#!/bin/bash
#
# Copyright (C) 2008-2011, William Trevor King <wking@drexel.edu>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

# generate a random password, defaults to 8 characters
#
# usage: passwd-gen [num-characters]

# You may want to modify NC to get the best performance depending on
# your usual choice of DEVICE and N.  For slower DEVICEs, it's better
# to have lower NC (wastes less usable characters).  For faster
# DEVICEs, it's better to have a higher NC (fewer slow shell loops).

N="${1:-8}"               # password length
NC="${NC:-4}"             # number of characters in a "chunk"
#SET="[:alnum:][:punct:]" # set of allowed characters (see tr(1))
SET="${SET:-[:alnum:]}"
DEVICE="${DEVICE:-/dev/random}" # use /dev/urandom for faster, weaker passwords

NA=0
PWD=""
while [ "${N}" -gt 0 ]; do
		ALL=$(head -c "${NC}" "${DEVICE}")
		let "NA = NA + ${#ALL}"
    NEW=$(echo -E "${ALL}" | tr -d -c "${SET}" | head -c "${N}")
    PWD="${PWD}${NEW}"
    let "N = N - ${#NEW}"
done

echo "${PWD}"
echo "Length of password: ${#PWD}"
echo "Total bytes read:   ${NA}"
echo "Device:             ${DEVICE}"
echo "Set:                ${SET}"

exit 0