Install Different PHP versions in Ubuntu

PHPVersions

// Check PHP version
$ php -v

// Add PPA for PHP
$ sudo add-apt-repository ppa:ondrej/php

// update
$ sudo apt-get update

//For Apache Web Server
$ sudo apt install php5.6
$ sudo apt install php7.2

// install appropreate php modules
$ sudo apt install php5.6-cli php5.6-xml php5.6-mysql 

// Set default PHP version
$ sudo update-alternatives --set php /usr/bin/php5.6

//Disable the current version and enable new version and restart apache
$ sudo a2dismod php5.6
$ sudo a2enmod php7.2
$ sudo systemctl restart apache2