PHP: Hypertext Preprocessor
Brian Wright
October 18, 2004
Introduction:
The acronym PHP stands for PHP: Hypertext Preprocessor, and is a web
development language that is syntactically similar to C. Not only is the language
syntactically similar to C but the underling development of PHP was performed using the
C language. The main objective of the language is to allow for the easy creation of
dynamic web pages. PHP has evolved to become a technology that is utilized by
approximately thirty-three percent of the web domains on the Internet (Lerdorf). Since
the prominence of PHP is so great, the goal of this paper is to provide the historical and
technical background on it as well as the advantages and disadvantages to using this
technology.
Historical Background – Prior PHP:
HTTP is a stateless system. This means that it does not save any data across
pages. Web pages that include forms need, most often, to save data. The way web page
forms were interpreted during the early to mid 90’s was through parsing the URLs for the
data. The mainly used technology to parse this information was C (Hudson).
For instance, take a hypothetical web page that includes two text-input boxes:
firstName, and lastName. Suppose that a user inputs “John” and “Smith” into the input
boxes on this web page and then clicks submit. By default, the URL generated would be
concluded with: firstName=John&lastName=Smith. Programmers would use the C
programming language to decipher this information into however necessary variables and
values. This process is known as parsing. Utilizing C to parse this information was,
according to Paul Hudson, the author of Practical PHP Programming, “very clunky to
program – a simple parsing program could easily take up fifty lines or more [of code].”
With the problems involved in parsing data in C came the creation of PERL—
Practical Extraction and Report Language. PERL allowed even novice programmers to
successfully parse HTML form data. One of the largest drawbacks to using PERL was
that it was written so that in order to output HTML, HTML must be embedded into the
PERL program. Another way to phrase this is that PERL is PERL-centric.
Historical Background – PHP:
The first version of PHP was created by Rasmus Lerdorf in 1995 and was called:
Personal Home Page/Form Interpreter: PHP/FI. According to Lerdorf’s article—entitled:
Do You PHP?—the reason he created PHP/FI was “purely a case of needing a tool to
solve real-world Web-related problems.” PHP is a HTML-centric language. This means
that PHP code is actually embedded inside the HTML (Hudson). PHP/FI was “mostly a C
library of common C functions that [Lerdorf] had written” (Lerdorf, Do You PHP?). An
early example of PHP/FI code is this:
<!--getenv HTTP_USER_AGENT-->
<!--ifsubstr $exec_result Mozilla-->
Hey, you are using Netscape!<p>
<!--endif-->
This code would check for the web browser agent and print a string if it the agent was
Mozilla.
Lerdorf was not satisfied with the original parser he wrote and decided to write a
new one. Instead of encompassing the commands with <!-- cmd -->, he chose to change
it to <? cmd > syntax—the syntax still used today. After recombining the original home
page tools and the new syntax, he released of PHP/FI v2 in mid 1997.
Later in 1997, two Israeli students—Zeev Suraski and Andi Gutmans—contacted
Lerdorf and asked whether or not he would be interested in working with a new code
engine that they had created. Lerdorf decided to pursue this option. With the combination
of Lerdorf, Suraski, Gutmans, and a few others that were submitting PHP/FI patches at
the time, the group released PHP Version 3 in June 1998. Lerdorf wrote, “[t]his was
probably the most crucial moments during the development of PHP. The project would
have died at that point if it had remained a one-man effort” (Lerdorf, Do You PHP?).
PHP Version 3 including several improvements to PHP/FI Version 2. Version 3
had gained limited objected oriented support. The language itself was also much stricter
syntactically—though since the language was moderately new, most were not affected by
this. There was also a great increase of speed in the parser. Language extensibility was in
the third version of PHP which allowed programmers to write their own modules for the
language. Version 3 also supported a wide range of databases such as Oracle, Sybase,
Solid, MySQL, mSQL, as well as ODBC data sources (Hudson).
After PHP Version 3, Suraski and Gutmans went to work on a new version of
PHP. Their objective was “abstracting the layer between the language and the web server,
adding a thread-safety mechanism, and adding a more advanced, two-stage parse/execute
tag-parsing system” (Lerdorf, Programming PHP). Combining parts of their first names,
Zeev Suraski and Andi Gutmans, named this creation the Zend Engine. After completing
the Zend Engine, the developers were joined by works of many other developers. This
compilation resulted in the release of PHP Version 4 on May 22, 2000.
PHP Version 5 was released in September 2004. This version includes object
oriented scripts. “Developers are now able to declare how their objects may be used,
which makes it easier for one developer to work with another's code” (Hudson). The new
version also brought new and better error checking in the form of Java’s try and catches.
With the increased usage of XML in the programming world, SimpleXML was added to
PHP Version 5’s extensions. This allows for easy interaction between XML documents.
Technical Background:
PHP has evolved from being a web form parser very functional web development
tool. PHP began as only a server-side scripting language that allowed for dynamic web
content. Now PHP can also be used for command line scripting—much like Perl, awk, or
the UNIX shell. Utilizing the PHP-GTK, it is possible to create cross platform GUI
applications in PHP—much like Java applications. Although PHP is capable of doing all
of the aforementioned tasks, its still best suited for server-side scripting. This paper will
only deal with server-side scripting aspects of PHP.
PHP can be used on all major operating systems including, Windows, Linux,
UNIX, FreeBSD, Solaris, and Mac OS X. To install PHP, one simply needs to download
the archive corresponding to their operating system at www.php.net. After following the
installation instructions the user needs to configure their web server to load the PHP
libraries when dealing with PHP code. Once this task is complete, the user now only
needs to write PHP web pages.
Since PHP is a server-side scripting language, the code is handled completely on
the server side. When the server encounters a PHP file request, it lets the PHP libraries
handle the request and then prints the results. The server receives these results and thus
the results are what are sent to the client. The client has no idea that the page is PHP
without noticing the web page’s file extension.
With PHP being a server-side scripting language, clients do not need to change
anything about their browsers. PHP pages are handled just as HTML pages are from the
client’s perspective. No plug-ins are required and no downloads are necessary for
viewing PHP pages.
PHP uses a combination of code compiling and interpreting. On Paul Hudson’s
online book he writes:
Behind the scenes, PHP compiles your script down to a series of instructions […]
whenever it is accessed. These instructions are then executed one by one until the
script terminates. This is different to conventional compiled languages such as
C++ where the code is compiled down to native executable code then that
executable is run from then on - PHP re-compiles your script each time it is
requested (Practical PHP Programming, 2004).
This provides quick error feedback because the code is not compiled unless error-free.
Main Body – Why PHP:
With plethora web development tools out there today, it is easy to ask: “why use
PHP?” There are many reasons to use PHP. One reason is that it is a server-side scripting
language and therefore the clients do not need to install any plug-ins or reconfigure their
web browsers. This also allows for security of PHP code. The client/server relationship is
maintained and the client only sees what the server chooses to allow the client to see.
Not only is PHP free but it is open-source. The source code for it is freely
available and this allows for many side development projects to better the language and
supply new changes at rapid rates.
According to Leon Atkinson, the author of Core PHP Programming: Using PHP
to Build Dynamic Web Sites, “PHP is better [than other web development tools]. It is
faster to code and faster to execute. The same PHP code runs unaltered on different Web
servers and different operation systems.”
PHP is supported commercially. The creators of the Zend engine, Suraski and
Gutmans sell supporting products as well as technical support for the language. The
language is also supported by the community. There are many popular web communities
that are available to help and assist with programming problems. Examples include
www.phpbuilder.com, www.phphub.com, and www.phpindex.com.
Because of the popularity of PHP, it is very capable of completing web-based
tasks. “There are thousands of pre-written functions to perform a wide variety of helpful
tasks - handling databases of all sorts (MySQL, Oracle, MS SQL, PostgreSQL, and many
others), file uploads, FTP, email, graphical interfaces, generating Flash movies, and
more” (Hudson).
With the quick feedback mechanism stated in the prior section, it is argued that
very little time is spent debugging PHP code. And, with the language constantly
expanding, performance and production efficiency is greatly improving.
Main Body – PHP Alternatives:
There are numerous PHP alternatives out there, the most notable is Perl. Perl is
the oldest. One of the major advantages to using Perl is its flexibility. There are many
modules already written for it and easy to obtain; however, Perl is has a signature
“messy” code appearance. The only obvious reason one should consider using Perl
instead of PHP is in the case of using already written modules. But, since PHP is
becoming much more popular there are more and more PHP modules available for usage.
Another alternative to PHP is Microsoft’s Active Server Pages (ASP). ASP is
automatically packaged in Microsoft’s web servers by default. ASP is a single-platform
language, it only works on Microsoft’s, but it has been implemented on others. If using
Internet Information Services(IIS), it runs at very fast speeds; but on other servers, if they
run it at all, it is notably slow.
A third alternative to PHP is Java Servlet Pages (JSP). A downfall to using JSPs is
the detrimental speeds; nevertheless, it does have some advantages. One advantage is that
JSP is highly promoted by the prominent company, Sun, and therefore has strong
patronage in large enterprises. Since JSP uses Java, it is a smart choice for companies that
run back-end processes in Java to use JSP in order to keep the development under a
single language. It is commonly argued that JSPs scale better than PHP, but according to
Paul Hudson’s Practical PHP Programming, PHP “scales perfectly” as long as the
developer utilizes the same design patterns that were used for the JSPs.
Main Body – When Not to Use PHP:
According to Paul Hudson, PHP is not always recommended for web
applications. One case is when speed is absolutely critical. Even though PHP’s speed is
drastically improving with each new version, it is still recommended that one should
resort to C or C++ when in need of superior performance. A way around this might be to
write the C code as an extension to the PHP code (Hudson).
Another situation in which one might not want to resort to using PHP is in the
case of an already completed system. If the system is already rather large and written in a
different language, it is often cumbersome to move on to PHP. It is recommended in this
situation that the old language remain in tact.
Main Body – Writing PHP Code:
Writing PHP code is not a difficult task. One way to approach this task is to
rename the original web pages to have the extension “.php” and add in the code to
perform the tasks. An example would be to insert this line into the body of an existing
HTML document:
<?php echo ‘hello, world’ ?>.
This would print out “hello, world” in the body. As stated in the technical section, since
PHP is a server-side scripting language the client’s web browser will not see this code.
Instead the source code from the client’s perspective will simply be: “hello, world”. PHP
statements end, like C, C++, Java and sever other languages, with a semicolon. Notice
that the above statement is an exclusion to the rule and that is because it is a one-liner.
Variables in PHP all have the prefix “$” such as “$name”. When creating a
variable, declaring the data type is not needed. There can be local, static and constant
variables. To create an array, the programmer needs to use the array() function to
construct it. An example is:
$junk = array(232,121231,123211);
This code would create an array named $junk that contained three elements: 232, 121231,
and 123211.
There are also stored environmental variables that are easily referenced such as
HTTP_USER_AGENT, which stores the browser agent of the client browsing the page.
Connecting to a database can be done in only two lines! The following example
was taken from Practical PHP Programming:
<?php
mysql_connect("localhost", "phpuser", "alm65z");
mysql_select_db("phpdb");
$result = mysql_query("SELECT * FROM usertable");
$numrows = mysql_num_rows($result);
print "There are $numrows people in usertable\n";
?>
It connects to a MySQL database named “phpdb” and selects all the records from the
table entitled “usertable.” Using the mysql_num_rows function it obtains the amount of
records in the result and then prints this number to the screen. Notice there was not any
include’s or import’s at the top of this code. It is all included in the PHP package.
Main Body – PHP IDEs:
There are several different PHP integrated development environments (IDEs). It
is often stated that most PHP developers use the humble text editors such as Notepad.
There are downsides to doing such. Using Notepad limits the developer to using code
techniques that they already know. In order for a PHP developer to truly achieve the
maximum PHP programming heights, it is recommended that developers utilize one of
the many powerful editors such as the Zend Studio. These power IDEs include many
features that minimize the hard work the programmer has in task.
Main Body – How One Can Contribute to the PHP Development:
Since PHP is an open-source development project it is possible for a user to
download the source code for it, modify it, and submit it back to the developers for
everyone to use. It is recommended that even those who cannot program contribute to the
development by submitting any bugs that they run in to. For the programmers, it is
recommended that contact with the PHP developers be made because there is plenty of
room for contributions (Hudson). The only way for PHP, or any open-source project for
that matter, to better, is for people to contribute to the project regardless of how small or
large the contributions are.
Summary
PHP’s history may only be of a ten year course, but its evolution is drastic. Its
usage has increased extremely over the course of its creation. A graph taken from
Lerdorf’s article on Oracle’s website shows the history of PHP usage on the web:
PHP has evolved from a simple scripting language into a highly versatile and
capable web development tool. PHP is an easy-to-learn and use language that ultimately
meets the needs of the ever-so-changing Internet. It allows for the basic home user to, for
free, have a highly complex website at the ease of an understandable programming
language. It also allows for corporations to expand their web bases because of PHP’s
enormous list of capabilities. The pile of C code that created PHP is ever growing due to
its open-source availability on the internet, and because of this, PHP will most likely
always be a competitor in the web development language race. Its pros outweigh its cons.
PHP is therefore rendered the ultimate web development tool of the day.
Works Cited:
Atkinson, Leon. Programming: Using PHP to Build Dynamic Web Sites. Prentice Hall,
2000.
Hudson, Paul. Practical PHP Programming. 2004 <http://www.hudzilla.org/php>.
Lerdorf, Rasmus. Do You PHP? 2004
<http://www.oracle.com/technology/pub/articles/php_experts/rasmus_php.html>.
Lerdorf, Rasmus and Kevin Tatroe. Programming PHP. Sebastopol: O’Reilly &
Associates, Inc, 2002.