works with the rename utility that comes with macOS. I retract my initial comment. – dhag Feb 23 '17 at 14:04

With the version of rename that you seem to be using, the following expression should do the transformation you request (exammple with a directory containing files named File_Ex_{1..11}.jpg):

$ rename -n -e 's/_(\d\.)/_0$1/g' -- *.jpg
'File_Ex_1.jpg' would be renamed to 'File_Ex_01.jpg'
'File_Ex_2.jpg' would be renamed to 'File_Ex_02.jpg'
'File_Ex_3.jpg' would be renamed to 'File_Ex_03.jpg'
'File_Ex_4.jpg' would be renamed to 'File_Ex_04.jpg'
'File_Ex_5.jpg' would be renamed to 'File_Ex_05.jpg'
'File_Ex_6.jpg' would be renamed to 'File_Ex_06.jpg'
'File_Ex_7.jpg' would be renamed to 'File_Ex_07.jpg'
'File_Ex_8.jpg' would be renamed to 'File_Ex_08.jpg'
'File_Ex_9.jpg' would be renamed to 'File_Ex_09.jpg'

(Remove flag -n to actually do the renaming.)

The argument to -e is a Perl search-and-replace expression; where _(\d\.) matches am underscore followed by a single digit and then a dot, and replaces the underscore with _0, thus inserting a leading zero. $1 is a back-reference to the group within parentheses, the digit and dot, and leaves it unchanged in the new file name.


While it can be done with prename command, I would like to provide a python alternative to that:

$ ls
File_Ex_1.jpg  File_Ex_2.jpg  File_Ex_3.jpg  File_Ex_4.jpg

$ ./pad_zeros.py *                                                                                                       

$ ls
File_Ex_01.jpg  File_Ex_02.jpg  File_Ex_03.jpg  File_Ex_04.jpg  pad_zeros.py*

The pad_zeros.py script is simple:

#!/usr/bin/env python
import sys,os,re

for file in sys.argv[1:]:
    if __file__ in file: continue
    words = re.split('_|\.',file)
    words[-2] = words[-2].zfill(2)
    new_name = "_".join(words[:-1]) + "." + words[-1]

It takes arguments on command-line, iterates over them, and pads zeros using .zfill() command(in this particular case to two characters). Since we're operating on all files in the same folder, glob-star can be used.

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