Latest revision as of 17:31, 24 August 2017

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. 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
  PHP Code In Here
?>

<?php
  PHP Code In Here
php?>

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

You may see the following shortcut syntax for declaring php, but it may not work unless the shortcut syntax is configured for your server, as such we generally recommend sticking with one of the first ways of declaring php.

<?
 PHP Code In Here
?>

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

<?php
  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:

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.

<?php
  #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):

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

 <?php 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:

<?php
$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.

Strings: Differences Between Java and PHP

In php, unlike in java, you can enclose strings in single quotes or double quotes

e.g. The following is a valid string, just like in java.

//A valid string in php and in java.
$str="hey jeff!";

And in PHP, the following is also a valid string

//A valid string in PHP, but invalid in java.
$str='hey jeff!'

However, there is a caveat when using the single quotes. If we want to then use MORE single quotes within the string We have to escape them To yield the string I'm Jeff's string

we could use either of the following definitions:

$str="I'm Jeff's string"

OR

$str='I\'m Jeff\'s string'

Additionally, when enclosing the string in single quotes we can use unescaped double quotes inside the string in the manner shown below which is especially useful when outputting html:

$str='The man said "yes."'

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

<?php 
  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:

 <?php
   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.

Note that upon submitting a form, the page specified in the form tag's action attribute is loaded (with variables sent via post or get).

Get: Passing Variables via URL

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:

<?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.

POST: Passing Variables via Form

In PHP one method for passing variables from page to page is by sending it to the other page via posting. The way post works in PHP is that PHP retrieves the variable names and values from a (slightly modified) html form and sends an those variables in the associative array named $_POST to the page specified in the FORM tag's action attribute.

Note that receiving the data from a form is very similar to getting it from the URL. Consider the following form:

<FORM action="info.php" method="post">
    <P>
    <LABEL for="firstnamelabel">First name: </LABEL>
    <INPUT type="text" name="firstname" id="firstnamelabel"><BR>
    <LABEL for="lastnamelabel">Last name: </LABEL>
    <INPUT type="text" name="lastname" id="lastnamelabel"><BR>
    <LABEL for="birthyearlabel">Birth Year: </LABEL>
    <INPUT type="text" name="birthyear" id="birthyearlabel"><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 accessed in info.php with the $_POST array.

<label> : The label tag just provides a text label for the form inputs.
<input type="input_type_here"> : The input tag provides various means of inputting information into the form, there are various types of inputs such as text, radio, submit, reset, etc.
<input ... name="input_name"> :
<label for="identifying_string"> and <INPUT ... id="identifying_string": The optional for attribute of the label tag associates the label with what we'll call an "identifying string", which should match the string specified in the corresponding id portion of the input tag. If both of these attributes are in place, then upon clicking on the label, the corresponding input will be selected.

info.php:

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

For further help with using HTML forms with PHP, we recommend this tutorial

Self-Submitting Forms

Oftentimes we don't want to pass form values to a different page, but rather to the same page as contains the form so that we can process the information and display output on that same page. The way we do this is to specify that the form should submit to $_SERVER['PHP_SELF'] and not say, other_page.php. Note that you can make self-submitting forms that use either the get or post method.

The following example simply takes the data input from a form and, via posting, echoes it back to the user as bold text on the same page:

bold_printer.php

<html>
<head><title>Bold Printer</title></head>
<body>

<form action= <?php echo $_SERVER['PHP_SELF'] ?> method="post">
    <label for="text_field">First name: </LABEL>
    <input type="text" name="user_text" id="text_field"><BR>
    <input type="submit" value="Print in Bold">
</form>

<?php
    if(isset($_POST['user_text']))
    echo "<b>", $_POST['user_text'], "</b>";
?>

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, in each php file, you should first initiate the session with the session_start() function call. After that, when you access a value with $_SESSION, it will become a session values. For example:

setsessionvars.php

<?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:

<?php
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:

<?php
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. For those of you who have used previous versions of PHP, note that mime_content_type($path) is now deprecated, use finfo_file instead. IMPORTANT The examples presented below are susceptible to a simple injection attack and should not be used in practice for publicly accessible websites or with untrusted users. For more information on building a secure file upload PHP script refer to the following websites: Secure PHP Uploading Sanitizing Input in PHP PHP Filter

<?php
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.

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