Ubuntu 上官方的源，比如 Ubuntu14.04 預設源中的是 PHP5.6.x 、 Ubuntu16.04 預設源中的是 PHP7.0.x，那麼如果想在 Ubuntu16.04 上安裝 PHP7.1，PHP7.2，應該怎麼辦呢？
答案是透過第三方的源來安裝，ppa:ondrej/php 是一個比較知名的 PHP 源（目前維護 php5.6,php7.0,php7.1,php7.2）。下面就用這個源來安裝自己想要的 PHP 版本。
1. 透過源安裝 PHP
sudo add-apt-repository ppa:ondrej/php
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install php7.1 # for PHP 7.1
sudo apt-get install php7.0 # for PHP 7.0
sudo apt-get install php5.6 # for PHP 5.6
2. 安裝相關版本的 PHP 模組
sudo apt-cache search php7*
…
php-all-dev – package depending on all supported PHP development packages
php7.0 – server-side, HTML-embedded scripting language (metapackage)
php7.0-cgi – server-side, HTML-embedded scripting language (CGI binary)
php7.0-cli – command-line interpreter for the PHP scripting language
php7.0-common – documentation, examples and common module for PHP
php7.0-curl – CURL module for PHP
php7.0-dev – Files for PHP7.0 module development
php7.0-gd – GD module for PHP
php7.0-gmp – GMP module for PHP
…
…
…
php7.1-xml – DOM, SimpleXML, WDDX, XML, and XSL module for PHP
php7.1-xmlrpc – XMLRPC-EPI module for PHP
php7.1-zip – Zip module for PHP
php7.1-opcache – Zend OpCache module for PHP
php7.1 – server-side, HTML-embedded scripting language (metapackage)
php7.1-xsl – XSL module for PHP (dummy)
…
…
php7.2-bcmath – Bcmath module for PHP
php7.2-bz2 – bzip2 module for PHP
php7.2-cgi – server-side, HTML-embedded scripting language (CGI binary)
php7.2-cli – command-line interpreter for the PHP scripting language
php7.2-common – documentation, examples and common module for PHP
php7.2-curl – CURL module for PHP
php7.2-dba – DBA module for PHP
3. 選擇需要的模組，安裝之
sudo apt-get install php7.2-curl php7.2-dev php7.2-gd php7.2-imap php7.2-intl php7.2-mbstring php7.2-mysql php7.2-xml php7.2-zip
4. 切換 PHP 版本
sudo update-alternatives –config php
5. 設定 Apache 與正確的 PHP 版本一起執行
sudo a2dismod php7.1 # unload the current version
sudo a2enmod php5.6 # load the version you need
sudo service apache2 restart # restart webserver to apply
到此結束，再也不用擔心安裝 PHP，切換 PHP 版本這些事情啦。
