standalone random string function

rndstr.bash

# Print or assign a random alphanumeric string of a given length.
# rndstr len [ var ]
function rndstr {
    if [[ $FUNCNAME == "${FUNCNAME[1]}" ]]; then
        unset -v a l
        printf "$@"
    elif [[ $1 != +([[:digit:]]) ]]; then
        return 1
    elif (( ! $1 )); then
        return
    else
        typeset -a a=({a..z} {A..Z} {0..9}) l=${#a[@]}
        eval '${2:+"$FUNCNAME" -v} "${2:-printf}" -- %s "${a[RANDOM%l]"{1..'"$1"'}"}"'
    fi
}