Simple batch rename shell

rename.sh

#!/bin/bash
# simple batch rename

cmd=""
ext=""

if [ "$#" -eq 1 ]; then
    ext=$1
    cmd="ls *."$ext
else
    echo "usage:$0 ext"
fi

n=1
for file in `$cmd`
do
    echo "mv $file to $n.$ext"
    mv $file $n"."$ext
    let "n = $n + 1"
done