---
name: "elvish-unix"
section: "7"
platform: "linux"
package: "elvish"
version: "0.15.0-1+b5"
release: "Debian 11 (Bullseye)"
platforms: ["linux"]
url: "https://new.carta.tech/elvish-unix"
---

# elvish-unix(7)

## Introduction

The `unix:` module provides access to features that only make sense on UNIX-like operating systems, such as Linux, FreeBSD, and macOS.

On non-UNIX operating systems, such as MS Windows, this namespace does not exist and `use unix` will fail. Use the `$platform:is-unix` variable to determine if this namespace is usable.

## Variables

### $unix:umask

The file mode creation mask. Its value is a string in Elvish octal representation; e.g. 0o027. This makes it possible to use it in any context that expects a `$number`.

When assigning a new value a string is implicitly treated as an octal number. If that fails the usual rules for interpreting numbers are used. The following are equivalent: `unix:umask = 027` and `unix:umask = 0o27`. You can also assign to it a `float64` data type that has no fractional component. The assigned value must be within the range \[0 ... 0o777\], otherwise the assignment will throw an exception.

You can do a temporary assignment to affect a single command; e.g. `umask=077 touch a_file`. After the command completes the old umask will be restored. **Warning**: Since the umask applies to the entire process, not individual threads, changing it temporarily in this manner is dangerous if you are doing anything in parallel. Such as via the `peach` command.