File existence and info checks in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What PHP function checks if a file exists?

The file_exists() function checks if a file or directory exists at the specified path.

beginner

How do you check if a path is a directory in PHP?

Use the is_dir() function to check if the given path is a directory.

beginner

What function returns the size of a file in bytes?

The filesize() function returns the size of a file in bytes.

beginner

How can you check if a file is readable in PHP?

Use the is_readable() function to check if the file can be read.

beginner

What does is_file() check in PHP?

It checks if the given path exists and is a regular file (not a directory).

Which PHP function checks if a file or directory exists?

A file_exists()

B is_file()

C is_dir()

D filesize()

file_exists() returns true if the file or directory exists.

What does is_dir() return if the path is a file?

A false

B true

C null

D throws error

is_dir() returns false if the path is not a directory.

Which function gives the size of a file in bytes?

A file_exists()

B filesize()

C is_readable()

D is_file()

filesize() returns the size of the file in bytes.

How to check if a file can be read by PHP?

A file_exists()

B is_writable()

C is_file()

D is_readable()

is_readable() returns true if the file is readable.

What does is_file() check?

A If file is readable

B If path is a directory

C If path is a regular file

D If file exists

is_file() returns true only if the path is a regular file.

Explain how to check if a file exists and is readable in PHP.

Think about first confirming the file is there, then if you can read it.

Describe the difference between is_file() and is_dir().

One checks files, the other checks folders.

Practice

1. Which PHP function checks if a file or directory exists at a given path?

easy

A. filesize()

B. is_file()

C. file_exists()

D. is_readable()

Solution

1. Step 1: Understand the purpose of file_exists()

   The function file_exists() returns true if the file or directory exists at the specified path.

2. Step 2: Compare with other functions

   Functions like is_file() check if the path is a file, filesize() returns size, and is_readable() checks permissions, but none check existence alone.

3. Final Answer:

   file_exists() -> Option C

4. Quick Check:

   Check existence = file_exists() [OK]

Hint: Use file_exists() to check any file or directory presence [OK]

Common Mistakes:

• Confusing is_file() with existence check
• Using filesize() to check existence
• Assuming is_readable() means file exists

2. Which of the following is the correct syntax to check if a path is a directory in PHP?

easy

A. is_directory($path);

B. is_dir($path);

C. file_is_dir($path);

D. dir_exists($path);

Solution

1. Step 1: Recall the correct function name

   PHP uses is_dir() to check if a path is a directory.

2. Step 2: Verify syntax correctness

   The function is called as is_dir($path); other options are invalid function names.

3. Final Answer:

   is_dir($path); -> Option B

4. Quick Check:

   Directory check = is_dir() [OK]

Hint: Remember: is_dir() checks directories, not is_directory() [OK]

Common Mistakes:

• Using non-existent functions like is_directory()
• Mixing up is_file() and is_dir()
• Missing parentheses in function call

3. What will the following PHP code output if the file 'example.txt' exists and is 150 bytes in size?

$file = 'example.txt';
if (file_exists($file)) {
    echo filesize($file);
} else {
    echo 'File not found';
}

medium

A. 150

B. Error

C. 0

D. File not found

Solution

1. Step 1: Check file existence

   The code uses file_exists() to confirm 'example.txt' exists, which it does.

2. Step 2: Output file size

   Since the file exists, filesize($file) returns 150, which is printed.

3. Final Answer:

   150 -> Option A

4. Quick Check:

   File exists, output size = 150 [OK]

Hint: filesize() returns size only if file_exists() is true [OK]

Common Mistakes:

• Assuming filesize() works without checking existence
• Confusing filesize() output with file content
• Expecting 'File not found' when file exists

4. Identify the error in this PHP code snippet that checks if a file is writable:

$filename = 'data.txt';
if (is_writeable($filename)) {
    echo 'Writable';
} else {
    echo 'Not writable';
}

medium

A. Missing semicolon after echo statements

B. is_writeable() does not check permissions

C. $filename should be in double quotes

D. The function name is misspelled; should be is_writable()

Solution

1. Step 1: Check function spelling

   The correct function to check if a file is writable is is_writable(), not is_writeable().

2. Step 2: Verify other syntax

   Semicolons are present, variable quotes are valid, and is_writable() does check permissions.

3. Final Answer:

   The function name is misspelled; should be is_writable() -> Option D

4. Quick Check:

   Correct spelling = is_writable() [OK]

Hint: Remember: writable has one 'e' after writ [OK]

Common Mistakes:

• Misspelling is_writable() as is_writeable()
• Thinking variable needs double quotes
• Confusing permission check with existence

5. You want to list all files in a directory 'docs/' that exist, are readable, and have been modified in the last 24 hours. Which PHP code snippet correctly implements this?

hard

A. $files = scandir('docs/');
foreach ($files as $file) {
$path = 'docs/' . $file;
if (file_exists($path) && is_readable($path) && (time() - filemtime($path) < 86400)) {
echo $file . "\n";
}
}

B. $files = scandir('docs/');
foreach ($files as $file) {
if (is_dir($file)) continue;
if (is_writable($file)) {
echo $file . "\n";
}
}

C. $files = scandir('docs/');
foreach ($files as $file) {
if (file_exists($file) && filesize($file) > 0) {
echo $file . "\n";
}
}

D. $files = scandir('docs/');
foreach ($files as $file) {
if (is_file($file) && is_readable($file)) {
echo $file . "\n";
}
}

Solution

1. Step 1: Understand requirements

   We need to list files in 'docs/' that exist, are readable, and modified within last 24 hours (86400 seconds).

2. Step 2: Analyze each option

   $files = scandir('docs/'); foreach ($files as $file) { $path = 'docs/' . $file; if (file_exists($path) && is_readable($path) && (time() - filemtime($path) < 86400)) { echo $file . "\n"; } } correctly scans 'docs/', builds full path, checks file_exists(), is_readable(), and filemtime() against current time minus 86400 seconds. Other options miss one or more conditions or use wrong paths.

3. Final Answer:

   Option A code snippet -> Option A

4. Quick Check:

   Check existence + readability + recent mod = $files = scandir('docs/'); foreach ($files as $file) { $path = 'docs/' . $file; if (file_exists($path) && is_readable($path) && (time() - filemtime($path) < 86400)) { echo $file . "\n"; } } [OK]

Hint: Combine file_exists(), is_readable(), and filemtime() with full path [OK]

Common Mistakes:

• Not using full path when checking files
• Ignoring file modification time condition
• Checking is_writable() instead of is_readable()