How to check if data is empty or whitespace only in PHP

Question

I have an input field that needs a username. The scenario is, how can i prevent user from providing whitespace or whitespaces in the that field? I already added required in the input field so i can prevent user from leaving it blank.

<input type="text" name="username" required>

but what if the user puts whitespace or as many whitespace as he can, is there any possible way i can detect this and throw error to the user?

in my php file i already have

if(empty($_POST['username'])){
echo "Username should not be empty!";
}

but this will fail because of the whitespaces the users put in the input field.

Answer 1

You could do like this.

if(isset($_POST['username']))
{
    if(strlen(trim($_POST['username'])) == 0){
        echo "Username should not be empty!";
    }
}

In the modern PHP it can be shorter

if (!trim($_POST['username'] ?? '')) {
    echo "Username should not be empty!";
}

or, if you need to assign $_POST['username'] to a variable

$username = trim($_POST['username'] ?? '');
if(!$username) {
    echo "Username should not be empty!";
}