$_FILES for file uploads in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code handling a file upload?

Consider the following PHP script that processes a file upload. What will be the output if a file named example.txt of size 1024 bytes is uploaded successfully?

PHP

<?php
if ($_FILES['upload']['error'] === UPLOAD_ERR_OK) {
    echo "File name: " . $_FILES['upload']['name'] . "\n";
    echo "File size: " . $_FILES['upload']['size'] . " bytes\n";
} else {
    echo "Upload failed with error code: " . $_FILES['upload']['error'];
}
?>

A Upload failed with error code: 1

B

File name: example.txt
File size: 1024 bytes

C

File name: 
File size: 0 bytes

D Upload failed with error code: 4

💡 Hint

Check the error value in $_FILES to confirm if the upload was successful.

If the file uploads without errors, $_FILES['upload']['error'] equals UPLOAD_ERR_OK (0). Then the script prints the file name and size.

🧠 Conceptual

intermediate

Which $_FILES key holds the temporary file path?

When a file is uploaded via a form in PHP, which key in the $_FILES array contains the temporary file path on the server?

A tmp_name

B error

C name

D size

💡 Hint

The temporary file path is where PHP stores the uploaded file before you move it.

The tmp_name key holds the temporary filename of the file stored on the server during upload.

🔧 Debug

advanced

Why does this PHP file upload code fail to move the uploaded file?

Examine the code below. It tries to move an uploaded file but fails. What is the cause?

PHP

<?php
if (move_uploaded_file($_FILES['file']['name'], '/uploads/' . $_FILES['file']['name'])) {
    echo "Upload successful.";
} else {
    echo "Upload failed.";
}
?>

A Using $_FILES['file']['name'] as source instead of $_FILES['file']['tmp_name']

B The destination path '/uploads/' is missing a trailing slash

C move_uploaded_file requires the file size as first argument

D The file input name should be 'upload' not 'file'

💡 Hint

Check the first argument of move_uploaded_file. It must be the temporary file path.

The first argument to move_uploaded_file must be the temporary file path stored in tmp_name, not the original file name.

📝 Syntax

advanced

What error does this PHP code produce when accessing $_FILES?

Consider this PHP snippet:

<?php
$file = $_FILES['upload'];
echo $file['name'];
echo $file['tmpname'];
?>

What error will this code produce?

A Parse error: syntax error, unexpected '['

B Fatal error: Cannot use string offset as an array

C Notice: Undefined index: tmpname

D No error, outputs the file name and empty string

💡 Hint

Check the spelling of the keys in the $_FILES array.

The key tmpname is incorrect; the correct key is tmp_name. This causes a notice about undefined index.

🚀 Application

expert

How many files are uploaded in this PHP script?

Given the following HTML and PHP code, how many files will be processed in the PHP script?

<form method="post" enctype="multipart/form-data">
  <input type="file" name="photos[]" multiple>
  <input type="submit">
</form>

<?php
if (!empty($_FILES['photos'])) {
    echo count($_FILES['photos']['name']);
} else {
    echo 0;
}
?>

A 1

B An error occurs because 'photos' is an array

C 0

D The number of files selected by the user

💡 Hint

Check how multiple file inputs are handled in $_FILES.

When using name="photos[]" with multiple, $_FILES['photos']['name'] is an array of all selected file names. The count reflects how many files were selected.