just/README.md

<div align=right>Table of Contents↗️</div>

<h1 align=center><code>just</code></h1>

<div align=center>
  <a href=https://crates.io/crates/just>
    <img src=https://img.shields.io/crates/v/just.svg alt="crates.io version">
  </a>
  <a href=https://github.com/casey/just/actions>
    <img src=https://github.com/casey/just/actions/workflows/ci.yaml/badge.svg alt="build status">
  </a>
  <a href=https://github.com/casey/just/releases>
    <img src=https://img.shields.io/github/downloads/casey/just/total.svg alt=downloads>
  </a>
  <a href=https://discord.gg/ezYScXR>
    <img src=https://img.shields.io/discord/695580069837406228?logo=discord alt="chat on discord">
  </a>
  <a href=mailto:casey@rodarmor.com?subject=Thanks%20for%20Just!>
    <img src=https://img.shields.io/badge/Say%20Thanks-!-1EAEDB.svg alt="say thanks">
  </a>
</div>
<br>

`just` is a handy way to save and run project-specific commands.

This readme is also available as a [book](https://just.systems/man/en/).

(中文文档在 [这里](https://github.com/casey/just/blob/master/README.中文.md),
快看过来!)

Commands, called recipes, are stored in a file called `justfile` with syntax
inspired by `make`:

![screenshot](https://raw.githubusercontent.com/casey/just/master/screenshot.png)

You can then run them with `just RECIPE`:

```sh
$ just test-all
cc *.c -o main
./test --all
Yay, all your tests passed!
```

`just` has a ton of useful features, and many improvements over `make`:

- `just` is a command runner, not a build system, so it avoids much of
  [`make`'s complexity and idiosyncrasies](#what-are-the-idiosyncrasies-of-make-that-just-avoids).
  No need for `.PHONY` recipes!

- Linux, MacOS, and Windows are supported with no additional dependencies.
  (Although if your system doesn't have an `sh`, you'll need to
  [choose a different shell](#shell).)

- Errors are specific and informative, and syntax errors are reported along
  with their source context.

- Recipes can accept [command line arguments](#recipe-parameters).

- Wherever possible, errors are resolved statically. Unknown recipes and
  circular dependencies are reported before anything runs.

- `just` [loads `.env` files](#dotenv-settings), making it easy to populate
  environment variables.

- Recipes can be [listed from the command line](#listing-available-recipes).

- Command line completion scripts are
  [available for most popular shells](#shell-completion-scripts).

- Recipes can be written in
  [arbitrary languages](#writing-recipes-in-other-languages), like Python or NodeJS.

- `just` can be invoked from any subdirectory, not just the directory that
  contains the `justfile`.

- And [much more](https://just.systems/man/en/)!

If you need help with `just` please feel free to open an issue or ping me on
[Discord](https://discord.gg/ezYScXR). Feature requests and bug reports are
always welcome!

Installation
------------

### Prerequisites

`just` should run on any system with a reasonable `sh`, including Linux, MacOS,
and the BSDs.

On Windows, `just` works with the `sh` provided by
[Git for Windows](https://git-scm.com),
[GitHub Desktop](https://desktop.github.com), or
[Cygwin](http://www.cygwin.com).

If you'd rather not install `sh`, you can use the `shell` setting to use the
shell of your choice.

Like PowerShell:

```just
# use PowerShell instead of sh:
set shell := ["powershell.exe", "-c"]

hello:
  Write-Host "Hello, world!"
```

…or `cmd.exe`:

```just
# use cmd.exe instead of sh:
set shell := ["cmd.exe", "/c"]

list:
  dir
```

You can also set the shell using command-line arguments. For example, to use
PowerShell, launch `just` with `--shell powershell.exe --shell-arg -c`.

(PowerShell is installed by default on Windows 7 SP1 and Windows Server 2008 R2
S1 and later, and `cmd.exe` is quite fiddly, so PowerShell is recommended for
most Windows users.)

### Packages

<table>
  <thead>
    <tr>
      <th>Operating System</th>
      <th>Package Manager</th>
      <th>Package</th>
      <th>Command</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td><a href=https://alpinelinux.org>Alpine Linux</a></td>
      <td><a href=https://wiki.alpinelinux.org/wiki/Alpine_Linux_package_management>apk-tools</a></td>
      <td><a href=https://pkgs.alpinelinux.org/package/edge/community/x86_64/just>just</a></td>
      <td><code>apk add just</code></td>
    </tr>
    <tr>
      <td><a href=https://www.archlinux.org>Arch Linux</a></td>
      <td><a href=https://wiki.archlinux.org/title/Pacman>pacman</a></td>
      <td><a href=https://archlinux.org/packages/extra/x86_64/just/>just</a></td>
      <td><code>pacman -S just</code></td>
    </tr>
    <tr>
      <td><a href=https://debian.org>Debian</a> and <a href=https://ubuntu.com>Ubuntu</a> derivatives</td>
      <td><a href=https://mpr.makedeb.org>MPR</a></td>
      <td><a href=https://mpr.makedeb.org/packages/just>just</a></td>
      <td>
        <code>git clone https://mpr.makedeb.org/just</code><br>
        <code>cd just</code><br>
        <code>makedeb -si</code>
      </td>
    </tr>
    <tr>
      <td><a href=https://debian.org>Debian</a> and <a href=https://ubuntu.com>Ubuntu</a> derivatives</td>
      <td><a href=https://docs.makedeb.org/prebuilt-mpr>Prebuilt-MPR</a></td>
      <td><a href=https://mpr.makedeb.org/packages/just>just</a></td>
      <td>
        <sup><b>You must have the <a href=https://docs.makedeb.org/prebuilt-mpr/getting-started/#setting-up-the-repository>Prebuilt-MPR set up</a> on your system in order to run this command.</b></sup><br>
        <code>sudo apt install just</code>
      </td>
    </tr>
    <tr>
      <td><a href=https://getfedora.org>Fedora Linux</a></td>
      <td><a href=https://dnf.readthedocs.io/en/latest/>DNF</a></td>
      <td><a href=https://src.fedoraproject.org/rpms/rust-just>just</a></td>
      <td><code>dnf install just</code></td>
    </tr>
    <tr>
      <td><a href=https://www.freebsd.org>FreeBSD</a></td>
      <td><a href=https://www.freebsd.org/doc/handbook/pkgng-intro.html>pkg</a></td>
      <td><a href=https://www.freshports.org/deskutils/just/>just</a></td>
      <td><code>pkg install just</code></td>
    </tr>
    <tr>
      <td><a href=https://www.gentoo.org>Gentoo Linux</a></td>
      <td><a href=https://wiki.gentoo.org/wiki/Portage>Portage</a></td>
      <td><a href=https://github.com/gentoo-mirror/guru/tree/master/dev-build/just>guru/dev-build/just</a></td>
      <td>
        <code>eselect repository enable guru</code><br>
        <code>emerge --sync guru</code><br>
        <code>emerge dev-build/just</code>
      </td>
    </tr>
    <tr>
      <td><a href=https://en.wikipedia.org/wiki/MacOS>macOS</a></td>
      <td><a href=https://www.macports.org>MacPorts</a></td>
      <td><a href=https://ports.macports.org/port/just/summary>just</a></td>
      <td><code>port install just</code></td>
    </tr>
    <tr>
      <td><a href=https://en.wikipedia.org/wiki/Microsoft_Windows>Microsoft Windows</a></td>
      <td><a href=https://chocolatey.org>Chocolatey</a></td>
      <td><a href=https://github.com/michidk/just-choco>just</a></td>
      <td><code>choco install just</code></td>
    </tr>
    <tr>
      <td><a href=https://en.wikipedia.org/wiki/Microsoft_Windows>Microsoft Windows</a></td>
      <td><a href=https://scoop.sh>Scoop</a></td>
      <td><a href=https://github.com/ScoopInstaller/Main/blob/master/bucket/just.json>just</a></td>
      <td><code>scoop install just</code></td>
    </tr>
    <tr>
      <td><a href=https://en.wikipedia.org/wiki/Microsoft_Windows>Microsoft Windows</a></td>
      <td><a href=https://learn.microsoft.com/en-us/windows/package-manager/>Windows Package Manager</a></td>
      <td><a href=https://github.com/microsoft/winget-pkgs/tree/master/manifests/c/Casey/Just>Casey/Just</a></td>
      <td><code>winget install --id Casey.Just --exact</code></td>
    </tr>
    <tr>
      <td><a href=https://nixos.org/nixos/>NixOS</a></td>
      <td><a href=https://nixos.org/nix/>Nix</a></td>
      <td><a href=https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/tools/just/default.nix>just</a></td>
      <td><code>nix-env -iA nixos.just</code></td>
    </tr>
    <tr>
      <td><a href=https://opensuse.org>openSUSE</a></td>
      <td><a href=https://en.opensuse.org/Portal:Zypper>Zypper</a></td>
      <td><a href=https://build.opensuse.org/package/show/Base:System/just>just</a></td>
      <td><code>zypper in just</code></td>
    </tr>
    <tr>
      <td><a href=https://getsol.us>Solus</a></td>
      <td><a href=https://getsol.us/articles/package-management/basics/en>eopkg</a></td>
      <td><a href=https://dev.getsol.us/source/just/>just</a></td>
      <td><code>eopkg install just</code></td>
    </tr>
    <tr>
      <td><a href=https://github.com/casey/just/releases>Various</a></td>
      <td><a href=https://asdf-vm.com>asdf</a></td>
      <td><a href=https://github.com/olofvndrhr/asdf-just>just</a></td>
      <td>
        <code>asdf plugin add just</code><br>
        <code>asdf install just &lt;version&gt;</code>
      </td>
    </tr>
    <tr>
      <td><a href=https://forge.rust-lang.org/release/platform-support.html>Various</a></td>
      <td><a href=https://www.rust-lang.org>Cargo</a></td>
      <td><a href=https://crates.io/crates/just>just</a></td>
      <td><code>cargo install just</code></td>
    </tr>
    <tr>
      <td><a href=https://docs.conda.io/en/latest/miniconda.html#system-requirements>Various</a></td>
      <td><a href=https://docs.conda.io/projects/conda/en/latest/index.html>Conda</a></td>
      <td><a href=https://anaconda.org/conda-forge/just>just</a></td>
      <td><code>conda install -c conda-forge just</code></td>
    </tr>
    <tr>
      <td><a href=https://docs.brew.sh/Installation>Various</a></td>
      <td><a href=https://brew.sh>Homebrew</a></td>
      <td><a href=https://formulae.brew.sh/formula/just>just</a></td>
      <td><code>brew install just</code></td>
    </tr>
    <tr>
      <td><a href=https://nixos.org/download.html#download-nix>Various</a></td>
      <td><a href=https://nixos.org/nix/>Nix</a></td>
      <td><a href=https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/tools/just/default.nix>just</a></td>
      <td><code>nix-env -iA nixpkgs.just</code></td>
    </tr>
    <tr>
      <td><a href=https://snapcraft.io/docs/installing-snapd>Various</a></td>
      <td><a href=https://snapcraft.io>Snap</a></td>
      <td><a href=https://snapcraft.io/just>just</a></td>
      <td><code>snap install --edge --classic just</code></td>
    </tr>
    <tr>
      <td><a href=https://voidlinux.org>Void Linux</a></td>
      <td><a href=https://wiki.voidlinux.org/XBPS>XBPS</a></td>
      <td><a href=https://github.com/void-linux/void-packages/blob/master/srcpkgs/just/template>just</a></td>
      <td><code>xbps-install -S just</code></td>
    </tr>
  </tbody>
</table>

![just package version table](https://repology.org/badge/vertical-allrepos/just.svg)

![rust:just package version table](https://repology.org/badge/vertical-allrepos/rust:just.svg)

### Pre-Built Binaries

Pre-built binaries for Linux, MacOS, and Windows can be found on
[the releases page](https://github.com/casey/just/releases).

You can use the following command on Linux, MacOS, or Windows to download the
latest release, just replace `DEST` with the directory where you'd like to put
`just`:

```sh
curl --proto '=https' --tlsv1.2 -sSf https://just.systems/install.sh | bash -s -- --to DEST
```

For example, to install `just` to `~/bin`:

```sh
# create ~/bin
mkdir -p ~/bin

# download and extract just to ~/bin/just
curl --proto '=https' --tlsv1.2 -sSf https://just.systems/install.sh | bash -s -- --to ~/bin

# add `~/bin` to the paths that your shell searches for executables
# this line should be added to your shells initialization file,
# e.g. `~/.bashrc` or `~/.zshrc`
export PATH="$PATH:$HOME/bin"

# just should now be executable
just --help
```

Note that `install.sh` may fail on GitHub Actions, or in other environments
where many machines share IP addresses. `install.sh` calls GitHub APIs in order
to determine the latest version of `just` to install, and those API calls are
rate-limited on a per-IP basis. To make `install.sh` more reliable in such
circumstances, pass a specific tag to install with `--tag`.

### GitHub Actions

Developers may be interested in running the same `just` commands that they use
locally on continuous integration platforms such as GitHub Actions. For example,
every time that a contributor creates a pull request, a GitHub Action could run
`just test` on the three major operating systems to provide feedback to both the
contributor and reviewers that tests are passing.

Demonstrate how to install and use just in GitHub Actions on the three major
operating systems without needing third-party GitHub Actions. Put the following
code into a `.github/workflows/just_test.yml` file.

```yaml
name: just_test
on: [pull_request, push]
jobs:
  ubuntu:
    runs-on: ubuntu-latest
    steps:
    - run: sudo snap install --edge --classic just
    - uses: actions/checkout@v4
    - run: just test
  macos:
    runs-on: macos-latest
    steps:
    - run: brew install just
    - uses: actions/checkout@v4
    - run: just test
  windows:
    runs-on: windows-latest
    steps:
    - run: choco install just
    - uses: actions/checkout@v4
    - run: just test
```

Or with [extractions/setup-just](https://github.com/extractions/setup-just):

```yaml
- uses: extractions/setup-just@v1
  with:
    just-version: 1.5.0  # optional semver specification, otherwise latest
```

Or with [taiki-e/install-action](https://github.com/taiki-e/install-action):

```yaml
- uses: taiki-e/install-action@just
```

### Release RSS Feed

An [RSS feed](https://en.wikipedia.org/wiki/RSS) of `just` releases is available [here](https://github.com/casey/just/releases.atom).

### Node.js Installation

[just-install](https://npmjs.com/package/just-install) can be used to automate
installation of `just` in Node.js applications.

`just` is a great, more robust alternative to npm scripts. If you want to
include `just` in the dependencies of a Node.js application, `just-install`
will install a local, platform-specific binary as part of the `npm install`
command. This removes the need for every developer to install `just`
independently using one of the processes mentioned above. After installation,
the `just` command will work in npm scripts or with npx. It's great for teams
who want to make the set up process for their project as easy as possible.

For more information, see the
[just-install README file](https://github.com/brombal/just-install#readme).

Backwards Compatibility
-----------------------

With the release of version 1.0, `just` features a strong commitment to
backwards compatibility and stability.

Future releases will not introduce backwards incompatible changes that make
existing `justfile`s stop working, or break working invocations of the
command-line interface.

This does not, however, preclude fixing outright bugs, even if doing so might
break `justfiles` that rely on their behavior.

There will never be a `just` 2.0. Any desirable backwards-incompatible changes
will be opt-in on a per-`justfile` basis, so users may migrate at their
leisure.

Features that aren't yet ready for stabilization are gated behind the
`--unstable` flag. Features enabled by `--unstable` may change in backwards
incompatible ways at any time. Unstable features can also be enabled by setting
the environment variable `JUST_UNSTABLE` to any value other than `false`, `0`,
or the empty string.

Editor Support
--------------

`justfile` syntax is close enough to `make` that you may want to tell your
editor to use `make` syntax highlighting for `just`.

### Vim and Neovim

#### `vim-just`

The [vim-just](https://github.com/NoahTheDuke/vim-just) plugin provides syntax
highlighting for `justfile`s.

Install it with your favorite package manager, like
[Plug](https://github.com/junegunn/vim-plug):

```vim
call plug#begin()

Plug 'NoahTheDuke/vim-just'

call plug#end()
```

Or with Vim's built-in package support:

```sh
mkdir -p ~/.vim/pack/vendor/start
cd ~/.vim/pack/vendor/start
git clone https://github.com/NoahTheDuke/vim-just.git
```

#### `tree-sitter-just`

[tree-sitter-just](https://github.com/IndianBoy42/tree-sitter-just) is an
[Nvim Treesitter](https://github.com/nvim-treesitter/nvim-treesitter) plugin
for Neovim.

#### Makefile Syntax Highlighting

Vim's built-in makefile syntax highlighting isn't perfect for `justfile`s, but
it's better than nothing. You can put the following in `~/.vim/filetype.vim`:

```vimscript
if exists("did_load_filetypes")
  finish
endif

augroup filetypedetect
  au BufNewFile,BufRead justfile setf make
augroup END
```

Or add the following to an individual `justfile` to enable `make` mode on a
per-file basis:

```text
# vim: set ft=make :
```

### Emacs

[just-mode](https://github.com/leon-barrett/just-mode.el) provides syntax
highlighting and automatic indentation of `justfile`s. It is available on
[MELPA](https://melpa.org/) as [just-mode](https://melpa.org/#/just-mode).

[justl](https://github.com/psibi/justl.el) provides commands for executing and
listing recipes.

You can add the following to an individual `justfile` to enable `make` mode on
a per-file basis:

```text
# Local Variables:
# mode: makefile
# End:
```

### Visual Studio Code

An extension for VS Code is [available here](https://github.com/nefrob/vscode-just).

Unmaintained VS Code extensions include
[skellock/vscode-just](https://github.com/skellock/vscode-just) and
[sclu1034/vscode-just](https://github.com/sclu1034/vscode-just).

### JetBrains IDEs

A plugin for JetBrains IDEs by [linux_china](https://github.com/linux-china) is
[available here](https://plugins.jetbrains.com/plugin/18658-just).

### Kakoune

Kakoune supports `justfile` syntax highlighting out of the box, thanks to
TeddyDD.

### Helix

[Helix](https://helix-editor.com/) supports `justfile` syntax highlighting
out-of-the-box since version 23.05.

### Sublime Text

The [Just package](https://github.com/nk9/just_sublime) by
[nk9](https://github.com/nk9) with `just` syntax and some other tools is
available on [PackageControl](https://packagecontrol.io/packages/Just).

### Micro

[Micro](https://micro-editor.github.io/) supports Justfile syntax highlighting
out of the box, thanks to [tomodachi94](https://github.com/tomodachi94).

### Other Editors

Feel free to send me the commands necessary to get syntax highlighting working
in your editor of choice so that I may include them here.

Quick Start
-----------

See [the installation section](#installation) for how to install `just` on your
computer. Try running `just --version` to make sure that it's installed
correctly.

For an overview of the syntax, check out
[this cheatsheet](https://cheatography.com/linux-china/cheat-sheets/justfile/).

Once `just` is installed and working, create a file named `justfile` in the
root of your project with the following contents:

```just
recipe-name:
  echo 'This is a recipe!'

# this is a comment
another-recipe:
  @echo 'This is another recipe.'
```

When you invoke `just` it looks for file `justfile` in the current directory
and upwards, so you can invoke it from any subdirectory of your project.

The search for a `justfile` is case insensitive, so any case, like `Justfile`,
`JUSTFILE`, or `JuStFiLe`, will work. `just` will also look for files with the
name `.justfile`, in case you'd like to hide a `justfile`.

Running `just` with no arguments runs the first recipe in the `justfile`:

```sh
$ just
echo 'This is a recipe!'
This is a recipe!
```

One or more arguments specify the recipe(s) to run:

```sh
$ just another-recipe
This is another recipe.
```

`just` prints each command to standard error before running it, which is why
`echo 'This is a recipe!'` was printed. This is suppressed for lines starting
with `@`, which is why `echo 'This is another recipe.'` was not printed.

Recipes stop running if a command fails. Here `cargo publish` will only run if
`cargo test` succeeds:

```just
publish:
  cargo test
  # tests passed, time to publish!
  cargo publish
```

Recipes can depend on other recipes. Here the `test` recipe depends on the
`build` recipe, so `build` will run before `test`:

```just
build:
  cc main.c foo.c bar.c -o main

test: build
  ./test

sloc:
  @echo "`wc -l *.c` lines of code"
```

```sh
$ just test
cc main.c foo.c bar.c -o main
./test
testing… all tests passed!
```

Recipes without dependencies will run in the order they're given on the command
line:

```sh
$ just build sloc
cc main.c foo.c bar.c -o main
1337 lines of code
```

Dependencies will always run first, even if they are passed after a recipe that
depends on them:

```sh
$ just test build
cc main.c foo.c bar.c -o main
./test
testing… all tests passed!
```

Examples
--------

A variety of example `justfile`s can be found in the
[examples directory](https://github.com/casey/just/tree/master/examples).

Features
--------

### The Default Recipe

When `just` is invoked without a recipe, it runs the first recipe in the
`justfile`. This recipe might be the most frequently run command in the
project, like running the tests:

```just
test:
  cargo test
```

You can also use dependencies to run multiple recipes by default:

```just
default: lint build test

build:
  echo Building…

test:
  echo Testing…

lint:
  echo Linting…
```

If no recipe makes sense as the default recipe, you can add a recipe to the
beginning of your `justfile` that lists the available recipes:

```just
default:
  just --list
```

### Listing Available Recipes

Recipes can be listed in alphabetical order with `just --list`:

```sh
$ just --list
Available recipes:
    build
    test
    deploy
    lint
```

`just --summary` is more concise:

```sh
$ just --summary
build test deploy lint
```

Pass `--unsorted` to print recipes in the order they appear in the `justfile`:

```just
test:
  echo 'Testing!'

build:
  echo 'Building!'
```

```sh
$ just --list --unsorted
Available recipes:
    test
    build
```

```sh
$ just --summary --unsorted
test build
```

If you'd like `just` to default to listing the recipes in the `justfile`, you
can use this as your default recipe:

```just
default:
  @just --list
```

Note that you may need to add `--justfile {{justfile()}}` to the line above.
Without it, if you executed `just -f /some/distant/justfile -d .` or
`just -f ./non-standard-justfile`, the plain `just --list` inside the recipe
would not necessarily use the file you provided. It would try to find a
justfile in your current path, maybe even resulting in a `No justfile found`
error.

The heading text can be customized with `--list-heading`:

```sh
$ just --list --list-heading $'Cool stuff…\n'
Cool stuff…
    test
    build
```

And the indentation can be customized with `--list-prefix`:

```sh
$ just --list --list-prefix ····
Available recipes:
····test
····build
```

The argument to `--list-heading` replaces both the heading and the newline
following it, so it should contain a newline if non-empty. It works this way so
you can suppress the heading line entirely by passing the empty string:

```sh
$ just --list --list-heading ''
    test
    build
```

### Working Directory

By default, recipes run with the working directory set to the directory that
contains the `justfile`.

The `[no-cd]` attribute can be used to make recipes run with the working
directory set to directory in which `just` was invoked.

```just
@foo:
  pwd

[no-cd]
@bar:
  pwd
```

```sh
$ cd subdir
$ just foo
/
: just bar
/subdir
```

### Aliases

Aliases allow recipes to be invoked on the command line with alternative names:

```just
alias b := build

build:
  echo 'Building!'
```

```sh
$ just b
echo 'Building!'
Building!
```

### Settings

Settings control interpretation and execution. Each setting may be specified at
most once, anywhere in the `justfile`.

For example:

```just
set shell := ["zsh", "-cu"]

foo:
  # this line will be run as `zsh -cu 'ls **/*.txt'`
  ls **/*.txt
```

#### Table of Settings

| Name | Value | Default | Description |
|------|-------|---------|-------------|
| `allow-duplicate-recipes` | boolean | `false` | Allow recipes appearing later in a `justfile` to override earlier recipes with the same name. |
| `allow-duplicate-variables` | boolean | `false` | Allow variables appearing later in a `justfile` to override earlier variables with the same name. |
| `dotenv-filename` | string | - | Load a `.env` file with a custom name, if present. |
| `dotenv-load` | boolean | `false` | Load a `.env` file, if present. |
| `dotenv-path` | string | - | Load a `.env` file from a custom path, if present. Overrides `dotenv-filename`. |
| `export` | boolean | `false` | Export all variables as environment variables. |
| `fallback` | boolean | `false` | Search `justfile` in parent directory if the first recipe on the command line is not found. |
| `ignore-comments` | boolean | `false` | Ignore recipe lines beginning with `#`. |
| `positional-arguments` | boolean | `false` | Pass positional arguments. |
| `shell` | `[COMMAND, ARGS…]` | - | Set the command used to invoke recipes and evaluate backticks. |
| `tempdir` | string | - | Create temporary directories in `tempdir` instead of the system default temporary directory. |
| `windows-powershell` | boolean | `false` | Use PowerShell on Windows as default shell. (Deprecated. Use `windows-shell` instead. |
| `windows-shell` | `[COMMAND, ARGS…]` | - | Set the command used to invoke recipes and evaluate backticks. |

Boolean settings can be written as:

```justfile
set NAME
```

Which is equivalent to:

```justfile
set NAME := true
```

#### Allow Duplicate Recipes

If `allow-duplicate-recipes` is set to `true`, defining multiple recipes with
the same name is not an error and the last definition is used. Defaults to
`false`.

```just
set allow-duplicate-recipes

@foo:
  echo foo

@foo:
  echo bar
```

```sh
$ just foo
bar
```

#### Allow Duplicate Variables

If `allow-duplicate-variables` is set to `true`, defining multiple variables
with the same name is not an error and the last definition is used. Defaults to
`false`.

```just
set allow-duplicate-variables

a := "foo"
a := "bar"

@foo:
  echo $a
```

```sh
$ just foo
bar
```

#### Dotenv Settings

If `dotenv-load`, `dotenv-filename` or `dotenv-path` is set, `just` will load
environment variables from a file.

If `dotenv-path` is set, `just` will look for a file at the given path.

Otherwise, `just` looks for a file named `.env` by default, unless
`dotenv-filename` set, in which case the value of `dotenv-filename` is used.
This file can be located in the same directory as your `justfile` or in a
parent directory.

The loaded variables are environment variables, not `just` variables, and so
must be accessed using `$VARIABLE_NAME` in recipes and backticks.

For example, if your `.env` file contains:

```sh
# a comment, will be ignored
DATABASE_ADDRESS=localhost:6379
SERVER_PORT=1337
```

And your `justfile` contains:

```just
set dotenv-load

serve:
  @echo "Starting server with database $DATABASE_ADDRESS on port $SERVER_PORT…"
  ./server --database $DATABASE_ADDRESS --port $SERVER_PORT
```

`just serve` will output:

```sh
$ just serve
Starting server with database localhost:6379 on port 1337…
./server --database $DATABASE_ADDRESS --port $SERVER_PORT
```

#### Export

The `export` setting causes all `just` variables to be exported as environment
variables. Defaults to `false`.

```just
set export

a := "hello"

@foo b:
  echo $a
  echo $b
```

```sh
$ just foo goodbye
hello
goodbye
```

#### Positional Arguments

If `positional-arguments` is `true`, recipe arguments will be passed as
positional arguments to commands. For linewise recipes, argument `$0` will be
the name of the recipe.

For example, running this recipe:

```just
set positional-arguments

@foo bar:
  echo $0
  echo $1
```

Will produce the following output:

```sh
$ just foo hello
foo
hello
```

When using an `sh`-compatible shell, such as `bash` or `zsh`, `$@` expands to
the positional arguments given to the recipe, starting from one. When used
within double quotes as `"$@"`, arguments including whitespace will be passed
on as if they were double-quoted. That is, `"$@"` is equivalent to `"$1" "$2"`…
When there are no positional parameters, `"$@"` and `$@` expand to nothing
(i.e., they are removed).

This example recipe will print arguments one by one on separate lines:

```just
set positional-arguments

@test *args='':
  bash -c 'while (( "$#" )); do echo - $1; shift; done' -- "$@"
```

Running it with _two_ arguments:

```sh
$ just test foo "bar baz"
- foo
- bar baz
```

#### Shell

The `shell` setting controls the command used to invoke recipe lines and
backticks. Shebang recipes are unaffected.

```just
# use python3 to execute recipe lines and backticks
set shell := ["python3", "-c"]

# use print to capture result of evaluation
foos := `print("foo" * 4)`

foo:
  print("Snake snake snake snake.")
  print("{{foos}}")
```

`just` passes the command to be executed as an argument. Many shells will need
an additional flag, often `-c`, to make them evaluate the first argument.

##### Windows Shell

`just` uses `sh` on Windows by default. To use a different shell on Windows,
use `windows-shell`:

```just
set windows-shell := ["powershell.exe", "-NoLogo", "-Command"]

hello:
  Write-Host "Hello, world!"
```

See
[powershell.just](https://github.com/casey/just/blob/master/examples/powershell.just)
for a justfile that uses PowerShell on all platforms.

##### Windows PowerShell

*`set windows-powershell` uses the legacy `powershell.exe` binary, and is no
longer recommended. See the `windows-shell` setting above for a more flexible
way to control which shell is used on Windows.*

`just` uses `sh` on Windows by default. To use `powershell.exe` instead, set
`windows-powershell` to true.

```just
set windows-powershell := true

hello:
  Write-Host "Hello, world!"
```

##### Python 3

```just
set shell := ["python3", "-c"]
```

##### Bash

```just
set shell := ["bash", "-uc"]
```

##### Z Shell

```just
set shell := ["zsh", "-uc"]
```

##### Fish

```just
set shell := ["fish", "-c"]
```

##### Nushell

```just
set shell := ["nu", "-c"]
```

If you want to change the default table mode to `light`:

```just
set shell := ['nu', '-m', 'light', '-c']
```

*[Nushell](https://github.com/nushell/nushell) was written in Rust, and **has
cross-platform support for Windows / macOS and Linux**.*

### Documentation Comments

Comments immediately preceding a recipe will appear in `just --list`:

```just
# build stuff
build:
  ./bin/build

# test stuff
test:
  ./bin/test
```

```sh
$ just --list
Available recipes:
    build # build stuff
    test # test stuff
```

### Variables and Substitution

Variables, strings, concatenation, path joining, and substitution using `{{…}}`
are supported:

```just
tmpdir  := `mktemp -d`
version := "0.2.7"
tardir  := tmpdir / "awesomesauce-" + version
tarball := tardir + ".tar.gz"

publish:
  rm -f {{tarball}}
  mkdir {{tardir}}
  cp README.md *.c {{tardir}}
  tar zcvf {{tarball}} {{tardir}}
  scp {{tarball}} me@server.com:release/
  rm -rf {{tarball}} {{tardir}}
```

#### Joining Paths

The `/` operator can be used to join two strings with a slash:

```just
foo := "a" / "b"
```

```
$ just --evaluate foo
a/b
```

Note that a `/` is added even if one is already present:

```just
foo := "a/"
bar := foo / "b"
```

```
$ just --evaluate bar
a//b
```

Absolute paths can also be constructed<sup>1.5.0</sup>:

```just
foo := / "b"
```

```
$ just --evaluate foo
/b
```

The `/` operator uses the `/` character, even on Windows. Thus, using the `/`
operator should be avoided with paths that use universal naming convention
(UNC), i.e., those that start with `\?`, since forward slashes are not
supported with UNC paths.

#### Escaping `{{`

To write a recipe containing `{{`, use `{{{{`:

```just
braces:
  echo 'I {{{{LOVE}} curly braces!'
```

(An unmatched `}}` is ignored, so it doesn't need to be escaped.)

Another option is to put all the text you'd like to escape inside of an
interpolation:

```just
braces:
  echo '{{'I {{LOVE}} curly braces!'}}'
```

Yet another option is to use `{{ "{{" }}`:

```just
braces:
  echo 'I {{ "{{" }}LOVE}} curly braces!'
```

### Strings

Double-quoted strings support escape sequences:

```just
string-with-tab             := "\t"
string-with-newline         := "\n"
string-with-carriage-return := "\r"
string-with-double-quote    := "\""
string-with-slash           := "\\"
string-with-no-newline      := "\
"
```

```sh
$ just --evaluate
"tring-with-carriage-return := "
string-with-double-quote    := """
string-with-newline         := "
"
string-with-no-newline      := ""
string-with-slash           := "\"
string-with-tab             := "     "
```

Strings may contain line breaks:

```just
single := '
hello
'

double := "
goodbye
"
```

Single-quoted strings do not recognize escape sequences:

```just
escapes := '\t\n\r\"\\'
```

```sh
$ just --evaluate
escapes := "\t\n\r\"\\"
```

Indented versions of both single- and double-quoted strings, delimited by
triple single- or double-quotes, are supported. Indented string lines are
stripped of a leading line break, and leading whitespace common to all
non-blank lines:

```just
# this string will evaluate to `foo\nbar\n`
x := '''
  foo
  bar
'''

# this string will evaluate to `abc\n  wuv\nxyz\n`
y := """
  abc
    wuv
  xyz
"""
```

Similar to unindented strings, indented double-quoted strings process escape
sequences, and indented single-quoted strings ignore escape sequences. Escape
sequence processing takes place after unindentation. The unindentation
algorithm does not take escape-sequence produced whitespace or newlines into
account.

Strings prefixed with `x` are shell expanded<sup>master</sup>:

```justfile
foobar := x'~/$FOO/${BAR}'
```

| Value | Replacement |
|------|-------------|
| `$VAR` | value of environment variable `VAR` |
| `${VAR}` | value of environment variable `VAR` |
| Leading `~` | path to current user's home directory |
| Leading `~USER` | path to `USER`'s home directory |

This expansion is performed at compile time, so variables from `.env` files and
exported `just` variables cannot be used. However, this allows shell expanded
strings to be used in places like settings and import paths, which cannot
depend on `just` variables and `.env` files.

### Ignoring Errors

Normally, if a command returns a non-zero exit status, execution will stop. To
continue execution after a command, even if it fails, prefix the command with
`-`:

```just
foo:
  -cat foo
  echo 'Done!'
```

```sh
$ just foo
cat foo
cat: foo: No such file or directory
echo 'Done!'
Done!
```

### Functions

`just` provides a few built-in functions that might be useful when writing
recipes.

#### System Information

- `arch()` — Instruction set architecture. Possible values are: `"aarch64"`,
  `"arm"`, `"asmjs"`, `"hexagon"`, `"mips"`, `"msp430"`, `"powerpc"`,
  `"powerpc64"`, `"s390x"`, `"sparc"`, `"wasm32"`, `"x86"`, `"x86_64"`, and
  `"xcore"`.
- `num_cpus()`<sup>1.15.0</sup> - Number of logical CPUs.
- `os()` — Operating system. Possible values are: `"android"`, `"bitrig"`,
  `"dragonfly"`, `"emscripten"`, `"freebsd"`, `"haiku"`, `"ios"`, `"linux"`,
  `"macos"`, `"netbsd"`, `"openbsd"`, `"solaris"`, and `"windows"`.
- `os_family()` — Operating system family; possible values are: `"unix"` and
  `"windows"`.

For example:

```just
system-info:
  @echo "This is an {{arch()}} machine".
```

```sh
$ just system-info
This is an x86_64 machine
```

The `os_family()` function can be used to create cross-platform `justfile`s
that work on various operating systems. For an example, see
[cross-platform.just](https://github.com/casey/just/blob/master/examples/cross-platform.just)
file.

#### External Commands

- `shell(command, args...)`<sup>master</sup> returns the standard output of shell script
  `command` with zero or more positional arguments `args`. The shell used to
  interpret `command` is the same shell that is used to evaluate recipe lines,
  and can be changed with `set shell := […]`.

  `command` is passed as the first argument, so if the command is `'echo $@'`,
  the full command line, with the default shell command `shell -cu` and `args`
  `'foo'` and `'bar'` will be:

  ```
  'shell' '-cu' 'echo $@' 'echo $@' 'foo' 'bar'
  ```

  This is so that `$@` works as expected, and `$1` refers to the first
  argument. `$@` does not include the first positional argument, which is
  expected to be the name of the program being run.

```just
# arguments can be variables or expressions
file := '/sys/class/power_supply/BAT0/status'
bat0stat := shell('cat $1', file)

# commands can be variables or expressions
command := 'wc -l'
output := shell(command + ' "$1"', 'main.c')

# arguments referenced by the shell command must be used
empty := shell('echo', 'foo')
full := shell('echo $1', 'foo')
error := shell('echo $1')
```

```just
# Using python as the shell. Since `python -c` sets `sys.argv[0]` to `'-c'`,
# the first "real" positional argument will be `sys.argv[2]`.
set shell := ["python3", "-c"]
olleh := shell('import sys; print(sys.argv[2][::-1])', 'hello')
```

#### Environment Variables

- `env_var(key)` — Retrieves the environment variable with name `key`, aborting
  if it is not present.

```just
home_dir := env_var('HOME')

test:
  echo "{{home_dir}}"
```

```sh
$ just
/home/user1
```

- `env_var_or_default(key, default)` — Retrieves the environment variable with
  name `key`, returning `default` if it is not present.
- `env(key)`<sup>1.15.0</sup> — Alias for `env_var(key)`.
- `env(key, default)`<sup>1.15.0</sup> — Alias for `env_var_or_default(key, default)`.

#### Invocation Directory

- `invocation_directory()` - Retrieves the absolute path to the current
  directory when `just` was invoked, before  `just` changed it (chdir'd) prior
  to executing commands. On Windows, `invocation_directory()` uses `cygpath` to
  convert the invocation directory to a Cygwin-compatible `/`-separated path.
  Use `invocation_directory_native()` to return the verbatim invocation
  directory on all platforms.

For example, to call `rustfmt` on files just under the "current directory"
(from the user/invoker's perspective), use the following rule:

```just
rustfmt:
  find {{invocation_directory()}} -name \*.rs -exec rustfmt {} \;
```

Alternatively, if your command needs to be run from the current directory, you
could use (e.g.):

```just
build:
  cd {{invocation_directory()}}; ./some_script_that_needs_to_be_run_from_here
```

- `invocation_directory_native()` - Retrieves the absolute path to the current
  directory when `just` was invoked, before  `just` changed it (chdir'd) prior
  to executing commands.

#### Justfile and Justfile Directory

- `justfile()` - Retrieves the path of the current `justfile`.

- `justfile_directory()` - Retrieves the path of the parent directory of the
  current `justfile`.

For example, to run a command relative to the location of the current
`justfile`:

```just
script:
  ./{{justfile_directory()}}/scripts/some_script
```

#### Just Executable

- `just_executable()` - Absolute path to the `just` executable.

For example:

```just
executable:
  @echo The executable is at: {{just_executable()}}
```

```sh
$ just
The executable is at: /bin/just
```

#### Just Process ID

- `just_pid()` - Process ID of the `just` executable.

For example:

```just
pid:
  @echo The process ID is: {{ just_pid() }}
```

```sh
$ just
The process ID is: 420
```

#### String Manipulation

- `append(suffix, s)`<sup>master</sup> Append `suffix` to whitespace-separated
  strings in `s`. `append('/src', 'foo bar baz')` → `'foo/src bar/src baz/src'`
- `prepend(prefix, s)`<sup>master</sup> Prepend `prefix` to
  whitespace-separated strings in `s`. `prepend('src/', 'foo bar baz')` →
  `'src/foo src/bar src/baz'`
- `encode_uri_component(s)`<sup>master</sup> - Percent-encode characters in `s`
  except `[A-Za-z0-9_.!~*'()-]`, matching the behavior of the
  [JavaScript `encodeURIComponent` function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURIComponent).
- `quote(s)` - Replace all single quotes with `'\''` and prepend and append
  single quotes to `s`. This is sufficient to escape special characters for
  many shells, including most Bourne shell descendants.
- `replace(s, from, to)` - Replace all occurrences of `from` in `s` to `to`.
- `replace_regex(s, regex, replacement)` - Replace all occurrences of `regex`
  in `s` to `replacement`. Regular expressions are provided by the
  [Rust `regex` crate](https://docs.rs/regex/latest/regex/). See the
  [syntax documentation](https://docs.rs/regex/latest/regex/#syntax) for usage
  examples. Capture groups are supported. The `replacement` string uses
  [Replacement string syntax](https://docs.rs/regex/latest/regex/struct.Regex.html#replacement-string-syntax).
- `trim(s)` - Remove leading and trailing whitespace from `s`.
- `trim_end(s)` - Remove trailing whitespace from `s`.
- `trim_end_match(s, pat)` - Remove suffix of `s` matching `pat`.
- `trim_end_matches(s, pat)` - Repeatedly remove suffixes of `s` matching
  `pat`.
- `trim_start(s)` - Remove leading whitespace from `s`.
- `trim_start_match(s, pat)` - Remove prefix of `s` matching `pat`.
- `trim_start_matches(s, pat)` - Repeatedly remove prefixes of `s` matching
  `pat`.

#### Case Conversion

- `capitalize(s)`<sup>1.7.0</sup> - Convert first character of `s` to uppercase
  and the rest to lowercase.
- `kebabcase(s)`<sup>1.7.0</sup> - Convert `s` to `kebab-case`.
- `lowercamelcase(s)`<sup>1.7.0</sup> - Convert `s` to `lowerCamelCase`.
- `lowercase(s)` - Convert `s` to lowercase.
- `shoutykebabcase(s)`<sup>1.7.0</sup> - Convert `s` to `SHOUTY-KEBAB-CASE`.
- `shoutysnakecase(s)`<sup>1.7.0</sup> - Convert `s` to `SHOUTY_SNAKE_CASE`.
- `snakecase(s)`<sup>1.7.0</sup> - Convert `s` to `snake_case`.
- `titlecase(s)`<sup>1.7.0</sup> - Convert `s` to `Title Case`.
- `uppercamelcase(s)`<sup>1.7.0</sup> - Convert `s` to `UpperCamelCase`.
- `uppercase(s)` - Convert `s` to uppercase.

#### Path Manipulation

##### Fallible

- `absolute_path(path)` - Absolute path to relative `path` in the working
  directory. `absolute_path("./bar.txt")` in directory `/foo` is
  `/foo/bar.txt`.
- `canonicalize(path)`<sup>1.24.0</sup> - Canonicalize `path` by resolving symlinks and removing
  `.`, `..`, and extra `/`s where possible.
- `extension(path)` - Extension of `path`. `extension("/foo/bar.txt")` is
  `txt`.
- `file_name(path)` - File name of `path` with any leading directory components
  removed. `file_name("/foo/bar.txt")` is `bar.txt`.
- `file_stem(path)` - File name of `path` without extension.
  `file_stem("/foo/bar.txt")` is `bar`.
- `parent_directory(path)` - Parent directory of `path`.
  `parent_directory("/foo/bar.txt")` is `/foo`.
- `without_extension(path)` - `path` without extension.
  `without_extension("/foo/bar.txt")` is `/foo/bar`.

These functions can fail, for example if a path does not have an extension,
which will halt execution.

##### Infallible

- `clean(path)` - Simplify `path` by removing extra path separators,
  intermediate `.` components, and `..` where possible. `clean("foo//bar")` is
  `foo/bar`, `clean("foo/..")` is `.`, `clean("foo/./bar")` is `foo/bar`.
- `join(a, b…)` - *This function uses `/` on Unix and `\` on Windows, which can
  be lead to unwanted behavior. The `/` operator, e.g., `a / b`, which always
  uses `/`, should be considered as a replacement unless `\`s are specifically
  desired on Windows.* Join path `a` with path `b`. `join("foo/bar", "baz")` is
  `foo/bar/baz`. Accepts two or more arguments.

#### Filesystem Access

- `path_exists(path)` - Returns `true` if the path points at an existing entity
  and `false` otherwise. Traverses symbolic links, and returns `false` if the
  path is inaccessible or points to a broken symlink.

##### Error Reporting

- `error(message)` - Abort execution and report error `message` to user.

#### UUID and Hash Generation

- `blake3(string)`<sup>1.25.0</sup> - Return [BLAKE3] hash of `string` as hexadecimal string.
- `blake3_file(path)`<sup>1.25.0</sup> - Return [BLAKE3] hash of file at `path` as hexadecimal
  string.
- `sha256(string)` - Return the SHA-256 hash of `string` as hexadecimal string.
- `sha256_file(path)` - Return SHA-256 hash of file at `path` as hexadecimal
  string.
- `uuid()` - Generate a random version 4 UUID.

[BLAKE3]: https://github.com/BLAKE3-team/BLAKE3/

#### Random

- `choose(n, alphabet)`<sup>master</sup> - Generate a string of `n` randomly
  selected characters from `alphabet`, which may not contain repeated
  characters. For example, `choose('64', HEX)` will generate a random
  64-character lowercase hex string.

#### Semantic Versions

- `semver_matches(version, requirement)`<sup>1.16.0</sup> - Check whether a
  [semantic `version`](https://semver.org), e.g., `"0.1.0"` matches a
  `requirement`, e.g., `">=0.1.0"`, returning `"true"` if so and `"false"`
  otherwise.

##### XDG Directories<sup>1.23.0</sup>

These functions return paths to user-specific directories for things like
configuration, data, caches, executables, and the user's home directory. These
functions follow the
[XDG Base Directory Specification](https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html),
and are implemented with the
[`dirs`](https://docs.rs/dirs/latest/dirs/index.html) crate.

- `cache_directory()` - The user-specific cache directory.
- `config_directory()` - The user-specific configuration directory.
- `config_local_directory()` - The local user-specific configuration directory.
- `data_directory()` - The user-specific data directory.
- `data_local_directory()` - The local user-specific data directory.
- `executable_directory()` - The user-specific executable directory.
- `home_directory()` - The user's home directory.

### Constants

A number of constants are predefined:

| Name | Value |
|------|-------------|
| `HEX`<sup>master</sup> | `"0123456789abcdef"` |
| `HEXLOWER`<sup>master</sup> | `"0123456789abcdef"` |
| `HEXUPPER`<sup>master</sup> | `"0123456789ABCDEF"` |

```just
@foo:
  echo {{HEX}}
```

```sh
$ just foo
0123456789abcdef
```

### Recipe Attributes

Recipes may be annotated with attributes that change their behavior.

| Name | Description |
|------|-------------|
| `[confirm]`<sup>1.17.0</sup> | Require confirmation prior to executing recipe. |
| `[confirm("prompt")]`<sup>1.23.0</sup> | Require confirmation prior to executing recipe with a custom prompt. |
| `[linux]`<sup>1.8.0</sup> | Enable recipe on Linux. |
| `[macos]`<sup>1.8.0</sup> | Enable recipe on MacOS. |
| `[no-cd]`<sup>1.9.0</sup> | Don't change directory before executing recipe. |
| `[no-exit-message]`<sup>1.7.0</sup> | Don't print an error message if recipe fails. |
| `[no-quiet]`<sup>1.23.0</sup> | Override globally quiet recipes and always echo out the recipe. |
| `[private]`<sup>1.10.0</sup> | See [Private Recipes](#private-recipes). |
| `[unix]`<sup>1.8.0</sup> | Enable recipe on Unixes. (Includes MacOS). |
| `[windows]`<sup>1.8.0</sup> | Enable recipe on Windows. |

A recipe can have multiple attributes, either on multiple lines:

```just
[no-cd]
[private]
foo:
    echo "foo"
```

Or separated by commas on a single line<sup>1.14.0</sup>:

```just
[no-cd, private]
foo:
    echo "foo"
```

#### Enabling and Disabling Recipes<sup>1.8.0</sup>

The `[linux]`, `[macos]`, `[unix]`, and `[windows]` attributes are
configuration attributes. By default, recipes are always enabled. A recipe with
one or more configuration attributes will only be enabled when one or more of
those configurations is active.

This can be used to write `justfile`s 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:

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

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

#### Disabling Changing Directory<sup>1.9.0</sup>

`just` normally executes recipes with the current directory set to the
directory that contains the `justfile`. This can be disabled using the
`[no-cd]` attribute. This can be used to create recipes which use paths
relative to the invocation directory, or which operate on the current
directory.

For example, this `commit` recipe:

```just
[no-cd]
commit file:
  git add {{file}}
  git commit
```

Can be used with paths that are relative to the current directory, because
`[no-cd]` prevents `just` from changing the current directory when executing
`commit`.

#### Requiring Confirmation for Recipes<sup>1.17.0</sup>

`just` normally executes all recipes unless there is an error. The `[confirm]`
attribute allows recipes require confirmation in the terminal prior to running.
This can be overridden by passing `--yes` to `just`, which will automatically
confirm any recipes marked by this attribute.

Recipes dependent on a recipe that requires confirmation will not be run if the
relied upon recipe is not confirmed, as well as recipes passed after any recipe
that requires confirmation.

```just
[confirm]
delete-all:
  rm -rf *
```

#### Custom Confirmation Prompt<sup>1.23.0</sup>

The default confirmation prompt can be overridden with `[confirm(PROMPT)]`:

```just
[confirm("Are you sure you want to delete everything?")]
delete-everything:
  rm -rf *
```

### Command Evaluation Using Backticks

Backticks can be used to store the result of commands:

```just
localhost := `dumpinterfaces | cut -d: -f2 | sed 's/\/.*//' | sed 's/ //g'`

serve:
  ./serve {{localhost}} 8080
```

Indented backticks, delimited by three backticks, are de-indented in the same
manner as indented strings:

````just
# This backtick evaluates the command `echo foo\necho bar\n`, which produces the value `foo\nbar\n`.
stuff := ```
    echo foo
    echo bar
  ```
````

See the [Strings](#strings) section for details on unindenting.

Backticks may not start with `#!`. This syntax is reserved for a future
upgrade.

### Conditional Expressions

`if`/`else` expressions evaluate different branches depending on if two
expressions evaluate to the same value:

```just
foo := if "2" == "2" { "Good!" } else { "1984" }

bar:
  @echo "{{foo}}"
```

```sh
$ just bar
Good!
```

It is also possible to test for inequality:

```just
foo := if "hello" != "goodbye" { "xyz" } else { "abc" }

bar:
  @echo {{foo}}
```

```sh
$ just bar
xyz
```

And match against regular expressions:

```just
foo := if "hello" =~ 'hel+o' { "match" } else { "mismatch" }

bar:
  @echo {{foo}}
```

```sh
$ just bar
match
```

Regular expressions are provided by the
[regex crate](https://github.com/rust-lang/regex), whose syntax is documented on
[docs.rs](https://docs.rs/regex/1.5.4/regex/#syntax). Since regular expressions
commonly use backslash escape sequences, consider using single-quoted string
literals, which will pass slashes to the regex parser unmolested.

Conditional expressions short-circuit, which means they only evaluate one of
their branches. This can be used to make sure that backtick expressions don't
run when they shouldn't.

```just
foo := if env_var("RELEASE") == "true" { `get-something-from-release-database` } else { "dummy-value" }
```

Conditionals can be used inside of recipes:

```just
bar foo:
  echo {{ if foo == "bar" { "hello" } else { "goodbye" } }}
```

Note the space after the final `}`! Without the space, the interpolation will
be prematurely closed.

Multiple conditionals can be chained:

```just
foo := if "hello" == "goodbye" {
  "xyz"
} else if "a" == "a" {
  "abc"
} else {
  "123"
}

bar:
  @echo {{foo}}
```

```sh
$ just bar
abc
```

### Stopping execution with error

Execution can be halted with the `error` function. For example:

```just
foo := if "hello" == "goodbye" {
  "xyz"
} else if "a" == "b" {
  "abc"
} else {
  error("123")
}
```

Which produce the following error when run:

```
error: Call to function `error` failed: 123
   |
16 |   error("123")
```

### Setting Variables from the Command Line

Variables can be overridden from the command line.

```just
os := "linux"

test: build
  ./test --test {{os}}

build:
  ./build {{os}}
```

```sh
$ just
./build linux
./test --test linux
```

Any number of arguments of the form `NAME=VALUE` can be passed before recipes:

```sh
$ just os=plan9
./build plan9
./test --test plan9
```

Or you can use the `--set` flag:

```sh
$ just --set os bsd
./build bsd
./test --test bsd
```

### Getting and Setting Environment Variables

#### Exporting `just` Variables

Assignments prefixed with the `export` keyword will be exported to recipes as
environment variables:

```just
export RUST_BACKTRACE := "1"

test:
  # will print a stack trace if it crashes
  cargo test
```

Parameters prefixed with a `$` will be exported as environment variables:

```just
test $RUST_BACKTRACE="1":
  # will print a stack trace if it crashes
  cargo test
```

Exported variables and parameters are not exported to backticks in the same scope.

```just
export WORLD := "world"
# This backtick will fail with "WORLD: unbound variable"
BAR := `echo hello $WORLD`
```

```just
# Running `just a foo` will fail with "A: unbound variable"
a $A $B=`echo $A`:
  echo $A $B
```

When [export](#export) is set, all `just` variables are exported as environment
variables.

#### Getting Environment Variables from the environment

Environment variables from the environment are passed automatically to the
recipes.

```just
print_home_folder:
  echo "HOME is: '${HOME}'"
```

```sh
$ just
HOME is '/home/myuser'
```

#### Setting `just` Variables from Environment Variables

Environment variables can be propagated to `just` variables using the functions
`env_var()` and `env_var_or_default()`. See
[environment-variables](#environment-variables).

### Recipe Parameters

Recipes may have parameters. Here recipe `build` has a parameter called
`target`:

```just
build target:
  @echo 'Building {{target}}…'
  cd {{target}} && make
```

To pass arguments on the command line, put them after the recipe name:

```sh
$ just build my-awesome-project
Building my-awesome-project…
cd my-awesome-project && make
```

To pass arguments to a dependency, put the dependency in parentheses along with
the arguments:

```just
default: (build "main")

build target:
  @echo 'Building {{target}}…'
  cd {{target}} && make
```

Variables can also be passed as arguments to dependencies:

```just
target := "main"

_build version:
  @echo 'Building {{version}}…'
  cd {{version}} && make

build: (_build target)
```

A command's arguments can be passed to dependency by putting the dependency in
parentheses along with the arguments:

```just
build target:
  @echo "Building {{target}}…"

push target: (build target)
  @echo 'Pushing {{target}}…'
```

Parameters may have default values:

```just
default := 'all'

test target tests=default:
  @echo 'Testing {{target}}:{{tests}}…'
  ./test --tests {{tests}} {{target}}
```

Parameters with default values may be omitted:

```sh
$ just test server
Testing server:all…
./test --tests all server
```

Or supplied:

```sh
$ just test server unit
Testing server:unit…
./test --tests unit server
```

Default values may be arbitrary expressions, but concatenations or path joins
must be parenthesized:

```just
arch := "wasm"

test triple=(arch + "-unknown-unknown") input=(arch / "input.dat"):
  ./test {{triple}}
```

The last parameter of a recipe may be variadic, indicated with either a `+` or
a `*` before the argument name:

```just
backup +FILES:
  scp {{FILES}} me@server.com:
```

Variadic parameters prefixed with `+` accept _one or more_ arguments and expand
to a string containing those arguments separated by spaces:

```sh
$ just backup FAQ.md GRAMMAR.md
scp FAQ.md GRAMMAR.md me@server.com:
FAQ.md                  100% 1831     1.8KB/s   00:00
GRAMMAR.md              100% 1666     1.6KB/s   00:00
```

Variadic parameters prefixed with `*` accept _zero or more_ arguments and
expand to a string containing those arguments separated by spaces, or an empty
string if no arguments are present:

```just
commit MESSAGE *FLAGS:
  git commit {{FLAGS}} -m "{{MESSAGE}}"
```

Variadic parameters can be assigned default values. These are overridden by
arguments passed on the command line:

```just
test +FLAGS='-q':
  cargo test {{FLAGS}}
```

`{{…}}` substitutions may need to be quoted if they contain spaces. For
example, if you have the following recipe:

```just
search QUERY:
  lynx https://www.google.com/?q={{QUERY}}
```

And you type:

```sh
$ just search "cat toupee"
```

`just` will run the command `lynx https://www.google.com/?q=cat toupee`, which
will get parsed by `sh` as `lynx`, `https://www.google.com/?q=cat`, and
`toupee`, and not the intended `lynx` and `https://www.google.com/?q=cat toupee`.

You can fix this by adding quotes:

```just
search QUERY:
  lynx 'https://www.google.com/?q={{QUERY}}'
```

Parameters prefixed with a `$` will be exported as environment variables:

```just
foo $bar:
  echo $bar
```

### Running Recipes at the End of a Recipe

Normal dependencies of a recipes always run before a recipe starts. That is to
say, the dependee always runs before the depender. These dependencies are
called "prior dependencies".

A recipe can also have subsequent dependencies, which run after the recipe and
are introduced with an `&&`:

```just
a:
  echo 'A!'

b: a && c d
  echo 'B!'

c:
  echo 'C!'

d:
  echo 'D!'
```

…running _b_ prints:

```sh
$ just b
echo 'A!'
A!
echo 'B!'
B!
echo 'C!'
C!
echo 'D!'
D!
```

### Running Recipes in the Middle of a Recipe

`just` doesn't support running recipes in the middle of another recipe, but you
can call `just` recursively in the middle of a recipe. Given the following
`justfile`:

```just
a:
  echo 'A!'

b: a
  echo 'B start!'
  just c
  echo 'B end!'

c:
  echo 'C!'
```

…running _b_ prints:

```sh
$ just b
echo 'A!'
A!
echo 'B start!'
B start!
echo 'C!'
C!
echo 'B end!'
B end!
```

This has limitations, since recipe `c` is run with an entirely new invocation
of `just`: Assignments will be recalculated, dependencies might run twice, and
command line arguments will not be propagated to the child `just` process.

### Writing Recipes in Other Languages

Recipes that start with `#!` are called shebang recipes, and are executed by
saving the recipe body to a file and running it. This lets you write recipes in
different languages:

```just
polyglot: python js perl sh ruby nu

python:
  #!/usr/bin/env python3
  print('Hello from python!')

js:
  #!/usr/bin/env node
  console.log('Greetings from JavaScript!')

perl:
  #!/usr/bin/env perl
  print "Larry Wall says Hi!\n";

sh:
  #!/usr/bin/env sh
  hello='Yo'
  echo "$hello from a shell script!"

nu:
  #!/usr/bin/env nu
  let hello = 'Hola'
  echo $"($hello) from a nushell script!"

ruby:
  #!/usr/bin/env ruby
  puts "Hello from ruby!"
```

```sh
$ just polyglot
Hello from python!
Greetings from JavaScript!
Larry Wall says Hi!
Yo from a shell script!
Hola from a nushell script!
Hello from ruby!
```

On Unix-like operating systems, including Linux and MacOS, shebang recipes are
executed by saving the recipe body to a file in a temporary directory, marking
the file as executable, and executing it. The OS then parses the shebang line
into a command line and invokes it, including the path to the file. For
example, if a recipe starts with `#!/usr/bin/env bash`, the final command that
the OS runs will be something like `/usr/bin/env bash
/tmp/PATH_TO_SAVED_RECIPE_BODY`.

Shebang line splitting is operating system dependent. When passing a command
with arguments, you may need to tell `env` to split them explicitly by using
the `-S` flag:

```just
run:
  #!/usr/bin/env -S bash -x
  ls
```

Windows does not support shebang lines. On Windows, `just` splits the shebang
line into a command and arguments, saves the recipe body to a file, and invokes
the split command and arguments, adding the path to the saved recipe body as
the final argument. For example, on Windows, if a recipe starts with `#! py`,
the final command the OS runs will be something like `py
C:\Temp\PATH_TO_SAVED_RECIPE_BODY`.

### Safer Bash Shebang Recipes

If you're writing a `bash` shebang recipe, consider adding `set -euxo
pipefail`:

```just
foo:
  #!/usr/bin/env bash
  set -euxo pipefail
  hello='Yo'
  echo "$hello from Bash!"
```

It isn't strictly necessary, but `set -euxo pipefail` turns on a few useful
features that make `bash` shebang recipes behave more like normal, linewise
`just` recipe:

- `set -e` makes `bash` exit if a command fails.

- `set -u` makes `bash` exit if a variable is undefined.

- `set -x` makes `bash` print each script line before it's run.

- `set -o pipefail` makes `bash` exit if a command in a pipeline fails. This is
  `bash`-specific, so isn't turned on in normal linewise `just` recipes.

Together, these avoid a lot of shell scripting gotchas.

#### Shebang Recipe Execution on Windows

On Windows, shebang interpreter paths containing a `/` are translated from
Unix-style paths to Windows-style paths using `cygpath`, a utility that ships
with [Cygwin](http://www.cygwin.com).

For example, to execute this recipe on Windows:

```just
echo:
  #!/bin/sh
  echo "Hello!"
```

The interpreter path `/bin/sh` will be translated to a Windows-style path using
`cygpath` before being executed.

If the interpreter path does not contain a `/` it will be executed without
being translated. This is useful if `cygpath` is not available, or you wish to
pass a Windows-style path to the interpreter.

### Setting Variables in a Recipe

Recipe lines are interpreted by the shell, not `just`, so it's not possible to
set `just` variables in the middle of a recipe:

```mf
foo:
  x := "hello" # This doesn't work!
  echo {{x}}
```

It is possible to use shell variables, but there's another problem. Every
recipe line is run by a new shell instance, so variables set in one line won't
be set in the next:

```just
foo:
  x=hello && echo $x # This works!
  y=bye
  echo $y            # This doesn't, `y` is undefined here!
```

The best way to work around this is to use a shebang recipe. Shebang recipe
bodies are extracted and run as scripts, so a single shell instance will run
the whole thing:

```just
foo:
  #!/usr/bin/env bash
  set -euxo pipefail
  x=hello
  echo $x
```

### Sharing Environment Variables Between Recipes

Each line of each recipe is executed by a fresh shell, so it is not possible to
share environment variables between recipes.

#### Using Python Virtual Environments

Some tools, like [Python's venv](https://docs.python.org/3/library/venv.html),
require loading environment variables in order to work, making them challenging
to use with `just`. As a workaround, you can execute the virtual environment
binaries directly:

```just
venv:
  [ -d foo ] || python3 -m venv foo

run: venv
  ./foo/bin/python3 main.py
```

### Changing the Working Directory in a Recipe

Each recipe line is executed by a new shell, so if you change the working
directory on one line, it won't have an effect on later lines:

```just
foo:
  pwd    # This `pwd` will print the same directory…
  cd bar
  pwd    # …as this `pwd`!
```

There are a couple ways around this. One is to call `cd` on the same line as
the command you want to run:

```just
foo:
  cd bar && pwd
```

The other is to use a shebang recipe. Shebang recipe bodies are extracted and
run as scripts, so a single shell instance will run the whole thing, and thus a
`pwd` on one line will affect later lines, just like a shell script:

```just
foo:
  #!/usr/bin/env bash
  set -euxo pipefail
  cd bar
  pwd
```

### Indentation

Recipe lines can be indented with spaces or tabs, but not a mix of both. All of
a recipe's lines must have the same type of indentation, but different recipes
in the same `justfile` may use different indentation.

Each recipe must be indented at least one level from the `recipe-name` but
after that may be further indented.

Here's a justfile with a recipe indented with spaces, represented as `·`, and
tabs, represented as `→`.

```justfile
set windows-shell := ["pwsh", "-NoLogo", "-NoProfileLoadTime", "-Command"]

set ignore-comments

list-space directory:
··#!pwsh
··foreach ($item in $(Get-ChildItem {{directory}} )) {
····echo $item.Name
··}
··echo ""

# indentation nesting works even when newlines are escaped
list-tab directory:
→ @foreach ($item in $(Get-ChildItem {{directory}} )) { \
→ → echo $item.Name \
→ }
→ @echo ""
```

```pwsh
PS > just list-space ~
Desktop
Documents
Downloads

PS > just list-tab ~
Desktop
Documents
Downloads
```

### Multi-Line Constructs

Recipes without an initial shebang are evaluated and run line-by-line, which
means that multi-line constructs probably won't do what you want.

For example, with the following `justfile`:

```mf
conditional:
  if true; then
    echo 'True!'
  fi
```

The extra leading whitespace before the second line of the `conditional` recipe
will produce a parse error:

```sh
$ just conditional
error: Recipe line has extra leading whitespace
  |
3 |         echo 'True!'
  |     ^^^^^^^^^^^^^^^^
```

To work around this, you can write conditionals on one line, escape newlines
with slashes, or add a shebang to your recipe. Some examples of multi-line
constructs are provided for reference.

#### `if` statements

```just
conditional:
  if true; then echo 'True!'; fi
```

```just
conditional:
  if true; then \
    echo 'True!'; \
  fi
```

```just
conditional:
  #!/usr/bin/env sh
  if true; then
    echo 'True!'
  fi
```

#### `for` loops

```just
for:
  for file in `ls .`; do echo $file; done
```

```just
for:
  for file in `ls .`; do \
    echo $file; \
  done
```

```just
for:
  #!/usr/bin/env sh
  for file in `ls .`; do
    echo $file
  done
```

#### `while` loops

```just
while:
  while `server-is-dead`; do ping -c 1 server; done
```

```just
while:
  while `server-is-dead`; do \
    ping -c 1 server; \
  done
```

```just
while:
  #!/usr/bin/env sh
  while `server-is-dead`; do
    ping -c 1 server
  done
```

#### Outside Recipe Bodies

Parenthesized expressions can span multiple lines:

```just
abc := ('a' +
        'b'
         + 'c')

abc2 := (
  'a' +
  'b' +
  'c'
)

foo param=('foo'
      + 'bar'
    ):
  echo {{param}}

bar: (foo
        'Foo'
     )
  echo 'Bar!'
```

Lines ending with a backslash continue on to the next line as if the lines were
joined by whitespace<sup>1.15.0</sup>:

```just
a := 'foo' + \
     'bar'

foo param1 \
  param2='foo' \
  *varparam='': dep1 \
                (dep2 'foo')
  echo {{param1}} {{param2}} {{varparam}}

dep1: \
    # this comment is not part of the recipe body
  echo 'dep1'

dep2 \
  param:
    echo 'Dependency with parameter {{param}}'
```

Backslash line continuations can also be used in interpolations. The line
following the backslash must be indented.

```just
recipe:
  echo '{{ \
  "This interpolation " + \
    "has a lot of text." \
  }}'
  echo 'back to recipe body'
```

### Command Line Options

`just` supports a number of useful command line options for listing, dumping,
and debugging recipes and variables:

```sh
$ just --list
Available recipes:
  js
  perl
  polyglot
  python
  ruby
$ just --show perl
perl:
  #!/usr/bin/env perl
  print "Larry Wall says Hi!\n";
$ just --show polyglot
polyglot: python js perl sh ruby
```

Some command-line options can be set with environment variables. For example:

```sh
$ export JUST_UNSTABLE=1
$ just
```

Is equivalent to:

```sh
$ just --unstable
```

Consult `just --help` to see which options can be set from environment
variables.

### Private Recipes

Recipes and aliases whose name starts with a `_` are omitted from `just --list`:

```just
test: _test-helper
  ./bin/test

_test-helper:
  ./bin/super-secret-test-helper-stuff
```

```sh
$ just --list
Available recipes:
    test
```

And from `just --summary`:

```sh
$ just --summary
test
```

The `[private]` attribute<sup>1.10.0</sup> may also be used to hide recipes or
aliases without needing to change the name:

```just
[private]
foo:

[private]
alias b := bar

bar:
```

```sh
$ just --list
Available recipes:
    bar
```

This is useful for helper recipes which are only meant to be used as
dependencies of other recipes.

### Quiet Recipes

A recipe name may be prefixed with `@` to invert the meaning of `@` before each
line:

```just
@quiet:
  echo hello
  echo goodbye
  @# all done!
```

Now only the lines starting with `@` will be echoed:

```sh
$ just quiet
hello
goodbye
# all done!
```

All recipes in a Justfile can be made quiet with `set quiet`:

```just
set quiet

foo:
  echo "This is quiet"

@foo2:
  echo "This is also quiet"
```

The `[no-quiet]` attribute overrides this setting:

```just
set quiet

foo:
  echo "This is quiet"

[no-quiet]
foo2:
  echo "This is not quiet"
```

Shebang recipes are quiet by default:

```just
foo:
  #!/usr/bin/env bash
  echo 'Foo!'
```

```sh
$ just foo
Foo!
```

Adding `@` to a shebang recipe name makes `just` print the recipe before
executing it:

```just
@bar:
  #!/usr/bin/env bash
  echo 'Bar!'
```

```sh
$ just bar
#!/usr/bin/env bash
echo 'Bar!'
Bar!
```

`just` normally prints error messages when a recipe line fails. These error
messages can be suppressed using the `[no-exit-message]`<sup>1.7.0</sup>
attribute. You may find this especially useful with a recipe that wraps a tool:

```just
git *args:
    @git {{args}}
```

```sh
$ just git status
fatal: not a git repository (or any of the parent directories): .git
error: Recipe `git` failed on line 2 with exit code 128
```

Add the attribute to suppress the exit error message when the tool exits with a
non-zero code:

```just
[no-exit-message]
git *args:
    @git {{args}}
```

```sh
$ just git status
fatal: not a git repository (or any of the parent directories): .git
```

### Selecting Recipes to Run With an Interactive Chooser

The `--choose` subcommand makes `just` invoke a chooser to select which recipes
to run. Choosers should read lines containing recipe names from standard input
and print one or more of those names separated by spaces to standard output.

Because there is currently no way to run a recipe that requires arguments with
`--choose`, such recipes will not be given to the chooser. Private recipes and
aliases are also skipped.

The chooser can be overridden with the `--chooser` flag. If `--chooser` is not
given, then `just` first checks if `$JUST_CHOOSER` is set. If it isn't, then
the chooser defaults to `fzf`, a popular fuzzy finder.

Arguments can be included in the chooser, i.e. `fzf --exact`.

The chooser is invoked in the same way as recipe lines. For example, if the
chooser is `fzf`, it will be invoked with `sh -cu 'fzf'`, and if the shell, or
the shell arguments are overridden, the chooser invocation will respect those
overrides.

If you'd like `just` to default to selecting recipes with a chooser, you can
use this as your default recipe:

```just
default:
  @just --choose
```

### Invoking `justfile`s in Other Directories

If the first argument passed to `just` contains a `/`, then the following
occurs:

1.  The argument is split at the last `/`.

2.  The part before the last `/` is treated as a directory. `just` will start
    its search for the `justfile` there, instead of in the current directory.

3.  The part after the last slash is treated as a normal argument, or ignored
    if it is empty.

This may seem a little strange, but it's useful if you wish to run a command in
a `justfile` that is in a subdirectory.

For example, if you are in a directory which contains a subdirectory named
`foo`, which contains a `justfile` with the recipe `build`, which is also the
default recipe, the following are all equivalent:

```sh
$ (cd foo && just build)
$ just foo/build
$ just foo/
```

Additional recipes after the first are sought in the same `justfile`. For
example, the following are both equivalent:

```sh
$ just foo/a b
$ (cd foo && just a b)
```

And will both invoke recipes `a` and `b` in `foo/justfile`.

### Imports

One `justfile` can include the contents of another using `import` statements.

If you have the following `justfile`:

```mf
import 'foo/bar.just'

a: b
  @echo A
```

And the following text in `foo/bar.just`:

```just
b:
  @echo B
```

`foo/bar.just` will be included in `justfile` and recipe `b` will be defined:

```sh
$ just b
B
$ just a
B
A
```

The `import` path can be absolute or relative to the location of the justfile
containing it. A leading `~/` in the import path is replaced with the current
users home directory.

Justfiles are insensitive to order, so included files can reference variables
and recipes defined after the `import` statement.

Imported files can themselves contain `import`s, which are processed
recursively.

When `allow-duplicate-recipes` is set, recipes in parent modules override
recipes in imports. In a similar manner, when `allow-duplicate-variables` is
set, variables in parent modules override variables in imports.

Imports may be made optional by putting a `?` after the `import` keyword:

```mf
import? 'foo/bar.just'
```

Missing source files for optional imports do not produce an error.

### Modules <sup>1.19.0</sup>

A `justfile` can declare modules using `mod` statements. `mod` statements are
currently unstable, so you'll need to use the `--unstable` flag, or set the
`JUST_UNSTABLE` environment variable to use them.

If you have the following `justfile`:

```mf
mod bar

a:
  @echo A
```

And the following text in `bar.just`:

```just
b:
  @echo B
```

`bar.just` will be included in `justfile` as a submodule. Recipes, aliases, and
variables defined in one submodule cannot be used in another, and each module
uses its own settings.

Recipes in submodules can be invoked as subcommands:

```sh
$ just --unstable bar b
B
```

Or with path syntax:

```sh
$ just --unstable bar::b
B
```

If a module is named `foo`, just will search for the module file in `foo.just`,
`foo/mod.just`, `foo/justfile`, and `foo/.justfile`. In the latter two cases,
the module file may have any capitalization.

Module statements may be of the form:

```mf
mod foo 'PATH'
```

Which loads the module's source file from `PATH`, instead of from the usual
locations. A leading `~/` in `PATH` is replaced with the current user's home
directory.

Environment files are only loaded for the root justfile, and loaded environment
variables are available in submodules. Settings in submodules that affect
environment file loading are ignored.

Recipes in submodules without the `[no-cd]` attribute run with the working
directory set to the directory containing the submodule source file.

`justfile()` and `justfile_directory()` always return the path to the root
justfile and the directory that contains it, even when called from submodule
recipes.

Modules may be made optional by putting a `?` after the `mod` keyword:

```mf
mod? foo
```

Missing source files for optional modules do not produce an error.

Optional modules with no source file do not conflict, so you can have multiple
mod statements with the same name, but with different source file paths, as
long as at most one source file exists:

```mf
mod? foo 'bar.just'
mod? foo 'baz.just'
```

See the
[module stabilization tracking issue](https://github.com/casey/just/issues/929)
for more information.

### Hiding `justfile`s

`just` looks for `justfile`s named `justfile` and `.justfile`, which can be
used to keep a `justfile` hidden.

### Just Scripts

By adding a shebang line to the top of a `justfile` and making it executable,
`just` can be used as an interpreter for scripts:

```sh
$ cat > script <<EOF
#!/usr/bin/env just --justfile

foo:
  echo foo
EOF
$ chmod +x script
$ ./script foo
echo foo
foo
```

When a script with a shebang is executed, the system supplies the path to the
script as an argument to the command in the shebang. So, with a shebang of
`#!/usr/bin/env just --justfile`, the command will be `/usr/bin/env just --justfile PATH_TO_SCRIPT`.

With the above shebang, `just` will change its working directory to the
location of the script. If you'd rather leave the working directory unchanged,
use `#!/usr/bin/env just --working-directory . --justfile`.

Note: Shebang line splitting is not consistent across operating systems. The
previous examples have only been tested on macOS. On Linux, you may need to
pass the `-S` flag to `env`:

```just
#!/usr/bin/env -S just --justfile

default:
  echo foo
```

### Formatting and dumping `justfile`s

Each `justfile` has a canonical formatting with respect to whitespace and
newlines.

You can overwrite the current justfile with a canonically-formatted version
using the currently-unstable `--fmt` flag:

```sh
$ cat justfile
# A lot of blank lines





some-recipe:
  echo "foo"
$ just --fmt --unstable
$ cat justfile
# A lot of blank lines

some-recipe:
    echo "foo"
```

Invoking `just --fmt --check --unstable` runs `--fmt` in check mode. Instead of
overwriting the `justfile`, `just` will exit with an exit code of 0 if it is
formatted correctly, and will exit with 1 and print a diff if it is not.

You can use the `--dump` command to output a formatted version of the
`justfile` to stdout:

```sh
$ just --dump > formatted-justfile
```

The `--dump` command can be used with `--dump-format json` to print a JSON
representation of a `justfile`.

### Fallback to parent `justfile`s

If a recipe is not found in a `justfile` and the `fallback` setting is set,
`just` will look for `justfile`s in the parent directory and up, until it
reaches the root directory. `just` will stop after it reaches a `justfile` in
which the `fallback` setting is `false` or unset.

As an example, suppose the current directory contains this `justfile`:

```just
set fallback
foo:
  echo foo
```

And the parent directory contains this `justfile`:

```just
bar:
  echo bar
```

```sh
$ just bar
Trying ../justfile
echo bar
bar
```

### Avoiding Argument Splitting

Given this `justfile`:

```just
foo argument:
  touch {{argument}}
```

The following command will create two files, `some` and `argument.txt`:

```sh
$ just foo "some argument.txt"
```

The users shell will parse `"some argument.txt"` as a single argument, but when
`just` replaces `touch {{argument}}` with `touch some argument.txt`, the quotes
are not preserved, and `touch` will receive two arguments.

There are a few ways to avoid this: quoting, positional arguments, and exported
arguments.

#### Quoting

Quotes can be added around the `{{argument}}` interpolation:

```just
foo argument:
  touch '{{argument}}'
```

This preserves `just`'s ability to catch variable name typos before running,
for example if you were to write `{{argument}}`, but will not do what you want
if the value of `argument` contains single quotes.

#### Positional Arguments

The `positional-arguments` setting causes all arguments to be passed as
positional arguments, allowing them to be accessed with `$1`, `$2`, …, and
`$@`, which can be then double-quoted to avoid further splitting by the shell:

```just
set positional-arguments

foo argument:
  touch "$1"
```

This defeats `just`'s ability to catch typos, for example if you type `$2`, but
works for all possible values of `argument`, including those with double
quotes.

#### Exported Arguments

All arguments are exported when the `export` setting is set:

```just
set export

foo argument:
  touch "$argument"
```

Or individual arguments may be exported by prefixing them with `$`:

```just
foo $argument:
  touch "$argument"
```

This defeats `just`'s ability to catch typos, for example if you type
`$argumant`, but works for all possible values of `argument`, including those
with double quotes.

### Configuring the Shell

There are a number of ways to configure the shell for linewise recipes, which
are the default when a recipe does not start with a `#!` shebang. Their
precedence, from highest to lowest, is:

1. The `--shell` and `--shell-arg` command line options. Passing either of
   these will cause `just` to ignore any settings in the current justfile.
2. `set windows-shell := [...]`
3. `set windows-powershell` (deprecated)
4. `set shell := [...]`

Since `set windows-shell` has higher precedence than `set shell`, you can use
`set windows-shell` to pick a shell on Windows, and `set shell` to pick a shell
for all other platforms.

Changelog
---------

A changelog for the latest release is available in
[CHANGELOG.md](https://raw.githubusercontent.com/casey/just/master/CHANGELOG.md).
Changelogs for previous releases are available on
[the releases page](https://github.com/casey/just/releases). `just --changelog`
can also be used to make a `just` binary print its changelog.

Miscellanea
-----------

### Re-running recipes when files change

[`watchexec`](https://github.com/mattgreen/watchexec) can re-run any command
when files change.

To re-run the recipe `foo` when any file changes:

```sh
watchexec just foo
```

See `watchexec --help` for more info, including how to specify which files
should be watched for changes.

### Running tasks in parallel

GNU parallel can be used to run tasks concurrently:

```just
parallel:
  #!/usr/bin/env -S parallel --shebang --ungroup --jobs {{ num_cpus() }}
  echo task 1 start; sleep 3; echo task 1 done
  echo task 2 start; sleep 3; echo task 2 done
  echo task 3 start; sleep 3; echo task 3 done
  echo task 4 start; sleep 3; echo task 4 done
```

### Shell Alias

For lightning-fast command running, put `alias j=just` in your shell's
configuration file.

In `bash`, the aliased command may not keep the shell completion functionality
described in the next section. Add the following line to your `.bashrc` to use
the same completion function as `just` for your aliased command:

```sh
complete -F _just -o bashdefault -o default j
```

### Shell Completion Scripts

Shell completion scripts for Bash, Zsh, Fish, PowerShell, and Elvish are
available in the
[completions](https://github.com/casey/just/tree/master/completions) directory.
Please refer to your shell's documentation for how to install them.

The `just` binary can also generate the same completion scripts at runtime,
using the `--completions` command:

```sh
$ just --completions zsh > just.zsh
```

*macOS Note:* Recent versions of macOS use zsh as the default shell. If you use
Homebrew to install `just`, it will automatically install the most recent copy
of the zsh completion script in the Homebrew zsh directory, which the built-in
version of zsh doesn't know about by default. It's best to use this copy of the
script if possible, since it will be updated whenever you update `just` via
Homebrew. Also, many other Homebrew packages use the same location for
completion scripts, and the built-in zsh doesn't know about those either. To
take advantage of `just` completion in zsh in this scenario, you can set
`fpath` to the Homebrew location before calling `compinit`. Note also that Oh
My Zsh runs `compinit` by default. So your `.zshrc` file could look like this:

```zsh
# Init Homebrew, which adds environment variables
eval "$(brew shellenv)"

fpath=($HOMEBREW_PREFIX/share/zsh/site-functions $fpath)

# Then choose one of these options:
# 1. If you're using Oh My Zsh, you can initialize it here
# source $ZSH/oh-my-zsh.sh

# 2. Otherwise, run compinit yourself
# autoload -U compinit
# compinit
```

### Man Page

`just` can print its own man page with `just --man`. Man pages are written in
[`roff`](https://en.wikipedia.org/wiki/Roff_%28software%29), a venerable markup
language and one of the first practical applications of Unix. If you have
[`groff`](https://www.gnu.org/software/groff/) installed you can view the man
page with  `just --man | groff -mandoc -Tascii | less`.

### Grammar

A non-normative grammar of `justfile`s can be found in
[GRAMMAR.md](https://github.com/casey/just/blob/master/GRAMMAR.md).

### just.sh

Before `just` was a fancy Rust program it was a tiny shell script that called
`make`. You can find the old version in
[contrib/just.sh](https://github.com/casey/just/blob/master/contrib/just.sh).

### Global and User `justfile`s

If you want some recipes to be available everywhere, you have a few options.

#### Global Justfile

`just --global-justfile`, or `just -g` for short, searches the following paths,
in-order, for a justfile:

- `$XDG_CONFIG_HOME/just/justfile`
- `$HOME/.config/just/justfile`
- `$HOME/justfile`
- `$HOME/.justfile`

You can put recipes that are used across many projects in a global justfile to
easily invoke them from any directory.

#### User justfile tips

You can also adopt some of the following workflows. These tips assume you've
created a `justfile` at `~/.user.justfile`, but you can put this `justfile`
at any convenient path on your system.

##### Recipe Aliases

If you want to call the recipes in `~/.user.justfile` by name, and don't mind
creating an alias for every recipe, add the following to your shell's
initialization script:

```sh
for recipe in `just --justfile ~/.user.justfile --summary`; do
  alias $recipe="just --justfile ~/.user.justfile --working-directory . $recipe"
done
```

Now, if you have a recipe called `foo` in `~/.user.justfile`, you can just type
`foo` at the command line to run it.

It took me way too long to realize that you could create recipe aliases like
this. Notwithstanding my tardiness, I am very pleased to bring you this major
advance in `justfile` technology.

##### Forwarding Alias

If you'd rather not create aliases for every recipe, you can create a single alias:

```sh
alias .j='just --justfile ~/.user.justfile --working-directory .'
```

Now, if you have a recipe called `foo` in `~/.user.justfile`, you can just type
`.j foo` at the command line to run it.

I'm pretty sure that nobody actually uses this feature, but it's there.

¯\\\_(ツ)\_/¯

##### Customization

You can customize the above aliases with additional options. For example, if
you'd prefer to have the recipes in your `justfile` run in your home directory,
instead of the current directory:

```sh
alias .j='just --justfile ~/.user.justfile --working-directory ~'
```

### Node.js `package.json` Script Compatibility

The following export statement gives `just` recipes access to local Node module
binaries, and makes `just` recipe commands behave more like `script` entries in
Node.js `package.json` files:

```just
export PATH := "./node_modules/.bin:" + env_var('PATH')
```

### Alternatives and Prior Art

There is no shortage of command runners! Some more or less similar alternatives
to `just` include:

- [make](https://en.wikipedia.org/wiki/Make_(software)): The Unix build tool
  that inspired `just`. There are a few different modern day descendents of the
  original `make`, including
  [FreeBSD Make](https://www.freebsd.org/cgi/man.cgi?make(1)) and
  [GNU Make](https://www.gnu.org/software/make/).
- [task](https://github.com/go-task/task): A YAML-based command runner written
  in Go.
- [maid](https://github.com/egoist/maid): A Markdown-based command runner
  written in JavaScript.
- [microsoft/just](https://github.com/microsoft/just): A JavaScript-based
  command runner written in JavaScript.
- [cargo-make](https://github.com/sagiegurari/cargo-make): A command runner for
  Rust projects.
- [mmake](https://github.com/tj/mmake): A wrapper around `make` with a number
  of improvements, including remote includes.
- [robo](https://github.com/tj/robo): A YAML-based command runner written in
  Go.
- [mask](https://github.com/jakedeichert/mask): A Markdown-based command runner
  written in Rust.
- [makesure](https://github.com/xonixx/makesure): A simple and portable command
  runner written in AWK and shell.
- [haku](https://github.com/VladimirMarkelov/haku): A make-like command runner
  written in Rust.

Contributing
------------

`just` welcomes your contributions! `just` is released under the maximally
permissive
[CC0](https://creativecommons.org/publicdomain/zero/1.0/legalcode.txt) public
domain dedication and fallback license, so your changes must also be released
under this license.

### Janus

[Janus](https://github.com/casey/janus) is a tool for checking whether a change
to `just` breaks or changes the interpretation of existing `justfile`s. It
collects and analyzes public `justfile`s on GitHub.

Before merging a particularly large or gruesome change, Janus should be run to
make sure that nothing breaks. Don't worry about running Janus yourself, Casey
will happily run it for you on changes that need it.

### Minimum Supported Rust Version

The minimum supported Rust version, or MSRV, is current stable Rust. It may
build on older versions of Rust, but this is not guaranteed.

### New Releases

New releases of `just` are made frequently so that users quickly get access to
new features.

Release commit messages use the following template:

```
Release x.y.z

- Bump version: x.y.z → x.y.z
- Update changelog
- Update changelog contributor credits
- Update dependencies
- Update man page
- Update version references in readme
```

Frequently Asked Questions
--------------------------

### What are the idiosyncrasies of Make that Just avoids?

`make` has some behaviors which are confusing, complicated, or make it
unsuitable for use as a general command runner.

One example is that under some circumstances, `make` won't actually run the
commands in a recipe. For example, if you have a file called `test` and the
following makefile:

```just
test:
  ./test
```

`make` will refuse to run your tests:

```sh
$ make test
make: `test' is up to date.
```

`make` assumes that the `test` recipe produces a file called `test`. Since this
file exists and the recipe has no other dependencies, `make` thinks that it
doesn't have anything to do and exits.

To be fair, this behavior is desirable when using `make` as a build system, but
not when using it as a command runner. You can disable this behavior for
specific targets using `make`'s built-in
[`.PHONY` target name](https://www.gnu.org/software/make/manual/html_node/Phony-Targets.html),
but the syntax is verbose and can be hard to remember. The explicit list of
phony targets, written separately from the recipe definitions, also introduces
the risk of accidentally defining a new non-phony target. In `just`, all
recipes are treated as if they were phony.

Other examples of `make`'s idiosyncrasies include the difference between `=`
and `:=` in assignments, the confusing error messages that are produced if you
mess up your makefile, needing `$$` to use environment variables in recipes,
and incompatibilities between different flavors of `make`.

### What's the relationship between Just and Cargo build scripts?

[`cargo` build scripts](http://doc.crates.io/build-script.html) have a pretty
specific use, which is to control how `cargo` builds your Rust project. This
might include adding flags to `rustc` invocations, building an external
dependency, or running some kind of codegen step.

`just`, on the other hand, is for all the other miscellaneous commands you
might run as part of development. Things like running tests in different
configurations, linting your code, pushing build artifacts to a server,
removing temporary files, and the like.

Also, although `just` is written in Rust, it can be used regardless of the
language or build system your project uses.

Further Ramblings
-----------------

I personally find it very useful to write a `justfile` for almost every
project, big or small.

On a big project with multiple contributors, it's very useful to have a file
with all the commands needed to work on the project close at hand.

There are probably different commands to test, build, lint, deploy, and the
like, and having them all in one place is useful and cuts down on the time you
have to spend telling people which commands to run and how to type them.

And, with an easy place to put commands, it's likely that you'll come up with
other useful things which are part of the project's collective wisdom, but
which aren't written down anywhere, like the arcane commands needed for some
part of your revision control workflow, to install all your project's
dependencies, or all the random flags you might need to pass to the build
system.

Some ideas for recipes:

- Deploying/publishing the project

- Building in release mode vs debug mode

- Running in debug mode or with logging enabled

- Complex git workflows

- Updating dependencies

- Running different sets of tests, for example fast tests vs slow tests, or
  running them with verbose output

- Any complex set of commands that you really should write down somewhere, if
  only to be able to remember them

Even for small, personal projects it's nice to be able to remember commands by
name instead of ^Reverse searching your shell history, and it's a huge boon to
be able to go into an old project written in a random language with a
mysterious build system and know that all the commands you need to do whatever
you need to do are in the `justfile`, and that if you type `just` something
useful (or at least interesting!) will probably happen.

For ideas for recipes, check out
[this project's `justfile`](https://github.com/casey/just/blob/master/justfile),
or some of the
`justfile`s
[out in the wild](https://github.com/search?q=path%3A**%2Fjustfile&type=code).

Anyways, I think that's about it for this incredibly long-winded README.

I hope you enjoy using `just` and find great success and satisfaction in all
your computational endeavors!

😸