I frequently need to add a prefix to the file names in a directory from the command line globally. An example would be .wav or .mp3 files in a particular directory. This way, I can distinguish similarly named files from other directories. My immediate need is to add a prefix such as '01-' to all the .wav files in a directory where the original files are named trk01.wav, trk02.wav, trk03.wav, etc. and they would be renamed 01-trk01.wav, 01-trk02.wav, 01-trk03.wav, etc.

I have forgotten how to do it using the mv command. I've also tried the rename command without much luck. I've looked into the two commands' manuals but to no avail. As a matter of fact, one recommended 'rename' example does not work in my Ubuntu 12.04 system.

I would appreciate seeing some simple illustrative examples. I am sory that due to poor typing my post was incomplete when it was submitted.

Julianvb

Examples :
Change all jpg files of a directory /tmp/user into mp3 files
Removing all blank space of all files of a directory /tmp/user
To convert all uppercase filenames to lowercase:
Suppose there are 55 files in the folder /usr/src/zz-folder/thumbnail_square as name1.txt name2.txt and so on and you want to change all into name1.jpg, name2.jpg and so on
Suppose there are files a,b,c,d,e,f in /tmp/user and you want to add prefix .txt in the files