install php 8 on ubuntu 18.04 LTS code example
Example 1: install php 8 ubuntu
sudo apt install php8.0-cli php8.0-common php8.0-imap php8.0-redis php8.0-snmp php8.0-xml
Example 2: install php 5.6 on ubuntu 18.04
$ sudo add-apt-repository ppa:ondrej/php