# Filename Extension
> [Regular expression][regexp] to capture a [POSIX][posix] filename extension.
## Usage
```javascript
var reExtnamePosix = require( '@stdlib/regexp/extname-posix' );
```
#### reExtnamePosix()
Returns a [regular expression][regexp] to capture a [POSIX][posix] filename extension.
```javascript
var RE_EXTNAME_POSIX = reExtnamePosix();
var ext = RE_EXTNAME_POSIX.exec( 'index.js' )[ 1 ];
// returns '.js'
```
#### reExtnamePosix.REGEXP
[Regular expression][regexp] to capture a [POSIX][posix] filename extension.
```javascript
var ext = reExtnamePosix.REGEXP.exec( 'index.js' )[ 1 ];
// returns '.js'
```
## Notes
- When executed against dotfile filenames (e.g., `.gitignore`), the [regular expression][regexp] does **not** capture the basename as a filename extension.
```javascript
var ext = reExtnamePosix.REGEXP.exec( '.bash_profile' )[ 1 ];
// returns ''
ext = reExtnamePosix.REGEXP.exec( '.travis.yml' )[ 1 ];
// returns '.yml'
```
## Examples
```javascript
var reExtnamePosix = require( '@stdlib/regexp/extname-posix' );
var RE_EXTNAME_POSIX = reExtnamePosix();
var ext;
ext = RE_EXTNAME_POSIX.exec( 'index.js' )[ 1 ];
// returns '.js'
ext = RE_EXTNAME_POSIX.exec( '/foo/bar/home.html' )[ 1 ];
// returns '.html'
ext = RE_EXTNAME_POSIX.exec( 'foo/file.pdf' )[ 1 ];
// returns '.pdf'
ext = RE_EXTNAME_POSIX.exec( 'beep.' )[ 1 ];
// returns '.'
ext = RE_EXTNAME_POSIX.exec( '' )[ 1 ];
// returns ''
ext = RE_EXTNAME_POSIX.exec( '/foo/bar/file' )[ 1 ];
// returns ''
ext = RE_EXTNAME_POSIX.exec( '/foo/bar/.gitignore' )[ 1 ];
// returns ''
```
[regexp]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions
[posix]: https://en.wikipedia.org/wiki/POSIX