PHP
Scripting was something which very few people even attempted, let alone mastered. Recently , more and more people have begun building their own websites and scripting languages have become more important. Because of this, scripting languages have evolved and as a consequence becoming easier to learn. PHP is one of the best and most powerful to date.
This article will give 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 article, 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 article.
Please note the sample scripts supplement explanation, and not suitable for copying and pasting into your project. Also when using samples from other sources you should ensure the related PHP version is the same as this server.
PHP Manual is an excellent starting point should you need further assistance.
What Is PHP?
(PHP Info)
PHP stands for Hypertext Pre-processor 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 as with JavaScript. PHP is relatively new (compared to
languages such as Perl (CGI) and Java) but is quickly becoming 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. We will deal with learning scripting languages first. Learning
a scripting language, or even understanding one, can open up many
new possibilities for your website. Although you can download
pre-made scripts from sites like Hot scripts, 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, guestbook's, 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 , PHP is a server-side scripting language. This means
that although your users will not need to install new software, your
web host (ISP) 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 your server does not support PHP you can ask your web
host to install it for you as it is free to download and install.
Writing PHP
Writing PHP on your computer is actually quite straight forward. You
don't need any special software, except for a text editor (like
textpad in Windows). Run this and you are ready to write your first
PHP script. Please note that some text editors (Notepad) introduced
non-displayed characters at the end of a line of text that may
confuse the PHP interpreter.
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
PHP Code In Here
?>
<?php
PHP Code In Here
?>
<script language="php">
PHP Code In Here
</script>
All of these work in exactly the same way but in this article we
will be using the first option (<? and ?>). There is no particular
reason for this, and you can use either of the options. You must
remember, 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:
<?php
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 you must
upload it to your server (TODO Transferring
Files). Using your browser, go the the URL (http://cet-apache-02.cet.bolton.ac.uk/student/[username]/[script
name] If it has worked (and if PHP is installed on your server) you
should get a long page full of the information about PHP on this
server.
If your script doesn't work and a blank page displays, you have
either mistyped your code or you have not referenced the file
correctly.
It is a good idea to keep this script for future reference.
Section 2
In the last section we explained some of the advantages of PHP as a
scripting language and showed you how to test your server for PHP.
In this section we will show you the basics of showing information
in the browser and how you can use variables to hold information.
Printing Text
To output text in your PHP script. As with several other techniques
in PHP, you can do it in a variety of different ways. The main one
we will be using, 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!");
Above line explanation:
print is a 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
by 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 sample:
<?php
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 sensitive 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:
<?php
$welcome_text = "Hello and welcome to my website.";
print($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 repetitive.
Everything is just output in the browser's default font. 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.
(TODO)
This means, though, that you can include standard HTML mark-up 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 difficult to output HTML code into the
browser but later in this we will show you another way of
doing this which can make it easier.
Section 3
Over the past
two sections we have shown you the basics of text in PHP and how to
store it as variables. In this part we will show you
how to use IF statements to make decisions in your scripts.
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 Structure
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 ($username == "webmaster")
which would compare the contents of the variable to the text string.
The THEN section of code will only be executed if the variable is
exactly the same as the contents of the quotation marks so if the
variable contained 'Webmaster' or 'WEBMASTER' it will be false.
Constructing The THEN
Statement
To add to your script, you can now add a THEN statement:
if ($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 ($username == "webmaster") {
echo "Please enter your password below";
} else {
echo "We are sorry but you are not a recognized user";
}
Of course, you are not limited to just one line of code. You can add
any PHP commands in between the curly brackets. You can even include
other IF statements (nested statements).
Other Comparisons
There are other ways you can use your IF statement to compare
values. Firstly, you can compare two different variables to see if
their values match e.g.
if ($enteredpass == $password)
You can also use the standard comparison symbols to check to see if
one variable is greater than or less than another:
if ($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";
}
Section 4
In the last parts of this tutorial I have showed you how to deal
with text and variables in PHP and how you can use IF statements to
compare them and to make decisions. In this part I am going to show
you how to use another important part of PHP, loops.
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 ++$current; line can be
placed anywhere in your WHILE loop, it does not matter. It can, of
course, add, subtract, multiply, divide or do anything else to the
number as well.
The other reason for this is that, if the ++$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 programming 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:
n
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 $x. This is
because the array numbering starts from 0, so to number the names
correctly in the output I must add one to the actual value.
Section 5
One of the
major uses of a server side scripting language is to provide a way
of sending e-mail from the server and, in particular, to take form
input and output it to an e-mail address. In this part I will show
you how to send e-mail messages using PHP.
The Mail Command
Mail is extremely easy to send from PHP, unlike using scripting
languages which require special setup (like CGI). There is actually
just one command, mail() for sending mail. It is used as follows:
mail($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 = "php@cet.bolton.ac.uk";
$subject = "PHP Is Great";
$body = "PHP is one of the best scripting languages around";
$headers = "From: webmaster@cet.bolton.ac.uk\n";
mail($to,$subject,$body,$headers);
echo "Mail sent to $to";
This code will actually do two things. First it will send a
message to php@gowansnet.com with the subject 'PHP Is Great' and the
text:
PHP is one of the best scripting languages around
and the e-mail will be from webmaster@gowansnet.com. It will also
output the text:
Mail sent to php@gowansnet.com
to the browser.
Formatting E-mail
Something you may have noticed from the example is that the From
line ended with \n. This is actually a very important character when
sending e-mail. It is the new line character and tells PHP to take a
new line in an e-mail. It is very important that this is put in
after each header you add so that your e-mail will follow the
international standards and will be delivered.
The \n code can also be used in the body section of the e-mail to
put line breaks in but should not be used in the subject or the To
field.
Mail Without Variables
The e-mail above could have been sent using different variable names
(it is the position of the variables in relation to the commas, not
the name of them which decides on their use). It could also have
been done on one line using text like this:
mail("php@cet.bolton.ac.uk","PHP Is Great","PHP is one of the best
scripting languages around","From: webmaster@cet.bolton.ac.uk\n");
But that would make your code slightly harder to read.
Error Control
As anyone who has been scripting for a while will know, it is
extremely easy to make mistakes in your code and it is also very
easy to input an invalid e-mail address (especially if you are using
your script for form to mail). Because of this, you can add in a
small piece of code which will check if the e-mail is sent:
if(mail($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 self explanatory. 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.
Section 6
In the last
part, I showed you how to use PHP to send e-mail messages using a
script. In this part I will continue this and also show you how to
use PHP and forms together to make your PHP scripts useful.
Setting Up Your Form
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. There are
basically two different methods of getting the data into PHP, which
depend on how they were submitted. There are two submission methods,
GET and POST, which can both be used by forms. The difference
between the two is that using GET, the variables and data will be
shown in the page address, but using POST it is invisible. The
benefit of GET, though is that you can submit information to the
script without a form, by simply editing the 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.
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 GET variables user,
referrer and area.
To get a variable which has been sent to a script using the POST
method you use the following code:
$variablename=$_POST['variable'];
which basically takes the variable from the POST (the name of a form
field) and assigns it to the variable $variablename.
Similarly, if you are using the GET method you should use the form:
$variablename=$_GET['variable'];
This should be done for each variable you wish to use from your form
(or URL).
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:
<?php
function checkOK($field)
{
if (eregi("\r",$field) || eregi("\n",$field)){
die("Invalid Input!");
}
}
$name=$_POST['name'];
checkOK($name);
$email=$_POST['email'];
checkOK($email);
$comments=$_POST['comments'];
checkOK($comments);
$to="php@cet.bolton.ac.uk";
$message="$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: $email\n")) {
echo "Thanks for your comments.";
} else {
echo "There was a problem sending the mail. Please check that you
filled in the form correctly.";
}
?>
Remember to replace php@gowansnet.com with your own e-mail address.
This script should be saved as mail.php and both should be uploaded.
Now, all you need to do is to fill in your comments form.
The first part of that script may look a bit strange:
function checkOK($field)
{
if (eregi("\r",$field) || eregi("\n",$field)){
die("Invalid Input!");
}
}
You don't really need to worry about what this is doing, but
basically, it stops spammers from using your form to send their spam
messages by checking special characters are not present in the input
which can be used to trick the computer into sending messages to
other addresses. It is a function which checks for these characters,
and if they are found, stops running the script.
The lines:
checkOK($name);
etc. run this check on each input to ensure it is valid.
Section
7
In the past 6
parts of this tutorial I have shown you the basics of writing PHP.
In this final part I will show you a few small things which don't
really warrant a section of their own.
Comments
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 ignored 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