CentOS 7 rename hostname

#!/usr/bin/env bash

OLD_HOSTNAME="$( cat /etc/hostname )"
NEW_HOSTNAME="$1"

if [ -z "$NEW_HOSTNAME" ]; then
 echo -n "Please enter new hostname: "
 read NEW_HOSTNAME < /dev/tty
fi

if [ -z "$NEW_HOSTNAME" ]; then
 echo "Error: no hostname entered. Exiting."
 exit 1
fi

echo "Changing hostname from $OLD_HOSTNAME to $NEW_HOSTNAME..."

hostname "$NEW_HOSTNAME"

echo $NEW_HOSTNAME > /etc/hostname

if [ -n "$( grep "$OLD_HOSTNAME" /etc/hosts )" ]; then
 sed -i "s/$OLD_HOSTNAME/$NEW_HOSTNAME/g" /etc/hosts
else
 echo -e "$( hostname -I | awk '{ print $1 }' )\t$NEW_HOSTNAME" >> /etc/hosts
fi

echo "Done."