time-to-botec/squiggle/node_modules/@stdlib/process/umask/README.md

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# umask

> Get/set the process mask.

<section class="intro">

A **mask** is a set of bits, each of which restricts how its corresponding permission is set for newly created files. On POSIX platforms, each file has a set of attributes that control who can read, write, or execute that file. Upon creating a file, file permissions must be set to an initial setting. The process mask restricts those permission settings.

If the mask contains a bit set to `1`, the corresponding initial file permission is disabled. If the mask contains a bit set to `0`, the corresponding permission is left to be determined by the requesting process and the system. The process mask is thus a filter that **removes** permissions as a file is created; i.e., each bit set to a `1` removes its corresponding permission.

In octal representation, a mask is a four digit number comprised as follows (using `0077` as an example):

-   `0`: special permissions (setuid, setgid, sticky bit)
-   `0`: (u)ser/owner permissions
-   `7`: (g)roup permissions
-   `7`: (o)thers/non-group permissions

Octal codes correspond to the following permissions:

-   `0`: read, write, execute
-   `1`: read, write
-   `2`: read, execute
-   `3`: read
-   `4`: write, execute
-   `5`: write
-   `6`: execute
-   `7`: no permissions

If provided fewer than four digits, the mask is left-padded with zeros. Note, however, that **only** the last three digits (i.e., the file permissions digits) of the mask are actually used when the mask is applied (i.e., `mask & 0777`).

Permissions can be represented using the following symbolic form:

```text
u=rwx,g=rwx,o=rwx
```

where

-   **u**: user permissions
-   **g**: group permissions
-   **o**: other/non-group permissions
-   **r**: read
-   **w**: write
-   **x**: execute

When setting permissions using symbolic notation, one may use a _mask expression_ of the form:

```text
[<classes>]<operator><symbols>
```

where `<classes>` may be a combination of

-   **u**: user
-   **g**: group
-   **o**: other/non-group
-   **a**: all

`<symbols>` may be a combination of

-   **r**: read
-   **w**: write
-   **x**: execute
-   **X**: special execute
-   **s**: setuid/gid on execution
-   **t**: sticky

and `<operator>` may be one of

-   **+**: enable
-   **-**: disable
-   **=**: enable specified and disable unspecified permissions

For example,

-   `u-w`: disable user write permissions
-   `u+w`: enable user write permissions
-   `u=w`: enable user write permissions and disable user read and execute

To specify multiple changes, one can specify a comma-separated list of mask expressions. For example,

```text
u+rwx,g-x,o=r
```

would enable user read, write, and execute permissions, disable group execute permissions, enable other read permissions, and disable other write and execute permissions.

The `a` class indicates "all", which is the same as specifying `ugo`. This is the default class if a class is omitted when specifying permissions. For example, `+x` is equivalent to `a+x` which is equivalent to `ugo+x` which is equivalent to `u+x,g+x,o+x` and enables execution for all classes.

</section>

<!-- /.intro -->

<section class="usage">

## Usage

```javascript
var umask = require( '@stdlib/process/umask' );
```

#### umask( \[mask,] \[options] )

Returns the process mask.

```javascript
var mask = umask();
// returns <number>
```

To set the process mask, provide a `mask` argument. When provided a `mask`, the function returns the previous mask value.

```javascript
var mask = umask();
// returns <number>

var prev = umask( 0 );
// returns <number>

var bool = ( prev === mask );
// returns true
```

The `mask` argument may be either an integer value or a `string` representing the mask using symbolic notation.

```javascript
var mask = umask( 'u=rwx,g=rw,o=rw' );
```

The function accepts the following `options`:

-   **symbolic**: `boolean` indicating whether to return the mask in symbolic notation. Default: `false`.

To return the process mask in symbolic notation, set the `symbolic` option to `true`.

```javascript
var opts = {
    'symbolic': true
};

// Get the mask:
var mask = umask( opts );
// e.g., returns 'u=rwx,g=rw,o=rw'

// Set the mask:
mask = umask( 0, opts );
// e.g., returns 'u=rwx,g=rw,o=rw'
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   To set the process mask using an octal `string` (e.g., `0777`), use `parseInt` to convert the `string` to an integer value.

    ```javascript
    umask( parseInt( '0777', 8 ) );
    ```

-   See [umask(2)][umask].

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var lpad = require( '@stdlib/string/left-pad' );
var umask = require( '@stdlib/process/umask' );

var mask;
var opts;

// Print the process mask as an integer:
mask = umask();
console.log( mask.toString() );

// Print the process mask as an octal string:
console.log( lpad( mask.toString(), 4, '0' ) );

// Print the process mask using symbolic notation:
opts = {
    'symbolic': true
};
console.log( umask( opts ) );
```

</section>

<!-- /.examples -->

* * *

<section class="cli">

## CLI

<section class="usage">

### Usage

```text
Usage: umask [options]

Options:

  -h,    --help                Print this message.
  -V,    --version             Print the package version.
  -p,    --print               Print the mask command.
  -S,    --symbolic            Print the mask using symbolic notation.
```

</section>

<!-- /.usage -->

<section class="examples">

### Examples

```bash
$ umask
```

To print the mask in command format, set the `-p` flag.

```bash
$ umask -p
```

</section>

<!-- /.examples -->

</section>

<!-- /.cli -->

<section class="links">

[umask]: http://man7.org/linux/man-pages/man2/umask.2.html

</section>

<!-- /.links -->