Form processing with PHP: part 4

Form Validation

Validating a form

You can perform form validation before a form is submitted via JavaScript or after the form is submitted via PHP.

I've actually already demonstrated simple validation using PHP in Form Processing with PHP: Part 1, with the input.php script. After the form is submitted, the script checks to see whether a variable does or does not exist.

PHP Code:

<?php
//check if submit button clicked and the input field isn't empty, print hello
if ($submit == "click" && $UserName !=""):
echo "Hello, $UserName";
 
//if submit button clicked and the input field is empty, print error
elseif ($UserName =="" && $submit == "click"):
echo "You did not enter a name.";
 
else:
echo " <html><body> 
<form method="post" action="input.php"> Enter Your Name 
<input type="text" name="UserName"><br/> 
<input type="submit" name="submit" value="click"> 
</form> </body></html> ";
endif;
?>

See it in action. ¦ Get complete code.

You can also use regular expressions with the ereg() and eregi() functions to validate the values submitted by a form. Regular expressions examine a string and search for patterns and variations to determine whether they match the search criteria you set.

An example:

This regular expression tests true if the user has entered only characters, from a to z, in lowercase or uppercase, and numbers from zero to nine. Also, checks whether the string is four to twelve characters in length.
The ^ indicates the beginning of a string and the $ the end of the string.

if (!ereg("^[A-Za-z0-9]{4,12}$",$Username)): echo "Your username must be at least 4 character, but not more than 12 characters.";

PHPBuilder.com has a good tutorial demonstrating how to use regular expressions called Learning to Use Regular Expressions by Example.

You could also use JavaScript to do client-side validation of form values before the form is submitted to a PHP script. Irt.org has a great tutorial - Addressing Form Field Validation with Regular Expressions and JavaScript 1.2 that explains how to use JavaScript and regular expressions to do form validation.

Here is an example:

JavaScript Code:

<script LANGUAGE="JavaScript" type="text/javascript">
<!--
.
.
.
for (var i = 0; i < string.length; i++) {
if (iChars.indexOf(string.charAt(i)) != -1)
// if one of the characters is found then the string is invalid
return false;
}
// otherwise the string is valid
return true;
}
 
function isReady(form) {
 
if (isProper(form.firstname.value) == false) {
alert("Please enter your firstname");
form.firstname.focus();
return false;
}
return true;
}
 
//-->
</SCRIPT>

See it in action. ¦ Get complete code.

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Form processing with PHP: part 4

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