randomise filenames / reverse the randomisation

randomise.sh

#!/bin/bash

# Usage:
#   $0          # renames all mp3 files in $PWD by prefixing a random sequence number and a hyphen
#   $0 clean    # renames all mp3 files in $PWD by removing any leading digits and a hyphen

ext=mp3
# making this a parameter is left as an exercise for the reader

if [ "$1" = "clean" ]
then
    for i in *.$ext
    do
        [[ $i =~ ^[0-9]+-(.*) ]] || continue
        mv ${BASH_REMATCH[0]} ${BASH_REMATCH[1]}
    done
else
    seq -w 1 `ls *.$ext | wc -l` | shuf | paste - <(ls *.$ext) | while read seq name
    do
        mv $name "$seq-$name"
    done
fi

sample session with above script

$ ls
capkin.mp3  catted.mp3  educ.mp3  fender.mp3  imaged.mp3  Marut.mp3  MIF.mp3  oleins.mp3  unwig.mp3  Yvonne.mp3

$ /tmp/randomise-files.sh

$ ls
01-imaged.mp3  03-catted.mp3  05-MIF.mp3     07-Yvonne.mp3  09-educ.mp3
02-Marut.mp3   04-oleins.mp3  06-fender.mp3  08-capkin.mp3  10-unwig.mp3

$ /tmp/randomise-files.sh clean

$ ls
capkin.mp3  catted.mp3  educ.mp3  fender.mp3  imaged.mp3  Marut.mp3  MIF.mp3  oleins.mp3  unwig.mp3  Yvonne.mp3