This post describe how to find out whether the user name is exist in your system using shell script.

Create a file name checkuser.sh and give execute permission,

#  touch /root/checkuser.sh

#  chmod +x /root/checkuser.sh


#!/bin/bash



echo " Enter the User Name : "

read USR_NAME

if id  -u  $USR_NAME >/dev/null 2>&1; then

    echo "The User Name is Already Exist, Give Different Name"

    else

    useradd  $USR_NAME

fi
local@host#  /root/checkuser.sh

If the user name is does not exist create a new user.