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.
(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, Windows, and other reasonable unixes 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, including
flags and options.
-
just has a rich expression language and many
built-in-functions.
-
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 Node.js.
-
just can be invoked from any subdirectory, not just the directory that
contains the justfile.
-
justfiles can be organized into multiple files using modules
and imports.
-
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
Just can be installed using your favorite package manager, by
downloading pre-built binaries, or building from source
with cargo install just.
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 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
SP1 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 shell's 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:
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@v3
with:
just-version: 1.5.0
Or with taiki-e/install-action:
- uses: taiki-e/install-action@just
Docker
just is available as a Docker image from
the GitHub Container Registry.
To copy just into a Docker image, add the following line to your
Dockerfile:
COPY --from=ghcr.io/casey/just:latest /just /usr/local/bin/
After copying, just may also be used as part of a docker build:
RUN just
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 setup process for their project as easy as possible.
For more information, see the
just-install README file.
Nix Flake
The just repository includes a
flake.nix that defines
a nix flake, allowing you to use just
as an input to another flake:
{
inputs = {
just.url = "github:casey/just";
}
outputs = {self, nixpkgs, just}: {
}
}
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 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.
Requiring a Minimum Just Version
If you use features of just which require a particular version, you may use
the minimum-version1.55.0 setting to make it an error to use older
versions of just:
set minimum-version := '1.55.0'
If just encounters a minimum version greater than its own version, it will
print an error message with the required version, which is hopefully better
than the confused error message it would have otherwise produced.
The minimum-version setting should be placed at the top of the justfile,
before any usage of the new feature that it guards.
Any features which change the lexer in forward-incompatible ways will still
produce an unhelpful error message, as the minimum version check is implemented
in the parser, which runs after the lexer.
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:
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.
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.
Zed
The zed-just extension by
jackTabsCode is available on the
Zed extensions page.
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.
Language Server Protocol
just-lsp provides a language server
protocol
implementation, enabling features such as go-to-definition, inline diagnostics,
and code completion.
Model Context Protocol
just-mcp provides a
model context protocol
adapter to allow LLMs to query the contents of justfiles and run recipes.
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 a file named 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.
By default, 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!
Recipes may depend on recipes in submodules:
mod foo
baz: foo::bar
Examples
A variety of justfiles can be found in the
examples directory and on
GitHub.
Recipes
The Default Recipe
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:
default: lint build test
build:
echo Building…
test:
echo Testing…
lint:
echo Linting…
If no recipe makes sense as the default recipe, you can use
default-list1.52.0 to list the available recipes instead:
set default-list := true
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 a 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}}
The number of arguments a variadic parameter accepts may be limited with the
[arg(ARG, min=MIN)] and [arg(ARG, max=MAX)] attributes1.56.0,
which require lists to be enabled:
set unstable
set lists
[arg('FILES', min='2', max='4')]
backup +FILES:
scp {{FILES}} me@server.com:
min and max also apply to default values.
{{…}} 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
Parameters may be constrained to match regular expression patterns using the
[arg("name", pattern=PATTERN)] attribute1.45.0:
[arg('n', pattern='\d+')]
double n:
echo $(({{n}} * 2))
The value of pattern may be a const expression1.55.0.
A leading ^ and trailing $ are added to the pattern, so it must match the
entire argument value.
You may constrain the pattern to a number of alternatives using the |
operator:
[arg('flag', pattern='--help|--version')]
info flag:
just {{flag}}
Regular expressions are provided by the
Rust regex crate. See the
syntax documentation for usage
examples.
Usage information for a recipe may be printed with the --usage
subcommand1.46.0:
$ just --usage foo
Usage: just foo [OPTIONS] bar
Arguments:
bar
Help strings may be added to arguments using the [arg(ARG, help=HELP)] attribute:
[arg("bar", help="hello")]
foo bar:
The value help may be a const expression1.55.0.
$ just --usage foo
Usage: just foo bar
Arguments:
bar hello
Recipe Flags and Options
Recipe parameters are positional by default.
In this justfile:
@foo bar:
echo bar={{bar}}
The parameter bar is positional:
$ just foo hello
bar=hello
The [arg(ARG, long=OPTION)]1.46.0 attribute can be used to make a
parameter a long option.
In this justfile:
[arg("bar", long="bar")]
foo bar:
The parameter bar is given with the --bar option:
$ just foo --bar hello
bar=hello
Options may also be passed with --name=value syntax:
$ just foo --bar=hello
bar=hello
The value of long may be omitted, in which case the option defaults to the
name of the parameter. With the following justfile, bar may be passed with
--bar:
[arg("bar", long)]
foo bar:
The [arg(ARG, short=OPTION)]1.46.0 attribute can be used to make a
parameter a short option.
In this justfile:
[arg("bar", short="b")]
foo bar:
The parameter bar is given with the -b option:
$ just foo -b hello
bar=hello
The value of short may be omitted, in which case the option defaults to the
first character of the name of the parameter. With the following justfile,
bar may be passed with -b:
[arg("bar", short)]
foo bar:
If a parameter has both a long and short option, it may be passed using either.
Multiple short options may be combined1.55.0, for example -abc is
equivalent to -a -b -c. A short option which takes a value may appear last,
for example -abcd VALUE.
Variadic * and + parameters may be options, in which case the option is
repeatable, with each occurrence contributing one value:
[arg('file', long)]
backup +file:
scp {{file}} me@server.com:
$ just backup --file FAQ.md --file GRAMMAR.md
scp FAQ.md GRAMMAR.md me@server.com:
As with positional variadic parameters, + options must be passed at least
once, whereas * options may be omitted.
The [arg(ARG, value=VALUE, …)]1.46.0 attribute can be used with
long or short to make a parameter a flag which does not take a value.
VALUE may be an expression1.54.0.
In this justfile:
[arg("bar", long="bar", value="hello")]
foo bar:
The parameter bar is given with the --bar option, but does not take a
value, and instead takes the value given in the [arg] attribute:
$ just foo --bar
bar=hello
This is useful for unconditionally requiring a flag like --force on dangerous
commands.
A flag is optional if its parameter has a default:
[arg("bar", long="bar", value="hello")]
foo bar="goodbye":
Causing it to receive the default when not passed in the invocation:
$ just foo
bar=goodbye
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 then be 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.
Positional Arguments
If positional-arguments is true, recipe arguments will be passed as
positional arguments to commands. For shell 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 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)])
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 recipe 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.
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
The number of simultaneously running recipes may be limited with the --jobs
option1.56.0. The num_jobs() function returns the number of jobs,
falling back to the empty list if --jobs was not passed.
GNU parallel may be used to run recipe lines 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
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
The value of [doc] may be a const expression1.56.0.
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.
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
Or a module1.55.0:
mod frontend
alias f := frontend
$ just f build
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] 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.
Enabling and Disabling Items
The [android], [dragonfly], [freebsd], [linux], [macos], [netbsd],
[openbsd], [unix], and [windows] attributes are conditional attributes.
By default, items are always enabled. An item with one or more conditional
attributes will only be enabled when one or more of those conditional
attributes is active.
The conditional attributes originally applied only to recipes, but may now be
applied to all top-level items1.56.0.
This can be used to write justfiles that behave differently depending on
which operating system they run on. The run recipe in this justfile will
compile and run main.c, using a different C compiler and using the correct
output binary name for that compiler depending on the operating system:
[unix]
run:
cc main.c
./a.out
[windows]
run:
cl main.c
main.exe
Similarly, a setting can be made conditional on the current operating system:
[unix]
set shell := ['sh', '-cu']
[windows]
set shell := ['cmd', '/c']
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
Expressions
Variables and Assignments
Module-level variables may be created by assigning them a value with :=:
foo := "hello"
bar := "world"
baz:
echo {{ foo + " " + bar }}
All variables in a module may be printed:
$ just --evaluate
bar := "world"
foo := "hello"
Or the value of a single variable:
$ just --evaluate foo
hello
All variables in a submodule or a single variable in a submodule may be printed
with a path to the submodule or variable1.49.0:
$ just --evaluate bob::bar
x := "world"
y := "hello"
$ just --evaluate bob::bar::y
hello
The format of exported variables may be controlled with
--evaluate-format1.49.0:
$ just --evaluate --evaluate-format shell
bar="world"
foo="hello"
The default format is --evaluate-format just:
$ just --evaluate --evaluate-format just
bar := "world"
foo := "hello"
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
Lazy
The lazy setting1.47.0 causes the evaluator to skip evaluating
unused variables. This can be beneficial when a justfile contains variables
that are expensive to evaluate but only sometimes used.
In the following justfile, token will be skipped when only invoking bar:
set lazy
token := `expensive-script-to-get-credentials`
foo:
curl -H "Authorization: Bearer {{ token }}" https://example.com/foo
bar:
cargo test
Because just cannot determine when exported variables are used, assignments
with export and assignments in a module with set export will always be
evaluated.
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
values1.37.0, similar to Python's and and or. The only false
value is the empty list []; every other value, including the empty string
'', is true.
These operators require set lists1.53.0, which is currently
unstable.
The && operator returns the empty list if the left-hand argument is false,
otherwise it returns the right-hand argument:
foo := [] && 'goodbye' # []
bar := 'hello' && 'goodbye' # 'goodbye'
The || operator returns the left-hand argument if it is true, 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 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.
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.
Shell-expanded strings
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.
Format strings
Strings prefixed with f are format strings1.44.0:
name := "world"
message := f'Hello, {{name}}!'
Format strings may contain interpolations delimited with {{…}} that contain
expressions. Format strings evaluate to the concatenated string fragments and
evaluated expressions.
Use {{{{ to include a literal {{ in a format string:
foo := f'I {{{{LOVE} curly braces!'
Lists
The lists setting1.53.0 allows values that are lists of strings.
It is currently unstable and will change in backwards incompatible ways. This
section documents changes in behavior when set lists is enabled.
It has not yet been decided how lists should behave with many of the built-in
functions. Functions that have been updated to accept lists are mentioned in
this section. Using lists with any other function is an error. The
join_list() function can be used to convert lists into space-separated
strings for use with un-upgraded functions. Feedback on how built-in functions
should behave with lists, and on lists in general, is most welcome! Feel free
to open an issue or leave a comment in the
set lists tracking issue.
Variadic recipe parameters are lists of strings instead of single
space-separated strings.
List literals are written [a, b, c]. List literals flatten their arguments,
since lists may only contain strings and not other lists. For example,
[["a", "b"], [], "c"] evaluates to ["a", "b", "c"].
Lists in recipe and f-string interpolations are joined with spaces into a
single string.
Each argument to a dependency binds to exactly one parameter, and supplying
extra arguments to a variadic dependency is an error.
Dependencies may be invoked once per element of a list with
*(recipe *argument).
A parameter evaluates to the default when the argument is the empty list.
Passing an empty list to a non-* parameter without a default is an error.
The else of an if may be omitted, in which case the if evaluates to []
when its condition is false.
Message values in assert(condition, message) and [confirm(message)] are
space-joined for display.
The + and / operators combine strings and lists. A string and a non-empty
list are combined by concatenating the string with each element of the list.
Two lists of the same length are combined into a list containing the pairwise
concatenated elements of both operands. Combining two lists of different
lengths is an error.
The ++ operator performs list concatenation.
Booleans
The canonical boolean true value is the string "true", and the canonical
boolean false value is the empty list []. All values other than the empty
list are truthy, including ''.
The condition of an if or assert() may be any expression, which is
evaluated for truthiness.
The comparison operators ==, !=, =~, and !~ may be used anywhere, not
just in if and assert(), and evaluate to "true" or [].
value =~ regexes is true if any element in value matches any regex in
regexes. It is false if either value or regexes is empty.
value !~ regexes is true if no element in value matches any regex in
regexes. It is true if either value or regexes is empty.
Values may be negated with !. !expression evaluates to "true" if
expression is [], otherwise it evaluates to [].
Settings
The script-interpreter, shell, and windows-shell settings flatten their
elements like list literals.
When positional-arguments is set, list arguments are space-joined unless they
are variadic, in which case they are passed as one positional argument per
element.
The --dotenv-filename and --dotenv-path options may be passed multiple
times, and the dotenv-filename and dotenv-path settings accept lists, in
which case multiple environment files may be loaded. The values of
dotenv-path are tried first. If none are found the current directory is
searched for the names in dotenv-filename, followed by its ancestors,
stopping in the first directory that contains any of them and loading all
matching files in that directory. If multiple environment files are loaded,
variables in files later in list take precedence over earlier ones.
Each element of the value of set dotenv-command is run as a command, with
variables from commands later in the list taking precedence over variables from
commands earlier in the list.
Attributes
The [arg(flag)] attribute makes the parameter a flag which does not take a
value on the command line. For example, with [arg('foo', long, flag)], foo
will be "true" when --foo is passed, and [] otherwise. Flag parameters
may not have a default.
The [arg(multiple)] attribute allows an option or flag to be passed more than
once, assigning the list of passed values to the parameter. When combined with
flag or value=VALUE, "true" or VALUE, respectively, are repeated for
each occurance of the flag.
The [arg(min=MIN)] and [arg(max=MAX)] attributes1.56.0 can be
used to limit the number of values an option or flag may receive.
The value of [arg(help)] may be a list, in which case the help string is the
elements of the list joined with spaces. If the list is empty, the argument has
no help string.
The value of [arg(pattern)] may be a list, in which case the argument is
accepted if it matches any pattern in the list. If the value is the empty list,
any argument is accepted. For example, with
[arg('foo', pattern=['--help', '--version'])], foo may be --help or
--version.
In [env(variable, value)] if value is [], variable is not set.
Otherwise it is set to value joined with spaces.
Functions
absolute_path() - Applies to each list element individually.append() - Applies to each list element individually and does not split
elements on whitespace.assert(condition, message) - Evaluates to condition.bool(value) Converts value to the canonical boolean values. Returns []
when value is "" "0" "false", or [], and "true" when value is
"1" or "true". All other values are an error. Can be used to parse
booleans passed as arguments or environment variables.env(keys, default) Checks for the environment variables named in keys in
order and returns the value of the first that is set. Returns default if
none are set or an error if default is omitted.is_dependency() - Returns the canonical booleans.join_list(value, separator) - Joins value into a single string. Elements
are joined with separator, or with a single space if separator is
omitted.len(value) - Returns the number of elements in value.path_exists() - Returns the canonical booleans.prepend() - Applies to each list element individually and does not split
elements on whitespace.quote() - Applies to each list element individually.semver_matches() - Returns the canonical booleans.show(value) - Converts value into a string containing its literal
representation. Brackets are used for empty and multi-element lists, e.g.,
"[]" and "["foo", "bar"]", but not single-element lists, e.g., "foo".split(string, separator) - Splits string into a list on each occurrence
of separator. If separator is omitted, string is split on whitespace,
with leading and trailing whitespace trimmed.which() - Returns the empty list when no executable is found.
Examples
Each list element is quote()'ed separately:
set unstable
set lists
@foo *args:
printf '%s\n' {{ quote(args) }}
$ just foo bar 'baz bob'
bar
baz bob
The return value of quote(args) is 'bar' 'baz bob', instead of
'bar baz bob', as would be the case without set lists.
Variadic positional arguments:
set unstable
set lists
set positional-arguments
foo *args: (bar args 'bob') (baz args)
@bar first second:
echo first=$1
echo second=$2
@baz *args:
echo '$1='$1
echo '$2='$2
$ just foo one two
first=one two
second=bob
$1=one
$2=two
A mapped dependency is invoked once per element of its starred argument, with
[parallel] to run them in parallel:
set unstable
set lists
[parallel]
build target *platform: *(compile target *platform)
@compile target platform:
echo compiling {{ target }} for {{ platform }}…
$ just build x86 foo bar
compiling foo for x86…
compiling bar for x86…
The canonical false value [] is recommended as a default for options:
set unstable
set lists
[arg('bar', long)]
foo bar=[]:
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" } }}
Multiple conditionals can be chained:
foo := if "hello" == "goodbye" {
"xyz"
} else if "a" == "a" {
"abc"
} else {
"123"
}
bar:
@echo {{foo}}
$ just bar
abc
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.
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 produces the following error when run:
error: Call to function `error` failed: 123
|
16 | error("123")
Built-in 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().
User-defined functions
New functions may be defined1.49.0:
set unstable
hello(name) := f"Hello, {{ name }}!"
foo:
echo '{{ hello("World") }}'
User-defined functions are currently unstable.
Functions may reference assignments in the same module:
set unstable
base := "foo"
join(extension) := base + "." + extension
create:
touch {{ join("c") }}
touch {{ join("html") }}
touch {{ join("txt") }}
Execution
Sigils
Commands in shell recipes may be prefixed with any combination of the sigils
-, @, and ?.
The @ sigil toggles command echoing:
foo:
@echo "This line won't be echoed!"
echo "This line will be echoed!"
@bar:
@echo "This line will be echoed!"
echo "This line won't be echoed!"
The - sigil causes recipe execution to continue even if the command returns a
nonzero exit status:
# execution will continue, even if bar doesn't exist
foo:
-rmdir bar
mkdir bar
echo 'so much good stuff' > bar/stuff.txt
The ? sigil1.47.0 causes the current recipe to stop executing if
the command exits with status code 1, however execution of other recipes will
continue. Exit status 0 causes the current recipe to continue execution as
normal. All other exit codes are reserved and should not be used, as they may
be given meaning in a future version of just.
If the guards setting is unset or false, ? sigils are ignored and instead
treated as part of the command.
set guards
@foo: bar
echo FOO
@bar:
?[[ -f baz ]]
echo BAR
$ just foo
FOO
$ touch baz
$ just foo
BAR
FOO
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 on individual recipes, or module-wide with
set no-exit-message1.39.0. 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
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.
With set default-script := true1.52.0, recipes default to script
recipes instead of shell recipes, unless overridden with the [shell]
attribute1.52.0.
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.
-
Falling back to the directory returned by
std::env::temp_dir.
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 "$hello from Bash!"
It isn't strictly necessary, but set -euxo pipefail turns on a few useful
features that make bash shebang recipes behave more like normal, shell just
recipes:
-
set -e makes bash exit if a command fails.
-
set -u makes bash exit if a variable is undefined.
-
set -x makes bash print each script line before it's run.
-
set -o pipefail makes bash exit if a command in a pipeline fails. This is
bash-specific, so isn't turned on in normal shell just recipes.
Together, these avoid a lot of shell scripting gotchas.
Shebang Recipe Execution on Windows
On Windows, shebang interpreter paths containing a / are translated from
Unix-style paths to Windows-style paths using cygpath, a utility that ships
with Cygwin.
For example, to execute this recipe on Windows:
echo:
#!/bin/sh
echo "Hello!"
The interpreter path /bin/sh will be translated to a Windows-style path using
cygpath before being executed.
If the interpreter path does not contain a / it will be executed without
being translated. This is useful if cygpath is not available, or you wish to
pass a Windows-style path to the interpreter.
Indentation
Recipe lines can be indented with spaces or tabs, but not a mix of both. All of
a recipe's lines must have the same type of indentation, but different recipes
in the same justfile may use different indentation.
Each recipe must be indented at least one level from the recipe-name but
after that may be further indented.
Here's a justfile with a recipe indented with spaces, represented as ·, and
tabs, represented as →.
[windows]
set shell := ["pwsh", "-NoLogo", "-NoProfileLoadTime", "-Command"]
set ignore-comments
list-space directory:
··#!pwsh
··foreach ($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 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'
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
Configuring the Shell
There are a number of ways to configure the shell for shell 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 := [...] (deprecated)set windows-powershell (deprecated)set shell := [...]
Use the [windows] and [unix] attributes with set shell to use different a
shells on Windows.
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 the [windows] attribute on the shell setting:
[windows]
set shell := ["powershell.exe", "-NoLogo", "-Command"]
hello:
Write-Host "Hello, world!"
See
powershell.just
for a justfile that uses PowerShell on all platforms.
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.
Environment Variables
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
You can also use the [env(NAME, VALUE)] attribute to export environment
variables to a specific recipe:
[env("RUST_BACKTRACE", "1")]
test:
# 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
Environment variables can be unexported with the unexport
keyword1.29.0:
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 env() function.
See
environment-variables.
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.
The command-line option --dotenv-filename, short form -F, can be used to
set or override dotenv-filename at runtime.
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.
If dotenv-command is set, just runs it with the configured shell and loads
its standard output as an environment file.
This is useful for sourcing secrets from a secret manager or vault:
set dotenv-command := 'sops -d .enc.env'
The command-line option --dotenv-command can be used to set or override
dotenv-command at runtime, and may be passed multiple times. Each value is
run as a command, with variables from later commands taking precedence over
variables from earlier commands.
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
Variables in environment files loaded in parent modules are inherited by
submodules.
Environment files are loaded in submodules1.49.0 and may override
variables defined in parent module environment files.
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
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
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 the directory in which just was invoked.
@foo:
pwd
[no-cd]
@bar:
pwd
$ cd subdir
$ just foo
/
$ just bar
/subdir
Note that this does not affect dotenv file search, or the working directory of
backtick and shell() invocations.
Use set no-cd1.51.0 to make all recipes in the current module
default to the same behavior.
set no-cd and set working-directory can be overridden on a per-recipe basis
with the [no-cd] and [working-directory] attributes.
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 an expression1.51.0 whose value is absolute or
relative. If it is relative it is interpreted relative to the default working
directory.
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
cd on one line will affect later lines, just like a shell script:
foo:
#!/usr/bin/env bash
set -euxo pipefail
cd bar
pwd
Disabling Changing Directory
just normally executes recipes with the current directory set to the
directory that contains the justfile. This can be disabled using the
[no-cd] attribute1.9.0. 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.
Note that this does not affect dotenv file search, or the working directory of
backtick and shell() invocations.
Organization
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
user's 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, see issue #2540 for
discussion on 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:
Modules
A justfile can declare modules using mod statements1.19.0.
mod statements were stabilized in just1.31.0.
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 loaded for each module, respecting that module's related
settings. Environment variables from parent modules are visible in child
modules.
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. If a recipe
or alias depends on a missing optional module, directly, or transitively, it
will be disabled. Attempting to invoke a disabled recipe or alias is an error,
but other non-disabled recipes can still be run.1.52.0
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.
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.
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
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.
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 ~'
Markdown justfiles
If the argument to --justfile ends in .md, just extracts the contents of
unindented just fenced code blocks and writes them to a justfile in a
temporary directory1.53.0:
# Project
Build the project:
```just
build:
echo Building…
```
$ just --justfile README.md build
echo Building…
Building…
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
Hiding justfiles
just looks for justfiles named justfile and .justfile, which can be
used to keep a justfile hidden.
Command Line
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 --list foo bar
Available recipes:
baz
$ just --list 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, set
default-list1.52.0:
set default-list := true
The setting is per-module, so invoking a module path with default-list
enabled lists that module's recipes.
You can also default to listing recipes this behavior by settting the
environment variable JUST_DEFAULT_LIST=true or passing
--default-list1.52.0.
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.
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
Variables in submodules can be overridden using the ::-separated path to the
variable. A variable named bar in a submodule named foo may be overridden
with foo::bar=VALUE or --set foo::bar VALUE.
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, whereas command-line options set with arguments are not.
Consult just --help for which options can be set with environment variables.
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
Requiring Confirmation for Recipes
just normally executes all recipes unless there is an error. The [confirm]
attribute1.17.0 allows recipes to 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
The default confirmation prompt can be overridden with
[confirm(PROMPT)]1.23.0:
[confirm("Are you sure you want to delete everything?")]
delete-everything:
rm -rf *
The confirmation prompt may also be an expression1.49.0 which may
reference assignments or recipe arguments:
[confirm("Deploy to " + env + "?")]
deploy env:
echo 'Deploying to {{env}}...'
Timestamps
just can print timestamps before each recipe command:
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.
The [timestamp] attribute1.58.0 can be used to enable timestamps
for a specific recipe:
[timestamp]
foo:
echo hello
$ just foo
[07:28:46] echo hello
hello
Which may include a format string:
[timestamp('%H:%M:%S%.3f')]
foo:
echo hello
$ just foo
[07:28:46.487] echo hello
hello
Signal Handling
Signals are messages sent to
running programs to trigger specific behavior. For example, SIGINT is sent to
all processes in the terminal foreground 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 processes, 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
endeavor.
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.
Continuing Execution
The [continue]1.54.0 attribute can be used to make just continue
execution even if it receives a fatal signal as long as the child process it's
running exits successfully.
With no arguments, [continue] handles SIGINT (ctrl-c) so SIGQUIT
(ctrl-\) can still be used to stop execution.
With arguments, one or more signals to handle may be given explicitly, as
"SIGHUP", "SIGINT", and "SIGQUIT".
In this example, if main.py catches SIGINT and exits successfully,
cleanup will still run and just will exit successfully:
[continue]
test: && cleanup
python3 main.py
cleanup:
echo cleanup
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.
Shell Completion Scripts
Shell completion scripts for Bash, Elvish, Fish, Nushell, PowerShell, and Zsh
are available in release archives.
The just binary can also generate the same completion scripts at runtime
using just --completions SHELL:
$ just --completions bash > just
Bash
The recommended approach is to use the bash-completions package to lazy-load
the completion script:
mkdir -p ~/.local/share/bash-completion/completions
just --completions bash > ~/.local/share/bash-completion/completions/just
If bash-completions is not installed, you can source the completion script in
your .bashrc:
source <(just --completions bash)
If you use an alias like alias j=just, you should also save the completion
script with the name j when lazy-loading:
just --completions bash > ~/.local/share/bash-completion/completions/j
Or if not lazy-loading, add this line after sourcing the completion script in
your .bashrc:
complete -F _clap_complete_just -o bashdefault -o default j
Elvish
In your rc.elv:
set edit:completion:arg-completer[just] = { |@args|
eval (just --completions elvish | slurp)
set @result = (edit:completion:arg-completer[just] $@args)
put $@result
}
Fish
Save the completion script to the completions directory to lazy-load it:
mkdir -p ~/.config/fish/completions
just --completions fish > ~/.config/fish/completions/just.fish
Nushell
First save the completion script:
just --completions nushell | save -f ($nu.default-config-dir | path join just.nu)
Then in config.nu:
source just.nu
PowerShell
In your PowerShell $PROFILE:
just --completions powershell | Out-String | Invoke-Expression
Zsh
First save the completion script:
mkdir -p ~/.zsh/completions
just --completions zsh > ~/.zsh/completions/_just
Then in your .zshrc:
fpath=(~/.zsh/completions $fpath)
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.
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 --fmt flag:
$ cat justfile
# A lot of blank lines
some-recipe:
echo "foo"
$ just --fmt
$ cat justfile
# A lot of blank lines
some-recipe:
echo "foo"
When the justfile is read from standard input with --justfile - or
extracted from a markdown file, --fmt prints the formatted justfile to
stdout.
Note that formatting is not covered by any backwards compatibility guarantee
and is subject to change from time to time.
Recipe bodies are indented with four spaces by default. This can be changed
with the --indentation command-line option, the JUST_INDENTATION
environment variable, or the indentation setting:
set indentation := " "
Invoking just --fmt --check 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.
Cached Recipes
just will skip invocations of recipes with the [cache]
attribute1.54.0 if it finds an entry matching the invocation in the
cache. The [cache] attribute may only be used with script recipes and is
currently unstable.
For example, this recipe will be skipped if image.jpg exists and the contents
of image.png and the output of convert -version haven't changed since the
last run:
set unstable
[script]
[cache(inputs = "image.png", outputs = "image.jpg", extra = `convert -version`)]
convert:
convert image.png image.jpg
Unlike many other features of just, which are, hopefully, well thought-out
and user-friendly, cached recipes are inherently fragile. It is important to
understand their limitations before relying on them. Please read this section
thoroughly, including the friendly admonitions below.
Friendly Admonitions
just will happily skip cached recipes, but it is your responsibility to make
sure that this is safe, and that the contents of the cache key capture enough
information about recipe invocations for caching to make sense in the first
place.
In particular, there are many details about the context in which a recipe runs
that are not captured by cache keys.
These include the time, input files, output files, system binaries, operating
system version, databases, systems over the network, the DNS, and any of the
myriad other things which may change the execution of a computer program.
Attempting to skip execution based on the type of crude heuristics that just
employs has a long and sordid history. However, it is an undeniably convenient
and powerful tool, and it is provided in the hopes that you find it useful.
Implementation
The cache is a directory named .justcache alongside the justfile and should
not be committed to version control systems. It contains cache entries named
HASH.json, where HASH is the BLAKE3 hash of a serialized cache key JSON
object.
The keys of the cache key object are:
body: evaluated recipe bodyenvironment: map of environment variable names to valuesexecutor: script interpreter or shebangextension: script file extensionextra: user-supplied valueinputs: map of file paths to content hashspositional: positional argumentsrecipe: ::-separated module path to invoked recipeworking_directory: current working directory
All keys other than extra and inputs are populated automatically.
Cache key objects for invoked recipes can be printed to standard error with
just -vv.
The environment variables included in environment may be controlled with
[cache(environment = EXPRESSION])1.59.0.
The value of extra may be supplied with [cache(extra = EXPRESSION)], where
EXPRESSION is an arbitrary expression evaluated with recipe arguments in
scope. Changes to the value of extra will cause a cache miss.
Before just runs a cached recipe, it creates a cache key, hashes it, and
looks for the corresponding cache entry.
If the cache entry is non-empty, it skips the invocation.
If the cache entry does not exist or is empty, it runs the invocation and
writes {} to the cache entry.
File locks are taken on cache entries, so concurrent execution of cached
recipes by multiple just processes is safe. If two processes run a recipe
invocation with the same cache key, the first will take the lock, run the
recipe, write to the cache entry, and relinquish the lock. The second will
block until the first relinquishes the lock, see that the entry is non-empty,
and skip the invocation.
The cache can be bypassed entirely with the --no-cache flag.
Clearing the Cache
The recipe cache is stored in a directory named .justcache alongside the
justfile. Deleting it will clear the cache.
The cache can also be cleared with just --clean, which can selectively clear
cache entries:
just --clean
just --clean foo
just --clean bar baz
just --clean bar
just --clean bar bob
just --clean bar::bob
Adding and Removing Environment Variables
By default, environment variables which are exported or unexported in the
justfile are included in the cache key, and environment variables exported
outside the justfile and inherited by just are not included.
Environment variables can be added or removed from the cache key using
[cache(environment = EXPRESSION)]1.59.0.
In this example, the environment variable foo will not be included in the
cache key, but PATH will:
set unstable
set lists
export foo := 'bar'
[script]
[cache(environment = ['PATH'])]
build:
cc lib.c main.c -o main
Input Files
Input files can be provided with [cache(inputs = FILES)], where FILES is an
expression that is evaluated with recipe arguments in scope and whose evaluated
elements are paths. Paths may be absolute or relative to the recipe's working
directory.
Each input file is hashed with BLAKE3 and added to the inputs cache key,
which contains a map of paths to hashes.
Any changes to the contents of an input file changes the cache key, which
causes the next invocation to miss the cache and re-run.
Missing inputs and paths to directories are errors.
In this example, the build recipe will re-run if lib.c or main.c change:
set unstable
set lists
[script]
[cache(inputs = ["lib.c", "main.c"])]
build:
cc lib.c main.c -o main
Output Files
Output files can be provided with [cache(outputs = FILES)], where FILES is
an expression that is evaluated with recipe arguments in scope and whose
evaluated elements are paths. Paths may be absolute or relative to the recipe's
working directory.
Outputs are not part of the cache key.
All output files must exist for an invocation to be skipped, and after an
invocation runs successfully, it is an error if any output file does not exist.
In this example, build re-runs whenever main is missing, and errors if it
runs without producing main:
set unstable
set lists
[script]
[cache(inputs = ["lib.c", "main.c"], outputs = "main")]
build:
cc lib.c main.c -o main
clean:
rm -f main
This forces build to re-run if main is deleted by clean.
Reference
Attributes
Recipes, mod statements, and aliases may be annotated with attributes that
change their behavior.
| Name | Type | Description |
|---|
[arg(ARG, help="HELP")]1.46.0 | recipe | Print help string HELP for ARG in usage messages. May be a const expression1.55.0. |
[arg(ARG, long="LONG")]1.46.0 | recipe | Require values of argument ARG to be passed as --LONG option. If the parameter is variadic, the option is repeatable1.55.0master. |
[arg(ARG, max="MAX")]1.56.0 | recipe | Allow at most MAX values to be passed to argument ARG. Requires multiple or a variadic parameter. |
[arg(ARG, min="MIN")]1.56.0 | recipe | Require at least MIN values to be passed to argument ARG. Requires multiple or a variadic parameter. |
[arg(ARG, pattern="PATTERN")]1.45.0 | recipe | Require values of argument ARG to match regular expression PATTERN. May be a const expression1.55.0. |
[arg(ARG, short="S")]1.46.0 | recipe | Require values of argument ARG to be passed as short -S option. If the parameter is variadic, the option is repeatable1.55.0. |
[arg(ARG, value=VALUE)]1.46.0 | recipe | Makes option ARG a flag which does not take a value. |
[cache]1.54.0 | recipe | Skip recipe invocations when a matching entry exists in the cache. See cached recipes for details. Currently unstable. |
[confirm(PROMPT)]1.23.0 | recipe | Require confirmation prior to executing recipe with a custom prompt. |
[confirm]1.17.0 | recipe | Require confirmation prior to executing recipe. |
[continue(SIGNALS)]1.54.0 |
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:
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. |
default-list | boolean | false | List recipes instead of running the default recipe. |
default-script1.52.0 | boolean | false | Default recipes to script instead of shell. |
dotenv-command1.54.0 | string | - | Run a command and load its output as an environment file. |
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 for justfile in parent directory if the first recipe on the command line is not found. |
guards1.47.0 |
Boolean settings can be written as:
set NAME
Which is equivalent to:
set NAME := true
Non-boolean settings can be set to both strings and
expressions1.46.0.
However, because settings affect the behavior of backticks and many functions,
those expressions may not contain backticks or function calls, directly or
transitively via reference.
Functions
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(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).
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.
bash := require("bash")
@test:
echo "bash: '{{bash}}'"
$ just
bash: '/bin/bash'
-
which(name)1.39.0 — Search directories in the PATH environment
variable for the executable name and return its full path, or the empty
list if not found. Requires set lists1.53.0.
set unstable
set lists
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.
-
num_jobs()1.56.0 — The value of --jobs or the empty list,
[], if it was not passed.
-
recipe_name()1.53.0 - Returns the name of the current recipe.
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 recipe:
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
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() 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.
Module and Module Directory
-
module_file() - Returns the path of the current module file.
-
module_directory() - Returns the path of the parent directory of the
current module file.
-
module_path() - Returns the ::-separated path to the current module.
module_file() and module_directory() behave the same as justfile() and
justfile_directory() in the root justfile, but will return the path and
directory, respectively, of the current mod source file when called from
within a submodule.
Just Process and Executable
just_executable() - Absolute path to the just executable.just_pid() - Process ID of the just executable.just_version()1.55.0 - Version of the just executable.
For example:
just-info:
@echo The executable is at: {{just_executable()}}
@echo The process ID is: {{ just_pid() }}
@echo The version is: {{ just_version() }}
$ just
The executable is at: /bin/just
The process ID is: 420
The version is: 1.54.0
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 with to.replace_regex(s, regex, replacement) - Replace all occurrences of regex
in s with 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 .
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
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 the string true if the path points at an
existing entity and the string false otherwise. Traverses symbolic links,
and returns the string 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 a
string.
Assertions and Error Reporting
assert(CONDITION, EXPRESSION)1.27.0 - Error with message
EXPRESSION if CONDITION is false. EXPRESSION may be
omitted1.53.0,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 the string "true" if so and the
string "false" otherwise.
Style
-
style(styles)1.37.0 - Return a terminal escape sequence
combining the named styles in styles.
The styles supported by version 1.37.0 and later can be used to duplicate
just's own styles:
command: echoed recipe lineserror: errorswarning: warnings
Additional styles supported by 1.55.0 and later include
named colors:
blackbluecyangreenmagentaredwhiteyellow
The 256 indexed colors, written as integers between 0 and 255, e.g., 1
or 67.
The 24-bit colors, written as #RRGGBB or #RGB hex codes, e.g., #065535
or #AAA.
And display properties:
blinkbolddimhiddenitalicreversestrikethroughunderline
Two stream names1.55.0 gate the style on whether just would
color the output stream, determined by --color, JUST_COLOR, and whether
the stream is connected to a terminal:
All color styles color the foreground by default, and come in explicit
foreground variants prefixed with fg: and background variants prefixed with
bg:, e.g., bg:blue, fg:133, and #FFF.
styles may be a list of styles, in which case all listed styles are
combined to produce the final escape sequence.
Note that the escape sequence returned by style(styles) are prefixes. You
can use the NORMAL constant to reset the style after use:
error message:
echo '{{style("error") + message + NORMAL}}'
-
User Directories
These functions1.23.0 return paths to user-specific directories for
things like configuration, data, caches, executables, and the user's home
directory.
On Unix, these functions follow the
XDG Base Directory Specification.
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.
See the dirs crate for more
details.
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.runtime_directory() - The user-specific runtime directory. Only defined on
Linux.
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:
xdg_config_dir := if env('XDG_CONFIG_HOME', '') =~ '^/' {
env('XDG_CONFIG_HOME')
} else {
home_directory() / '.config'
}
Constants
A number of constants are predefined:
| Name | Value | Value on Windows |
|---|
HEX1.27.0 | "0123456789abcdef" | |
HEXLOWER1.27.0 | "0123456789abcdef" | |
HEXUPPER1.27.0 | "0123456789ABCDEF" | |
PATH_SEP1.41.0 | "/" | "\" |
PATH_VAR_SEP1.41.0 | ":" | ";" |
CLEAR1.37.0 | "\ec" | |
NORMAL1.37.0 | "\e[0m" | |
BOLD1.37.0 | "\e[1m" | |
ITALIC1.37.0 | "\e[3m" | |
UNDERLINE1.37.0 | "\e[4m" | |
INVERT1.37.0 | "\e[7m" | |
HIDE1.37.0 | "\e[8m" | |
STRIKETHROUGH1.37.0 | "\e[9m" | |
BLACK1.37.0 | "\e[30m" | |
RED1.37.0 | "\e[31m" | |
GREEN1.37.0 | "\e[32m" | |
YELLOW1.37.0 | "\e[33m" | |
BLUE1.37.0 | "\e[34m" | |
MAGENTA1.37.0 | "\e[35m" | |
@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}}'
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.
Shell Alias
For lightning-fast command running, put alias j=just in your shell's
configuration file.
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.
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, 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 also used to convert Unix-style shebang lines into
Windows paths. As an alternative, the [script] attribute can be used, which
does not depend on cygpath.exe.
If cygpath.exe is available, you can use it to convert between path styles:
foo_unix := '/hello/world'
foo_windows := shell('cygpath --windows $1', foo_unix)
bar_windows := 'C:\hello\world'
bar_unix := shell('cygpath --unix $1', bar_windows)
Printing Complex Strings
echo can be used to print strings, but because it processes escape sequences,
like \n, and different implementations of echo recognize different escape
sequences, using printf is often a better choice.
printf takes a C-style format string and any number of arguments, which are
interpolated into the format string.
This can be combined with indented, triple quoted strings to emulate shell
heredocs.
Substituting complex strings into recipe bodies with {{…}} can also lead to
trouble as it may be split by the shell into multiple arguments depending on
the presence of whitespace and quotes. Exporting complex strings as environment
variables and referring to them with "$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"
Skill for Agents
A skill for agents is available in
skills/just and may
be installed manually or with npx skills add casey/just --global.
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 descendants 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.
- mise: A development environment tool manager written
in Rust supporting tasks in TOML files and standalone scripts.
Metadata
Metadata in the form of lists of strings may be attached to recipes with the
[metadata(METADATA)] attribute1.42.0:
[metadata("hello", "goodbye")]
foo:
Metadata can be read using just --dump --dump-format json.
Python Recipes with uv
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 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!")
Activating Environments
Some tools require an activation step, such as Python virtual environments:
. .venv/bin/activate
Because these tools modify the environment of a running shell, it is not
possible for just to perform this activation step for you. However, there are
some workarounds.
The best workaround for Python environment management is to switch to
uv. uv sets up the correct environment for
each command, so no activation step is needed.
If that isn't possible, and for other tools, you can create a shared prelude
and include it in script recipes that need it. It can span multiple lines and
include any number of steps:
prelude := '''
set -eux
. .venv/bin/activate
'''
[script]
run:
{{ prelude }}
python script.py
This workaround doesn't work with shell recipes, which spawn a new shell for
each command.
Contributing
[!NOTE]
just is not currently accepting pull requests. The contributing section is
retained for posterity.
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 no 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
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.
Adding a New Attribute
-
Write a new integration test in
tests/attributes.rs.
-
Add a new variant to the
Attribute
enum.
-
Implement the functionality of the new attribute.
-
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!
😸
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