is_dir()

What is the is_dir() Function?

The is_dir() function is a built-in PHP function that tells you whether a given path exists and points to a directory (folder). It returns true when the path is an existing directory, and false for everything else — a regular file, a path that does not exist, or a path you do not have permission to read.

It is one of PHP's filesystem "type-check" functions, alongside is_file(), is_link(), and file_exists(). Use is_dir() whenever you need to confirm a directory is there before reading it, writing into it, or creating it.

Syntax

is_dir(string $filename): bool

• $filename — the path to test. It can be absolute (/var/www/uploads) or relative to the script's current working directory (uploads). A trailing slash is allowed.
• Return value — true if $filename exists and is a directory, otherwise false.

Basic Example

__DIR__ is a magic constant that always resolves to an existing directory, so this example reliably prints the "is a directory" branch.

Telling a Directory From a File

The most common use of is_dir() is to branch on what a path actually is. Compare it with is_file():

<?php

$paths = [__DIR__, __FILE__, '/path/that/does/not/exist'];

foreach ($paths as $path) {
    if (is_dir($path)) {
        echo "$path -> directory\n";
    } elseif (is_file($path)) {
        echo "$path -> file\n";
    } else {
        echo "$path -> missing\n";
    }
}

__FILE__ is the full path of the current script, so it is reported as a file, while the made-up path is reported as missing.

A Practical Use: Create the Directory Only If It Is Missing

Guarding mkdir() with is_dir() avoids a warning when the folder already exists:

<?php

$dir = sys_get_temp_dir() . '/my_app_cache';

if (!is_dir($dir)) {
    mkdir($dir, 0755, true); // true = create parent dirs too
    echo "Created: $dir";
} else {
    echo "Already exists: $dir";
}

Common Gotchas

• is_dir() returns false, not an error, when the path does not exist. A false result does not mean "this is a file" — it could simply be missing. Use file_exists() if you only care that something is there.
• Symbolic links are followed. If the path is a symlink that points at a directory, is_dir() returns true. To detect the link itself, use is_link().
• Results are cached. PHP caches stat() results, so if a directory is created or deleted by another process mid-script you may see a stale answer. Call clearstatcache() to force a fresh check.
• Relative paths depend on the working directory. is_dir('data') is resolved against the current working directory (getcwd()), not the script's location. Use __DIR__ . '/data' when you mean "next to this script."

Related Functions

Conclusion

is_dir() is the safe, standard way to confirm a path is an existing directory before you act on it. Remember that it follows symlinks, caches its result, and resolves relative paths against the current working directory — pairing it with file_exists(), is_file(), and mkdir() covers nearly every directory-handling situation you will meet.

Practice