#!/bin/sh

# $Id: drgenpass 44 2011-09-15 23:17:50Z jtk $
# http://dragonresearchgroup.org

usage() {
    echo $0 [password_length] [number_of_passwords] ['character_set']
    echo
    echo 'password_length       positive integer, default=16, optional'
    echo 'number_of_passwords   positive integer, default=1, optional'
    echo 'character_set         string, default=[:graph:], optional'
    exit 1
}

# is_positive_int() derived from Portable Shell Scripting, Blinn, p. 134
is_positive_int() {
    if [ $# -ne 1 ]
    then
        return 1
    fi

    expr "$1" + 1 > /dev/null 2>&1
    if [ $? -ge 2 ]
    then
        return 1
    fi

    if [ $1 -lt 1 ]
    then
        return 1
    fi

    return 0
}

LEN=${1:-16}          # arg1, length of password, optional
NUM=${2:-1}           # arg2, number of passwords to generate, optional
SET=${3:-[:graph:]}   # arg3, character class or set, optional

is_positive_int $LEN || usage
is_positive_int $NUM || usage

# tr and fold technique derived from:
#   <http://blog.colovirt.com/2009/01/07/linux-generating-strong-passwords-using-randomurandom/>
# NOTE: LANG=C is a hack for when tr is locale aware
cat /dev/urandom | LANG=C tr -cd $SET | fold -w $LEN | head -n $NUM