#!/bin/bash
# Reads username:password per line in plain text from stdin
# and feeds smbpasswd to add/update users, similiar to chpasswd
while read line
do
    username="$(echo ${line} | cut -d: -f1)"
    password="$(echo ${line} | cut -d: -f2)"
    (echo $password; echo $password) | smbpasswd -s -a $username
done