Generate random passwords on a POSIX system

randpass

#!/bin/bash

##
# Generate a random password on a UNIX system.
#
# See the regex or re_format documentation for the syntax of
# "chars".
#
# Example:
#
# Generate a 12 character password with only capital ASCII letters:
# ./randpass 12 A-Z
#
# Generate an 8 character password with any printable ASCII character:
# ./randpass 8 '[:print:]'
#
# Generate a 16 character alphanumeric password:
# ./randpass 16 '[:alnum:]'

main() {
	local -x LC_CTYPE=C
	local len="$1"
	local chars="$2"
	tr -dc "$chars" < /dev/urandom | dd bs="$len" count=1 2>/dev/null
}

main "$@"