This script will create a new stpf user with non interactive mode.

change-password.sh

#!/usr/bin/expect -f
set newUser [lindex $argv 0]
set newPassword [lindex $argv 1]
spawn passwd $newUser
expect "New password:"
send "$newPassword\r"
expect "Retype new password:"
send "$newPassword\r"
expect "passwd: all authentication tokens updated successfully."
send "exit\r"
expect eof

create-user-ftp.sh

#!/bin/sh
# sudo ./create-user-ftp.sh NEW_USER 

if [ "$#" -eq 0 ]; then
  me=`basename "$0"`
  echo "./$me [USERNAME]" >&2
  exit 1
fi

if [ "$EUID" -ne 0 ]
  then echo "Please run as root"
  exit
fi

newUser=$1
echo "new user: $newUser"
newPassword=$(</dev/urandom tr -dc '12345!@#$%qwertQWERTasdfgASDFGzxcvbZXCVB' | head -c8; echo "")
echo "new password: $newPassword"

#sftp-user create $newUser
/home/ec2-user/create-user-ftp2.sh  $newUser $newPassword

#sudo passwd $newUser
/home/ec2-user/change-password.sh $newUser $newPassword

usermod -G sftp $newUser

create-user-ftp2.sh

#!/usr/bin/expect -f
set newUser [lindex $argv 0]
set newPassword [lindex $argv 1]
spawn sftp-user create $newUser
expect "Enter password:"
send "$newPassword\r"
send "exit\r"
expect eof