Another stupid password generator in bash

passgen.sh

#! /bin/bash
#
# Version: 1.0
# Date: 31-07-2013
# Author: Alberto Alcolea ([email protected])
#

function usage() {
	echo "USAGE: $0 [OPTIONS] [LENGTH]"
	echo "  Options:"
	echo "    -h, --help: this help."
	echo "    -l: lower case characters"
	echo "    -d: digits"
	echo "    -u: upper case characters"
	echo "    -o: other printable characters"
	echo
	echo "Default options: -ld 6"
}

# Default options
LENGTH=6
SET=''

# Get the args
while [ $# -gt 0 ]
do
	if [ "$1" = '-h' ] || [ "$1" = '--help' ]
	then
		usage
		exit 0

	elif [[ "$1" =~ ^-[lduo]+$ ]]
	then
		if [[ "$1" =~ l ]]
		then
			SET=$SET'[:lower:]'
		fi
		if [[ "$1" =~ d ]]
		then
			SET=$SET'[:digit:]'
		fi
		if [[ "$1" =~ u ]]
		then
			SET=$SET'[:upper:]'
		fi
		if [[ "$1" =~ o ]]
		then
			SET=$SET'[:punct:]'
		fi

	elif [ $# -eq 1 ] && [[ "$1" =~ ^[0-9]+$ ]]
	then
		LENGTH="$1"

	else
		usage
		exit 1
	fi
	shift
done

# Default characters set
if [ ! $SET ]
then
	SET='[:lower:][:digit:]'
fi

# Print the password
echo $(cat /dev/urandom | tr -dc $SET | fold -w $LENGTH | head -n 1)

exit 0