@stdlib/fs/append-file/README.md

Filesystem APIs.

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# Append File

> Append data to a file.

<section class="usage">

## Usage

```javascript
var appendFile = require( '@stdlib/fs/append-file' );
```

#### appendFile( file, data\[, options], clbk )

Asynchronously appends `data` to a `file`.

```javascript
var join = require( 'path' ).join;

var fpath = join( __dirname, 'examples', 'fixtures', 'file.txt' );

appendFile( fpath, 'beep boop\n', onAppend );

function onAppend( error ) {
    if ( error ) {
        console.log( error instanceof Error );
        // => false
    }
}
```

The `data` argument may be either a `string` or a [`Buffer`][@stdlib/buffer/ctor].

```javascript
var join = require( 'path' ).join;
var string2buffer = require( '@stdlib/buffer/from-string' );

var fpath = join( __dirname, 'examples', 'fixtures', 'file.txt' );

appendFile( fpath, string2buffer( 'beep boop\n' ), onAppend );

function onAppend( error ) {
    if ( error ) {
        console.log( error instanceof Error );
        // => false
    }
}
```

The function accepts the same `options` and has the same defaults as [`fs.appendFile()`][node-fs].

#### appendFile.sync( file, data\[, options] )

Synchronously appends `data` to a `file`.

```javascript
var join = require( 'path' ).join;

var fpath = join( __dirname, 'examples', 'fixtures', 'file.txt' );

var err = appendFile.sync( fpath, 'beep boop\n' );
if ( err instanceof Error ) {
    throw err;
}
```

The function accepts the same `options` and has the same defaults as [`fs.appendFileSync()`][node-fs].

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   The difference between this `appendFile.sync` and [`fs.appendFileSync()`][node-fs] is that [`fs.appendFileSync()`][node-fs] will throw if an `error` is encountered (e.g., if given a non-existent directory path) and this API will return an `error`. Hence, the following anti-pattern

    <!-- eslint-disable node/no-sync -->

    ```javascript
    var fs = require( 'fs' );

    // Check for directory path existence to prevent an error being thrown...
    if ( fs.existsSync( '/path/to' ) ) {
        fs.appendFileSync( '/path/to/file.txt', 'beep boop\n' );
    }
    ```

    can be replaced by an approach which addresses existence via `error` handling.

    <!-- eslint-disable node/no-sync -->

    ```javascript
    var appendFile = require( '@stdlib/fs/append-file' );

    // Explicitly handle the error...
    var err = appendFile.sync( '/path/to/file.txt', 'boop beep\n' );
    if ( err instanceof Error ) {
        // You choose what to do...
        throw err;
    }
    ```

</section>

<!-- /.notes -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var join = require( 'path' ).join;
var appendFile = require( '@stdlib/fs/append-file' );

var fpath = join( __dirname, 'examples', 'fixtures', 'file.txt' );

// Synchronously append data to a file:

var error = appendFile.sync( fpath, 'beep boop\n', 'utf8' );
// Function successfully executes and returns null

console.log( error instanceof Error );
// => false

// Asynchronously append data to a file:

appendFile( fpath, 'beep boop\n', onAppend );

function onAppend( error ) {
    if ( error ) {
        console.error( 'Error: %s', error.message );
    }
    console.log( 'Success!!!' );
}
```

</section>

<!-- /.examples -->

* * *

<section class="cli">

## CLI

<section class="usage">

### Usage

```text
Usage: append-file [options] <filepath>

Options:

  -h,    --help                Print this message.
  -V,    --version             Print the package version.
  --enc, --encoding encoding   Encoding. Default: 'utf8'.
         --flag flag           Flag. Default: 'a'.
         --mode mode           Mode. Default: 0o666.
```

</section>

<!-- /.usage -->

<section class="notes">

### Notes

-   Relative output file paths are resolved relative to the current working directory.
-   Errors are written to `stderr`.
-   File contents should be provided over `stdin` as part of a [standard stream][standard-stream] pipeline.

</section>

<!-- /.notes -->

<section class="examples">

### Examples

```bash
$ printf 'beep boop\n' | append-file ./examples/fixtures/file.txt
```

</section>

<!-- /.examples -->

</section>

<!-- /.cli -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="links">

[node-fs]: https://nodejs.org/api/fs.html

[@stdlib/buffer/ctor]: https://www.npmjs.com/package/@stdlib/buffer-ctor

[standard-stream]: https://en.wikipedia.org/wiki/Pipeline_%28Unix%29

</section>

<!-- /.links -->