How to validate a Form in php?

What is Validation?

The required field will check whether the field is filled or not in the proper way. Most of cases we will use the * symbol for the required field

Validation means checking the input submitted by the user. There are two types of validation are available in PHP. They are as follows −

  • Client-Side Validation − Validation is performed on the client machine web browsers.
  • Server Side Validation − After submitted data, The data has sent to a server, and perform validation checks in the server machine.

Empty String:

The code below checks that the field is not empty. If the user leaves the required field empty, it will show an error message. Put these lines of code to validate the required field

if (emptyempty ($_POST["name"])) {  
    $errMsg = "Error! You didn't enter the Name.";  
       echo $errMsg;  
} else {  
    $name = $_POST["name"];  
}

Validate String

The code below checks that the field will contain only alphabets and whitespace, for example – name. If the name field does not receive valid input from the user, then it will show an error message:

$name = $_POST ["Name"];  
if (!preg_match ("/^[a-zA-z]*$/", $name) ) {  
    $ErrMsg = "Only alphabets and whitespace are allowed.";  
             echo $ErrMsg;  
} else {  
    echo $name;  
}

Validate Number

$mobileno = $_POST ["Mobile_no"];  
if (!preg_match ("/^[0-9]*$/", $mobileno) ){  
    $ErrMsg = "Only numeric value is allowed.";  
    echo $ErrMsg;  
} else {  
    echo $mobileno;  
}

Validate Email

Below code shows the validation of the Email address

$email = $_POST ["Email"];  
$pattern = "^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$^";  
if (!preg_match ($pattern, $email) ){  
    $ErrMsg = "Email is not valid.";  
            echo $ErrMsg;  
} else {  
    echo "Your valid email address is: " .$email;  
}

Input Length Validation

The below code shows the input length validation

$mobileno = strlen ($_POST ["Mobile"]);  
$length = strlen ($mobileno);  
  
if ( $length < 10 && $length > 10) {  
    $ErrMsg = "Mobile must have 10 digits.";  
            echo $ErrMsg;  
} else {  
    echo "Your Mobile number is: " .$mobileno;  
}

Validate URL

$websiteURL = $_POST["website"];  
if (!preg_match("/\b(?:(?:https?|ftp):\/\/|www\.)[-a-z0-9+&@#\/%?=~_|!:,.;]*[-a-z0-9+&@#\/%=~_|]/i",$website)) {  
  $websiteErr = "URL is not valid";  
  echo $websiteErr;  
} else {  
    echo "Website URL is: " .$websiteURL;  
}

Button Click Validate

if (isset ($_POST['submit']) {  
    echo "Submit button is clicked.";  
    if ($_SERVER["REQUEST_METHOD"] == "POST") {  
        echo "Data is sent using POST method ";  
    }  
} else {  
    echo "Data is not submitted";  
}

Create a registration form using HTML and perform server-side validation. Follow the below instructions as given:

Create and validate a Registration form

<!DOCTYPE html>  
<html>  
<head>  
<style>  
.error {color: #FF0001;}  
</style>  
</head>  
<body>    
  
<?php  
// define variables to empty values  
$nameErr = $emailErr = $mobilenoErr = $genderErr = $websiteErr = $agreeErr = "";  
$name = $email = $mobileno = $gender = $website = $agree = "";  
  
//Input fields validation  
if ($_SERVER["REQUEST_METHOD"] == "POST") {  
      
//String Validation  
    if (emptyempty($_POST["name"])) {  
         $nameErr = "Name is required";  
    } else {  
        $name = input_data($_POST["name"]);  
            // check if name only contains letters and whitespace  
            if (!preg_match("/^[a-zA-Z ]*$/",$name)) {  
                $nameErr = "Only alphabets and white space are allowed";  
            }  
    }  
      
    //Email Validation   
    if (emptyempty($_POST["email"])) {  
            $emailErr = "Email is required";  
    } else {  
            $email = input_data($_POST["email"]);  
            // check that the e-mail address is well-formed  
            if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {  
                $emailErr = "Invalid email format";  
            }  
     }  
    
    //Number Validation  
    if (emptyempty($_POST["mobileno"])) {  
            $mobilenoErr = "Mobile no is required";  
    } else {  
            $mobileno = input_data($_POST["mobileno"]);  
            // check if mobile no is well-formed  
            if (!preg_match ("/^[0-9]*$/", $mobileno) ) {  
            $mobilenoErr = "Only numeric value is allowed.";  
            }  
        //check mobile no length should not be less and greator than 10  
        if (strlen ($mobileno) != 10) {  
            $mobilenoErr = "Mobile no must contain 10 digits.";  
            }  
    }  
      
    //URL Validation      
    if (emptyempty($_POST["website"])) {  
        $website = "";  
    } else {  
            $website = input_data($_POST["website"]);  
            // check if URL address syntax is valid  
            if (!preg_match("/\b(?:(?:https?|ftp):\/\/|www\.)[-a-z0-9+&@#\/%?=~_|!:,.;]*[-a-z0-9+&@#\/%=~_|]/i",$website)) {  
                $websiteErr = "Invalid URL";  
            }      
    }  
      
    //Empty Field Validation  
    if (emptyempty ($_POST["gender"])) {  
            $genderErr = "Gender is required";  
    } else {  
            $gender = input_data($_POST["gender"]);  
    }  
  
    //Checkbox Validation  
    if (!isset($_POST['agree'])){  
            $agreeErr = "Accept terms of services before submit.";  
    } else {  
            $agree = input_data($_POST["agree"]);  
    }  
}  
function input_data($data) {  
  $data = trim($data);  
  $data = stripslashes($data);  
  $data = htmlspecialchars($data);  
  return $data;  
}  
?>  
  
<h2>Registration Form</h2>  
<span class = "error">* required field </span>  
<br><br>  
<form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]); ?>" >    
    Name:   
    <input type="text" name="name">  
    <span class="error">* <?php echo $nameErr; ?> </span>  
    <br><br>  
    E-mail:   
    <input type="text" name="email">  
    <span class="error">* <?php echo $emailErr; ?> </span>  
    <br><br>  
    Mobile No:   
    <input type="text" name="mobileno">  
    <span class="error">* <?php echo $mobilenoErr; ?> </span>  
    <br><br>  
    Website:   
    <input type="text" name="website">  
    <span class="error"><?php echo $websiteErr; ?> </span>  
    <br><br>  
    Gender:  
    <input type="radio" name="gender" value="male"> Male  
    <input type="radio" name="gender" value="female"> Female  
    <input type="radio" name="gender" value="other"> Other  
    <span class="error">* <?php echo $genderErr; ?> </span>  
    <br><br>  
    Agree to Terms of Service:  
    <input type="checkbox" name="agree">  
    <span class="error">* <?php echo $agreeErr; ?> </span>  
    <br><br>                            
    <input type="submit" name="submit" value="Submit">   
    <br><br>                             
</form>  
  
<?php  
    if(isset($_POST['submit'])) {  
    if($nameErr == "" && $emailErr == "" && $mobilenoErr == "" && $genderErr == "" && $websiteErr == "" && $agreeErr == "") {  
        echo "<h3 color = #FF0001> <b>You have sucessfully registered.</b> </h3>";  
        echo "<h2>Your Input:</h2>";  
        echo "Name: " .$name;  
        echo "<br>";  
        echo "Email: " .$email;  
        echo "<br>";  
        echo "Mobile No: " .$mobileno;  
        echo "<br>";  
        echo "Website: " .$website;  
        echo "<br>";  
        echo "Gender: " .$gender;  
    } else {  
        echo "<h3> <b>You didn't filled up the form correctly.</b> </h3>";  
    }  
    }  
?>  
  
</body>  
</html>

When the above code runs on a browser, the output will be like the screenshot below:

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