Phing is a tool based on Apache ant to automate tasks. Sometimes we as developers do repetitive tasks such as copy from a host to another, checkout new branches even deploying to a new server, in this scenario Phing comes to stage to help us to automate everything.
"PHing Is Not GNU make; it's a PHP project build system or build tool based on Apache Ant. You can do anything with it that you could do with a traditional build system like GNU make, and its use of simple XML build files and extensible PHP "task" classes make it an easy-to-use and highly flexible build framework. Features include running PHPUnit and SimpleTest unit tests (including test result and coverage reports), file transformations (e.g. token replacement, XSLT transformation, Smarty template transformations), file system operations, interactive build support, SQL execution, CVS/SVN operations, tools for creating PEAR packages, documentation generation (DocBlox, PhpDocumentor) and much more." (phing.info)
From official documentation, Phing is defined as :
"Phing is a project build system based on Apache ant (See ant ). You can do anything with Phing that you could do with a traditional build system like Gnu make (See gnumake ), and Phing's use of simple XML build files and extensible PHP task classes make it an easy-to-use and highly flexible build framework." (phing.info)
Developers are lazy, right ? Better, good developers are lazy. We know that humans are more likely to make mistakes doing repetitive tasks even in computers. Usually in projects we have a process to do before to start to code. Checkout the repository, run unit tests, run integration tests, create coverage and finally start to code (this process was created with example purposes, you could have a process much bigger or smaller than that). It looks boring, isn't it ? Maybe for just one project its fine to do manually those steps, but think about two, three or four projects. Shall we repeat every step in each project manually ? What will happened if we forget to run unit tests and then start to code ? How about the integration test?
Phing comes on stage to helps us to automate everything ! With Phing is easy to automate boring tasks such as cloning a repository and run unit tests. Of course Phing is much stronger than that. Phing can integrate with a bunch of tools such as dbDeploy and Jenkins to make our life easier.
Phing has a great documentation and a great folks involved on it, you can find more about it in in the official documentation here or in the offical website here. Also if you want to contribute they are open source and you can check the github repository here.
Phing uses XML to compose tasks. Every build.xml file must have an root node called project, with an atributte called default(you have to fill default with your default task you would like to run when Phing is activated, you can see in the example below I use dist, it must be the same name of one target) and at least one child node called target.
Actually our build.xml doesn't do anything but you can read Phing documentation to find out core tasks and how to create your own as well.
Phing assumes by default a build.xml to run. In other words if you don't specify with -f what file you want to run, Phing will run build.xml automatically.
I would like to recommend you dear reader, to have a quickly view here, in the core tasks. They are really important, because with core tasks (MkdirTask to create directories, DeleteTask to remove directories, EchoTask to show an message, CopyTask to copy files)you have many tasks already in Phing, you just have to use it, and you don't have to re-create it.
To understand what is the difference between core and optional tasks just keep in mind the most essential task we do in our day, for example, creating folders, giving user feedback, logging and so on those are essensial tasks that every project must have and is not dependent of the used feature, and in Phing's world are known as Core Tasks. Otherwise Optional tasks comes in a different approach, lets say for instance I'm going to use phpunit to run my unit test suit, but you can use behat or phpspec and those are your choice, and thats why they are called Optional Tasks.