How to batch rename files in a terminal?

I want to rename the files in a directory to sequential numbers.

stars_01_012.png
stars_01_014.png
stars_01_015.png
stars_01_017.png
stars_02_012.png
stars_02_014.png
stars_02_015.png
stars_02_017.png

And change it into

stars_01_001.png
stars_01_002.png
stars_01_003.png
stars_01_004.png
stars_02_001.png
stars_02_002.png
stars_02_003.png
stars_02_004.png

Relatives but not completely: How to Batch Rename Files in a macOS Terminal? How can I batch rename files using the Terminal?

Solution

You can do it with rename which you can install on macOS with homebrew using:

brew install rename

The command then looks like this:

rename --dry-run -X -e 'my @parts=split /_/; my $this=$parts[0].$parts[1]; if(!defined($ENV{previous}) || $this ne $ENV{previous}){$ENV{previous}=$this; $ENV{N}=0}; $ENV{N}=$ENV{N}+1; $_ = $parts[0]."_".$parts[1]."_".$ENV{N}' *png

Sample Output

'stars_01_012.png' would be renamed to 'stars_01_1.png'
'stars_01_014.png' would be renamed to 'stars_01_2.png'
'stars_01_015.png' would be renamed to 'stars_01_3.png'
'stars_01_017.png' would be renamed to 'stars_01_4.png'
'stars_02_012.png' would be renamed to 'stars_02_1.png'
'stars_02_014.png' would be renamed to 'stars_02_2.png'
'stars_02_015.png' would be renamed to 'stars_02_3.png'
'stars_02_017.png' would be renamed to 'stars_02_4.png'
'stars_88_099.png' would be renamed to 'stars_88_1.png'

Explanation:

my @parts=split /_/ splits the filename into 3 parts using the underscore as the separator,

my $this=$parts[0].$parts[1] saves the first two parts simply concatenated together, e.g. "stars01",

the if statement tests if either of the first two parts have changed, then

$ENV{previous}=$this; $ENV{N}=0 saves the current stem of the filename in an environment variable called previous and the current sequential counter in another environment variable N,

$ENV{N}=$ENV{N}+1 increments the sequential counter, and

$_ = $parts[0]."_".$parts[1]."_".$ENV{N} creates the new output filename from the various parts.

If that all looks correct, remove the --dry-run and run it again - probably in a spare directory with a copy of your files until you are sure all is ok :-)

The above may be easier to read like this:

#!/bin/bash

rename --dry-run -X -e '
      my @parts=split /_/;                      # split filename into parts based on underscore
      my $this=$parts[0].$parts[1];             # save first two parts of filename in $this
                                                # see if it is a new stem
      if(!defined($ENV{previous}) || $this ne $ENV{previous}){
         $ENV{previous}=$this; $ENV{N}=0};      # save new initial part, reset N
      $ENV{N}=$ENV{N}+1;                        # increment N
      $_ = $parts[0]."_".$parts[1]."_".$ENV{N}  # formulate new filename from parts
    ' *png

Change the last line to the following if you want to zero-pad the numbers out to three digits:

  $_ = sprintf("%s_%s_%03d",$parts[0],$parts[1],$ENV{N})  # formulate new filename from parts

Note:

I save the previous file prefix and sequential counter into environment variables to preserve them between files - there may be easier ways - if anyone knows, please ping me! Thanks.