Batch rename sequential files by padding with zeroes

Question

I have a bunch of files named like so:

output_1.png
output_2.png
...
output_10.png
...
output_120.png

What is the easiest way of renaming t

Answer 1

$rename output_ output_0 output_?   # adding 1 zero to names ended in 1 digit
$rename output_ output_0 output_??  # adding 1 zero to names ended in 2 digits
$rename output_ output_0 output_??? # adding 1 zero to names ended in 3 digits

That's it!

Answer 2

I'm following on from Adam's solution for OSX.

Some gotchyas I encountered in my scenario were:

1. I had a set of .mp3 files, so the sed was catching the '3' in the '.mp3' suffix. (I used basename instead of echo to rectify this)
2. My .mp3's had spaces within their names, E.g., "audio track 1.mp3", this was causing basename+sed to screw up a little bit, so I had to quote the "$i" parameter.

In the end, my conversion line looked like this:

for i in *.mp3 ; do mv "$i" `printf "track_%02d.mp3\n" $(basename "$i" .mp3 | sed 's/[^0-9]*//g')` ; done