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How to test new PHP version before running an upgrade?

This is the first question of every IT-Manager: This new version is fantastic, but will my old code run on it? Caribation Labs develops webs for the future and constantly upgrades its LAMP environment. Here we share some basic experience in testing PHP scripts for upwards compatibility.

Let us start with two common questions:

Can I test two PHP Versions within the same .php script?
NO.

Can I run two PHP Versions within the same directory?
YES.

Creating test environment

In order to have two PHP versions (for example 5.2 and 5.3) available in the same directory you need to edit .htaccess file located in this directory. Supposing your current version executing .php scripts is 5.2.17 and you want to try if a script or a group of scripts, classes or functions would run under 5.3.

Exercise 1:
Add these two lines to the .htaccess file

You have just told the Apache Server to process scripts which carry the extension .php53 (mytest.php53 for example) with PHP 5.3. You have told nothing about your other .php scripts (the default), so all standard .php files will be processed by any older PHP version you might have installed, for example by 5.2.17.

Caution:
The parameters for the Action and AddHandler statements vary from server to server. We are hosting our webs at HostGator and the examples shown here are real, but you must check with your hoster the exact syntax to be used. The extention name (.php53 in this example), however, is always up to you to choose.

Testing two PHP versions

Exercise 2:
Create a php script with the code you want to test and save it twice: as .php and .php53, for example as mytest.php and mytest.php53. The script may include an existing class, of course. For the test purpose you just need absolutely the same script but under two different names. For a quick start you can use this chunk of code:

The results: easy to guess

As you have probably guessed by now, running the mytest.php will result in an error:

Parse error: syntax error, unexpected T_STRING

On the other hand, mytest.php53 will execute correctly because it will be processed by PHP 5.3

What do you think? Space for your experience, remarks, questions...

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