# Exists
[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]
> Test whether a path exists on the filesystem.
## Installation
```bash
npm install @stdlib/fs-exists
```
## Usage
```javascript
var exists = require( '@stdlib/fs-exists' );
```
#### exists( path, clbk )
Asynchronously tests whether a path exists on the filesystem.
```javascript
exists( __dirname, done );
function done( bool ) {
if ( bool ) {
console.log( '...path exists.' );
} else {
console.log( '...path does not exist.' );
}
}
```
The above callback signature matches the now **deprecated** [`fs.exists()`][node-fs-exists] API. The function also accepts the more conventional `error`-first style callback signature found in most asynchronous Node APIs.
```javascript
exists( __dirname, done );
function done( error, bool ) {
if ( error ) {
console.error( error.message );
}
if ( bool ) {
console.log( '...path exists.' );
} else {
console.log( '...path does not exist.' );
}
}
```
#### exists.sync( path )
Synchronously tests whether a path exists on the filesystem.
```javascript
var bool = exists.sync( __dirname );
// returns
```
## Notes
- The following is considered an anti-pattern:
```javascript
var path = require( 'path' );
var readFileSync = require( '@stdlib/fs-read-file' ).sync;
var file = path.join( __dirname, 'foo.js' );
if ( exists.sync( __dirname ) ) {
file = readFileSync( file );
}
```
Because time elapses between checking for existence and performing IO, at the time IO is performed, the path is no longer guaranteed to exist. In other words, a race condition exists between the process attempting to read and another process attempting to delete.
Instead, the following pattern is preferred, where `errors` are handled explicitly:
```javascript
var path = require( 'path' );
var readFileSync = require( '@stdlib/fs-read-file' ).sync;
var file = path.join( __dirname, 'foo.js' );
try {
file = readFileSync( file );
} catch ( error ) {
console.log( 'unable to read file.' );
console.error( error );
}
```
- Nevertheless, use cases exist where one desires to check existence **without** performing IO. For example,
```javascript
var path = require( 'path' );
var writeFileSync = require( '@stdlib/fs-write-file' ).sync;
var file = path.join( __dirname, 'foo.js' );
if ( exists.sync( file ) ) {
console.log( 'Don\'t overwrite the file!' );
} else {
writeFileSync( file, 'beep', {
'encoding': 'utf8'
});
}
```
## Examples
```javascript
var exists = require( '@stdlib/fs-exists' );
/* Sync */
console.log( exists.sync( __dirname ) );
// => true
console.log( exists.sync( 'beepboop' ) );
// => false
/* Async */
exists( __dirname, done );
exists( 'beepboop', done );
function done( error, bool ) {
if ( error ) {
console.error( error.message );
} else {
console.log( bool );
}
}
```
* * *
## CLI
## Installation
To use the module as a general utility, install the module globally
```bash
npm install -g @stdlib/fs-exists
```
### Usage
```text
Usage: exists [options]
Options:
-h, --help Print this message.
-V, --version Print the package version.
```
### Notes
- Relative paths are resolved relative to the current working directory.
- Errors are written to `stderr`.
- Results are written to `stdout`.
### Examples
```bash
$ exists ./../
true ||
```
* * *
## Notice
This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].
#### Community
[![Chat][chat-image]][chat-url]
---
## License
See [LICENSE][stdlib-license].
## Copyright
Copyright © 2016-2022. The Stdlib [Authors][stdlib-authors].
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[npm-url]: https://npmjs.org/package/@stdlib/fs-exists
[test-image]: https://github.com/stdlib-js/fs-exists/actions/workflows/test.yml/badge.svg
[test-url]: https://github.com/stdlib-js/fs-exists/actions/workflows/test.yml
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[coverage-url]: https://codecov.io/github/stdlib-js/fs-exists?branch=main
[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules
[deno-url]: https://github.com/stdlib-js/fs-exists/tree/deno
[umd-url]: https://github.com/stdlib-js/fs-exists/tree/umd
[esm-url]: https://github.com/stdlib-js/fs-exists/tree/esm
[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg
[chat-url]: https://gitter.im/stdlib-js/stdlib/
[stdlib]: https://github.com/stdlib-js/stdlib
[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors
[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/fs-exists/main/LICENSE
[node-fs-exists]: https://nodejs.org/api/fs.html#fs_fs_exists_path_callback
[@stdlib/fs/read-file]: https://www.npmjs.com/package/@stdlib/fs-read-file
[@stdlib/fs/read-dir]: https://www.npmjs.com/package/@stdlib/fs-read-dir