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2000-05-09
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An Introduction to PHP
by Shaun McCormick
Lesson I: An Intro
PHP, or Hypertext Preprocessor,
is a embedded server-side scripting
language. Not only is PHP's
popularity growing among web
designers, but its features are
growing with the release and
development of PHP4. This article
will cover the aspect of basic
programming with PHP3, however,
since PHP4 is only in the Beta 3
stage. PHP is embedded straight
into HTML code, and is
automatically parsed when the
viewer loads a document. It is
mostly used as a module with the
Apache web server for Linux;
however, it can easily be used in
other OS-based servers such as
Microsoft's IIS or Netscape's
Enterprise server. PHP can be
downloaded freely at its homepage,
www.php.net.
PHP is highly similar to
Microsoft's ASP (Active Server
Pages) and Coldfusion. However, PHP
is free and cross-platform. As a
combination of C++ and CGI
techniques, PHP can send HTTP
headers, cookies, communicate
flawlessly with databases, and much
more. Unlike CGI, all PHP requires
is a installation and your
PHP-coded files to have the
extension .php3 (it can also be
configured to use .php, .phtml, and
others.). To implement code, one
would simply start as if you were
writing a HTML file. To separate
the coding from the HTML, you place
the separators:
<?php
?>
(You can also configure PHP to use
ASP-style tags (<% %>) or even
<script LANGUAGE="php"></script>.)
To output from the code, one would
use the command:
echo "Hello, $name";
The $name will automatically be
parsed and printed. For instance,
if $name was John, it would have
printed:
Hello, Shaun.
print $variable; can also be used,
as well as printf("Hello, world!");
Since PHP is like C++ and CGI,
statements MUST end with a
semicolon, ;
echo "Hi!"
Doesn't work, while
echo "Hi!";
Does.
Hence, one would create a file
named hello.php3 and put this code
in it:
<html><head><title>PHP
Test</title></head>
<body>
<?php
$name = "John";
echo "Hello $name\n";
?>
</body></html>
Comments are also used in PHP.
// This is a comment.
/* So is this! */
# Well, I am too!
Onto the next lesson!
Lesson II: Usefulness? Sure, why
not!
Let's start with some interesting
code.
<?php
if(strstr($HTTP_USER_AGENT,"MSIE"))
{
echo "You are using Internet
Explorer<br>";
}
?>
Wow, lots of new concepts to grasp
today. We'll start with the if
statement. The going for a if
statement is as follows:
if ($name == $myname) { run_code; }
// or...
if ($name == "John") { run_code; }
// Else statments can be used too:
if ($name == "John") { echo "Hi
John!"; } else { echo "Who are
you?"; } // Don't forget elseif!
if ($name == "John") { echo "Hi
John!"; } elseif ($name == "Suzy")
{ echo "Heya Suzy!"; } else { echo
"Who are you?"; }
Notice that the == has two equals.
== is comparative. To see if they
are unequal, one would use !=
Just one equals sign, or =, is used
for assigning values, not
comparing.
Now that we've got that out of the
way, let's move on.
if
(strstr($HTTP_USER_AGENT,"MSIE")) {
Ok, strstr() is a PHP function that
checks if one string includes
another. $HTTP_USER_AGENT is a
HTTP-sent variable. It is sent by
the requesting browser of the
visitor. So if $HTTP_USER_AGENT
contains MSIE, the code will print
out:
You are using Internet Explorer<br>
Of course, the <br> will be
interpreted by the server and sent
out as a newline.
Variables in PHP are dealt with
very similar to CGI and C++.
$var = 23;
$othervar = 12;
$var++; // This makes $var be 24.
$var = $var + 2; // $var now is 26.
It can also be written as $var +=
2;
$var = $var + $othervar; // $var is
now 26 + 12, or 38.
Strings are dealt with a little
differently.
$firstname = "John";
$lastname = "Doe";
$fullname = $firstname . $lastname;
// A . is used combine strings.
$firstname .= " " . $lastname //
Makes $firstname become "John Doe".
Note the " " to add the space
between the names.
echo "Hi, $firstname!\n"; //
Outputs "Hi, John Doe!" with a
newline in the code. Newlines are
used to make code easier to read.
Next lesson!
Lesson III: Loops, loops, and more
loops!
What is a loop? A loop is simply a
structure of code that repeats
itself until a certain point has
been reached. Let's start with the
while loop.
echo "Let's count to 10!";
// There's no need to set $x to 0,
PHP assumes all unset variables to
be 0.
while ($x < 11) { // < means less
than, > means more than. You could
also make this $x != 11
echo $x . " ";
$x++;
}
This would output: 1 2 3 4 5 6 7 8
9 10
Simple, eh? The code can also be
structured like so:
do {
echo $x . " ";
$x++;
} while ($x < 11);
Same exact output, just the while
statement is checked at the end of
the code.
For loops are quite similar, and a
little more complex.
for($x = 1; $x < 11; $x++) {
echo $x . " ";
}
On we go!
Lesson IV: Using Forms
Now that you've heard all this talk
of variables and loops and the
such, you're probably asking, "How
in the heck is this going to help
me?" Well, I'll show you. Say you
had a php3 file named demo.php3
with the following form in it:
<?php
function displayform() { //
functions are code that is run only
when called.
global $PHP_SELF; // The script
itself, demo.php3. To make the
variable accessible in all
functions, use global.
?>
<FORM METHOD="POST" ACTION="<?php
echo $PHP_SELF; ?>"> // see how we
made it act on itself?
Name: <INPUT TYPE="text"
NAME="name">
<input type="submit"
value="Submit"><input type="reset"
value="Reset">
</FORM>
<?
}
function doform() {
global $name;
if ($name = "John Smith") { echo
"Hey John!"; } else { echo "Who are
you?"; }
}
if (empty($name)) {
displayform(); // If the variable
wasn't set, make the form reappear.
} else {
doform(); // If it was, process the
form.
}
Of course, there is many more
practical usages and ways to code
this. It's coded simply so you
could easily understand. Next
lesson!
Lesson V: Cookies!
Cookies, although often put down,
are a very powerful part of web
programming. Let's say you wanted
to give a user a nickname, but you
wanted it to store over a long
period of time. No problem! Here's
the code for cookie.php3
<?php
function addcookie() {
$nick = "Sammy"; // The value of
the cookie
$var = "nick"; // The name of the
cookie
setcookie($var,$nick,time()+360);
// add the cookie, with the name
"nick" and the value "Sammy", and
make it last 5 minutes.
Header("Location: cookie.php3"); //
Send the user back to this script.
Note: Header must be used BEFORE
any other output.
}
function docookie() {
$nickname =
$HTTP_COOKIE_VARS["nick"]; // set
the value of the cookie "nick" to
$nickname
echo " Hi $nickname!";
}
if (!$HTTP_COOKIE_VARS["nick"]) {
// Check to see if the cookie
"nick" exists, if not, set it. If
so, execute the code.
addcookie();
} else { docookie(); }
?>
Easy, huh? That's about it for now,
look for more advanced stuff coming
your way soon.
⌐ 1999 Shaun McCormick
⌐ 1999 dotcomma. All Rights Reserved.