How to Reliably Detect File Uploads in PHP?

Checking for File Uploads in PHP

When handling form validation in PHP, it can be crucial to determine if a user has uploaded a file. This knowledge allows developers to skip unnecessary validation if no file was uploaded.

To achieve this, one common approach is to check whether the size of the $_FILES['myfile']['size'] is less than or equal to 0. However, this approach is not recommended.

Instead, a more reliable method is to utilize the is_uploaded_file() function. This function specifically checks if the file was indeed uploaded via HTTP POST, enhancing security by preventing malicious users from tricking the script into working on files it shouldn't.

Here's how you can use is_uploaded_file():

<code class="php">if(!file_exists($_FILES['myfile']['tmp_name']) || !is_uploaded_file($_FILES['myfile']['tmp_name'])) {
    echo 'No upload';
}</code>

As the PHP documentation states, this function returns TRUE if the specified file was uploaded through HTTP POST and is considered a valuable tool for ensuring that uploaded files do not compromise system security.

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