just

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

This readme is also available as a book.

(中文文档在 这里, 快看过来!)

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

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:

• just is a command runner, not a build system, so it avoids much of make’s complexity and idiosyncrasies. 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.)

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

• Recipes can accept command line arguments.

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

• just loads .env files, making it easy to populate environment variables.

• Recipes can be listed from the command line.

• Command line completion scripts are available for most popular shells.

• Recipes can be written in arbitrary languages, like Python or NodeJS.

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

• And much more!

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

Cross-platform

BSD

Linux

Windows

macOS

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.

Releases include a SHA256SUM file which can be used to verify the integrity of pre-built binary archives.

To verify a release, download the pre-built binary archive along with the SHA256SUM file and run:

shasum --algorithm 256 --ignore-missing --check SHA256SUMS

GitHub Actions

just can be installed on GitHub Actions in a few ways.

Using package managers pre-installed on GitHub Actions runners on MacOS with brew install just, and on Windows with choco install just.

With extractions/setup-just:

- uses: extractions/setup-just@v2
  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 marked as unstable and may be changed or removed at any time. Using unstable features produces an error by default, which can be suppressed with by passing the --unstable flag, set unstable, or 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 justfiles can be found in the examples directory and on GitHub.

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

Recipes in submodules can be listed with just --list PATH, where PATH is a space- or ::-separated module path:

$ cat justfile
mod foo
$ cat foo.just
mod bar
$ cat bar.just
baz:
$ just foo bar
Available recipes:
    baz
$ just foo::bar
Available recipes:
    baz

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 ····
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:

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

Invoking Multiple Recipes

Multiple recipes may be invoked on the command line at once:

build:
  make web

serve:
  python3 -m http.server -d out 8000

$ just build serve
make web
python3 -m http.server -d out 8000

Keep in mind that recipes with parameters will swallow arguments, even if they match the names of other recipes:

build project:
  make {{project}}

serve:
  python3 -m http.server -d out 8000

$ just build serve
make: *** No rule to make target `serve'.  Stop.

The --one flag can be used to restrict command-line invocations to a single recipe:

$ just --one build serve
error: Expected 1 command-line recipe invocation but found 2.

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.

@foo:
  pwd

[no-cd]
@bar:
  pwd

$ cd subdir
$ just foo
/
$ just bar
/subdir

You can override working directory with set working-directory := '…', whose value is relative to the default working directory.

set working-directory := 'bar'

@foo:
  pwd

$ pwd
/home/bob
$ just foo
/home/bob/bar

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

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 any of dotenv-load, dotenv-filename, dotenv-path, or dotenv-required are set, just will try to load environment variables from a file.

If dotenv-path is set, just will look for a file at the given path, which may be absolute, or relative to the working directory.

The command-line option --dotenv-path, short form -E, can be used to set or override dotenv-path at runtime.

If dotenv-filename is set just will look for a file at the given path, relative to the working directory and each of its ancestors.

If dotenv-filename is not set, but dotenv-load or dotenv-required are set, just will look for a file named .env, relative to the working directory and each of its ancestors.

dotenv-filename and dotenv-path are similar, but dotenv-path is only checked relative to the working directory, whereas dotenv-filename is checked relative to the working directory and each of its ancestors.

It is not an error if an environment file is not found, unless dotenv-required is set.

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

Positional arguments may also be turned on on a per-recipe basis with the [positional-arguments] attribute^1.29.0:

[positional-arguments]
@foo bar:
  echo $0
  echo $1

Note that PowerShell does not handle positional arguments in the same way as other shells, so turning on positional arguments will likely break recipes that use PowerShell.

If using PowerShell 7.4 or better, the -CommandWithArgs flag will make positional arguments work as expected:

set shell := ['pwsh.exe', '-CommandWithArgs']
set positional-arguments

print-args a b c:
  Write-Output @($args[1..($args.Count - 1)])

Shell

The shell setting controls the command used to invoke recipe lines and backticks. Shebang recipes are unaffected. The default shell is sh -cu.

# 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

The [doc] attribute can be used to set or suppress a recipe’s doc comment:

# This comment won't appear
[doc('Build stuff')]
build:
  ./bin/build

# This one won't either
[doc]
test:
  ./bin/test

$ just --list
Available recipes:
    build # Build stuff
    test

Expressions and Substitutions

Various operators and function calls are supported in expressions, which may be used in assignments, default recipe arguments, and inside recipe body {{…}} substitutions.

tmpdir  := `mktemp -d`
version := "0.2.7"
tardir  := tmpdir / "awesomesauce-" + version
tarball := tardir + ".tar.gz"
config  := quote(config_dir() / ".project-config")

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

Concatenation

The + operator returns the left-hand argument concatenated with the right-hand argument:

foobar := 'foo' + 'bar'

Logical Operators

The logical operators && and || can be used to coalesce string values^master, similar to Python’s and and or. These operators consider the empty string '' to be false, and all other strings to be true.

These operators are currently unstable.

The && operator returns the empty string if the left-hand argument is the empty string, otherwise it returns the right-hand argument:

foo := '' && 'goodbye'      # ''
bar := 'hello' && 'goodbye' # 'goodbye'

The || operator returns the left-hand argument if it is non-empty, otherwise it returns the right-hand argument:

foo := '' || 'goodbye'      # 'goodbye'
bar := 'hello' || 'goodbye' # 'hello'

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 constructed^1.5.0:

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:

carriage-return   := "\r"
double-quote      := "\""
newline           := "\n"
no-newline        := "\
"
slash             := "\\"
tab               := "\t"
unicode-codepoint := "\u{1F916}"

$ just --evaluate
"arriage-return   := "
double-quote      := """
newline           := "
"
no-newline        := ""
slash             := "\"
tab               := "     "
unicode-codepoint := "🤖"

The unicode character escape sequence \u{…}^1.36.0 accepts up to six hex digits.

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 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.

Strings prefixed with x are shell expanded^1.27.0:

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

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 -:

foo:
  -cat foo
  echo 'Done!'

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

Functions

just provides many built-in functions for use in expressions, including recipe body {{…}} substitutions, assignments, and default parameter values.

All functions ending in _directory can be abbreviated to _dir. So home_directory() can also be written as home_dir(). In addition, invocation_directory_native() can be abbreviated to invocation_dir_native().

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()^1.15.0 - 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:

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.

External Commands

• shell(command, args...)^1.27.0 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 sh -cu and args 'foo' and 'bar' will be:

  'sh' '-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.

# 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')

# 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.

home_dir := env_var('HOME')

test:
  echo "{{home_dir}}"

$ 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)^1.15.0 — Alias for env_var(key).
• env(key, default)^1.15.0 — Alias for env_var_or_default(key, default).

Invocation Information

• is_dependency() - Returns the string true if the current recipe is being run as a dependency of another recipe, rather than being run directly, otherwise returns the string false.

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

Source and Source Directory

• source_file()^1.27.0 - Retrieves the path of the current source file.

• source_directory()^1.27.0 - Retrieves the path of the parent directory of the current source file.

source_file() and source_directory() behave the same as justfile() and justfile_directory() in the root justfile, but will return the path and directory, respectively, of the current import or mod source file when called from within an import or submodule.

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

• append(suffix, s)^1.27.0 Append suffix to whitespace-separated strings in s. append('/src', 'foo bar baz') → 'foo/src bar/src baz/src'
• prepend(prefix, s)^1.27.0 Prepend prefix to whitespace-separated strings in s. prepend('src/', 'foo bar baz') → 'src/foo src/bar src/baz'
• encode_uri_component(s)^1.27.0 - Percent-encode characters in s except [A-Za-z0-9_.!~*'()-], matching the behavior of the JavaScript encodeURIComponent function.
• 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.

Random

• choose(n, alphabet)^1.27.0 - 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.

Datetime

• datetime(format)^1.30.0 - Return local time with format.
• datetime_utc(format)^1.30.0 - Return UTC time with format.

The arguments to datetime and datetime_utc are strftime-style format strings, see the chrono library docs for details.

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 Directories^1.23.0

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.

Constants

A number of constants are predefined:

@foo:
  echo {{HEX}}

$ just foo
0123456789abcdef

Constants starting with \e are ANSI escape sequences.

CLEAR clears the screen, similar to the clear command. The rest are of the form \e[Nm, where N is an integer, and set terminal display attributes.

Terminal display attribute escape sequences can be combined, for example text weight BOLD, text style STRIKETHROUGH, foreground color CYAN, and background color BG_BLUE. They should be followed by NORMAL, to reset the terminal back to normal.

Escape sequences should be quoted, since [ is treated as a special character by some shells.

@foo:
  echo '{{BOLD + STRIKETHROUGH + CYAN + BG_BLUE}}Hi!{{NORMAL}}'

Attributes

Recipes, mod statements, and aliases may be annotated with attributes that change their behavior.

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

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

Or separated by commas on a single line^1.14.0:

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

Enabling and Disabling Recipes^1.8.0

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 Directory^1.9.0

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 Recipes^1.17.0

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 Prompt^1.23.0

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

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

Groups

Recipes and modules may be annotated with a group name:

[group('lint')]
js-lint:
    echo 'Running JS linter…'

[group('rust recipes')]
[group('lint')]
rust-lint:
    echo 'Running Rust linter…'

[group('lint')]
cpp-lint:
  echo 'Running C++ linter…'

# not in any group
email-everyone:
    echo 'Sending mass email…'

Recipes are listed by group:

$ just --list
Available recipes:
    email-everyone # not in any group

    [lint]
    cpp-lint
    js-lint
    rust-lint

    [rust recipes]
    rust-lint

just --list --unsorted prints recipes in their justfile order within each group:

$ just --list --unsorted
Available recipes:
    (no group)
    email-everyone # not in any group

    [lint]
    js-lint
    rust-lint
    cpp-lint

    [rust recipes]
    rust-lint

Groups can be listed with --groups:

$ just --groups
Recipe groups:
  lint
  rust recipes

Use just --groups --unsorted to print groups in their justfile order.

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.

The shell(…) function provides a more general mechanism to invoke external commands, including the ability to execute the contents of a variable as a command, and to pass arguments to a command.

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.

Unexporting Environment Variables^1.29.0

Environment variables can be unexported with the unexport keyword:

unexport FOO

@foo:
  echo $FOO

$ export FOO=bar
$ just foo
sh: FOO: unbound variable

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 expressions containing the +, &&, ||, or / operators 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

Dependencies

Dependencies run before recipes that depend on them:

a: b
  @echo A

b:
  @echo B

$ just a
B
A

In a given invocation of just, a recipe with the same arguments will only run once, regardless of how many times it appears in the command-line invocation, or how many times it appears as a dependency:

a:
  @echo A

b: a
  @echo B

c: a
  @echo C

$ just a a a a a
A
$ just b c
A
B
C

Multiple recipes may depend on a recipe that performs some kind of setup, and when those recipes run, that setup will only be performed once:

build:
  cc main.c

test-foo: build
  ./a.out --test foo

test-bar: build
  ./a.out --test bar

$ just test-foo test-bar
cc main.c
./a.out --test foo
./a.out --test bar

Recipes in a given run are only skipped when they receive the same arguments:

build:
  cc main.c

test TEST: build
  ./a.out --test {{TEST}}

$ just test foo test bar
cc main.c
./a.out --test foo
./a.out --test 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 immediately 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.

Shebang Recipes

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.

Script Recipes

Recipes with a [script(COMMAND)]^1.32.0 attribute are run as scripts interpreted by COMMAND. This avoids some of the issues with shebang recipes, such as the use of cygpath on Windows, the need to use /usr/bin/env, and inconsistences in shebang line splitting across Unix OSs.

Recipes with an empty [script] attribute are executed with the value of set script-interpreter := […]^1.33.0, defaulting to sh -eu.

The body of the recipe is evaluated, written to disk in the temporary directory, and run by passing its path as an argument to COMMAND.

The [script(…)] attribute is unstable, so you’ll need to use set unstable, set the JUST_UNSTABLE environment variable, or pass --unstable on the command line.

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 ·, and tabs, represented as →.

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 ""

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

Parenthesized expressions can span multiple lines:

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^1.15.0:

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.

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:

$ 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:

$ export JUST_UNSTABLE=1
$ just

Is equivalent to:

$ 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:

test: _test-helper
  ./bin/test

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

$ just --list
Available recipes:
    test

And from just --summary:

$ just --summary
test

The [private] attribute^1.10.0 may also be used to hide recipes or aliases without needing to change the name:

[private]
foo:

[private]
alias b := bar

bar:

$ 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:

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

Now only the lines starting with @ will be echoed:

$ just quiet
hello
goodbye
# all done!

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

set quiet

foo:
  echo "This is quiet"

@foo2:
  echo "This is also quiet"

The [no-quiet] attribute overrides this setting:

set quiet

foo:
  echo "This is quiet"

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

Shebang recipes are quiet by default:

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

$ just foo
Foo!

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

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

$ 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]^1.7.0 attribute. You may find this especially useful with a recipe that wraps a tool:

git *args:
    @git {{args}}

$ 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:

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

$ 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:

default:
  @just --choose

Invoking justfiles 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:

$ (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:

$ 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:

import 'foo/bar.just'

a: b
  @echo A

And the following text in foo/bar.just:

b:
  @echo B

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

$ 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 imports, 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:

import? 'foo/bar.just'

Importing the same source file multiple times is not an error^master. This allows importing multiple justfiles, for example foo.just and bar.just, which both import a third justfile containing shared recipes, for example baz.just, without the duplicate import of baz.just being an error:

# justfile
import 'foo.just'
import 'bar.just'

# foo.just
import 'baz.just'
foo: baz

# bar.just
import 'baz.just'
bar: baz

# baz
baz:

Modules^1.19.0

A justfile can declare modules using mod statements.

mod statements were stabilized in just^1.31.0. In earlier versions, you’ll need to use the --unstable flag, set unstable, or set the JUST_UNSTABLE environment variable to use them.

If you have the following justfile:

mod bar

a:
  @echo A

And the following text in bar.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:

$ just bar b
B

Or with path syntax:

$ just 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:

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. PATH may point to the module source file itself, or to a directory containing the module source file with the name mod.just, justfile, or .justfile. In the latter two cases, the module file may have any capitalization.

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:

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:

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

Modules may be given doc comments which appear in --list output^1.30.0:

# foo is a great module!
mod foo

$ just --list
Available recipes:
    foo ... # foo is a great module!

Modules are still missing a lot of features, for example, the ability to depend on recipes and refer to variables in other modules. See the module improvement tracking issue for more information.

Hiding justfiles

just looks for justfiles 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:

$ 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:

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

default:
  echo foo

Formatting and dumping justfiles

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:

$ 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:

$ 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 justfiles

If a recipe is not found in a justfile and the fallback setting is set, just will look for justfiles 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:

set fallback
foo:
  echo foo

And the parent directory contains this justfile:

bar:
  echo bar

$ just bar
Trying ../justfile
echo bar
bar

Avoiding Argument Splitting

Given this justfile:

foo argument:
  touch {{argument}}

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

$ just foo "some argument.txt"

The user’s 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:

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:

set positional-arguments

foo argument:
  touch "$1"

This defeats just’s ability to catch typos, for example if you type $2 instead of $1, 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:

set export

foo argument:
  touch "$argument"

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

foo $argument:
  touch "$argument"

This defeats just’s ability to catch typos, for example if you type $argument, 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.

Timestamps

just can print timestamps before each recipe commands:

recipe:
  echo one
  sleep 2
  echo two

$ just --timestamp recipe
[07:28:46] echo one
one
[07:28:46] sleep 2
[07:28:48] echo two
two

By default, timestamps are formatted as HH:MM:SS. The format can be changed with --timestamp-format:

$ just --timestamp recipe --timestamp-format '%H:%M:%S%.3f %Z'
[07:32:11:.349 UTC] echo one
one
[07:32:11:.350 UTC] sleep 2
[07:32:13:.352 UTC] echo two
two

The argument to --timestamp-format is a strftime-style format string, see the chrono library docs for details.

Changelog

A changelog for the latest release is available in CHANGELOG.md. Changelogs for previous releases are available on the releases page. just --changelog can also be used to make a just binary print its changelog.

Miscellanea

Re-running recipes when files change

watchexec can re-run any command when files change.

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

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:

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:

complete -F _just -o bashdefault -o default j

Shell Completion Scripts

Shell completion scripts for Bash, Elvish, Fish, Nushell, PowerShell, and Zsh are available release archives.

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

$ just --completions zsh > just.zsh

Please refer to your shell’s documentation for how to install them.

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:

# 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, a venerable markup language and one of the first practical applications of Unix. If you have groff installed you can view the man page with just --man | groff -mandoc -Tascii | less.

Grammar

A non-normative grammar of justfiles can be found in 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.

Global and User justfiles

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:

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:

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:

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:

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

Paths on Windows

On Windows, functions that return paths will return \-separated paths. When not using PowerShell or cmd.exe these paths should be quoted to prevent the \s from being interpreted as character escapes:

ls:
    echo '{{absolute_path(".")}}'

Remote Justfiles

If you wish to include a mod or import source file in many justfiles without needing to duplicate it, you can use an optional mod or import, along with a recipe to fetch the module source:

import? 'foo.just'

fetch:
  curl https://raw.githubusercontent.com/casey/just/master/justfile > foo.just

Given the above justfile, after running just fetch, the recipes in foo.just will be available.

Printing Complex Strings

echo can be used to print strings, but because it processes escape sequences, like \n, and different implementations of echo recognize different escape sequences, using printf is often a better choice.

printf takes a C-style format string and any number of arguments, which are interpolated into the format string.

This can be combined with indented, triple quoted strings to emulate shell heredocs.

Substitution complex strings into recipe bodies with {…} can also lead to trouble as it may be split by the shell into multiple arguments depending on the presence of whitespace and quotes. Exporting complex strings as environment variables and referring to them with "$NAME", note the double quotes, can also help.

Putting all this together, to print a string verbatim to standard output, with all its various escape sequences and quotes undisturbed:

export FOO := '''
  a complicated string with
  some dis\tur\bi\ng escape sequences
  and "quotes" of 'different' kinds
'''

bar:
  printf %s "$FOO"

Alternatives and Prior Art

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

• make: The Unix build tool that inspired just. There are a few different modern day descendents of the original make, including FreeBSD Make and GNU Make.
• task: A YAML-based command runner written in Go.
• maid: A Markdown-based command runner written in JavaScript.
• microsoft/just: A JavaScript-based command runner written in JavaScript.
• cargo-make: A command runner for Rust projects.
• mmake: A wrapper around make with a number of improvements, including remote includes.
• robo: A YAML-based command runner written in Go.
• mask: A Markdown-based command runner written in Rust.
• makesure: A simple and portable command runner written in AWK and shell.
• haku: A make-like command runner written in Rust.

Contributing

just welcomes your contributions! just is released under the maximally permissive CC0 public domain dedication and fallback license, so your changes must also be released under this license.

Getting Started

just is written in Rust. Use rustup to install a Rust toolchain.

just is extensively tested. All new features must be covered by unit or integration tests. Unit tests are under src, live alongside the code being tested, and test code in isolation. Integration tests are in the tests directory and test the just binary from the outside by invoking just on a given justfile and set of command-line arguments, and checking the output.

You should write whichever type of tests are easiest to write for your feature while still providing good test coverage.

Unit tests are useful for testing new Rust functions that are used internally and as an aid for development. A good example are the unit tests which cover the unindent() function, used to unindent triple-quoted strings and backticks. unindent() has a bunch of tricky edge cases which are easy to exercise with unit tests that call unindent() directly.

Integration tests are useful for making sure that the final behavior of the just binary is correct. unindent() is also covered by integration tests which make sure that evaluating a triple-quoted string produces the correct unindented value. However, there are not integration tests for all possible cases. These are covered by faster, more concise unit tests that call unindent() directly.

Existing integration tests are in two forms, those that use the test! macro and those that use the Test struct directly. The test! macro, while often concise, is less flexible and harder to understand, so new tests should use the Test struct. The Test struct is a builder which allows for easily invoking just with a given justfile, arguments, and environment variables, and checking the program’s stdout, stderr, and exit code .

Contribution Workflow

1. Make sure the feature is wanted. There should be an open issue about the feature with a comment from @casey saying that it’s a good idea or seems reasonable. If there isn’t, open a new issue and ask for feedback.

   There are lots of good features which can’t be merged, either because they aren’t backwards compatible, have an implementation which would overcomplicate the codebase, or go against just’s design philosophy.

2. Settle on the design of the feature. If the feature has multiple possible implementations or syntaxes, make sure to nail down the details in the issue.

3. Clone just and start hacking. The best workflow is to have the code you’re working on in an editor alongside a job that re-runs tests whenever a file changes. You can run such a job by installing cargo-watch with cargo install cargo-watch and running just watch test.

4. Add a failing test for your feature. Most of the time this will be an integration test which exercises the feature end-to-end. Look for an appropriate file to put the test in in tests, or add a new file in tests and add a mod statement importing that file in tests/lib.rs.

5. Implement the feature.

6. Run just ci to make sure that all tests, lints, and checks pass.

7. Open a PR with the new code that is editable by maintainers. PRs often require rebasing and minor tweaks. If the PR is not editable by maintainers, each rebase and tweak will require a round trip of code review. Your PR may be summarily closed if it is not editable by maintainers.

8. Incorporate feedback.

9. Enjoy the sweet feeling of your PR getting merged!

Feel free to open a draft PR at any time for discussion and feedback.

Hints

Here are some hints to get you started with specific kinds of new features, which you can use in addition to the contribution workflow above.

Adding a New Attribute

1. Write a new integration test in tests/attributes.rs.

2. Add a new variant to the Attribute enum.

3. Implement the functionality of the new attribute.

4. Run just ci to make sure that all tests pass.

Janus

Janus is a tool for checking whether a change to just breaks or changes the interpretation of existing justfiles. It collects and analyzes public justfiles 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 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:

test:
  ./test

make will refuse to run your tests:

$ 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, 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 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, or some of the justfiles out in the wild.

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!

😸