Chances are, you've seen the acronym PEAR at some point in your use of PHP, whether it was in passing or when installing and using a package from pear.php.net. If you've investigated, you might have probably heard of popular software provided by PEAR, such as the DB database abstraction package, or the HTML_QuickForm package. What you may not realize is that PEAR is much more than just a collection of packages that you can use. PEAR also contains the most versatile installation program for PHP, the PEAR installer. With the PEAR installer, you can do much more than just install packages from pear.php.net. You can install packages from other PEAR channels, distribute your own software projects using your own PEAR channel, and even maintain a complex intranet web project, all using the PEAR installer. Surprised? Read on, this book will reveal the intimate secrets of the PEAR installer and how it will revolutionize your everyday development with the PHP programming language.

The primary purpose of PEAR is to support code reuse. PEAR stands for the PHP Extension and Application Repository. PEAR provides both an advanced installer and a code repository at http://pear.php.net. Unlike competing PHP code repositories that you may be familiar with such as http://www.phpclasses.org or general purpose development sites like http://www.sourceforge.net, all PEAR code is organized into discrete reusable components called packages. A package consists of a group of files and a descriptor file called package.xml that contains meta-data about the package's contents, such as the package version, any special dependencies, and textual information such as the package description and authors.

Although most packages contain PHP code, there is no special restriction on the contents of a package. Some packages, such as http://pear.php.net/HTML_AJAX provide JavaScript files as well as PHP files. One of the example packages mentioned in Chapter 4 bundles only MP3 music files. Literally anything you can save as a file can be distributed in a PEAR package.

The software that transforms a package from an inert grouping of files into a dynamic software package is called the PEAR installer and is itself a PEAR package, located at http://pear.php.net/PEAR. In other words, the PEAR installer can be used to upgrade itself. It is truly a very powerful application.

Traditionally, PHP software has been distributed with a passive installation approach, following these typical steps:

For lack of a better name, we'll call this the "unzip-and-go" system of PHP software distribution. Although this in fact works very well for small, single-developer low-traffic websites, it contains a hidden cost that is not immediately apparent. There is one single fact about the unzip-and-go software installation system that limits its ultimate usefulness:

In today's fast-paced development world, one of the weaknesses of the Internet is security. Quite often, serious security vulnerabilities are discovered in software that requires an immediate upgrade to fix. When using a complete unzip-and-go software application, upgrading involves a large degree of risk. First of all, once the upgrade is complete, if the software is broken, reverting the upgrade requires either restoring from a backup or re-installing the old software. Reverting to an earlier package version with the PEAR installer is a one-line command and is very straightforward.

$ pear upgrade PackageName

The advantages of using the PEAR installer over a simple unzip-and-go solution are most apparent when projects grow in complexity. Let's look at a short list of the advantages:

Before using the PEAR installer, it is important to understand the disadvantages of using the PEAR installer over unzip-and-go:

The most significant barrier to using PEAR has traditionally been the effort it takes to install the PEAR installer itself, and this has been the focus of recent efforts to improve the installer's installation process. There is a great deal of possibility in recent innovations made possible by PHP version 5.1.0 or newer, as evidenced by work made possible by the PHP_Archive PEAR package (http://pear.php.net/PHP_Archive) and its sibling, the phar PECL extension (http://pecl.php.net/phar). These packages enable the distribution of an application in a single file that greatly enhances the capabilities of an installer.