Difference between revisions of "PHP Original"

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==Sending a file to the Browser==
 
==Sending a file to the Browser==
  
Another useful function to know is the ''readfile'' function.  It takes a file on the webserver's file system and sends it to the web browser.  A simple example is given below, but note that you'll probably need to specify addition header fields in order to have the web browser download the file correctly.
+
Another useful function to know is the ''readfile'' function.  It takes a file on the webserver's file system and sends it to the web browser.  A simple example is given below, but note that you'll probably need to specify addition header fields in order to have the web browser download the file correctly. Note that
  
 
<code><pre>
 
<code><pre>

Revision as of 14:06, 10 June 2010

PHP5

PHP is a server-side language. When a web request for PHP file comes in, the web server processes the PHP file to produce HTML output. That is, the main function of most PHP scripts is to dynamically create HTML content. PHP5 support for Apache is provided by mod_php5. In Ubuntu, you can provide PHP5 support by installing php5. This will install the apache2 module and the php5 command line interpreter (useful for debugging). PHP files may have different extensions, but .php is the most common. In the Apache configuration, you can specify which extensions are going to be treated as PHP scripts by adding the extensions to the list in the /etc/httpd/conf.d/php.conf file:

 AddType text/html .php .phtml .php3

Declaring PHP

If a PHP file is requested by a web user, Apache parses and interprets the file. Any code declared between PHP tags is then executed and the total HTML output is sent back to the user. PHP code can be declared in a script file in any of the following ways, with the first being the most common:

<?
  PHP Code In Here
?>
<?php
  PHP Code In Here
php?>
<script language="php">
  PHP Code In Here
</script>

For example, edit a new PHP file named info.php, and put these lines in the file:

<? 
  phpinfo();
?>

Put the file in the web directory for your user account (remember that this is ~username/.html/ if you completed the first Module). Then access the web page by going to http://server/~username/info.php. You will see something similar to the picture below:

Php info.png


If you look at the HTML code, you will see quite a lot of HTML output:

 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "DTD/xhtml1-transitional.dtd">
 <html><head>
<style type="text/css">
 body {background-color: #ffffff; color: #000000;}
 body, td, th, h1, h2 {font-family: sans-serif;}
 pre {margin: 0px; font-family: monospace;}
 a:link {color: #000099; text-decoration: none; background-color: #ffffff;}
 a:hover {text-decoration: underline;}
 table {border-collapse: collapse;}
 .center {text-align: center;}
 .center table { margin-left: auto; margin-right: auto; text-align: left;}
 .center th { text-align: center !important; }
 td, th { border: 1px solid #000000; font-size: 75%; vertical-align: baseline;}
 h1 {font-size: 150%;}
 h2 {font-size: 125%;}
 .p {text-align: left;}
 .e {background-color: #ccccff; font-weight: bold; color: #000000;}
 .h {background-color: #9999cc; font-weight: bold; color: #000000;}
 .v {background-color: #cccccc; color: #000000;}
 .vr {background-color: #cccccc; text-align: right; color: #000000;}
 img {float: right; border: 0px;}
 hr {width: 600px; background-color: #cccccc; border: 0px; height: 1px; color: #000000;}
 </style>
 <title>phpinfo()</title></head>
 <body><div class="center">
 <table border="0" cellpadding="3" width="600">
 ....

Of course, none of that HTML was in the info.php file. Instead, the phpinfo() line is a built-in PHP function that produces all of that HTML.

Variables and Arrays

Variables require $ at the beginning of their names (regardless of the purpose, be it setting, be it accessing). You don't need to specify the type of the variable; PHP will use the variable as the correct type based on how it is used in the code.

<?
  #this is an integer
  $i=5;
  #this is a string
  $msg="my string";
?>

As in many other languages, statements end with a ;. To actually produce HTML output, you simply print the HTML from the PHP code. The simplest way is to use the print function:

print $msg;

If you use a variable inside of a string, the value of the variable will be put in the string (you might also look at the echo function):

<?
  $i=5;
  print "The value of i is $i";
?>

This will generate the string

The value of i is 5

If you create a file with just the above code, you will notice that your browser will only receive the above line. That is, there is no html tag or anything else. Thus, PHP files are normally a mix of HTML code and PHP code. Most PHP scripts, then, look more like this:

<html>
<body>
<?
  $i=5;
  print "The value of i is $i";
?>
</body>
</html>

The code that the browser will receive is then:

<html>
<body>
  The value of i is 5
</body>
</html>

You can have any number of PHP segments and HTML segments in a PHP file. For example:

<html>
<body>
<? $i=5; ?>
The value of i is <?  print "$i"; ?>
</body>
</html>

Of course, whatever you print out will be interpreted as HTML by the client's browser, so you can (and will) use HTML tags in the output you produce. For example:

 <? print "This is a <b> test </b> ?> 

This results in the following at the user's browser:

 This is a <b> test </b>

Which would then render test in bold.

Arrays

Declaring arrays is very easy in PHP. Either you can enter all elements one by one, or you can enter them together:

$student[0]="Alice";
$student[1]="Bruce";
$student[2]="Charlie";
$student[3]="Dan";

or alternatively

$student=array("Alice","Bruce","Charlie","Dan");

Then you can access the contents with an index into the array, as normal:

print $student[2];


You can find the size of an array with count function, e.g., count($student)

In PHP, you can also have associative arrays, which are arrays whose members can be accessible with string indices. Here is an example:

<?
$test["test1"]=1;
$test["test2"]=2;

echo "test1=",$test[test1],"<br>";
echo "test2=",$test[test2],"<br>";
?>

You can access array keys through array_keys function.

Conditional Statements

if/elseif/else statements provide the conditional statements. The general format is

if ( CONDITION )
{
  some statements
}
elseif( ANOTHER_CONDITION )
{
  more statements
}
else
{
   yet more statements
}

You can use standard comparison operators such as ==,<,> etc.

if ( $string == "this is my string") {
  echo "strings are equal";
}

or

 if ($average_temperature>100) {
   echo "No, no, there is no such thing as global warming!!!!";
 }

Loops

PHP has for and while loops, similar to Java and C:

for(initialization;condition;loop_increment){
}
 
while (condition){
}

For example, the following code will print the sum of numbers from 1 to 10.

  $sum=0;
  $i=1;
  while($i<=10) {
    $sum=$sum+$i;
    $i++;
  }
 
 echo "sum is $sum";
 

The advantage of loops becomes more obvious when you have to create a long table:

<table border="1">
<tr><td>Number</td><td>Square</td></tr>
<?
for($i=0;$i<100;$i++) {
echo "<tr><td>$i </td><td>",$i*$i,"</td></tr>\n";
}
?>
</table>

This creates a table with two columns, each row contains a number and its square.

break and continue are special commands that will interrupt normal control flow through a loop. break jumps out of the loop entirely, while continue jumps to the end of the current loop iteration and flow resumes with the next loop iteration.

Functions

PHP functions are identified with the keyword function followed by a function name and argument list for the function.

function name($arg1 [= constant], $arg2 [= constant], ...) {
}

For example

<? 
  function add($x,$y) {
    return ($x+$y);
  }
  echo "Sum of 2+5=",add(2,5); 
?>

If an argument has a default value, it can be specified with the argument on the list:

 <?
   function helloMsg($name="there") {
      print "hello $name how are you today?<br>";
   }
   helloMsg("Alice");
   helloMsg();
 ?>

The above code will output:

 hello Alice how are you today?<br>
 hello there how are you today?<br>

Passing Variables

Input values can be passed to a script either through the URL request line or through data submitted by a form. Built in arrays $_GET['var'] and $_POST['var'] return the value of var depending on the access method. As we will see in the next section, values can also be passed through session variables. Finally, you can use cookies to store and retrieve values.

If you want to pass values in a URL, the format is http://yourserver/yourphpfile.php?var1=value1&var2=value2.....

For example, the following PHP code would be used to print the previous hello message according to a name given in the URL:

greeting.php:

<?
 $person= $_GET['name'];
 helloMsg($person);
 function helloMsg($name="there") {
     print "hello $name how are you today?</br>";
 }
?>

If you access the URL like this: greeting.php?name=Alice, it will show hello Alice how are you today?. However, if you access it with greeting.php, it will print hello how are you today?. Note that it does not use the default value there since $name is now a string (in this case, an empty string) and so there is argument being being passed to helloMsg.

Receiving the data from a form is very similar. Consider the following form:

<FORM action="info.php" method="post">
    <P>
    <LABEL for="firstname">First name: </LABEL>
    <INPUT type="text" name="firstname"><BR>
    <LABEL for="lastname">Last name: </LABEL>
    <INPUT type="text" name="lastname"><BR>
    <LABEL for="birthyear">Birth Year: </LABEL>
    <INPUT type="text" name="birthyear"><BR>
    <INPUT type="radio" name="gender" value="Male"> Male<BR>
    <INPUT type="radio" name="gender" value="Female"> Female<BR>
    <INPUT type="submit" value="Send">
    <INPUT type="reset">
    </P>
</FORM>

This posts the form data to info.php, with inputs firstname, lastname, birthyear, and gender. The values passed through the form for each input can be accssed in info.php with the $_POST array.

info.php:

<?
 echo  "Personal Data:", $_POST['firstname'], " ", $_POST['lastname'], "<br>";
 $birthyear=$_POST['birthyear'];
 echo  "Birth year:", $_birthyear, " (Age:" , 2007-$birthyear, ")<br>";
 echo "Gender: ", $_POST['gender'];
?>

Session Variables

PHP provides a global array, $_SESSION, for values that are available globally throughout a session. The values will stay there until either you remove them in a PHP script, the user's browser is closed, or their session expires (you can tune the timeout period in the PHP configuration files).

In order to access session values, you should first initiate the session with the session_start() function call. After that, when you access a values with $_SESSION, it will become a session values. For example:

setsessionvars.php

<?
session_start();

$_SESSION['SESSION']=42;
$_SESSION['username']="ArthurDent";
?>

This sets two variables, SESSION and username to be accessible by other pages in this session. In another page, you can access them like so:

<?
session_start();
if (!isset($_SESSION['SESSION'])) {
  echo "error session is not registered";
}
else echo "username=",$_SESSION['username'];
?>

You can also remove a session variable from the session with unset command:

unset($_SESSION['SESSION']);

Redirect the browser to a different page

It is often useful to redirect the user's browser to a different webpage, for example, after processing inputs from a form. Here is a simple example that shows how to do this, based on whether or not the LOGIN session variable is set:

<?
if(isset($_SESSION["LOGIN"])){
	Header("Location:/welcome.php");
}else{
	Header("Location:/login.php");
}
?>

Note that anytime you call the Header function, it is adding information to the header section in the HTML object that is being requested. As such, all Header calls should go before any other HTML output in the PHP script.

Sending a file to the Browser

Another useful function to know is the readfile function. It takes a file on the webserver's file system and sends it to the web browser. A simple example is given below, but note that you'll probably need to specify addition header fields in order to have the web browser download the file correctly. Note that

<?
session_start();

$file=$_GET['file'];
$name = $_SESSION["UNAME"];
$path="/home/uploads/$name/$file";

$finfo = finfo_open(FILEINFO_MIME_TYPE); // return mime type ala mimetype extension
if (!$finfo) {
 	echo "Opening fileinfo database failed";
}

$mime=finfo_file($finfo, $path);
finfo_close($finfo);

header('content-type:'. $mime);
readfile($path);    
?>

Uploading files with PHP

This section describes one way to upload files with PHP. First, you need an HTML form that contains an input with type file:

transfer.php

<form enctype="multipart/form-data" action="uploader.php" method="POST">
<input type="hidden" name="MAX_FILE_SIZE" value="100000" />
Choose a file to upload: <input name="uploadedfile" type="file" /><br>
<input type="submit" value="Upload File" />
</form>

When you use a file input in a form, PHP automatically adds an entry in the $_FILES array with information about the file. For example, transfer.php called the file uploadedfile, so $_FILES['uploadedfile'] refers to file that the user selected in the form. The name of the original file is $_FILES['uploadedfile']['name']. When you upload a file, it is put in a temporary location by the web server. This temporary name is $_FILES['uploadedfile']['tmp_name']. In PHP, you can move a file from its original location to a new location by calling a built-in function, move_uploaded_file, which takes an argument for the source (temporary location) and destination location. Note that relative paths in the destination location are relative to the location of the PHP script being executed.

uploader.php:

$target_path = "uploads/";
$target_path = $target_path . basename($_FILES['uploadedfile']['name']);

if(move_uploaded_file($_FILES['uploadedfile']['tmp_name'], $target_path)) {
    echo "The file ".  basename( $_FILES['uploadedfile']['name']) . " has been uploaded";
} else{
    echo "There was an error uploading the file, please try again!";
}

Eclipse

For those of you who like programming with IDEs, Eclipse has support for PHP. See: http://www.eclipse.org.