A quick guide to debugging PHP

Every time there's a long gap between projects, I sometimes forget all the little tricks to debug PHP code. This should serve as kind of a placeholder for my own brain (possibly yours?).

The guide

Required tools

Installation of xdebug

I assume you have PHP installed somewhere, so installation of PHP and Pear won't be covered here.

Pear Method

As root, execute:

pear install xdebug

RPM

manually download my RPM and install it.

From source

Read the Authoritative guide, but below works if you're impatient.

Download the source
Unpack the source, and cd into the top-level folder
run phpize
./configure --enable-xdebug
cp modules/xdebug.so /path/to/lib/php/modules/
Add "extension=xdebug.so" somewhere into php.ini
restart Apache

Modifying your PHP code

This part is pretty simple. We use php's built-in function ini_set() to enable error reporting on a per-page basis (instead of system-wide when modifying it in php.ini). We then set the error level we wish to see using error_reporing().

Example:

$debug = true;	// sentinel for all kinds of debugging options
if($debug) {
	ini_set( 'display_errors', true );
	error_reporting( E_ALL );
}

Now when you run your code, you'll get some very nicely formatted call-back lists to help you trace out where your code failed, and why. Not to mention links to the online PHP manual if you have a syntax error.

Future enhacnements

There's a way to even compile xdebug to have a client hook for gdb. Not sure how, but when I figure it out, I'll post it here.

Optional Reading

Here's a few links on the subject that have helped me in the past..