Shell Script To Rename File Name To Lowercase

#!/bin/bash
# Write a shell script that changes the name of the file passed as argument
# to lowercase.
# -------------------------------------------------------------------------
# Copyright (c) 2003 nixCraft project
# This script is licensed under GNU GPL version 2.0 or above
# -------------------------------------------------------------------------
# This script is part of nixCraft shell script collection (NSSC)
# Visit http://bash.cyberciti.biz/ for more information.
# -------------------------------------------------------------------------

file="$1"
if [ $# -eq 0 ]
then
echo "$(basename $0) file"
exit 1
fi

if [ ! $file ]
then
echo "$file not a file"
exit 2
fi

lowercase=$(echo $file | tr '[A-Z]' '[a-z]'])

if [ -f $lowercase ]
then
echo "Error - File already exists!"
exit 3
fi

# change file name
/bin/mv $file $lowercase