Howto Linux rename multiple files at a shell prompt

Q. How do I rename rename multiple files at a shell prompt under Linux or UNIX?

A. Renaming multiple files at a shell prompt is always considered as a black art by many UNIX gurus.

To be frank if you understand regex then it is not a black art anymore. But what the hell regex is? A regular expression is a string that describes or matches a set of strings, according to certain syntax rules (see regex @ wikipedia for more information). Linux (and *BSD) comes with handy utility called rename. As a name suggest 'rename' renames the filenames supplied according to the rule specified (syntax):
rename "regex-rule" files

Rename command syntax

rename oldname newname *.files

For example rename all *.bak file as *.txt, enter:
$ rename .bak .txt *.bak

Linux rename multiple files - more examples

Let us see couple of practical examples:

A) Convert all mp3 filenames to more readable and usable format. Most of the time MP3 got multiple blank spaces, which my confuse many Linux utilities and mp3 players (before rename command):

$ ls 

Output:

06 -  Gorillaz - Feel Good Inc.mp3
DDR - Kung- Fu Fighting (bus stop).mp3
AXEL CRAZYFROG.mp3

Remove all blank space with rename command:
$ rename "s/ *//g" *.mp3
$ ls
Output:

06-Gorillaz-FeelGoodInc.mp3
DDR-Kung-FuFighting(busstop).mp3
AXEL-CRAZYFROG.mp3

Linux Shell script to rename files

Before rename command I was using following shell script to rename my mp3s:

#!/bin/bash
# To remove blank space
if [ $# -eq 0 ];
then
 echo "Syntax: $(basename $0) file-name [command]"
 exit 1
fi
FILES=$1
CMD=$2
for i in $FILES
do
# remove all blanks and store them OUT
OUT=$(echo $i | sed 's/  *//g')
if [ "$CMD" == "" ];
then
#just show file
echo $OUT
else
#else execute command such as mv or cp or rm
[ "$i" != "$OUT" ] && $($CMD  "$i"  "$OUT")
fi
done

B) To remove .jpg file extension, you write command as follows:

$ rename 's/\.jpg$//' *.jpg

C) To convert all uppercase filenames to lowercase:

$ rename 'y/A-Z/a-z/' *

Read man page of rename command for more information.