PHP Server Side Form Validation

In this article, you will learn how to validate an HTML form on the server side using the PHP programming language. It is important to validate the form data submitted by users because it may contain some inappropriate values that can harm your software. Form validation also helps the user to provide inputs in the correct format.

The server-side form validation is more secure than the client-side form validation. Suppose you are validating an HTML form using JavaScript client-side form validation. And if the user has disabled JavaScript in their browser, then the validation will not work. Server side form validation is done on the server side after the data has been submitted. This validates the data before storing it in the database.

The code below validates a simple HTML form that collects the employee information.

index.php

This is the main file that we will call in the browser. This HTML form contains five input fields to collect employee information and a submit button. We have included the form validation file form_validation.php at the top.

<?php 
	include('form_validation.php'); 
?>
<html>
	<head>
		<title>Server Side Form Validation</title>
		<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css">
		<style>.error { color: red;}</style>
	</head>
	<body>
		<div class="container">
		<form action="" method="post" name="emp_form">
		<div class="form-group">
			<label class="control-label col-sm-2" for="textinput">Employee Name</label>  
			<div  class="col-sm-8">
			<input id="textinput" name="name" placeholder="Enter your employee name" class="form-control input-md" type="text">
			<?php echo $error_empname; ?>
			</div>
		</div>
		<div class="form-group">
			<label class="control-label col-sm-2" for="textinput">Email</label>  
			<div class="col-sm-8">
			<input id="textinput" name="name" placeholder="Enter your email address" class="form-control input-md" type="text">
			<?php echo $error_email; ?>
			</div>
		</div>
		<div class="form-group">
			<label class="control-label col-sm-2" for="textinput">Phone</label>  
			<div class="col-sm-8">
			<input id="textinput" name="phone" placeholder="Enter your phone address" class="form-control input-md" type="text">
			<?php echo $error_ph; ?>
			</div>
		</div>
		<div class="form-group">
			<label class="control-label col-sm-2" for="textinput">Username</label>  
			<div class="col-sm-8">
			<input id="textinput" name="phone" placeholder="Enter your username" class="form-control input-md" type="text">
			<?php echo $error_username; ?>
			</div>
		</div>
		<div class="form-group">
			<label class="control-label col-sm-2" for="textinput">Password</label>  
			<div class="col-sm-8">
			<input type="password" name="password" value="<?php echo $password; ?>" />
			<?php echo $error_password; ?>
			</div>
		</div>
		<div class="form-group">
			<label class="control-label col-sm-2" for="textinput">Confirm Password</label>  
			<div class="col-sm-8">
			<input type="password" name="confirm" value="<?php echo $confirm; ?>" />
			<?php echo $error_confirm; ?>
			</div>
		</div>
		<div class="form-group">		
			<input type="submit" name="Submit" value="Submit" />
		</div>
		</form>
		</div>
	</body>
</html>

form_validation.php

The PHP validation code is here for validating the above HTML form. In the given code, the isset() function first checks whether the form has been submitted or not. If it is, then it trims all the white spaces in field values using the trim() function. After that, this script validates an empty input field, validates email, validates phone, and validates username and password. If any field values do not follow the validation rules, then the server sends back an error message to the client web page.

<?php
 
if(isset($_POST['Submit'])){ 
	$emp_name=trim($_POST["emp_name"]);
	$emp_email=trim($_POST["email"]);
	$emp_ph=trim($_POST["phone"]);
	$emp_uname=trim($_POST["username"]);
	$password=trim($_POST["password"]);
	$confirm=trim($_POST["confirm"]);

	if($emp_name =="") {
	$error_empname=  "<span class='error'>Please enter your name.</span>";
	}

	elseif($emp_email == "") {
	$error_email=  "<span class='error'>Please enter your email</span>"; 
	} 

	elseif(!preg_match("/^[_\.0-9a-zA-Z-]+@([0-9a-zA-Z][0-9a-zA-Z-]+\.)+[a-zA-Z]{2,6}$/i", $emp_email)){
	$error_email= "<span class='error'>Please enter valide email, like This email address is being protected from spambots. You need JavaScript enabled to view it.</span>";
	}

	elseif($emp_ph == ""){
	$error_ph =  "<span class='error'>Please enter phone number.</span>";
	}

	elseif(is_numeric(trim($emp_ph)) == false){
	$error_ph =  "<span class='error'>Please enter numeric value.</span>";
	}

	elseif($emp_uname == ""){
	$error_username =  "<span class='error'>Please enter uername.</span>";
	}

	elseif(strlen($emp_uname)<5){
	$error_username =  "<span class='error'>Username should be atleast five characters.</span>";
	}

	elseif($password == ""){
	$error_password=  "<span class='error'>Please enter password</span>";
	}

	elseif($confirm == ""){
	$error_confirm=  "<span class='error'>Please enter confirm password</span>";
	}

	elseif($password != $confirm) {
	$error_confirm=  "<span class='error'>Password and confirm password does not match</span>";
	}

	else{
	// Mysql insert statement
	// After successful form submission, it will be redirect to thankyou.php file.
	header("Location: thankyou.php");
	}
}
?>

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