PHP Form Validation

PHP Form Validation

PHP Form Validation Example

* required field.

Name: *

E-mail: *

Website:

Comment:

Gender: Female Male *

Your Input:

The validation rules for the form above are as follows:

Field	Validation Rules
Name	Required. + Must only contain letters and whitespace
E-mail	Required. + Must contain a valid email address (with @ and .)
Website	Optional. If present, it must contain a valid URL
Comment	Optional
Gender	Required. Must select one

First we will look at the plain HTML code for the form:

---

Text Fields

The name, email, website, and comment fields are text input elements and the HTML code looks like this:

<label>Name:</label><input type="text" name="name">
< label>E-mail:</label><input type="text" name="email">
<label>Website:</label><input type="text" name="website">
<label>Comment:</label><input type="text" name="comment">

---

Radio Buttons

The gender fields are radio buttons and the HTML code looks like this:

<label>Gender:</label>
<input type="radio" name="gender" value="female">Female
<input type="radio" name="gender" value="male">Male

---

The Form Element

The HTML code of the form looks like this:

<form method="post" action="<?php $_SERVER["PHP_SELF"];?>">

When the form is submitted, the form data is sent with method="post".
$_SERVER["PHP_SELF"] sends the form data to the page itself, instead of jumping to a different page. This way, the user will get error messages on the same page as the form.

---

Validate Form Data With PHP

The first thing we will do is to pass all variables through PHP's htmlspecialchars() function.
The htmlspecialchars() function converts special characters to HTML entities. This means that it will replace HTML characters like < and > with &lt; and &gt;. This prevents attackers from exploiting the code by injecting HTML or Javascript code (Cross-site Scripting attacks) in form fields.
When we use the htmlspecialchars() function; then if a user tries to submit the following in a text field:
<script>location.href('http://www.hacked.com')</script>
- this would not be executed, because it would be saved as HTML escaped code, like this:
&lt;script&gt;location.href('http://www.hacked.com')&lt;/script&gt;
The code is now safe to be displayed on a page or inside an e-mail.

	Cross-site scripting (XSS) is a type of computer security vulnerability typically found in Web applications. XSS enables attackers to inject client-side script into Web pages viewed by other users.

We will also do two more things when the user submits the form:

1. Strip unnecessary characters (extra space, tab, newline) from the user input data (with the PHP trim() function)
2. Remove backslashes (\) from the user input data (with the PHP stripslashes() function)

The next step is to create a function that will do all the checking for us (which is much more convenient than writing the same code over and over again).
We will name the function test_input().
Now, we can check each $_POST variable with the test_input() function, and the script look like this:

Example

<?php
// define variables and set to empty values
$name = $email = $gender = $comment = $website = "";

if ($_SERVER["REQUEST_METHOD"] == "POST")
{
  $name = test_input($_POST["name"]);
  $email = test_input($_POST["email"]);
  $website = test_input($_POST["website"]);
  $comment = test_input($_POST["comment"]);
  $gender = $_POST["gender"];
}

function test_input($data)
{
  $data = trim($data);
  $data = stripslashes($data);
  $data = htmlspecialchars($data);
  return $data;
}
?>

Run example »

Notice that at the start of the script, we check whether the form has been submitted using $_SERVER["REQUEST_METHOD"]. If the REQUEST_METHOD is POST, then the form has been submitted - and it should be validated. If it has not been submitted, skip the validation and display a blank form.
However, in the example above, all input fields are optional. The script works fine even if the user do not enter any data.
The next step is to make input fields required and create error messages if needed.