How to Check if Post Exists in PHP

PHP $_POST is a super-global variable that can contain key-value pair of HTML form data submitted via the post method. We will learn different methods to check if $_POST exists and contains some data in this article. These methods will use isset(), empty(), and empty string check.

Check if $_POST Exists With isset()

The isset() function is a PHP built-in function that can check if a variable is set, and not NULL. Also, it works on arrays and array-key values. PHP $_POST contains array-key values, so, isset() can work on it.

To check if $_POST exists, pass it as a value to the isset() function. At the same time, you can check if a user submitted a particular form input. If a user submits a form input, it will be available in $_POST, even if it’s empty.

The following HTML provides us with something to work with. It has a form field with a prepopulated name field.

<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
	<label>First Name</label>
	<input type="text" name="first_name" value="DelftStack">
	<input type="submit">
</form>

The following PHP will check if $_POST exists when you click the submit button:

<?php
    if (isset($_POST['first_name'])) {
        $first_name = $_POST['first_name'];
        echo $first_name;
    }
?>

Output:

DelftStack

Check if $_POST Exists With the Empty() Function

You can check the existence of $ _POST with the empty() function. But, the empty() function will return true in the following cases:

• When all $_POST values are empty strings
• The argument is zero

The following HTML is like the previous one, this time, the name is different:

<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
    <label>First Name</label>
    <input type="text" name="first_name" value="Mathias Jones">
    <input type="submit">
</form>

The next code block will show you how to check for $_POST with the empty() function:

<?php
    if (!empty($_POST)) {
        $first_name = $_POST['first_name'];

        echo $first_name;
    }
?>

Output:

Mathias Jones

Check if $_POST Exists With isset() Function and Empty String Check

The isset()function returns true if the value of $_POST is an empty string, but it will return false for NULL values. if you try to print the values of isset($_POST['x']) = NULL and isset($_POST['x']) = '', in both cases, you’ll get an empty string.

As a result, you will need to check for empty strings. The combination of isset() and empty string check eliminates the possibility that $_POST contains empty strings before you process its data.

In the next code block, we have an HTML to work with:

<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
    <label>First Name</label>
    <input type="text" name="first_name" value="Mertens Johanssen">
    <input type="submit">
</form>

Check if $_POST exists:

<?php
    if (isset($_POST['first_name']) && $_POST['first_name'] !== "") {

        $first_name = $_POST['first_name'];

        echo $first_name;
    }
?

Output:

Mertens Johanssen

Check if $_POST Exists With Negation Operator

The negation operator (!) will turn a true statement into false and a false statement into true. Therefore, you can check if $_POST exists with the negation operator. To check for $_POST, prepend it with the negation operator in an if-else statement.

In the first part, if $_POST is empty, you can stop the p processing of its data. In the second part of the conditional, you can process the data.

First, the HTML:

<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
    <label>First Name</label>
    <input type="text" name="first_name" value="Marcus Alonso">
    <input type="submit">
</form>

The next code block demonstrates checking if $_ POST exists with the negation operator.

<?php
    if (!$_POST) {
        echo "Post does not exist";
    } else {
        $first_name = $_POST['first_name'];

        echo $first_name;
    }
?>

Output:

Marcus Alonso