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Table of Contents↗️

just


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

This readme is also available as a book.

(δΈ­ζ–‡ζ–‡ζ‘£εœ¨ θΏ™ι‡Œ, εΏ«ηœ‹θΏ‡ζ₯!)

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

screenshot

You can then run them with just RECIPE:

$ 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:

If you need help with just please feel free to open an issue or ping me on Discord. 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, GitHub Desktop, or Cygwin.

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

Like PowerShell:

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

hello:
  Write-Host "Hello, world!"

…or cmd.exe:

# 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

Operating System Package Manager Package Command
Alpine Linux apk-tools just apk add just
Arch Linux pacman just pacman -S just
Debian and Ubuntu derivatives MPR just git clone https://mpr.makedeb.org/just
cd just
makedeb -si
Debian and Ubuntu derivatives Prebuilt-MPR just You must have the Prebuilt-MPR set up on your system in order to run this command.
sudo apt install just
Fedora Linux DNF just dnf install just
FreeBSD pkg just pkg install just
Gentoo Linux Portage guru/dev-build/just eselect repository enable guru
emerge --sync guru
emerge dev-build/just
macOS MacPorts just port install just
Microsoft Windows Chocolatey just choco install just
Microsoft Windows Scoop just scoop install just
Microsoft Windows Windows Package Manager Casey/Just winget install --id Casey.Just --exact
NixOS Nix just nix-env -iA nixos.just
openSUSE Zypper just zypper in just
Solus eopkg just eopkg install just
Various asdf just asdf plugin add just
asdf install just <version>
Various Cargo just cargo install just
Various Conda just conda install -c conda-forge just
Various Homebrew just brew install just
Various Nix just nix-env -iA nixpkgs.just
Various Snap just snap install --edge --classic just
Void Linux XBPS just xbps-install -S just

just package version table

rust:just package version table

Pre-Built Binaries

Pre-built binaries for Linux, MacOS, and Windows can be found on the releases page.

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:

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

For example, to install just to ~/bin:

# 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.

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:

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

Or with taiki-e/install-action:

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

Release RSS Feed

An RSS feed of just releases is available here.

Node.js Installation

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.

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 justfiles 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 plugin provides syntax highlighting for justfiles.

Install it with your favorite package manager, like Plug:

call plug#begin()

Plug 'NoahTheDuke/vim-just'

call plug#end()

Or with Vim's built-in package support:

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 is an Nvim Treesitter plugin for Neovim.

Makefile Syntax Highlighting

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

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:

# vim: set ft=make :

Emacs

just-mode provides syntax highlighting and automatic indentation of justfiles. It is available on MELPA as just-mode.

justl 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:

# Local Variables:
# mode: makefile
# End:

Visual Studio Code

An extension for VS Code is available here.

Unmaintained VS Code extensions include skellock/vscode-just and sclu1034/vscode-just.

JetBrains IDEs

A plugin for JetBrains IDEs by linux_china is available here.

Kakoune

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

Helix

Helix supports justfile syntax highlighting out-of-the-box since version 23.05.

Sublime Text

The Just package by nk9 with just syntax and some other tools is available on PackageControl.

Micro

Micro supports Justfile syntax highlighting out of the box, thanks to 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 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.

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

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:

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

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

$ 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:

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:

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

test: build
  ./test

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

$ 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:

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

Examples

A variety of example justfiles can be found in the examples directory.

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:

test:
  cargo test

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

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:

default:
  just --list

Listing Available Recipes

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

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

just --summary is more concise:

$ just --summary
build test deploy lint

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

test:
  echo 'Testing!'

build:
  echo 'Building!'
$ just --list --unsorted
Available recipes:
    test
    build
$ 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:

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:

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

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

$ just --list --list-prefix Β·Β·Β·Β·
Available recipes:
Β·Β·Β·Β·test
Β·Β·Β·Β·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:

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

Aliases

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

alias b := build

build:
  echo 'Building!'
$ 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:

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:

set NAME

Which is equivalent to:

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.

set allow-duplicate-recipes

@foo:
  echo foo

@foo:
  echo bar
$ 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.

set allow-duplicate-variables

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

@foo:
  echo $a
$ 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:

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

And your justfile contains:

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:

$ 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.

set export

a := "hello"

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

set positional-arguments

@foo bar:
  echo $0
  echo $1

Will produce the following output:

$ 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:

set positional-arguments

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

Running it with two arguments:

$ 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.

# 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:

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

hello:
  Write-Host "Hello, world!"

See 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.

set windows-powershell := true

hello:
  Write-Host "Hello, world!"
Python 3
set shell := ["python3", "-c"]
Bash
set shell := ["bash", "-uc"]
Z Shell
set shell := ["zsh", "-uc"]
Fish
set shell := ["fish", "-c"]
Nushell
set shell := ["nu", "-c"]

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

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

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:

# build stuff
build:
  ./bin/build

# test stuff
test:
  ./bin/test
$ just --list
Available recipes:
    build # build stuff
    test # test stuff

Variables and Substitution

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

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:

foo := "a" / "b"
$ just --evaluate foo
a/b

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

foo := "a/"
bar := foo / "b"
$ just --evaluate bar
a//b

Absolute paths can also be constructed1.5.0:

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 {{{{:

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:

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

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

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

Strings

Double-quoted strings support escape sequences:

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

single := '
hello
'

double := "
goodbye
"

Single-quoted strings do not recognize escape sequences:

escapes := '\t\n\r\"\\'
$ just --evaluate
escapes := "\t\n\r\"\\"

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

# 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.

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 -:

foo:
  -cat foo
  echo 'Done!'
$ 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() β€” Instruction set architecture. Possible values are: "aarch64", "arm", "asmjs", "hexagon", "mips", "msp430", "powerpc", "powerpc64", "s390x", "sparc", "wasm32", "x86", "x86_64", and "xcore".
  • num_cpus()1.15.0 - Number of logical CPUs.
  • os() β€” Operating system. Possible values are: "android", "bitrig", "dragonfly", "emscripten", "freebsd", "haiku", "ios", "linux", "macos", "netbsd", "openbsd", "solaris", and "windows".
  • os_family() β€” Operating system family; possible values are: "unix" and "windows".

For example:

system-info:
  @echo "This is an {{arch()}} machine".
$ just system-info
This is an x86_64 machine

The os_family() function can be used to create cross-platform justfiles that work on various operating systems. For an example, see cross-platform.just file.

Environment Variables

  • env_var(key) β€” Retrieves the environment variable with name key, aborting if it is not present.
home_dir := env_var('HOME')

test:
  echo "{{home_dir}}"
$ just
/home/user1
  • env_var_or_default(key, default) β€” Retrieves the environment variable with name key, returning default if it is not present.
  • env(key)1.15.0 β€” Alias for env_var(key).
  • env(key, default)1.15.0 β€” 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:

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.):

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:

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

Just Executable

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

For example:

executable:
  @echo The executable is at: {{just_executable()}}
$ just
The executable is at: /bin/just

Just Process ID

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

For example:

pid:
  @echo The process ID is: {{ just_pid() }}
$ just
The process ID is: 420

String Manipulation

  • 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. See the syntax documentation for usage examples. Capture groups are supported. The replacement string uses 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)1.7.0 - Convert first character of s to uppercase and the rest to lowercase.
  • kebabcase(s)1.7.0 - Convert s to kebab-case.
  • lowercamelcase(s)1.7.0 - Convert s to lowerCamelCase.
  • lowercase(s) - Convert s to lowercase.
  • shoutykebabcase(s)1.7.0 - Convert s to SHOUTY-KEBAB-CASE.
  • shoutysnakecase(s)1.7.0 - Convert s to SHOUTY_SNAKE_CASE.
  • snakecase(s)1.7.0 - Convert s to snake_case.
  • titlecase(s)1.7.0 - Convert s to Title Case.
  • uppercamelcase(s)1.7.0 - 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)1.24.0 - 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)1.25.0 - Return BLAKE3 hash of string as hexadecimal string.
  • blake3_file(path)1.25.0 - 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.

Semantic Versions

  • semver_matches(version, requirement)1.16.0 - Check whether a semantic version, e.g., "0.1.0" matches a requirement, e.g., ">=0.1.0", returning "true" if so and "false" otherwise.
XDG Directories1.23.0

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, and are implemented with the dirs 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.

Recipe Attributes

Recipes may be annotated with attributes that change their behavior.

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

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

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

Or separated by commas on a single line1.14.0:

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

Enabling and Disabling Recipes1.8.0

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

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

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

Disabling Changing Directory1.9.0

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:

[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 Recipes1.17.0

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.

[confirm]
delete-all:
  rm -rf *

Custom Confirmation Prompt1.23.0

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

[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:

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:

# 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 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:

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

bar:
  @echo "{{foo}}"
$ just bar
Good!

It is also possible to test for inequality:

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

bar:
  @echo {{foo}}
$ just bar
xyz

And match against regular expressions:

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

bar:
  @echo {{foo}}
$ just bar
match

Regular expressions are provided by the regex crate, whose syntax is documented on docs.rs. 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.

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

Conditionals can be used inside of recipes:

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:

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

bar:
  @echo {{foo}}
$ just bar
abc

Stopping execution with error

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

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.

os := "linux"

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

build:
  ./build {{os}}
$ just
./build linux
./test --test linux

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

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

Or you can use the --set flag:

$ 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:

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:

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.

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

When 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.

print_home_folder:
  echo "HOME is: '${HOME}'"
$ 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.

Recipe Parameters

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

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

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

$ 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:

default: (build "main")

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

Variables can also be passed as arguments to dependencies:

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:

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

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

Parameters may have default values:

default := 'all'

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

Parameters with default values may be omitted:

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

Or supplied:

$ 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:

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:

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:

$ 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:

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:

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

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

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

And you type:

$ 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:

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

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

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 &&:

a:
  echo 'A!'

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

c:
  echo 'C!'

d:
  echo 'D!'

…running b prints:

$ 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:

a:
  echo 'A!'

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

c:
  echo 'C!'

…running b prints:

$ 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:

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!"
$ 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:

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:

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.

For example, to execute this recipe on Windows:

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:

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:

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:

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, 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:

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:

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:

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:

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 Β·, and tabs, represented as β†’.

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

set ignore-comments

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

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

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

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

$ 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

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

for loops

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

while loops

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

Outside Recipe Bodies