The phar extension provides a way to put entire PHP applications into a single file called a "phar" (PHP Archive) for easy distribution and installation. In addition to providing this service, the phar extension also provides a file-format abstraction method for creating and manipulating tar and zip files through the PharData class, much as PDO provides a unified interface for accessing different databases. Unlike PDO, which cannot convert between different databases, Phar also can convert between tar, zip and phar file formats with a single line of code. see Phar::convertToExecutable() for one example.
What is phar? Phar archives are best characterized as a convenient way to group several files into a single file. As such, a phar archive provides a way to distribute a complete PHP application in a single file and run it from that file without the need to extract it to disk. Additionally, phar archives can be executed by PHP as easily as any other file, both on the commandline and from a web server. Phar is kind of like a thumb drive for PHP applications.
Phar implements this functionality through a Stream Wrapper. Normally, to use an external file within a PHP script, you would use include
Example #1 Using an external file
<?php
include '/path/to/external/file.php';
?>
PHP can be thought of as actually translating /path/to/external/file.php into a stream wrapper as file:///path/to/external/file.php, and under the hood it does in fact use the plain file stream wrapper stream functions to access all local files.
To use a file named file.php contained with a phar archive /path/to/myphar.phar, the syntax is very similar to the file:// syntax above.
Example #2 Using a file within a phar archive
<?php
include 'phar:///path/to/myphar.phar/file.php';
?>
In fact, one can treat a phar archive exactly as if it were an external disk, using any of fopen()-related functions, opendir() and mkdir()-related functions to read, change, or create new files and directories within the phar archive. This allows complete PHP applications to be distributed in a single file and run directly from that file.
The most common usage for a phar archive is to distribute a complete application in a single file. For instance, the PEAR Installer that is bundled with PHP versions is distributed as a phar archive. To use a phar archive distributed in this way, the archive can be executed on the command-line or via a web server.
Phar archives can be distributed as tar archives, zip archives, or as the custom phar file format designed specifically for the phar extension. Each file format has advantages and disadvantages. The tar and zip file formats can be read or extracted by any third-party tool that can read the format, but require the phar extension in order to run with PHP. The phar file format is customized and unique to the phar extension, and can only be created by the phar extension or the PEAR package » PHP_Archive, but has the advantage that applications created in this format will run even if the phar extension is not enabled.
In other words, even with the phar extension disabled, one can execute or include a phar-based archive. Accessing individual files within a phar archive is only possible with the phar extension unless the phar archive was created by PHP_Archive.
The phar extension is also capable of converting a phar archive from tar to zip or to phar file format in a single command:
Example #3 Converting a phar archive from phar to tar file format
<?php
$phar = new Phar('myphar.phar');
$pgz = $phar->convertToExecutable(Phar::TAR, Phar::GZ); // makes myphar.phar.tar.gz
?>
Phar can compress individual files or an entire archive using gzip compression or bzip2 compression, and can verify archive integrity automatically through the use of MD5, SHA-1, SHA-256 or SHA-512 signatures.
Lastly, the Phar extension is security-conscious, and disables write access to executable phar archives by default, and requires system-level disabling of the phar.readonly php.ini setting in order to create or modify phar archives. Normal tar and zip archives without an executable stub can always be created or modified using the PharData class.
If you are creating applications for distribution, you will want to read How to create Phar Archives. If you want more information on the differences between the three file formats that phar supports, you should read Phar, Tar and Zip.
If you are using phar applications, there are helpful tips in How to use Phar Archives
The word phar is a portmanteau of PHP and Archive and is based loosely on the jar (Java Archive) familiar to Java developers.
The implementation for Phar archives is based on the PEAR package » PHP_Archive, and the implementation details are similar, although the Phar extension is much more powerful. In addition, the Phar extension allows most PHP applications to be run unmodified while PHP_Archive-based phar archives often require extensive modification in order to work.