PHP (recursive acronym for PHP: Hypertext Preprocessor) is a widely-used open source general-purpose scripting language that is especially suited for web development and can be embedded into HTML.
Nice, but what does that mean? An example:
Example #1 An introductory example
<!DOCTYPE html>
<html>
<head>
<title>Example</title>
</head>
<body>
<?php
echo "Hi, I'm a PHP script!";
?>
</body>
</html>
Instead of lots of commands to output HTML (as seen in C or Perl),
PHP pages contain HTML with embedded code that does
something (in this case, output Hi, I'm a PHP script!).
The PHP code is enclosed in special start and end processing
instructions <?php and ?>
that allow jumping in and out of PHP mode.
What distinguishes PHP from something like client-side JavaScript is that the code is executed on the server, generating HTML which is then sent to the client. The client would receive the results of running that script, but would not know what the underlying code was. A web server can even be configured to process all HTML files with PHP, and then there's no way that users can tell that PHP is being used.
The best part about using PHP is that it is extremely simple for a newcomer, but offers many advanced features for a professional programmer. Don't be afraid to read the long list of PHP's features. With PHP, almost anyone can get up and running and be writing simple scripts in no time at all.
Although PHP's development is focused on server-side scripting, much more can be done with it. Read on, and see more in the What can PHP do? section, or go right to the introductory tutorial to jump straight to learning about web programming.
Anything. PHP is mainly focused on server-side scripting, so it can do anything any other CGI program can do, such as collect form data, generate dynamic page content, or send and receive cookies. But PHP can do much more.
There are two main areas where PHP scripts are used.
PHP can be used on all major operating systems, including Linux, many Unix variants (including HP-UX, Solaris and OpenBSD), Microsoft Windows, macOS, RISC OS, and probably others. PHP also has support for most of the web servers today. This includes Apache, IIS, and many others. And this includes any web server that can utilize the FastCGI PHP binary, like lighttpd and nginx. PHP works as either a module, or as a CGI processor.
So with PHP, developers have the freedom of choosing an operating system and a web server. Furthermore, they also have the choice of using procedural programming or object-oriented programming (OOP), or a mixture of them both.
PHP is not limited to outputting HTML. PHP's abilities include outputting rich file types, such as images or PDF files, encrypting data, and sending emails. It can also output easily any text, such as JSON or XML. PHP can autogenerate these files, and save them in the file system, instead of printing it out, forming a server-side cache for dynamic content.
One of the strongest and most significant features in PHP is its support for a wide range of databases. Writing a database-enabled web page is incredibly simple using one of the database specific extensions (e.g., for mysql), or using an abstraction layer like PDO, or connect to any database supporting the Open Database Connection standard via the ODBC extension. Other databases may utilize cURL or sockets, like CouchDB.
PHP also has support for talking to other services using protocols such as LDAP, IMAP, SNMP, NNTP, POP3, HTTP, COM (on Windows) and countless others. It can also open raw network sockets and interact using any other protocol. PHP has support for the WDDX complex data exchange between virtually all Web programming languages. Talking about interconnection, PHP has support for instantiation of Java objects and using them transparently as PHP objects.
PHP has useful text processing features, which includes the Perl compatible regular expressions (PCRE), and many extensions and tools to parse and access XML documents. PHP standardizes all of the XML extensions on the solid base of libxml2, and extends the feature set adding SimpleXML, XMLReader and XMLWriter support.
And many other interesting extensions exist, which are categorized both alphabetically and by category. And there are additional PECL extensions that may or may not be documented within the PHP manual itself, like » XDebug.
This page is not enough to list all the features and benefits PHP can offer. Read on in the sections about installing PHP, and see the function reference part for explanation of the extensions mentioned here.