Batch renaming files to create a numbered file sequence

rename.sh

#!/bin/bash

# Assuming that you have a number of
# PNGs in a folder pngs/, this script
# will rename them to a file sequence
# like 0001.png, 0002.png, ...

n=0
for f in pngs/*.png; do
	n=`expr $n + 1`;
	name=`printf "%04d" $n`.png;
	mv $f pngs/$name
done