umask

Get/set the process mask.

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:

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:

[<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,

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.

Usage

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

umask( [mask,] [options] )

Returns the process mask.

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.

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.

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.

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'

Notes

To set the process mask using an octal string (e.g., 0777), use parseInt to convert the string to an integer value.
```
umask( parseInt( '0777', 8 ) );
```
See umask(2).

Examples

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

// Print the process mask as an integer:
var 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:
var opts = {
    'symbolic': true
};
console.log( umask( opts ) );

CLI

Usage

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.

Examples

$ umask

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

$ umask -p