The FilterChain element is where the power of Phing really comes into its own. This element will allow you to change the contents of the files of a fileset. This can range from a simple stripping of comments, to replacing values and numerous other filters.

One of the simplest thing that can be done with filterset is to strip all comments from the files in question. Take the following PHP file with two comments.

Aside from assigning and using your own properties Phing also comes with a set of built in properties that can be used to find out all sorts of information regarding the system that Phing is run on.

As an example, lets say you wanted to found out the operating system that phing is being run on. In this case you would use the variable host.os, which on a Windows XP system would print out WINNT.

Phing allows you to set up certain parameters that can be used throughout the rest of the script. These might be used to define a non standard build directory, or to store database connection details that can be written to the connection file during the build.

Properties are defined using the property element, which you should place at the top of your build.xml file in order to make it easy for other developers to see what is going on. The following example defines a property and the uses the main target to print the property out.

When a project gets complicated then so to can the build.xml file associated with it. You might find it necessary to have multiple different filesets, each of which do something different, but all of which have the same core files that they use. Multiple filesets are useful if you want to create a version of your project with all of the testing files in place so that it can be tested by external developers.

One of the main reasons to use Phing is to create a copy of your project in another directory that you can then use as your distribution copy. Your working directory might contain lots of testing code that is not needed in the final build.

To copy a file from one directory to another using Phing you need to use the copy element. Here is a simple example where a single file is copied from one directory to another.

By default, Phing will look for a file in the current working directory called build.xml when you run it. This document tells Phing what it will be doing during the build. You can change this by using the -f or the -buildfile property of phing and giving the build file as the parameter. The following code makes phing look for a build file called wibble.xml.

Assuming that the project is called myProject, then a minimal buildfile would be look like the following: