Generate random password

random_password.sh

# Usage: rpasswd [LENGTH] [CHARS]
# Generate random password
# 
# CHARS
#  'a': Alphabet, a-z A-Z
#  'n': Numeric, 0-9
#  'c': Character, print characters in ascii code
#
rpasswd() {
    len=12
    char='!-~'

    if [[ $# -gt 0 ]]; then
        if [[ "$1" =~ ^[0-9]+$ ]]; then
            len=$1
        fi;

        if [[ $# -gt 1 ]]; then
            nchar=""
            for (( i=0; i<${#2}; i++ )); do
                reg=""
                case "${2:$i:1}" in
                    a | A)
                        reg='a-zA-Z';;
                    c | C)
                        reg='!-/:-@[-`{-~';;
                    n | N)
                        reg='0-9';;
                esac;
                nchar="${reg}${nchar}"
            done;

            if [ ! -z "$nchar" ]; then
                char=$nchar
            fi;
        fi;
    fi;

    cat /dev/urandom | tr -dc $char | fold -w $len | head -n 1
}