|PHP Vs CGI
By Christopher S L Heng
|PHP seems very much in
vogue now - with an increasingly greater number of web hosts
providing support for it. For those who have only vaguely heard
of it and are not too sure what it is, this article discusses
PHP and informally compares it with writing CGI scripts in Perl.
PHP is a free server side scripting language. It can be built
into web servers like Apache and you can use it to generate
your pages dynamically. You would probably use it in situations
you would have otherwise used a CGI script for. For example,
thefreecountry.com's Feedback form (among other things) uses
a PHP script to generate the form and send the message to me.
1. The Language
learning PHP would probably be a piece of cake. In fact, you
probably can get started writing your scripts almost immediately
It uses typeless variables the way Perl does, prefixed with
a "$" sign and holding any data type you wish. For example,
$whatever can be a variable that you can use to contain strings,
numbers, whatever. If $whatever contained a number, you can
increment its value using
$whatever += 1 ;
$whatever = $whatever + 1 ;
2. Built-in Facilities
Unlike Perl, which is a general purpose scripting language that
you can use for a wide variety of purposes (and not just generating
web pages), PHP was designed from the ground up to be used for
scripting web pages. As a result, it has lots of facilities
built into that you may have to write yourself or use some pre-written
module if you were using Perl.
For example, do you want to send email to yourself from a form
on the web page? In Perl, you probably would have to code something
like the following:
open ( MAIL,"|/usr/sbin/sendmail -t");
print MAIL "To: myself\@mydomain.com\n" ;
print MAIL "From: visitor\@hisdomain.com\n" ;
print MAIL "Subject: Comments from Web Form\n\n" ;
print MAIL $mainmessage ;
close ( MAIL ) ;
In PHP, the same thing would be coded as follows:
mail ( "email@example.com", "Comments from Web Form",
$mainmessage, "From: firstname.lastname@example.org"
Nifty, huh? The same goes for other facilities like sending
or retrieving a document via HTTP or FTP, etc. Since PHP was
specially designed for a website, the facilities that web designers
typically want in a scripting language are built into it.
Another convenience is its handling of form input. Take for
example a form with a field like:
<input type=text name="dateofbirth">
You can immediately access that field with the $dateofbirth
variable. No need to parse form inputs and the like. All fields
in the form are automatically converted to variables that you
Accessing databases is just as easy. There are built-in facilities
in PHP to access MySQL, MSQL, Dbase, Oracle, InterBase, and
so on (the list is very long). Need to MIME encode your message?
There's a function to do it for you too.
There're lots more. I obviously can't run through the entire
list - it would take a whole book to be exhaustive. This is
just to whet your appetite.
3. Generating web pages
By default anything you type in your PHP document is given verbatim
to the web browser. So a simple PHP script might look like the
<head><title>My First PHP Script</title></head>
<h1>My First PHP Script</h1>
Welcome, Internet user from IP address
<?echo $REMOTE_ADDR?>. Hope you like my first
Notice that it looks exactly like a web page, except for the
<? ... ?> bit, which encloses the PHP script. In this
case, all we want is for the script to output the visitor's
IP address to the page, hence we use the "echo" function. The
web server's environment variable REMOTE_ADDR is automatically
made available to the PHP script via a variable of the same
name (as are all other environment variables and form inputs).
There are many ways to embed your PHP script into your page,
or to design your page itself. But you got the general idea.
As I said, PHP was designed for web pages, so the idea of output
to the server is built into its design. It makes writing such
scripts a very pleasant task.
4. Debugging With PHP Vs Perl CGI
Interestingly, if you're debugging your scripts online, PHP
Normally, when a Perl CGI script goes awry, you'll get a cryptic
error message in your browser: something to the effect of "500
Internal Server Error".
With PHP scripts, you get error messages pinpointing the offending
lines in your code to help you locate the error. However, the
message is sometimes a cryptic "parse error" or the like, so
you still have to crack your head to figure out the problem.
But at least you know where it occurred. Contrast that with
Perl CGI scripts, where an "Internal Server Error" could have
arisen from any number of causes, from a syntax error to a simple
case of forgetting to make the file executable or uploading
it in text mode.
Debugging offline, however, is another story. Some people have
found that the Perl interpreter gives more helpful messages
than the PHP interpreter, which tends to label many things as
"parse error". This may change, though, as newer versions of
the PHP interpreter is released.
4. What's the Catch?
While I obviously enjoy using PHP as my web scripting language,
I do not claim that it is the perfect solution for all your
You might want to consider the following prior to committing
yourself ot it. The list, incidentally, is not exhaustive.
a. Not all web hosts provide PHP facilities. While it is true
that many also do not provide CGI access, the number providing
PHP is even less!
In fact, where free web space providers are concerned, the number
providing PHP can probably be counted with one hand. Indeed,
even if you manage to find free web hosting with PHP access,
you have to ask yourself whether you really want to depend on
it for your site. There might be a day when you need to move
your site, and you may be hard-pressed to find another free
web host that supports PHP.
However, if you host with commercial web hosting companies,
you probably will have less problems. It seems to me like the
large majority of vendors support PHP, and even those who currently
don't provide it plan to support it in the near future.
b. Like all web scripting languages (Perl included), debugging
the script can be a pain in the neck unless you download and
install your own copy of PHP. Otherwise you might spend many
hours online trying to test and debug your script (unless of
course it's a trivial script).
Incidentally, you can also operate your own Apache web server
at home, so as to mimic the entire environment of your actual
site (or as close to it as necessary).
Of course if you have a Linux box around, you're probably all
set. Just dig up your installation CDROMs and install the server
and PHP module from there if you've not already done so. (Most
modern Linux distributions come bundled with the Apache server
and PHP Apache module.)
c. It is not a general purpose language. While it has many facilities
specifically catered towards web programming, it is not Perl
(or C or C++ or Java). I personally however find PHP more than
adequate for my web programming needs.
5. Where to Get It?
The entire PHP documentation set comprising the reference manual
for the various PHP language features and functions can be downloaded
from the PHP web site at:
The sources and binaries for PHP can also be found on that site
should you wish to run a copy on your own machine for testing
Copyright by Christopher S L Heng. All rights reserved.
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