All About PHP Extensions

Pear (PHP Extension and Application Repository) packages are 100% php code. They are just PHP codes that are structured based on Pear’s standards and that are  deposited in a local directory and referenced in php.ini.

PECL packages are php extensions and need to be compiled and the resulted .so files must be deposited in the extensions directory (extension_dir in php.ini).

When you run a command such as

yum install php5-gd

or

apt-get install php5-gd

The dynamic shared library file (.so) is generated and installed for you automatically.

Pear
http://pear.php.net/manual/en/

PECL
http://pecl.php.net/packages.php

Introduction to extension writing
http://devzone.zend.com/303/extension-writing-part-i-introduction-to-php-and-zend/

Wrapping C++ Classes in a PHP Extension
http://devzone.zend.com/1435/wrapping-c-classes-in-a-php-extension/

phpize info
http://us.php.net/manual/en/install.pecl.phpize.php

Writing Php Extensions http://www.tuxradar.com/practicalphp/20/0/0

About php extensions
http://www.boutell.com/newfaq/creating/phpextensions.html

PHP Coding Standards
http://pear.php.net/manual/en/standards.php