Introduction to PHP programming
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PHP is a language for easily building dynamic web pages. It provides
an easier way to accomplish web related programming tasks, which
are accomplished only with difficulty in more complex and powerful
languages, such as Perl or C. It is ideally suited to the web because
PHP scripts live inside web pages right along with the HTML tags and
content. For that reason, PHP is called an embedded scripting
language. Developers can embed programs in their web pages, making
the dynamic. They can treat programs just like web pages. PHP pages
can contain both regular HTML and PHP code. This allows you to
develop web applications quickly. However, unlike some web scripting
languages, PHP makes a clear distinction between sections of PHP code
and sections of the HTML document. When the web server fills a
request for a PHP enabled page, it first looks through the page content
for sections of PHP code and executes any it finds. Any normal HTML
sections are passed to the browser without any changes. This means
that you can freely mix snippets of program into a web page
anywhere.
Why Use PHP?
Here are a few good reasons to choose PHP for enabling interactive
content on your web site (besides being open source):
Because it uses similar syntax and constructs, knowledge of PHP can
help you in learning the C language.
The data types and structures of PHP are easy to use and understand,
PHP knows what you mean and can convert types automatically.
You don't have to know any special commands to compile your
program, it runs right in your web browser.
You don't have to know everything there is to know about PHP to start
writing useful programs.
PHP serves as a "wrapper" for many standard C libraries, which are
easily compiled into the language giving it the flexibility to respond
more rapidly to changes in web technology or trends.
Things you can do in PHP can be done in other languages, but PHP was
designed to work in a web context, so things that are difficult or
tedious for the applications programmer to "roll their own" in Perl (my
favorite language) are easy in PHP. PHP enabled web sites can be
deployed with amazing rapidity, due to its being tuned for dynamic
pages and database backends.
You don't have to know everything there is to know about PHP before
you can write useful programs. So we will start with a few simple
examples.
Embedding snippets of code into a web page has many uses. For
example, in an otherwise static web page you may obtain the value of
a variable and later use it to dynamically change the content of the
page. This PHP example displays the text identifying the web browser
on a web page.
<?php
$browser = getenv("HTTP_USER_AGENT");
?>
<P>You are using the <?php echo($browser);?> web browser.
</P>
Hello World
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The quickest way to learn PHP is to start using it and see what
happens. We'll start by diving right into the good old "Hello World"
script you may have seen when learning other languages. It simply
prints "Hello World" to the browser screen using the echo() function.
Each line of code is requires a semicolon at the end. You will probably
forget to add the semicolon from time to time and your script will
display a syntax error. They are easy to miss. I still leave them off. If
you've used a number of programming languages, they all do not use
the semicolon as their end of line terminating character, so it's easy to
slip up. I sometimes find myself typing C in Perl or Perl in PHP. Perl
syntax is very different from PHP, which is more formal with its C
influenced functional syntax. For example in Perl you can pretty much
drop a regular expression into a statement anywhere, but in PHP you
must explicitly make a function call to a regular expression function
(ereg() or the Perl-like preg(). What might be natural for a Perl
aficionado to code right into their program without thinking, requires
putting the regular expression into a function in PHP.
PHP code is delimited by left < and right > brackets. This gives a one
line PHP program the appearance of an HTML tag. One liners are often
used for outputing content mixed right into HTML.
<?php echo("Hello World\n"); ?>
<?php print "Hello World\n"; ?>
<?php print "Hello World<br>"; ?>
Most people favor the print function over echo(), I think for clarity.
"echo" is a term that might cause confusion while "print" is obvious.
The echo() function sends one or more strings of text to the browser
for display. Actually, echo is not function but a "language construct"
but you do not have to worry about that. It acts like a function. But it
does mean that you can save some typing. As a result, the parenthesis
are not required. Now, lets take a look at some of the typical PHP
syntax in the script. The beginning and end of a PHP code section is
marked by angle brackets (less than and greater than signs) followed
or preceded by a question mark. The end of each line is marked by a
semicolon. The "\n" is a special "escape code" meaning print a new
line (or "newline") that represents a line break in plain text. This is
how you would print text to be displayed in a textarea field. For
printing to a web page, you need to specify line break tags as the third
example shows. Something more appropriate for the web, which leads
us into the next topic.
Hello Web
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Hello World was great for programs that ran on the command line or in
a graphical user interface. But the Hello World script needs to be
updated for the web, where the basic unit of interaction is the form.
>This is the simplest possible form handling script. It accepts a value
from one input, the person's name and then responds by displaying it
in the browser window.
hello-web.html
<form action="hello-web.php" method="post">
<td>Name:</td>
<td><input type="text" name="frmName" size="24">
<input type="submit" value="Submit">
</form>
Because PHP accepts the values submitted from the form and
automatically creates variables from the form input names, only one
line is needed to generate a response. And because PHP assumes that
it is working within the context of a web page, it automatically
generates a HTTP header, telling the browser to display any text
output.
hello-web.php
<p>Hello
<?php echo($frmName); ?>!
First, PHP outputs a content type header stating the following output is
to be HTML. It then sends the P tag and "Hello" to the browser
untouched. Once encountering the PHP start tag, it then executes the
code until it reaches the PHP end tag. We value from the input
parameter "for free" as PHP automatically creates it and initializes it
with the value input by the form. In PHP, a variable will be created for
any form input value or URL parameter and environment variable that
has a value. At that point, it switches back to HTML mode and outputs
the exclamation point and the script terminates.
A slightly more complete example than the hello-web script is
presented here. It illustrates the concept all in one package without
needing a separate html form. This is the basic structure of many
browser based applications.
If the form variable does not exist in the CGI enviorment, we know to
display the form asking the user for their name. It illustrates the
concept all in one package without needing a separate html form. This
is the basic structure of many browser based applications.
<?php
if(!$frmName)
{
// Switch to HTML mode to display form
?>
<form action="hello-web.php" method="post">
Name:
<input type="text" name="frmName" size="24">
<input type="submit" value="Submit">
<?php
}else{
?>
Hello <?php echo($frmName); ?>
!
<?php
}
?>
At the very end we switch back to PHP mode just to close the else
clause. This may be overkill in this small application, but this kind of
mode switching part of the php-way. You could use echo or print
commands and forget the mode switching. Which to use depends on
the situation and your mood. ;)
This script hints at how "finite-state machines" implemented as
switch/case statements are at the core of many scripts that handle
web based interactions. This one has only two states: invite the user
to submit data and post submitted data back to the web. So an IF
statement is sufficient.
Dynamic Content
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I'm sure you're interested in doing more with PHP than saying hello to
the world. Otherwise, you probably would not be here reading about
an HTML-embedded scripting language. You want a script that does
something useful. Let's go deeper into PHP by writing a Tip of the Day
script. It will introduce several new functions and concepts, but you do
not have to understand them all at once. It also offers an introduction
to working with the file system.
<?php
srand((double)microtime()*1000000);
$tiplist = file("photo.tips");
$ntips = sizeof($tiplist);
$rtip = rand(0,$ntips-1);
$tip = $tiplist[$rtip];
echo $tip;
?>
The first line of the script opens a file called photo.tips (remember,
Unix does not care about so-called "file extensions" found in Windows,
so we don't need ".txt" at the end to identify it as a text file). There is
no need to write anything to the file because we will just be reading
and displaying a line of text from it. Using the file() function, each line
of the file is read into the array $tiplist. We do not have to specify any
file handles because the file() function takes a filename as an
argument and returns an array as a result.. Each element of the array
corresponds to a line of the file. The newline character is still attached
to each string in the array. The tips file contains several tips, each on a
line.
Next, we find the number of elements in the tips list array by using the
sizeof() function. It returns the number of elements in an array. The
following line generates a random number between zero and the
number of tips read from the tips file. rand(n,m) returns a random
number between n and m (we must specify a range between 0 and 3 if
there are 3 tips because the range is inclusive). Because PHP arrays
start a zero, we set our random number to between zero and the
number of tips minus one. The randomly generated number is used as
an index into the tips list. The script randomly selects a tip from the
list using this index. The text of the selected tip is then output to the
browser through the echo() function. Since we already have the
string in a variable, we don't need any quotes around it.
Note: easytips.php3 is available for examination. You can try it out by
clicking on the link and see it's source by clicking on the Source link.
Copy the source to your own file and upload it to your web server
running PHP. Try it!
This script nicely illustrates the PHP philosophy of working within the
what is called "the HTML-context." If you notice, the script is inside the
HTML code, and that the script is a web page that can be placed
anywhere on the site. Because PHP scripts generate output after a
"Content-type: text/html" MIME header is output to the browser, any
output they generate will appear in the browser window. This also
allows PHP code to be directly mixed with HTML code on the page. A
special cgi-bin is unnecessary for PHP scripts.
htaccess Password Protection
Learn how to super protect your files without the use of mySQL.
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This tutorial will help you learn how to password protect your file quickly and easily in a few lines of
code.
The code can be split up into three if-else statements. Let's take a look at what we will have to do in
order to set up the password protection:
1.
If the user has not been authenticated, then use the PHP header and ask for a username
and password.
2.
Else, if the user's name is "spoono" and the password is "spoono", log in. Inside here you
would put all the code for the user.
3.
Else tell them the user/password failed.
Finally, here is the PHP Code:
<?
//part 1
if (!isset($PHP_AUTH_USER))
{
header("WWW-Authenticate: Basic realm=\"Spoono Password.\"");
Header("HTTP/1.0 401 Unauthorized");
exit;
}
//part 2
else if(($PHP_AUTH_USER=="spoono") && ($PHP_AUTH_PW=="spoono"))
{
echo "You got in...";
//place the code for the whole user page in here
//you can also set up a redirect to the user page if you want
}
//part 3
else
{
echo "<html><body bgcolor=ffffcc>Faiiiiiiiil";
//fail try again
}
?>
Some notes about this script: it is essential to note that this username and password will last the
whole session, that means that as long as that explorer window is open, the name and password
will be saved for that realm. So if you mistyped the name or the password, you'll have to close the
explorer window and re-open it and try again. Not too tough was it? Well thats it folks. I hope it
works out for you and if it doesn't, email for help at webmaster@spoono.com and we'll try to help
you out.