$_FILES for file uploads in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to access the uploaded file's name.

PHP

<?php
$filename = $_FILES['userfile']['[1]'];
echo $filename;
?>

Drag options to blanks, or click blank then click option'

Aname

Btmp_name

Csize

Dtype

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'tmp_name' instead of 'name' to get the file's original name.

Confusing 'size' or 'type' keys with the file name.

The name key in $_FILES holds the original name of the uploaded file.

2fill in blank

medium

Complete the code to check if the file upload was successful.

PHP

<?php
if ($_FILES['userfile']['[1]'] === 0) {
    echo 'Upload successful';
} else {
    echo 'Upload failed';
}
?>

Drag options to blanks, or click blank then click option'

Atype

Berror

Ctmp_name

Dsize

Attempts:

3 left

💡 Hint

Common Mistakes

Checking 'size' or 'tmp_name' instead of 'error' to verify upload success.

Using 'type' key to check for errors.

The error key in $_FILES holds an error code. A value of 0 means no error.

3fill in blank

hard

Fix the error in the code to move the uploaded file to the 'uploads/' directory.

PHP

<?php
$uploadDir = 'uploads/';
$uploadFile = $uploadDir . basename($_FILES['userfile']['[1]']);
if (move_uploaded_file($_FILES['userfile']['tmp_name'], $uploadFile)) {
    echo 'File is valid, and was successfully uploaded.';
} else {
    echo 'Possible file upload attack!';
}
?>

Drag options to blanks, or click blank then click option'

Asize

Berror

Ctmp_name

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'tmp_name' inside basename() instead of 'name'.

Confusing 'error' or 'size' keys for file name.

The basename function needs the original file name, which is in the name key.

4fill in blank

hard

Fill both blanks to create an array of file sizes for all uploaded files in a multiple upload form.

PHP

<?php
$fileSizes = [1]['[2]'];
?>

Drag options to blanks, or click blank then click option'

A$_FILES['userfile']['size']

B$_FILES['userfile']

Csize

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'name' instead of 'size' to get file sizes.

Using the wrong variable for the files array.

To get all file sizes in a multiple upload, use $_FILES['userfile']['size']. Here, $_FILES['userfile'] is the array, and 'size' is the key.

5fill in blank

hard

Fill all three blanks to check if the uploaded file is a JPEG image and its size is less than 2MB.

PHP

<?php
if ($_FILES['userfile']['[1]'] === 'image/jpeg' && $_FILES['userfile']['[2]'] < [3]) {
    echo 'Valid JPEG file under 2MB.';
} else {
    echo 'Invalid file.';
}
?>

Drag options to blanks, or click blank then click option'

Atype

Bsize

C2097152

Derror

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'error' instead of 'type' to check MIME type.

Comparing size to 2 instead of 2MB in bytes.

The type key holds the MIME type, size holds the file size in bytes, and 2MB equals 2097152 bytes.

Practice

1. What does the $_FILES superglobal in PHP store?

easy

A. Database connection details

B. User session data

C. Information about files uploaded via an HTML form

D. Server environment variables

Solution

1. Step 1: Understand the purpose of $_FILES

   $_FILES is a special PHP variable that holds details about files uploaded through a form.

2. Step 2: Compare with other options

   User session data is stored in $_SESSION, database details are not stored here, and server variables are in $_SERVER.

3. Final Answer:

   Information about files uploaded via an HTML form -> Option C

4. Quick Check:

   $_FILES = Uploaded file info [OK]

Hint: Remember: $_FILES always relates to uploaded files [OK]

Common Mistakes:

• Confusing $_FILES with $_SESSION
• Thinking $_FILES holds server info
• Assuming $_FILES stores form text inputs

2. Which of the following is the correct way to access the name of an uploaded file with input name userfile?

easy

A. $_FILES['userfile']['filename']

B. $_FILES['userfile']['file']

C. $_FILES['userfile']['file_name']

D. $_FILES['userfile']['name']

Solution

1. Step 1: Recall the structure of $_FILES

   Each uploaded file's info is stored in an array with keys like 'name', 'type', 'tmp_name', 'error', and 'size'.

2. Step 2: Identify the correct key for the original filename

   The key for the original filename is 'name', not 'filename' or 'file_name'.

3. Final Answer:

   $_FILES['userfile']['name'] -> Option D

4. Quick Check:

   Filename key = 'name' [OK]

Hint: Use 'name' key to get original filename from $_FILES [OK]

Common Mistakes:

• Using 'filename' or 'file_name' instead of 'name'
• Confusing keys with other $_FILES elements
• Trying to access $_POST for file names

3. What will the following PHP code output if a file named 'photo.jpg' is uploaded successfully?

if ($_FILES['pic']['error'] === 0) {
    echo $_FILES['pic']['name'];
} else {
    echo 'Upload failed';
}

medium

A. photo.jpg

B. Upload failed

C. 0

D. Undefined index error

Solution

1. Step 1: Check the error code for the uploaded file

   An error code of 0 means the upload was successful with no errors.

2. Step 2: Output the original filename

   Since error is 0, the code echoes the original filename stored in $_FILES['pic']['name'], which is 'photo.jpg'.

3. Final Answer:

   photo.jpg -> Option A

4. Quick Check:

   Error 0 means success, so filename prints [OK]

Hint: Error 0 means success; print 'name' to get filename [OK]

Common Mistakes:

• Assuming error 0 means failure
• Printing error code instead of filename
• Not checking if 'pic' index exists

4. Identify the error in this PHP snippet handling file upload:

if ($_FILES['upload']['error'] == 0) {
    move_uploaded_file($_FILES['upload']['name'], 'uploads/' . $_FILES['upload']['name']);
    echo 'File saved';
} else {
    echo 'Error uploading';
}

medium

A. Not checking file size before moving

B. Using 'name' instead of 'tmp_name' in move_uploaded_file

C. Checking error with == instead of ===

D. Missing semicolon after echo statement

Solution

1. Step 1: Understand move_uploaded_file parameters

   The first parameter must be the temporary file path stored in tmp_name, not the original filename.

2. Step 2: Identify the incorrect usage

   The code incorrectly uses $_FILES['upload']['name'] as the source file, which is wrong and causes failure.

3. Final Answer:

   Using 'name' instead of 'tmp_name' in move_uploaded_file -> Option B

4. Quick Check:

   move_uploaded_file needs tmp_name as source [OK]

Hint: Use 'tmp_name' as source file in move_uploaded_file [OK]

Common Mistakes:

• Using original filename instead of temp file path
• Ignoring error codes before moving files
• Not validating file size or type

5. You want to save an uploaded file only if it is less than 2MB and has no errors. Which code snippet correctly checks these conditions before moving the file?

if (/* condition here */) {
    move_uploaded_file($_FILES['file']['tmp_name'], 'uploads/' . $_FILES['file']['name']);
    echo 'Upload successful';
} else {
    echo 'Upload failed';
}

hard

A. if ($_FILES['file']['error'] === 0 && $_FILES['file']['size'] < 2097152)

B. if ($_FILES['file']['error'] == 1 || $_FILES['file']['size'] > 2097152)

C. if ($_FILES['file']['error'] !== 0 && $_FILES['file']['size'] <= 2097152)

D. if ($_FILES['file']['error'] === 0 || $_FILES['file']['size'] > 2097152)

Solution

1. Step 1: Check for no upload errors

   The error code must be exactly 0 to confirm no errors during upload.

2. Step 2: Check file size limit

   The file size must be less than 2MB (2 * 1024 * 1024 = 2097152 bytes).

3. Step 3: Combine conditions correctly

   Both conditions must be true, so use logical AND (&&) with strict equality and less-than size check.

4. Final Answer:

   if ($_FILES['file']['error'] === 0 && $_FILES['file']['size'] < 2097152) -> Option A

5. Quick Check:

   Error 0 and size < 2MB = correct check [OK]

Hint: Use error === 0 and size < 2MB with && [OK]

Common Mistakes:

• Using || instead of && for conditions
• Checking error != 0 instead of === 0
• Confusing size units or limits