What is PHP?
PHP (PHP: Hypertext Preprocessor) is an open-source, programming language. PHP as most of us will be using it runs as a web server application. It takes the output of the written code, the script, and processes it to produce a complete page that can be displayed in a browser. PHP also allows dynamic web pages to be created from functions or data that is stored in a database or even simple text files.
In the 14 short years since the initial creation (1994), PHP has transformed the web hosting industry. The 4.x version which is still widely installed is quickly being replaced by PHP5 which was released in July 2004. PHP5 should be the dominant version by the end of 2008. As this article is being revised (11-18-2008) no official release date has been set for PHP6.
Speaking as a person who has built sites since 1999, I feel fairly secure in saying that PHP has delivered the functionality that the SSI functions teased us with. It is a suitable scripting language for the beginning webmaster and it can power a workhorse professional site.
Using PHP this page was created from six files. Those are a header, footer, 2 navigation sources, ad copy and the main content portion. If any item needs to be changed only one file has to be modified for the change to take place site wide. How much faster is it to modify one page as compared to 25-50 or even a 100 single pages?
All of the information necessary to create the pages might be pulled from a database to create dynamic pages on the fly. Currently this site does not use a database to create the Article Pages. Future articles may well be stored in a database and the semi-static page will blend completely with the dynamic ones due to the power and versatility of PHP.
PHP treats anything not inside the <?PHP ?> tags as standard html. Because it is so easy to inter-mix PHP code and standard html many beginners do it this way. In simple sites that are mainly using PHP to include other files there really is no harm in doing it that way. In long and complex scripts it is best to completely separate the code from the html by using the include function of PHP to include those templates. That way the code and the html are separated and modifying either is much simpler.
There are many great sites where you can learn PHP; so we won't do a poor job of duplicating their efforts here.
Article rewritten 11-18-2008 to reflect the changes in the last 2 years.