# Is This Path Inside This Other Path?
It turns out this question isn't trivial to answer using Node's built-in path APIs. A naive `indexOf`-based solution will fail sometimes on Windows, which is case-insensitive (see e.g. [isaacs/npm#4214][]). You might then think to be clever with `path.resolve`, but you have to be careful to account for situations whether the paths have different drive letters, or else you'll cause bugs like [isaacs/npm#4313][]. And let's not even get started on trailing slashes.
The **path-is-inside** package will give you a robust, cross-platform way of detecting whether a given path is inside another path.
## Usage
Pretty simple. First the path being tested; then the potential parent. Like so:
```js
var pathIsInside = require("path-is-inside");
pathIsInside("/x/y/z", "/x/y") // true
pathIsInside("/x/y", "/x/y/z") // false
```
Paths are considered to be inside themselves:
```js
pathIsInside("/x/y", "/x/y"); // true
```
## OS-Specific Behavior
Like Node's built-in path module, path-is-inside treats all file paths on Windows as case-insensitive, whereas it treats all file paths on *-nix operating systems as case-sensitive. Keep this in mind especially when working on a Mac, where, despite Node's defaults, the OS usually treats paths case-insensitively.
In practice, this means:
```js
// On Windows
pathIsInside("C:\\X\\Y\\Z", "C:\\x\\y") // true
// On *-nix, including Mac OS X
pathIsInside("/X/Y/Z", "/x/y") // false
```
[isaacs/npm#4214]: https://github.com/isaacs/npm/pull/4214
[isaacs/npm#4313]: https://github.com/isaacs/npm/issues/4313
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