Add user to Debian or Ubuntu

add_user.sh

#!/bin/bash

user="<user_name>"
key="<user_key>"
users_home=/home
sudoers_filename="99-transparent-sudoers"

dpkg-query -W sudo || apt update && apt install -y sudo

str=$(grep "PermitEmptyPasswords" /etc/ssh/sshd_config)
if [[ ${str} =~ ^# || ${str} =~ no$ ]]; then
  echo "PermitEmptyPasswords is disabled."
else
  sed -i 's~^PermitEmptyPasswords .*$~PermitEmptyPasswords no~g' /etc/ssh/sshd_config
  service ssh restart || service sshd restart
  echo "PermitEmptyPasswords has been disabled."
fi

# Add user
if [[ ! $(getent passwd ${user}) ]]; then
  useradd ${user} -m -s /bin/bash
  echo
  echo "${user} user has been created."
else
  echo
  echo "${user} user already exists."
fi

# Add public key
if [[ ! -f ${users_home}/${user}/.ssh/authorized_keys ]]; then
  mkdir -p ${users_home}/${user}/.ssh/
  chown ${user}:${user} ${users_home}/${user}/.ssh/
  chmod 0700 ${users_home}/${user}/.ssh/
  echo ${key} >> ${users_home}/${user}/.ssh/authorized_keys
  chown ${user}:${user} ${users_home}/${user}/.ssh/authorized_keys
  chmod 0600 ${users_home}/${user}/.ssh/authorized_keys
  echo
  echo "Public key has been added for ${user} user."
else
  echo
  echo "Public key already set for ${user} user."
fi

if [[ ! -d /etc/sudoers.d/ ]]; then
  echo "Sudo is not installed. You need to install it manually."
elif [[ ! -f /etc/sudoers.d/${sudoers_filename} ]]; then
  echo "${user} ALL=(ALL) NOPASSWD:ALL" >> /etc/sudoers.d/${sudoers_filename}
  chmod 0440 /etc/sudoers.d/${sudoers_filename}
  echo
  echo "${user} user has been added to sudoers."
else
  echo
  echo "/etc/sudoers.d/${sudoers_filename} file already exists. Check that the ${user} user is in this file..."
  if [[ ! $(grep "${user} ALL=(ALL) NOPASSWD:ALL" /etc/sudoers.d/${sudoers_filename}) ]]; then
    echo "${user} ALL=(ALL) NOPASSWD:ALL" >> /etc/sudoers.d/${sudoers_filename}
    chmod 0440 /etc/sudoers.d/${sudoers_filename}
    echo "${user} user has been added to sudoers."
  else
    echo
    echo "${user} user already has administrative privileges."
  fi
fi