Form Handling
The most important thing to notice when dealing with HTML forms and PHP is that any form element in an HTML page will automatically be available to your PHP scripts.
Example
The example below contains an HTML form with two input fields and a submit button:
<html>
<body>
<form action="welcome.php" method="post">
Name: <input type="text" name="fname" />
Age: <input type="text" name="age" />
<input type="submit" />
</form>
</body>
</html>
When a user fills out the form above and click on the submit button, the form data is sent to a PHP file, called "welcome.php".
"welcome.php" looks like this:
<html>
<body>
Welcome <?php echo $_POST["fname"]; ?>!<br />
You are <?php echo $_POST["age"]; ?> years old.
</body>
</html>
Output could be something like this:
Welcome John!
You are 28 years old.
The PHP $_GET and $_POST variables will be explained in the next sections.
Form Validation
User input should be validated on the browser whenever possible (by client scripts). Browser validation is faster and reduces the server load.
You should consider server validation if the user input will be inserted into a database. A good way to validate a form on the server is to post the form to itself, instead of jumping to a different page. The user will then get the error messages on the same page as the form. This makes it easier to discover the error.
The $_GET Variable
In Php, the predefined $_GET variable is used to collect values in a form with method="get"
Information sent from a form with the GET method is visible to everyone (it will be displayed in the browser's address bar) and has limits on the amount of information to send.
Example
<form action="welcome.php" method="get">
Name: <input type="text" name="fname" />
Age: <input type="text" name="age" />
<input type="submit" />
</form>
When the user clicks the "Submit" button, the URL sent to the server could look something like this:
http://www.w3schools.com/welcome.php?fname=Peter&age=37
The "welcome.php" file can now use the $_GET variable to collect form data (the names of the form fields will automatically be the keys in the $_GET array):
Welcome <?php echo $_GET["fname"]; ?>.<br />
You are <?php echo $_GET["age"]; ?> years old!
When to use method="get"?
When using method="get" in HTML forms, all variable names and values are displayed in the URL.
Note: This method should not be used when sending passwords or other sensitive information!
However, because the variables are displayed in the URL, it is possible to bookmark the page. This can be useful in some cases.
Note: The get method is not suitable for very large variable values. It should not be used with values exceeding 2000 characters.
The $_POST Variable
The predefined $_POST variable is used to collect values from a form sent with method="post".
Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.
Note: However, there is an 8 Mb max size for the POST method, by default (can be changed by setting the post_max_size in the php.ini file).
Example
<form action="welcome.php" method="post">
Name: <input type="text" name="fname" />
Age: <input type="text" name="age" />
<input type="submit" />
</form>
When the user clicks the "Submit" button, the URL will look like this:
http://www.mywebsite.com/welcome.php
The "welcome.php" file can now use the $_POST variable to collect form data (the names of the form fields will automatically be the keys in the $_POST array):
Welcome <?php echo $_POST["fname"]; ?>!<br />
You are <?php echo $_POST["age"]; ?> years old.
When to use method="post"?
Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.
However, because the variables are not displayed in the URL, it is not possible to bookmark the page.
The PHP $_REQUEST Variable
The predefined $_REQUEST variable contains the contents of both $_GET, $_POST, and $_COOKIE.
The $_REQUEST variable can be used to collect form data sent with both the GET and POST methods.
Example
Welcome <?php echo $_REQUEST["fname"]; ?>!<br />
You are <?php echo $_REQUEST["age"]; ?> years old.
You are <?php echo $_REQUEST["age"]; ?> years old.
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