user and group

#!/bin/bash   
# Script to add a user to Linux system  
if [ $(id -u) -eq 0 ]; then  
        read -p "Enter username : " username  
        read -s -p "Enter password : " password  
        egrep "^$username" /etc/passwd >/dev/null  
        if [ $? -eq 0 ]; then  
                echo "$username exists!"  
                exit 1  
        else  
                pass=$(perl -e 'print crypt($ARGV[0], "password")' $password)  
                useradd -m -p $pass $username  
                [ $? -eq 0 ] && echo "User has been added to system!" || echo "Failed to add a user!"  
        fi  
else  
        echo "Only root may add a user to the system"  
        exit 2  
fi

http://www.cyberciti.biz/tips/howto-write-shell-script-to-add-user.html