The way rename works is rename s/old/new/. The period stands for any character. If you precede the period with a backslash, it means a literal period. The dollar sign means the end of the string (there can be nothing after it, so m4b, not m4b*).

Rename is described here

Changing Extensions#

Linux#

In Linux, for example, to rename *.m4b -> *.m4a

First, to see what will happen,

$ rename -n 's/\.m4b$/\.m4a/' *.m4b

then, if the results are satisfactory, run again without the -n extension.

Mac#

On Mac, the rename command doesn't exist. You can type following however to convert *.txt to *.xml

for i in *.txt; do base=`basename "$i" .txt`; mv "$i" "$base".xml;done

Stripping from the front of the file name#

iTunes sometimes puts the track number twice. You end up with filenames like

01 01 Lord Hornblower.mp3

2-01 01 Post Captain.m4b

To fix this, run

$ rename 's/.. //' *.mp3

01 Lord Hornblower.mp3

2-01 01 Post Captain.m4b

Change %20 to space in filenames#

$ rename 's/.20/ /g' *mp3