The **`is_dir()`** function in PHP checks whether the given filename is a directory. 

# Syntax
```c
is_dir(string: $name):bool
```

# Parameters

`name`: This specifies the path to the file we want to check.

# Return value

`is_dir()` returns `true` if the provided filename exists and is also a directory. Otherwise, it returns `false`.

# Code
The following code shows the use of the `is_dir()` function.

<?php
$file = "test.txt";
mkdir("documents");

if(is_dir($file)) 
{
  echo ("$file is a directory");
} 
else 
{
  echo ("$file is not a directory");
}
echo "\n";
if(is_dir("documents")) 
{
  echo ("Documents is a directory");
} 
else 
{
  echo ("Documents is not a directory");
}
?>

## Explanation
In the code above, the file `test.txt` is passed to the function. Since it is not a directory, `is_dir()` returns `false`.

The `mkdir` function makes a directory named `documents` and returns `true` when it is checked using the `is_dir()` function.
> This function produces cache output. We have to clear the cache by using the `clearstatcache()` function.

What is the is_dir() function in PHP?

`is_dir()` checks if a path is a directory, returns true if so, else false.