just is a handy way to save and run project-specific commands. Commands, called recipes, are stored in a file called justfile with syntax inspired by make
Just: A Command Runner for Efficient Task Automation
Just is a command runner designed to save and run project-specific commands, streamlining your workflow with ease. It allows you to define tasks as recipes in a justfile, inspired by make syntax, making task automation both intuitive and efficient.
Key features include cross-platform compatibility, enabling use on various operating systems, and seamless integration with winget for straightforward installation. Its simple yet powerful approach ensures that even complex workflows can be managed effortlessly.
Ideal for developers, DevOps engineers, and anyone handling repetitive tasks, Just enhances productivity by automating project-specific commands. By organizing tasks in a justfile, you can execute them quickly, saving time and reducing errors. Whether you're working on scripts, configurations, or deployments, Just simplifies task management, helping you focus on what matters most.
With Just, efficiency meets simplicity, empowering you to tackle your projects with confidence and speed.
README
Table of Contents↗️
just
just is a handy way to save and run project-specific commands.
This readme is also available as a book. The
book reflects the latest release, whereas the
readme on GitHub
reflects latest master.
Linux, MacOS, Windows, and other reasonable unices 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.
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.
Windows
On Windows, just works with the sh provided by
Git for Windows,
GitHub Desktop, or
Cygwin. After installation, sh must be
available in the PATH of the shell you want to to invoke just from.
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
Package Manager
Package
Command
<a href="https://github.com/alexellis/arkade">arkade</a>
just
arkade get just
<a href="https://asdf-vm.com">asdf</a>
<a href="https://github.com/olofvndrhr/asdf-just">just</a>
asdf plugin add just
asdf install just <version>
<a href="https://www.rust-lang.org">Cargo</a>
<a href="https://crates.io/crates/just">just</a>
cargo install just
<a href="https://docs.conda.io/projects/conda/en/latest/index.html">Conda</a>
<a href="https://anaconda.org/conda-forge/just">just</a>
conda install -c conda-forge just
<a href="https://brew.sh">Homebrew</a>
<a href="https://formulae.brew.sh/formula/just">just</a>
brew install just
<a href="https://nixos.org/nix/">Nix</a>
<a href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/by-name/ju/just/package.nix">just</a>
nix-env -iA nixpkgs.just
<a href="https://www.npmjs.com/">npm</a>
<a href="https://www.npmjs.com/package/rust-just">rust-just</a>
npm install -g rust-just
<a href="https://pipx.pypa.io/stable/">pipx</a>
<a href="https://pypi.org/project/rust-just/">rust-just</a>
pipx install rust-just
<a href="https://snapcraft.io">Snap</a>
<a href="https://snapcraft.io/just">just</a>
snap install --edge --classic just
BSD
Operating System
Package Manager
Package
Command
<a href="https://www.freebsd.org">FreeBSD</a>
<a href="https://www.freebsd.org/doc/handbook/pkgng-intro.html">pkg</a>
<a href="https://www.freshports.org/deskutils/just/">just</a>
pkg install just
Linux
Operating System
Package Manager
Package
Command
<a href="https://alpinelinux.org">Alpine</a>
<a href="https://wiki.alpinelinux.org/wiki/Alpine_Linux_package_management">apk-tools</a>
<a href="https://pkgs.alpinelinux.org/package/edge/community/x86_64/just">just</a>
apk add just
<a href="https://www.archlinux.org">Arch</a>
<a href="https://wiki.archlinux.org/title/Pacman">pacman</a>
<a href="https://archlinux.org/packages/extra/x86_64/just/">just</a>
pacman -S just
<a href="https://debian.org">Debian 13</a> and
<a href="https://ubuntu.com">Ubuntu 24.04</a> derivatives
<a href="https://en.wikipedia.org/wiki/APT_(software)">apt</a>
<a href="https://packages.debian.org/trixie/just">just</a>
apt install just
<a href="https://debian.org">Debian</a> and <a href="https://ubuntu.com">Ubuntu</a> derivatives
<a href="https://mpr.makedeb.org">MPR</a>
<a href="https://mpr.makedeb.org/packages/just">just</a>
git clone https://mpr.makedeb.org/just
cd just
makedeb -si
<a href="https://debian.org">Debian</a> and <a href="https://ubuntu.com">Ubuntu</a> derivatives
<a href="https://docs.makedeb.org/prebuilt-mpr">Prebuilt-MPR</a>
<a href="https://mpr.makedeb.org/packages/just">just</a>
<b>You must have the <a href="https://docs.makedeb.org/prebuilt-mpr/getting-started/#setting-up-the-repository">Prebuilt-MPR set up</a> on your system in order to run this command.</b>
apt install just
<a href="https://getfedora.org">Fedora</a>
<a href="https://dnf.readthedocs.io/en/latest/">DNF</a>
<a href="https://src.fedoraproject.org/rpms/rust-just">just</a>
dnf install just
<a href="https://www.gentoo.org">Gentoo</a>
<a href="https://wiki.gentoo.org/wiki/Portage">Portage</a>
<a href="https://github.com/gentoo-mirror/guru/tree/master/dev-build/just">guru/dev-build/just</a>
eselect repository enable guru
emerge --sync guru
emerge dev-build/just
<a href="https://nixos.org/nixos/">NixOS</a>
<a href="https://nixos.org/nix/">Nix</a>
<a href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/by-name/ju/just/package.nix">just</a>
nix-env -iA nixos.just
<a href="https://opensuse.org">openSUSE</a>
<a href="https://en.opensuse.org/Portal:Zypper">Zypper</a>
<a href="https://build.opensuse.org/package/show/Base:System/just">just</a>
zypper in just
<a href="https://getsol.us">Solus</a>
<a href="https://getsol.us/articles/package-management/basics/en">eopkg</a>
<a href="https://dev.getsol.us/source/just/">just</a>
eopkg install just
<a href="https://voidlinux.org">Void</a>
<a href="https://wiki.voidlinux.org/XBPS">XBPS</a>
<a href="https://github.com/void-linux/void-packages/blob/master/srcpkgs/just/template">just</a>
xbps-install -S just
Package Manager
Package
Command
<a href="https://www.macports.org">MacPorts</a>
<a href="https://ports.macports.org/port/just/summary">just</a>
port install just
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:
# 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.
Another way to avoid rate-limiting is to pass a GitHub authentication token to
install.sh as an environment variable named GITHUB_TOKEN, allowing it to
authenticate its requests.
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:
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.
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 version 9.1.1042 or better and Neovim version 0.11 or better support
Justfile syntax highlighting out of the box, thanks to
pbnj.
vim-just
The vim-just plugin provides syntax
highlighting for justfiles.
Install it with your favorite package manager, like
Plug:
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:
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!
When just is invoked without a recipe, it runs the recipe with the
[default] attribute, or the first recipe in the justfile if no recipe has
the [default] attribute.
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:
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 the working directory for all recipes with
set working-directory := '…':
set working-directory := 'bar'
@foo:
pwd
$ pwd
/home/bob
$ just foo
/home/bob/bar
You can override the working directory for a specific recipe with the
working-directory attribute1.38.0:
[working-directory: 'bar']
@foo:
pwd
$ pwd
/home/bob
$ just foo
/home/bob/bar
The argument to the working-directory setting or working-directory
attribute may be absolute or relative. If it is relative it is interpreted
relative to the default working directory.
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!
The target of an alias may be a recipe in a submodule:
mod foo
alias baz := foo::bar
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-override
boolean
false
Override existing environment variables with values from the .env file.
dotenv-path
string
-
Load a .env file from a custom path and error if not present. Overrides dotenv-filename.
dotenv-required
boolean
false
Error if a .env file isn't found.
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.
quiet
boolean
false
Disable echoing recipe lines before executing.
script-interpreter1.33.0
[COMMAND, ARGS…]
['sh', '-eu']
Set command used to invoke recipes with empty [script] attribute.
shell
[COMMAND, ARGS…]
-
Set command used to invoke recipes and evaluate backticks.
tempdir
string
-
Create temporary directories in tempdir instead of the system default temporary directory.
unstable1.31.0
boolean
false
Enable unstable features.
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.
working-directory1.33.0
string
-
Set the working directory for recipes and backticks, relative to the default working directory.
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-override, 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.
If dotenv-override is set, variables from the environment file will override
existing environment variables.
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] attribute1.29.0:
[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.
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
values1.37.0, 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:
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
'single', "double", and '''triple''' quoted string literals are
supported. Unlike in recipe bodies, {{…}} interpolations are not supported
inside strings.
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 expanded1.27.0:
foobar := x'~/$FOO/${BAR}'
Value
Replacement
$VAR
value of environment variable VAR
${VAR}
value of environment variable VAR
${VAR:-DEFAULT}
value of environment variable VAR, or DEFAULT if VAR is not set
Leading ~
path to current user's home directory
Leading ~USER
path to USER's home directory
This expansion is performed at compile time, so variables from .env files and
exported just variables cannot be used. However, this allows shell expanded
strings to be used in places like settings and import paths, which cannot
depend on just variables and .env files.
Ignoring Errors
Normally, if a command returns a non-zero exit status, execution will stop. To
continue execution after a command, even if it fails, prefix the command with
-:
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".
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(key)1.15.0 — Retrieves the environment variable with name key, aborting
if it is not present.
home_dir := env('HOME')
test:
echo "{{home_dir}}"
$ just
/home/user1
env(key, default)1.15.0 — Retrieves the environment variable with
name key, returning default if it is not present.
env_var(key) — Deprecated alias for env(key).
env_var_or_default(key, default) — Deprecated alias for env(key, default).
A default can be substituted for an empty environment variable value with the
|| operator, currently unstable:
set unstable
foo := env('FOO') || 'DEFAULT_VALUE'
Executables
require(name)1.39.0 — Search directories in the PATH
environment variable for the executable name and return its full path, or
halt with an error if no executable with name exists.
which(name)1.39.0 — Search directories in the PATH environment
variable for the executable name and return its full path, or the empty
string if no executable with name exists. Currently unstable.
set unstable
bosh := which("bosh")
@test:
echo "bosh: '{{bosh}}'"
$ just
bosh: ''
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:
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:
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, substring) - Remove suffix of s matching substring.
trim_end_matches(s, substring) - Repeatedly remove suffixes of s matching
substring.
trim_start(s) - Remove leading whitespace from s.
trim_start_match(s, substring) - Remove prefix of s matching substring.
trim_start_matches(s, substring) - Repeatedly remove prefixes of s
matching substring.
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.
read(path)1.39.0 - Returns the content of file at path as
string.
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.
Style
style(name)1.37.0 - Return a named terminal display attribute
escape sequence used by just. Unlike terminal display attribute escape
sequence constants, which contain standard colors and styles, style(name)
returns an escape sequence used by just itself, and can be used to make
recipe output match just's own output.
Recognized values for name are 'command', for echoed recipe lines,
error, and warning.
For example, to style an error message:
scary:
@echo '{{ style("error") }}OH NO{{ NORMAL }}'
User Directories1.23.0
These functions return paths to user-specific directories for things like
configuration, data, caches, executables, and the user's home directory.
On MacOS and Windows, these functions return the system-specified user-specific
directories. For example, cache_directory() returns ~/Library/Caches on
MacOS and {FOLDERID_LocalAppData} on Windows.
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.
If you would like to use XDG base directories on all platforms you can use the
env(…) function with the appropriate environment variable and fallback,
although note that the XDG specification requires ignoring non-absolute paths,
so for full compatibility with spec-compliant applications, you would need to
do:
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.
Make recipe, alias, or variable private. See Private Recipes.
[script]1.33.0
recipe
Execute recipe as script. See script recipes for more details.
[script(COMMAND)]1.32.0
recipe
Execute recipe as a script interpreted by COMMAND. See script recipes for more details.
[unix]1.8.0
recipe
Enable recipe on Unixes. (Includes MacOS).
[windows]1.8.0
recipe
Enable recipe on Windows.
[working-directory(PATH)]1.38.0
recipe
Set recipe working directory. PATH may be relative or absolute. If relative, it is interpreted relative to the default working directory.
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"
Attributes with a single argument may be written with a colon:
[group: 'bar']
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 *
Groups
Recipes and modules may be annotated with one or more group names:
[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.
Variadic parameters prefixed with * accept zero or more arguments and
expand to a string containing those arguments separated by spaces, or an empty
string if no arguments are present:
just 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.
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, inconsistencies in shebang line splitting across Unix OSs, and
requiring a temporary directory from which files can be executed.
Recipes with an empty [script] attribute are executed with the value of set script-interpreter := […]1.33.0, defaulting to sh -eu, and not
the value of set shell.
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.
Script and Shebang Recipe Temporary Files
Both script and shebang recipes write the recipe body to a temporary file for
execution. Script recipes execute that file by passing it to a command, while
shebang recipes execute the file directly. Shebang recipe execution will fail
if the filesystem containing the temporary file is mounted with noexec or is
otherwise non-executable.
The directory that just writes temporary files to may be configured in a
number of ways, from highest to lowest precedence:
Globally with the --tempdir command-line option or the JUST_TEMPDIR
environment variable1.41.0.
On a per-module basis with the tempdir setting.
Globally on Linux with the XDG_RUNTIME_DIR environment variable.
uv is an excellent cross-platform python
project manager, written in Rust.
Using the [script] attribute and script-interpreter setting, just can
easily be configured to run Python recipes with uv:
set unstable
set script-interpreter := ['uv', 'run', '--script']
[script]
hello:
print("Hello from Python!")
[script]
goodbye:
# /// script
# requires-python = ">=3.11"
# dependencies=["sh"]
# ///
import sh
print(sh.echo("Goodbye from Python!"), end='')
Of course, a shebang also works:
hello:
#!/usr/bin/env -S uv run --script
print("Hello from Python!")
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 $x
Sharing Environment Variables Between Recipes
Each line of each recipe is executed by a fresh shell, so it is not possible to
share environment variables between recipes.
Using Python Virtual Environments
Some tools, like Python's venv,
require loading environment variables in order to work, making them challenging
to use with just. As a workaround, you can execute the virtual environment
binaries directly:
Each recipe line is executed by a new shell, so if you change the working
directory on one line, it won't have an effect on later lines:
foo:
pwd # This `pwd` will print the same directory…
cd bar
pwd # …as this `pwd`!
There are a couple ways around this. One is to call cd on the same line as
the command you want to run:
foo:
cd bar && pwd
The other is to use a shebang recipe. Shebang recipe bodies are extracted and
run as scripts, so a single shell instance will run the whole thing, and thus a
cd on one line will affect later lines, just like a shell script:
foo:
#!/usr/bin/env bash
set -euxo pipefail
cd bar
pwd
Indentation
Recipe lines can be indented with spaces or tabs, but not a mix of both. All of
a recipe's lines must have the same type of indentation, but different recipes
in the same justfile may use different indentation.
Each recipe must be indented at least one level from the recipe-name but
after that may be further indented.
Here's a justfile with a recipe indented with spaces, represented as ·, and
tabs, represented as →.
set windows-shell := ["pwsh", "-NoLogo", "-NoProfileLoadTime", "-Command"]
set ignore-comments
list-space directory:
··#!pwsh
··foreach ($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:
Lines ending with a backslash continue on to the next line as if the lines were
joined by whitespace1.15.0:
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
Setting Command-line Options with Environment Variables
Some command-line options can be set with environment variables
For example, unstable features can be enabled either with the --unstable
flag:
$ just --unstable
Or by setting the JUST_UNSTABLE environment variable:
$ export JUST_UNSTABLE=1
$ just
Since environment variables are inherited by child processes, command-line
options set with environment variables are inherited by recursive invocations
of just, where as command line options set with arguments are not.
Consult just --help for which options can be set with environment variables.
Private Recipes
Recipes and aliases whose name starts with a _ are omitted from just --list:
The [private] attribute1.10.0 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:
The argument is split at the last /.
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.
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.
allow-duplicate-recipes and allow-duplicate-variables allow duplicate
recipes and variables, respectively, to override each other, instead of
producing an error.
Within a module, later definitions override earlier definitions:
set allow-duplicate-recipes
foo:
foo:
echo 'yes'
When imports are involved, things unfortunately get much more complicated and
hard to explain.
Shallower definitions always override deeper definitions, so recipes at the top
level will override recipes in imports, and recipes in an import will override
recipes in an import which itself imports those recipes.
When two duplicate definitions are imported and are at the same depth, the one
from the earlier import will override the one from the later import.
This is because just uses a stack when processing imports, pushing imports
onto the stack in source-order, and always processing the top of the stack
next, so earlier imports are actually handled later by the compiler.
This is definitely a bug, but since just has very strong backwards
compatibility guarantees and we take enormous pains not to break anyone's
justfile, we have created issue #2540 to discuss whether or not we can
actually fix it.
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 error1.37.0.
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:
Modules1.19.0
A justfile can declare modules using mod statements.
mod statements were stabilized in just1.31.0. 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
output1.30.0:
# 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 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 < 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:
The --shell and --shell-arg command line options. Passing either of
these will cause just to ignore any settings in the current justfile.
set windows-shell := [...]
set windows-powershell (deprecated)
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.
Signal Handling
Signals are messsages sent to
running programs to trigger specific behavior. For example, SIGINT is sent to
all processes in the terminal forground process group when CTRL-C is pressed.
just tries to exit when requested by a signal, but it also tries to avoid
leaving behind running child proccesses, two goals which are somewhat in
conflict.
If just exits leaving behind child processes, the user will have no recourse
but to ps aux | grep for the children and manually kill them, a tedious
endevour.
Fatal Signals
SIGHUP, SIGINT, and SIGQUIT are generated when the user closes the
terminal, types ctrl-c, or types ctrl-\, respectively, and are sent to all
processes in the foreground process group.
SIGTERM is the default signal sent by the kill command, and is delivered
only to its intended victim.
When a child process is not running, just will exit immediately on receipt of
any of the above signals.
When a child process is running, just will wait until it terminates, to
avoid leaving it behind.
Additionally, on receipt of SIGTERM, just will forward SIGTERM to any
running children1.41.0, since unlike other fatal signals, SIGTERM,
was likely sent to just alone.
Regardless of whether a child process terminates successfully after just
receives a fatal signal, just halts execution.
SIGINFO
SIGINFO is sent to all processes in the foreground process group when the
user types ctrl-t on
BSD-derived
operating systems, including MacOS, but not Linux.
just responds by printing a list of all child process IDs and
commands1.41.0.
Windows
On Windows, just behaves as if it had received SIGINT when the user types
ctrl-c. Other signals are unsupported.
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.
Parallelism
Dependencies may be run in parallel with the [parallel] attribute.
In this justfile, foo, bar, and baz will execute in parallel when
main is run:
[parallel]
main: foo bar baz
foo:
sleep 1
bar:
sleep 1
baz:
sleep 1
GNU parallel may be used to run recipe lines concurrently:
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:
On Windows, all functions that return paths, except invocation_directory()
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(".")}}'
cygpath.exe is an executable included in some distributions of Unix userlands
for Windows, including Cygwin and
Git for Windows.
just uses cygpath.exe in two places:
For backwards compatibility, invocation_directory(), uses cygpath.exe to
convert the invocation directory into a unix-style /-separated path. Use
invocation_directory_native() to get the native, Windows-style path. On unix,
invocation_directory() and invocation_directory_native() both return the
same unix-style path.
cygpath.exe is used also used to convert Unix-style shebang lines into
Windows paths. As an alternative, the [script] attribute, currently unstable,
can be used, which does not depend on cygpath.exe.
If cygpath.exe is available, you can use it to convert between path styles:
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:
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.
mise: A development environment tool manager written
in Rust supporing tasks in TOML files and standalone scripts.
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.
Integration tests use the Test struct, 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
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.
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.
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.
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.
Implement the feature.
Run just ci to make sure that all tests, lints, and checks pass. Requires
mdBook and
mdbook-linkcheck.
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.
Incorporate feedback.
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.
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:
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.
