Just Programmer's Manual

Enabling and Disabling Items

The [android], [dragonfly], [freebsd], [linux], [macos], [netbsd], [openbsd], [unix], and [windows] attributes are conditional attributes. By default, items are always enabled. An item with one or more conditional attributes will only be enabled when one or more of those conditional attributes is active.

The conditional attributes originally applied only to recipes, but may now be applied to all top-level items^1.56.0.

This can be used to write justfiles that behave differently depending on which operating system they run on. The run recipe in this justfile will compile and run main.c, using a different C compiler and using the correct output binary name for that compiler depending on the operating system:

[unix]
run:
  cc main.c
  ./a.out

[windows]
run:
  cl main.c
  main.exe

Similarly, a setting can be made conditional on the current operating system:

[unix]
set shell := ['sh', '-cu']

[windows]
set shell := ['cmd', '/c']