Debugging a PHP application can involve quite a bit of machinery, and effort getting that machinery setup. But it's worth it because what alternative is there? echo? Come on!
Thanks to Derick Rethans, xdebug can do a ton of cool things for you. For example, it overloads var_dump() and gives you control over how you want deeply nested data structures to be displayed.
First get Xdebug setup
Xdebug is the project for debugging PHP. The wizard will show you how to upgrade your package version. In my case, the Xdebug packaged for Ubuntu was 2.2.3, but the more recent version is 2.3.3
Summary
Here is what the wizard reported for me AFTER my recent installation of xdebug
Xdebug installed: 2.3.3
Server API: Apache 2.0 Handler
Windows: no
Zend Server: no
PHP Version: 5.5.9-1
Zend API nr: 220121212
PHP API nr: 20121212
Debug Build: no
Thread Safe Build: no
Configuration File Path: /etc/php5/apache2
Configuration File: /etc/php5/apache2/php.ini
Extensions directory: /usr/lib/php5/20121212+lfs
Caveat: the wizard can't really tell where the xdebug configuration lives (in the case of many subsidiary ini files). In Ubuntu, there might be a file in /etc/php5/conf.d In my case I actually did have /etc/php5/conf.d/xdebug.ini, but that file is superfluous because there are symbolic links for both apache2 and cli that go to
/etc/php5/mods-available/xdebug.ini (which helps PHP configuration to be the same for both runtimes.) Bottom line: run locate xdebug.ini to find out whether you have a duplicate/conflicting file; merge those files down to one; and make any overrides that you need from the default settings which xdebug will use if left unconfigured. Then sudo service apache2 restart and check the output of phpinfo() for correctness.
The defaults are probably all good, but you may want to specify some of the following:
; the old one installed by apt-get
; zend_extension=/usr/lib/php5/20090626+lfs/xdebug.so
; as of php 5.5 you no longer need to supply a full path to the zend_extension= token
; but it doesn't hurt, and may be required if you have multiple .so files lying around
zend_extension=/usr/lib/php5/20121212+lfs/xdebug.so
; enable debugging
xdebug.remote_enable = On
; working from local machine
; xdebug.remote_host = "127.0.0.1"
; debugging from any machine on the local network, as well as through the router
xdebug.remote_host = "192.168.1.0/24,127.0.0.1"
; set which debug client protocol we want
xdebug.remote_handler = "dbgp"
; enable anyone with access to the machine to start a debugging session
; this setting also helps when you're having difficulty with the connection setup
; xdebug.remote_connect_back 1
Once you see xdebug in your phpinfo() output, you know it's enabled -- which means that you can already get xdebug functionality out of your PHP scripts (e.g. var_dump() is overridden). But how do you get debugging working so that you can use it with your IDE? That is covered in the 'remote' section of the manual.
Following the sage advice of the Netbeans wiki, you want to get xdebug's debugclient working on localhost first, then add Netbeans.
xdebug provides several configuration parameters as well as functions that you can use in your debugging code. One important parameter is the xdebug.file_link_format which determines the format of the links that are shown in stack traces. This allows for integration with your IDE so that, for example, Netbeans will find and open the file in your local sources.
Profiling your PHP code is another feature enabled by xdebug.