PHP is_dir Function

last modified April 3, 2025

The PHP is_dir function checks whether a path is a directory. It's essential for filesystem operations where directory validation is needed.

Basic Definition

The is_dir function checks if the given filename is a directory. It returns true if the filename exists and is a directory, false otherwise.

Syntax: is_dir(string $filename): bool. The function caches results, so multiple calls may return cached values until clearstatcache() is called.

Basic is_dir Example

This shows the simplest usage of is_dir to check a directory.

basic_is_dir.php

<?php

declare(strict_types=1);

$path = "/var/www/html";
$isDirectory = is_dir($path);

var_dump($isDirectory); // Outputs: bool(true) if directory exists

This checks if "/var/www/html" is a directory. The function returns true only if the path exists and is a directory, not a file or symlink.

Checking Relative Paths

is_dir works with relative paths from the current working directory.

relative_path.php

<?php

declare(strict_types=1);

$path = "docs";
$isDirectory = is_dir($path);

echo $isDirectory ? "Directory exists" : "Not a directory";

This checks if "docs" is a directory relative to the current script location. Remember that relative paths depend on the current working directory.

Checking Non-Existent Path

is_dir returns false for paths that don't exist or aren't directories.

nonexistent_path.php

<?php

declare(strict_types=1);

$path = "/nonexistent/path";
$isDirectory = is_dir($path);

var_dump($isDirectory); // Outputs: bool(false)

The function returns false for non-existent paths. It doesn't throw errors for invalid paths, making it safe for existence checking.

Checking File vs Directory

This example demonstrates differentiating between files and directories.

file_vs_dir.php

<?php

declare(strict_types=1);

$path1 = "/var/www/html/index.php";
$path2 = "/var/www/html";

$result1 = is_dir($path1) ? "Directory" : "Not directory";
$result2 = is_dir($path2) ? "Directory" : "Not directory";

echo $result1 . "\n"; // Outputs: Not directory
echo $result2 . "\n"; // Outputs: Directory

This shows how is_dir correctly identifies files vs directories. It's useful for filesystem traversal where you need to handle each differently.

Windows Path Example

is_dir works with Windows-style paths using backslashes.

windows_path.php

<?php

declare(strict_types=1);

$path = "C:\\Windows\\System32";
$isDirectory = is_dir($path);

echo $isDirectory ? "Valid Windows directory" : "Invalid directory";

The function handles Windows paths correctly. Note that backslashes need to be escaped in PHP strings, or you can use forward slashes which also work.

Best Practices

Permission Checks: Verify read permissions before checking.
Error Handling: Combine with file_exists for robust checks.
Symbolic Links: Use is_link with is_dir for symlink handling.
Performance: Cache results when checking repeatedly.
Security: Sanitize paths before filesystem operations.

Source

PHP is_dir Documentation

This tutorial covered the PHP is_dir function with practical examples showing directory validation in different scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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