How to check whether the user uploaded a file in PHP?

In PHP, you can use the $_FILES superglobal array to check if a file has been uploaded. The $_FILES array contains information about all files that have been uploaded in the current request.

You can check if a file has been uploaded by checking if the $_FILES array is not empty and if the error code for the file is UPLOAD_ERR_OK, which indicates that the file was uploaded successfully. Here's an example:

<?php

if (!empty($_FILES) && $_FILES['file']['error'] === UPLOAD_ERR_OK) {
  // File was uploaded
} else {
  // File was not uploaded
}

In this example, file is the name of the file input field in the HTML form used to upload the file.

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You may also want to check for other error codes like UPLOAD_ERR_NO_FILE to check if the user did not upload any file or UPLOAD_ERR_INI_SIZE if the file size exceeds the allowed limit.