Passing Data to PHP
Workshop Requirements
Before beginning this workshop ensure that you have the facility to upload PHP files to a PHP enabled webserver.
You should also have completed the following Virtual Workshops:
You should also have some experience with HTML programming and using HTML Forms.
Passing Variables to a script
When we were learning about variables and arrays in the previous workshop we were assigning values values statically as part of the code. This is obviously not very helpful in any 'real world' application, as we need to be able to pass different values to a PHP script, which are then assigned to our variables. There are two ways we can pass these values; as part of the URL or from an HTML form.
Variables as Part of a URL
If we look at the normal URL of a file (for example this one) it will look something like this:
http://www.keithjbrown.co.uk/vworks/php/php_p2.php
This is asking the webserver if we can download and view a a file called php_p2.php . However more information can be passed to that file as part of the URL. This can quite often be seen as part of the URLs that search engines use when displaying results. For example searching for 'PHP' using Google produces this URL:
http://www.google.com/search?hl=en&q=PHP
What we can see is that a file called search is being asked for and then there are variables being passed as part of what is known as the QUERY_STRING which the script will use to search the database of stored websites for 'PHP'. The QUERY_STRING is the part of the URL after the '?' and contains a series of name/value pairs separated by an ampersand ('&'). Thus the Google query string is...
hl=en&q=PHP
...which contains the following variables and values:
| Variable Name | Value |
| hl | en |
| q | PHP |
So the next stage for us it to create a PHP file that will recognise variables that are passed to it via the query string. Create a new file called variables.php and put the following code into the file:
<html>
<head>
<title>My Variables PHP Script</title>
</head>
<body>
<p>The query string is: <?php echo $_SERVER['QUERY_STRING']; ?></p>
</body>
</html>
As you can see we are trying to echo the $_SERVER array member QUERY_STRING, which is a predefined variable. Save and upload this file to your webserver and then view the file. You will see the text 'The query string is:' but nothing else as we haven't included anything in the query string. The QUERY_STRING is a blank value as there is nothing after the filename as part of the URL and thus doesn't display anything when we echo it into the HTML.
The QUERY_STRING
In order to create a QUERY_STRING enter the following after your file name when you view the file:
variables.php?firstname=keith&lastname=brown
As we have included a QUERY_STRING, the text that will be displayed is now 'The query string is: firstname=keith&lastname=brown'. Change the URL so that it reflects your name and watch the output change. This method of transferring data to a script is known as the 'GET' method, and one of several requests that a webserver understands.
Knowing the QUERY_STRING is, again, of little use in real world applications, however it is a starting point for most scripting languages which then split this query string into name/value variables. As PHP had been designed with the web in mind it automatically puts all the names (keys) and values into an associative array called $_GET from which we can retrieve our data. We do this the same as other associative array, by specifying a Key (in this case the name) to retrieve the value. To illustrate we can now change our variables.php script to echo these array members (firstname and lastname).
<html>
<head>
<title>My Variables PHP Script</title>
</head>
<body>
<p>The query string is: <?php echo $_SERVER['QUERY_STRING']; ?></p>
<p>Firstname: <? echo $_GET['firstname'] ?></p>
<p>Lastname: <? echo $_GET['lastname']; ?></p>
</body>
</html>
You can now see how this could begin to become useful. However typing in pairs of variables and values as part of the URL isn't very user-friendly and thus we will now look at using standard HTML form fields to collect values.
HTML Forms
To begin our look at forms we will create a file called myvars.htm which contains an HTML form that is set up to send the data it collects to our variables.php file.
<html>
<head>
<title>My Variables HTML Form</title>
</head>
<body>
<h4>My HTML Form</h4>
<form name="myform" method="get" action="variables.php">
Enter Firstname: <input type="text" name="firstname"><br>
Enter Lastname: <input type="text" name="lastname"><br><br>
<input type="submit" name="Submit" value="Submit">
</form>
</body>
</html>
The important parts of this are that the 'action' attribute is pointing towards the correct file (variables.php) and that the names given to each text input field are the same as the array elements in the script, otherwise nothing will happen. Upload this file, try typing different names, and look at the effect on the output. You will also notice that there is still a QUERY_STRING in the URL when we submit the form. This is because we have used the 'GET' method. There is another that we will look at and use, the POST method.
The 'POST' method includes its information in the 'body' of a http request rather than in the URL and thus cannot be seen. We can see this in action if we change the method in our myvars.htm file
<form name="myform" method="post" action="variables.php">
When the form is submitted to the PHP script, nothing happens. That is because our script is using the $_GET array which stores values passed via the GET method, rather the $_POST array (that stores the values passed by POST). Thus we need to change this in the variables.php script to accept POST values.
<html>
<head>
<title>My Variables PHP Script</title>
</head>
<body>
<p>The query string is: <?php echo $_SERVER['QUERY_STRING']; ?></p>
<p>Firstname: <? echo $_POST['firstname'] ?></p>
<p>Lastname: <? echo $_POST['lastname']; ?></p>
</body>
</html>
The script should now work again.
Using $_REQUEST
There is a third array that stores values. If we want the values to be available no matter which method was used to pass the variables then we could use the $_REQUEST array (which combines the members from both $_GET and $_POST).
<html>
<head>
<title>My Variables PHP Script</title>
</head>
<body>
<p>The query string is: <?php echo $_SERVER['QUERY_STRING']; ?></p>
<p>Firstname: <? echo $_REQUEST['firstname'] ?></p>
<p>Lastname: <? echo $_REQUEST['lastname']; ?></p>
</body>
</html>
Mini-Exercise
Add other HTML form elements that you may have used before to the myvars.htm file and then using the echo function, print them to the screen when posted to the variables.php file.
Further Reading
Lastest 10 Threads - view all
Agree with other posters
Posted By: Bob B at 22:04:01 on Thursday the 13th of September 2007
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Passing Variables With URL
Posted By: Steven Pearl at 16:48:43 on Wednesday the 5th of September 2007
In your examples you show how you can use an HTML form to pass variables FROM the form to a URL. How would I do the opposite where I want the URL to pass the variables (i.e firstname, lastname) TO a form that has those corresponding fields?
Thanks, Steve
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