Introduction
Up until recently, scripting on the internet was something which very few people
even attempted, let alone mastered. Recently though, more and more people have
been building their own websites and scripting languages have become more important.
Because of this, scripting languages are becomming easier to learn and PHP is
one of the easiest and most powerful yet.
What Is PHP?
PHP stands for Hypertext Preprocessor and is a server-side language. This means
that the script is run on your web server, not on the user's browser, so you
do not need to worry about compatibility issues. PHP is relatively new (compared
to languages such as Perl (CGI) and Java) but is quickly becomming one of the
most popular scripting languages on the internet.
Why PHP?
You may be wondering why you should choose PHP over other languages such as
Perl or even why you should learn a scripting language at all. I will deal with
learning scripting languages first. Learning a scripting language, or even understanding
one, can open up huge new possibilities for your website. Although you can download
pre-made scripts from sites like Hotscripts (www.hotscripts.com), these will
often contain advertising for the author or will not do exactly what you want.
With an understanding of a scripting language you can easily edit these scripts
to do what you want, or even create your own scripts.
Using scripts on your website allows you to add many new 'interactive' features
like feedback forms, guestbooks, message boards, counters and even more advanced
features like portal systems, content management, advertising managers etc.
With these sort of things on your website you will find that it gives a more
professional image. As well as this, anyone wanting to work in the site development
industry will find that it is much easier to get a job if they know a scripting
language.
What Do I Need?
As mentioned earlier, PHP is a server-side scripting language. This means that,
although your users will not need to install new software, you web host will
need to have PHP set up on their server. It should be listed as part of your
package but if you don't know if it is installed you can find out using the
first script in this tutorial. If you server does not support PHP you can ask
your web host to install it for you as it is free to download and install. If
you need a low cost web host which supports PHP I would recommmend HostRocket.
Writing PHP
Writing PHP on your computer is actually very simple. You don't need any specail
software, except for a text editor (like Notepad in Windows). Run this and you
are ready to write your first PHP script.
Declaring PHP
PHP scripts are always enclosed in between two PHP tags. This tells your server
to parse the information between them as PHP. The three different forms are
as follows:
<?
PHP Code In Here
?>
<?php
PHP Code In Here
php?>
<script language="php">
PHP Code In Here
</script>
All of these work in exactly the same way but in this tutorial I will be using
the first option (<? and ?>). There is no particular reason for this,
though, and you can use either of the options. You must remember, though, to
start and end your code with the same tag (you can't start with <? and end
with </script> for example).
Your First Script
The first PHP script you will be writing is very basic. All it will do is print
out all the information about PHP on your server. Type the following code into
your text editor:
<?
phpinfo();
?>
As you can see this actually just one line of code. It is a standard PHP function
called phpinfo which will tell the server to print out a standard table of information
giving you information on the setup of the server.
One other thing you should notice in this example is that the line ends in
a semicolon. This is very important. As with many other scripting and programming
languages nearly all lines are ended with a semicolon and if you miss it out
you will get an error.
Finishing and Testing Your Script
Now you have finished your script save it as phpinfo.php and upload it to your
server in the normal way. Now, using your browser, go the the URL of the script.
If it has worked (and if PHP is installed on your server) you should get a huge
page full of the information about PHP on your server.
If your script doesn't work and a blank page displays, you have either mistyped
your code or your server does not support this function (although I have not
yet found a server that does not). If, instead of a page being displayed, you
are prompted to download the file, PHP is not installed on your server and you
should either serach for a new web host or ask your current host to install
PHP.
It is a good idea to keep this script for future reference
Printing Text
To output text in your PHP script is actually very simple. As with most other
things in PHP, you can do it in a variety of different ways. The main one you
will be using, though, is print. Print will allow you to output text, variables
or a combination of the two so that they display on the screen.
The print statement is used in the following way:
print("Hello world!");
I will explain the above line:
print is the command and tells the script what to do. This is followed by the
information to be printed, which is contained in the brackets. Because you are
outputting text, the text is also enclosed instide quotation marks. Finally,
as with nearly every line in a PHP script, it must end in a semicolon. You would,
of course, have to enclose this in your standard PHP tags, making the following
code:
<?
print("Hello world!");
?>
Which will display:
Hello world!
on the screen.
Variables
As with other programming languages, PHP allows you to define variables. In
PHP there are several variable types, but the most common is called a String.
It can hold text and numbers. All strings begin with a $ sign. To assign some
text to a string you would use the following code:
$welcome_text = "Hello and welcome to my website.";
This is quite a simple line to understand, everything inside the quotation
marks will be assigned to the string. You must remember a few rules about strings
though:
Strings are case sensetive so $Welcome_Text is not the same as $welcome_text
String names can contain letters, numbers and underscores but cannot begin with
a number or underscore
When assigning numbers to strings you do not need to include the quotes so:
$user_id = 987
would be allowed.
Outputting Variables
To display a variable on the screen uses exactly the same code as to display
text but in a slightly different form. The following code would display your
welcome text:
<?
$welcome_text = "Hello and welcome to my website.";
print($welcome_text);
?>
As you can see, the only major difference is that you do not need the quotation
marks if you are printing a variable.
Formatting Your Text
Unfortunately, the output from your PHP programs is quite boring. Everything
is just output in the browser's default font. It is very easy, though, to format
your text using HTML. This is because, as PHP is a server side language, the
code is executed before the page is sent to the browser. This means that only
the resulting information from the script is sent, so in the example above the
browser would just be sent the text:
Hello and welcome to my website.
This means, though, that you can include standard HTML markup in your scripts
and strings. The only problem with this is that many HTML tags require the "
sign. You may notice that this will clash with the quotation marks used to print
your text. This means that you must tell the script which quotes should be used
(the ones at the beginning and end of the output) and which ones should be ignored
(the ones in the HTML code).
For this example I will change the text to the Arial font in red. The normal
code for this would be:
<font face="Arial" color="#FF0000">
</font>
As you can see this code contains 4 quotation marks so would confuse the script.
Because of this you must add a backslash before each quotation mark to make
the PHP script ignore it. The code would change to:
<font face=\"Arial\" color=\"#FF0000\">
</font>
You can now include this in your print statement:
print("<font face=\"Arial\" color\"#FF0000\">Hello
and welcome to my website.</font>");
which will make the browser display:
Hello and welcome to my website.
because it has only been sent the code:
<font face="Arial" color="#FF0000">Hello and welcome
to my website.</font>
This does make it quite difficult to output HTML code into the browser but
later in this tutorial I will show you another way of doing this which can make
it a bit easier
The Basics Of IF
If statements are used to compare two values and carry out different actions
based on the results of the test. If statements take the form IF, THEN, ELSE.
Basically the IF part checks for a condition. If it is true, the then statement
is executed. If not, the else statement is executed.
IF Strucure
The structure of an IF statement is as follows:
IF (something == something else) (
THEN Statement
} else {
ELSE Statement
}
Variables
The most common use of an IF statement is to compare a variable to another
piece of text, a number, or another variable. For example:
if ($username == "webmaster")
which would compare the contents of the variable to the text string. The THEN
section of code will only be executed if the variable is exactly the same as
the contents of the quotation marks so if the variable contained 'Webmaster'
or 'WEBMASTER' it will be false.
Constructing The THEN Statment
To add to your script, you can now add a THEN statement:
if ($username == "webmaster") {
echo "Please enter your password below";
}
This will only display this text if the username is webmaster. If not, nothing
will be displayed. You can actually leave an IF statement like this, as there
is no actual requirement to have an ELSE part. This is especially useful if
you are using multiple IF statements.
Constructing The ELSE Statement
Adding The ELSE statement is as easy as the THEN statement. Just add some extra
code:
if ($username == "webmaster") {
echo "Please enter your password below";
} else {
echo "We are sorry but you are not a recognised user";
}
Of course, you are not limited to just one line of code. You can add any PHP
commands in between the curly brackets. You can even include other IF statments
(nested statements).
Other Comparisons
There are other ways you can use your IF statement to compare values. Firstly,
you can compare two different variables to see if their values match e.g.
if ($enteredpass == $password)
You can also use the standard comparision symbols to check to see if one variable
is greater than or less than another:
if ($age < "13")
Or :
if ($date > $finished)
You can also check for multiple tests in one IF statement. For instance, if
you have a form and you want to check if any of the fields were left blank you
could use:
if ($name == "" || $email == "" || $password == "")
{
echo "Please fill in all the fields";
}
The WHILE Loop
The WHILE loop is one of the most useful commands in PHP. It is also quite
easy to set up and use. A WHILE loop will, as the name suggests, execute a piece
of code until a certain condition is met.
Repeating A Set Number Of Times
If you have a piece of code which you want to repeat several times without
retyping it, you can use a while loop. For instance if you wanted to print out
the words "Hello World" 5 times you could use the following code:
$times = 5;
$x = 0;
while ($x < $times) {
echo "Hello World";
++$x;
}
I will now explain this code. The first two lines are just setting the variables.
The $times variable holds the number of times you want to repeat the code. The
$x variable is the one which will count the number of times the code has been
executed. After these is the WHILE line. This tells the computer to repeat the
code while $i is less than $times (or to repeat it until $i is equal to $times).
This is followed by the code to be executed which is enclosed in { }.
After the echo line which prints out the text, there is another very important
line:
++$x;
What this does is exactly the same as writing:
$x = $x + 1;
It adds one to the value of $x. This code is then repeated (as $x now equals
1). It continues being repeated until $x equals 5 (the value of times) when
the computer will then move on to the next part of the code.
Using $x
The variable counting the number of repeats ($x in the above example) can be
used for much more than just counting. For example if you wanted to create a
web page with all the numbers from 1 to 1000 on it, you could either type out
every single one or you could use the following code:
$number = 1000;
$current = 0;
while ($current < $number) {
++$current;
echo "$current<br>";
}
There are a few things to notice about this code. Firstly, you will notice
that I have placed the ++$current; before the echo statement. This is because,
if I didn't do this it would start printing numbers from 0, which is not what
we want. The ++$current; line can be placed anywhere in your WHILE loop, it
does not matter. It can, of course, add, subtract, multiply, divide or do anthing
else to the number as well.
The other reason for this is that, if the ++$current; line was after the echo
line, the loop would also stop when the number showed 999 because it would check
$current which would equal 1000 (set in the last loop) and would stop, even
though 1000 had not yet been printed.
Arrays
Arrays are common to many programing languages. They are special variables
which can hold more than one value, each stored in its own numbered 'space'
in the array. Arrays are extremely useful, especially when using WHILE loops.
Setting Up An Array
Setting up an array is slightly different to setting up a normal variable.
In this example I will set up an array with 5 names in it:
$names[0] = 'John';
$names[1] = 'Paul';
$names[2] = 'Steven';
$names[3] = 'George';
$names[4] = 'David';
As you can see, the parts of an array are all numbered, starting from 0. To
add a value to an array you must specify the location in the array by putting
a number in [ ].
Reading From An Array
Reading from an array is just the same as putting information in. All you have
to do is to refer to the array and the number of the piece of data in the array.
So if I wanted to print out the third name I could use the code:
echo "The third name is $names[2]";
Which would output:
The third name is Steven
Using Arrays And Loops
One of the best uses of a loop is to output the information in an array. For
instance if I wanted to print out the following list of names:
Name 1 is John
Name 2 is Paul
Name 3 is Steven
Name 4 is George
Name 5 is David
I could use the following code:
$number = 5
$x = 0
while ($x < $number) {
$namenumber = $x + 1
echo "Name $namenumber is $names[$x]<br>";
++$x
}
As you can see, I can use the variable $x from my loop to print out the names
in the array. You may have noticed I am also using the variable $namenumber
which is always 1 greater than $x. This is because the array numbering starts
from 0, so to number the names correctly in the output I must add one to the
actual value
Mail is extremely easy to send from PHP, unlike using scripting languages which
require special setup (like CGI). There is actually just one command, mail()
for sending mail. It is used as follows:
mail($to,$subject,$body,$headers);
In this example I have used variables as they have descriptive names but you
could also just place text in the mail command. Firstly, $to. This variable
(or section of the command) contains the e-mail address to which the mail will
be sent. $subject is the section for the subject of the e-mail and $body is
the actual text of the e-mail.
The section $headers is used for any additional e-mail headers you may want
to add. The most common use of this is for the From field of an e-mai but you
can also include other headers like cc and bcc.
Sending An E-mail
Before sending your mail, if you are using variables, you must, of course,
set up the variable content beforehand. Here is some simple code for sending
a message:
$to = "david@gowansnet.com";
$subject = "PHP Is Great";
$body = "PHP is one of the best scripting languages around";
$headers = "From: webmaster@gowansnet.com\n";
mail($to,$subject,$body,$headers);
echo "Mail sent to $to";
This code will acutally do two things. Firstly it will send a message to david@gowansnet.com
with the subject 'PHP Is Great' and the text:
PHP is one of the best scripting languages around
and the e-mail will be from webmaster@gowansnet.com. It will also output the
text:
Mail sent to david@gowansnet.com
to the browser.
Formatting E-mail
Something you may have noticed from the example is that the From line ended
with \n. This is acutally a very important character when sending e-mail. It
is the new line character and tells PHP to take a new line in an e-mail. It
is very important that this is put in after each header you add so that your
e-mail will follow the international standards and will be delivered.
The \n code can also be used in the body section of the e-mail to put line
breaks in but should not be used in the subject or the To field.
Mail Without Variables
The e-mail above could have been sent using different variable names (it is
the position of the variables in relation to the commas, not the name of them
which decides on their use). It could also have been done on one line using
text like this:
mail("david@gowansnet.com","PHP Is Great","PHP is
one of the best scripting languages around","From: webmaster@gowansnet.com\n");
But that would make your code slightly harder to read.
Error Control
As anyone who has been scription for a while will know, it is extremely easy
to make mistakes in your code and it is also very easy to input an invalid e-mail
address (especially if you are using your script for form to mail). Because
of this, you can add in a small piece of code which will check if the e-mail
is sent:
if(mail($to,$subject,$body,$headers)) {
echo "An e-mail was sent to $to with the subject: $subject";
} else {
echo "There was a problem sending the mail. Check your code and make sure
that the e-mail address $to is valid";
}
This code is quite self explanitory. If the mail is sent successfully it will
output a message to the browser telling the user, if not, it will display an
error message with some suggestions for correcting the problem.
Setting up a form for use with a PHP script is exactly the same as normal in
HTML. As this is a PHP tutorial I will not go into depth in how to write your
form but I will show you three of the main pieces of code you must know:
<input type="text" name="thebox" value="Your Name">
Will display a text input box with Your Name written in it as default. The
value section of this code is optional. The information defined by name will
be the name of this text box and should be unique.
<textarea name="message">
Please write your message here.
</textarea>
Will display a large scrolling text box with the text 'Please write your message
here.' as default. Again, the name is defined and should be unique.
<input type="submit" value="Submit">
This will create a submit button for your form. You can change what it says
on the button by changing the button's value.
All the elements for your form must be enclosed in the <form> tags. They
are used as follows:
<form action="process.php" method="post">
Form elements and formatting etc.
</form>
The form's action tells it what script to send its data to (in this case its
process.php). This can also be a full URL (e.g. http://www.mysite.com/scripts/private/processors/process.php).
The method tells the form how to submit its data. POST will send the data in
a data stream to the script when it is requested. GET is the other option. GET
will send the form data in the form of the url so it would appear after a question
mark e.g. http://www.mysite.com/process.php?name=david
It really makes no difference which system you use but it is normally better
to use POST if you are using passwords or sensitive information as they should
not be shown in the browser's address bar.
Getting The Form Information
The next step is to get the data the form has submitted into your script so
that you can do something with it. This is, unlike many scripting languages,
extremely simple. Basically, the data can be used in the script using the name
you gave the form element in the input page. For example, above there was a
field called message. If you wanted to use this input in your script you would
could use the variable $message which would contain the appropriate data. You
must be careful though not to accidentally overwrite these values in your script
as defining the variables as something else.
One other point which I should mention here is that you can also submit information
to the script in a standard URL. This works the same as submitting a form using
GET. The advantage of this is that you can create links to your scripts which
do different things depending on the link clicked. For example you could create
a script which will show different pages depending on the link clicked:
yourpage.php?user=david
could show David's page and:
yourpage.php?user=tom
could show Tom's page, using the same script.
You can access these variables, as above, using the $user variable.
It is also possible to pass more than one piece of information to the script
using this system by separating them with the & symbol:
yourpage.php?user=david&referrer=gowansnet&area=6
These could all be accessed separately using the variables $user, $referrer
and $area.
Creating The Form To Mail Script
To finish off this section, I will show you how to use what you have learnt
in this part and the last to create a system which will e-mail a user's comments
to you.
Firstly, create this form for your HTML page:
<form action="mail.php" method="post">
Your Name: <input type="text" name="name"><br>
E-mail: <input type="text" name = "email"><br><br>
Comments<br>
<textarea name="comments"></textarea><br><br>
<input type="submit" value="Submit">
</form>
This will make a simple form where the user can enter their e-mail address,
their name and their comments. You can, of course, add extra parts to this form
but remember to update the script too. Now create the PHP script:
<?
$to="webmaster@gowansnet.com";
$message="$name just filled in your comments form. They said:\n$comments\n\nTheir
e-mail address was: $email";
if(mail($to,"Comments From Your Site",$message,"From: $email\n"))
{
echo "Thanks for your comments.";
} else {
echo "There was a problem sending the mail. Please check that you filled
in the form correctly.";
}
?>
Remember to replace webmaster@gowansnet.com with your own e-mail address. This
script should be saved as mail.php and both should be uploaded. Now, all you
need to do is to fill in your comments form
As with any programming language, it is quite important to comment in your
script. If you are working on a script with someone else you must let them know
what you code does and if you are distributing your script you will need to
show people how to edit it. Even if you are the only one who will use your script
it is useful to comment so that you can edit it at a later date.
In PHP there are two ways you can comment. One way is used for single line
comments and the other is used mainly for comments that go over one line. A
single line comment is written as follows:
// Your comment can go in here
Everything after the // will be ingnored when the script is executed. You can
even place these on the end of another line e.g.
print "Hello $name"; // Welcome to the user
Another way of commenting is by using multi-line comments:
/* The following piece of code will take the input
the user gave and will check that it is valid before
adding it to the database */
Anything between the /* and the */ will be ignored. It is important that you
always close this type of comment as not doing so could make your script not
work.
Print, Echo and HTML
As you may have noticed during this tutorial I have actually used 4 different
ways of outputting information to the browser:
echo("Text here");
echo "Text here";
print("Text here";
print "Text here";
To clarify, all of these do the same thing and you can use any or all of them
in a script. There is no reason to even use the same type all through a script.
The only problem you may find is that, as I explained in part 2, all the "
in the HTML code must be replaced with \" which, if you have a lot of code,
could take a very long time. This brings me to a very useful part of PHP. If,
for example, you created the header of a page dynamically in PHP, then had the
static page and finally a dynamic footer you can do the following:
<?
Top PHP code in here
?>
HTML Code
<?
Bottom PHP code in here
?>
This gets even better as the PHP code will just continue from where it was
left off so you could do the following:
<?
IF Statement {
?>
HTML For IF Being Correct
<?
} else {
?>
HTML For IF Being Wrong
<?
}
?>
You must always remember to close IF statements and loops, though, as it is
very easy to forget.
One Line Prints
Being able to place HTML code into your PHP is very useful, but what happens
if you want to put the value of a variable into the code. Unlike when using
an echo or print statement, you can't just put in the variable name as this
section is not actually part of the PHP code. Instead you must just put in a
little PHP.
For example if you wanted to print someone's name from a script with HTML formatting
you would do the following:
<font face="Arial" size="7" color="red"><b><?
echo($variablename); ?></b></font>
In the above code you have just added in the following PHP:
<? echo($variablename); ?>
Which is exactly the same as the following PHP code:
<?
echo($variablename);
?>
But all put onto one line.
Conclusion
This tutorial has given you some of the basics of PHP and should allow you
to do most things you will want to. For a much more in depth look you should
visit PHP.net, the official homepage of PHP. One major omission of this tutorial,
you may have noticed, is using PHP with a database. As this is one of the major
reasons that people use PHP and because there are many options I will put this
in a separate PHP/MySQL tutorial
