`just`

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

(非官方中文文档,这里,快看过来!)

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

You can then run them with just RECIPE:

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

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

just is a command runner, not a build system, so it avoids much of make’s complexity and idiosyncrasies. No need for `.PHONY recipes!
Linux, MacOS, and Windows are supported with no additional dependencies. (Although if your system doesn’t have an sh, you’ll need to choose a different shell.)
Errors are specific and informative, and syntax errors are reported along with their source context.
Recipes can accept command line arguments.
Wherever possible, errors are resolved statically. Unknown recipes and circular dependencies are reported before anything runs.
just loads .env files, making it easy to populate environment variables.
Recipes can be listed from the command line.
Command line completion scripts are available for most popular shells.
Recipes can be written in arbitrary languages, like Python or NodeJS.
just can be invoked from any subdirectory, not just the directory that contains the justfile.
And much more!

If you need help with just please feel free to open an issue or ping me on Discord. Feature requests and bug reports are always welcome!

Manual

Installation
Editor Support
Quick Start
Examples
Features
Miscellanea
Contributing
- Janus
Frequently Asked Questions
- What are the idiosyncrasies of Make that Just avoids?
- What’s the relationship between Just and Cargo build scripts?
Further Ramblings

Installation

Prerequisites

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

On Windows, just works with the sh provided by Git for Windows, GitHub Desktop, or Cygwin.

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

Like PowerShell:

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

hello:
  Write-Host "Hello, world!"

…or cmd.exe:

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

list:
  dir

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

Packages

Operating System	Package Manager	Package	Command
Various	Cargo	just	`cargo install just`
Microsoft Windows	Scoop	just	`scoop install just`
macOS	Homebrew	just	`brew install just`
macOS	MacPorts	just	`port install just`
Arch Linux	pacman	just	`pacman -S just`
NixOS, Linux, macOS	Nix	just	`nix-env -iA nixos.just`
Solus	eopkg	just	`eopkg install just`
Void Linux	XBPS	just	`xbps-install -S just`
FreeBSD	pkg	just	`pkg install just`
Alpine Linux	apk-tools	just	`apk add just`
Fedora Linux	DNF	just	`dnf install just`
Gentoo Linux	Portage	dm9pZCAq overlay: sys-devel/just	`eselect repository enable dm9pZCAq && emerge --sync dm9pZCAq && emerge sys-devel/just`

Pre-Built Binaries

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

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

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

GitHub Actions

extractions/setup-just can be used to install just in a GitHub Actions workflow.

Example usage:

- uses: extractions/setup-just@v1
  with:
    just-version: 0.8  # optional semver specification, otherwise latest

Release RSS Feed

An RSS feed of just releases is available here.

Editor Support

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

Vim and Neovim

`vim-just`

The vim-just plugin provides syntax highlighting for justfiles.

Install it with your favorite package manager, like Plug:

call plug#begin()

Plug 'NoahTheDuke/vim-just'

call plug#end()

Or with Vim’s built-in package support:

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

vim-just is also available from vim-polyglot, a multi-language Vim plugin.

`tree-sitter-just`

tree-sitter-just is an Nvim Treesitter plugin for Neovim.

Makefile Syntax Highlighting

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

if exists("did_load_filetypes")
  finish
endif

augroup filetypedetect
  au BufNewFile,BufRead justfile setf make
augroup END

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

# vim: set ft=make :

Emacs

There is a MELPA package, just-mode, for automatic Emacs syntax highlighting and automatic indentation in justfiles.

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 by skellock is available here. (repository)

You can install it from the command line by running:

code --install-extension skellock.just

Kakoune

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

Sublime Text

A syntax file for Sublime Text written by TonioGela is available in extras/just.sublime-syntax.

Other Editors

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

Quick Start

See Installation for how to install just on your computer. Try running just --version to make sure that it’s installed correctly.

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

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

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

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

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

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

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

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

$ just another-recipe
This is another recipe.

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

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

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

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

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

test: build
    ./test

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

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

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

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

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

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

Examples

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

This blog post discusses using just to improve management of shared machines, and includes a number of example justfiles.

Features

Listing Available Recipes

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

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

just --summary is more concise:

$ just --summary
build test deploy lint

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

test:
  echo 'Testing!'

build:
  echo 'Building!'

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

$ just --summary --unsorted
test build

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

default:
  @just --list

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

Aliases

Aliases allow recipes to be invoked with alternative names:

alias b := build

build:
  echo 'Building!'

$ just b
build
echo 'Building!'
Building!

Settings

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

For example:

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

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

Table of Settings

Name	Value	Description
`dotenv-load`	boolean	Load a `.env` file, if present.
`export`	boolean	Export all variables as environment variables.
`positional-arguments`	boolean	Pass positional arguments.
`shell`	`[COMMAND, ARGS…]`	Set the command used to invoke recipes and evaluate backticks.

Boolean settings can be written as:

set NAME

Which is equivalent to:

set NAME := true

Dotenv Load

If dotenv-load is true, a .env file will be loaded if present. Defaults to true.

Export

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

set export

a := "hello"

@foo b:
  echo $a
  echo $b

$ just foo goodbye
hello
goodbye

Positional Arguments

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

For example, running this recipe:

set positional-arguments

@foo bar:
  echo $0
  echo $1

Will produce the following output:

$ just foo hello
foo
hello

Shell

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

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

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

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

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

Python 3

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

Bash

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

Z Shell

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

Fish

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

Documentation Comments

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

# build stuff
build:
  ./bin/build

# test stuff
test:
  ./bin/test

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

Variables and Substitution

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

version := "0.2.7"
tardir  := "awesomesauce-" + version
tarball := tardir + ".tar.gz"

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

Escaping `{{`

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

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

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

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

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

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

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

Strings

Double-quoted strings support escape sequences:

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

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

Strings may contain line breaks:

single := '
hello
'

double := "
goodbye
"

Single-quoted strings do not recognize escape sequences:

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

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

Indented versions of both single- and double-quoted strings, delimited by triple single- or triple double-quotes, are supported. Indented string lines are stripped of 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\nbar\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 unindention algorithm does not take escape-sequence produced whitespace or newlines into account.

Ignoring Errors

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

foo:
    -cat foo
    echo 'Done!'

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

Functions

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

System Information

arch() – Instruction set architecture. Possible values are: "aarch64", "arm", "asmjs", "hexagon", "mips", "msp430", "powerpc", "powerpc64", "s390x", "sparc", "wasm32", "x86", "x86_64", and "xcore".
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

Environment Variables

env_var(key) – Retrieves the environment variable with name key, aborting if it is not present.
env_var_or_default(key, default) – Retrieves the environment variable with name key, returning default if it is not present.

Invocation Directory

invocation_directory() - Retrieves the path of the current working directory, before just changed it (chdir’d) prior to executing commands.

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

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

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

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

Justfile and Justfile Directory

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

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

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

Just Executable

just_executable() - Absolute path to the just executable.

For example:

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

$ just
The executable is at: /bin/just

String Manipulation

uppercase(s) - Convert s to uppercase.
lowercase(s) - Convert s to lowercase.
trim(s) - Remove leading and trailing whitespace from s.
replace(s, from, to) - Replace all occurrences of from in s to to.

Dotenv Integration

just will load environment variables from a file named .env. This file can be located in the same directory as your justfile or in a parent directory. These variables are environment variables, not just variables, and so must be accessed using $VARIABLE_NAME in recipes and backticks.

For example, if your .env file contains:

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

And your justfile contains:

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

Path Manipulation

Fallible

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

join(a, b) - Join path a with path b. join("foo/bar", "baz") is foo/bar/baz.
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.

Command Evaluation Using Backticks

Backticks can be used to store the result of commands:

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

serve:
    ./serve {{localhost}} 8080

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

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

See the Strings section for details on unindenting.

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

Conditional Expressions

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

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

bar:
  @echo "{{foo}}"

$ just bar
Good!

It is also possible to test for inequality:

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

bar:
  @echo {{foo}}

$ just bar
xyz

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

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

Conditionals can be used inside of recipes:

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

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

Multiple conditionals can be chained:

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

bar:
  @echo {{foo}}

$ just bar
abc

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

Environment Variables

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

export RUST_BACKTRACE := "1"

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

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

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

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

export FOO := "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

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

Parameters may have default values:

default := 'all'

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

Parameters with default values may be omitted:

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

Or supplied:

$ just test server unit
Testing server:unit...
./test --tests unit server

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

arch := "wasm"

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

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

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

Variadic parameters prefixed with + accept one or more arguments and expand to a string containing those arguments separated by spaces:

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

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

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

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

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

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

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

And you type:

$ just search "cat toupee"

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

You can fix this by adding quotes:

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

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

foo $bar:
  echo $bar

Running Recipes at the End of a Recipe

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

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

a:
  echo 'A!'

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

c:
  echo 'C!'

d:
  echo 'D!'

…running 'b' prints:

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

Running Recipes in the Middle of a Recipe

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

a:
  echo 'A!'

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

c:
  echo 'C!'

…running 'b' prints:

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

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

Writing Recipes in Other Languages

Recipes that start with a #! are executed as scripts, so you can write recipes in other languages:

polyglot: python js perl sh ruby

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!"

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!
Hello from ruby!

Safer Bash Shebang Recipes

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

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

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

set -e makes bash exit if a command fails.
set -u makes bash exit if a variable is undefined.
set -x makes bash print each script line before it’s run.
set -o pipefail makes bash exit if a command in a pipeline fails.

Together, these avoid a lot of shell scripting gotchas.

Shebang Recipe Execution on Windows

On Windows, shebang interpreter paths containing a / are translated from Unix-style paths to Windows-style paths using cygpath, a utility that ships with Cygwin.

For example, to execute this recipe on Windows:

echo:
  #!/bin/sh

  echo "Hello!"

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

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

Setting Variables in a Recipe

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

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

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

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

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

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

Changing the Working Directory in a Recipe

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

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

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

foo:
  cd bar && pwd

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

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

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
        do ping -c 1 server
    done

Command Line Options

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

$ 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

Run just --help to see all the options.

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

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

Quiet Recipes

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

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

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

$ j quiet
hello
goodbye
# all done!

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                                                                                    ~/src/just
#!/usr/bin/env bash
echo 'Bar!'
Bar!

Selecting Recipes to Run With an Interactive Chooser

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

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

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

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

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

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

default:
  @just --choose

Invoking Justfiles in Other Directories

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

The argument is split at the last /.
The part before the last / is treated as a directory. just will start its search for the justfile there, instead of in the current directory.
The part after the last slash is treated as a normal argument, or ignored if it is empty.

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

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

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

Hiding Justfiles

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

Just Scripts

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

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

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

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

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

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

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

default:
  echo foo

Changelog

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

Miscellanea

Companion Tools

Tools that pair nicely with just include:

watchexec — a simple tool that watches a path and runs a command whenever it detects modifications.

Shell Alias

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

Shell Completion Scripts

Shell completion scripts for Bash, Zsh, Fish, PowerShell, and Elvish are available in the completions directory. Please refer to your shell’s documentation for how to install them.

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

$ just --completions zsh > just.zsh

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 extras/just.sh.

Non-Project Specific Justfile

If you want some commands to be available everywhere, put them in ~/.global.justfile and add the following to your shell’s initialization file:

alias .j='just --justfile ~/.global.justfile --working-directory ~'

Or, if you’d rather they run in the current directory:

alias .j='just --justfile ~/.global.justfile --working-directory .'

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

¯\_(ツ)_/¯

Contributing

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

Janus

Janus is a tool that collects and analyzes justfiles, and can determine if a new version of just breaks or changes the interpretation of existing justfiles.

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.

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, 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!

😸

License

psibi/just

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