list all of the available PHP 7.0-related packages for review:
$ apt-cache pkgnames | grep php7.0
Install PHP 7 and related packages in Ubuntu:
$ sudo apt-get install -y php7.0 libapache2-mod-php7.0 php7.0-cli php7.0-common php7.0-mbstring php7.0-gd php7.0-intl php7.0-xml php7.0-mysql php7.0-mcrypt php7.0-zip
Switch between PHP versions for apache web server:
$ sudo a2dismod php7.0
$ sudo a2enmod php5.6
$ sudo systemctl restart apache2
$ sudo service apache2 restart
After switching from one version to another, you can find your PHP configuration file, by running the command below.
$ which php
$ which php5.6
$ which php7.3
$ sudo update-alternatives --set php /usr/bin/php5.6
$ php -i | grep "Loaded Configuration File"
To create a phpinfo file, open a plain text file, add the following lines, and save as "phpinfo.php":
<?php
// Show all information, defaults to INFO_ALL
phpinfo();
?>
To serve public folder of a framework/webapp:
$ php -S 0.0.0.0:8080 -t public