`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 are stored in a file called justfile with syntax inspired by make:

build:
    cc *.c -o main

# test everything
test-all: build
    ./test --all

# run a specific test
test TEST: build
    ./test --test {{TEST}}

You can then run them with just COMMAND:

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

just produces detailed error messages and avoids make’s idiosyncrasies, so debugging a justfile is easier and less surprising than debugging a makefile.

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

Manual

Installation
Quick Start
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, and Cygwin.

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

Like cmd.exe:

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

list:
  dir

…or Powershell:

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

hello:
  Write-Host "Hello, world!"

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	Yay	just ^AUR	`yay -S just`
NixOS, Linux, macOS	Nix	just	`nix-env -iA nixos.just`
Void Linux	XBPS	just	`xbps-install -S just`
Solus	eopkg	just	`eopkg install just`

Pre-built Binaries

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

You can use the following command to download the latest binary for MacOS or Windows, just replace DESTINATION_DIRECTORY with the directory where you’d like to put just:

curl -LSfs https://japaric.github.io/trust/install.sh | \
  sh -s -- --git casey/just --to DESTINATION_DIRECTORY

On Linux, use:

curl -LSfs https://japaric.github.io/trust/install.sh | \
  sh -s -- --git casey/just --target x86_64-unknown-linux-musl --to DESTINATION_DIRECTORY

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.

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!

Features

Listing Available Recipes

Recipes can be listed with just --list :

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

just --summary is more concise:

$ just --summary
build test deploy lint

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
`shell`	`[COMMAND, ARGS…]`	Set the command used to invoke recipes and evaluate backticks.

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}}")

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!'}}'

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           := "\\"

$ just --evaluate
"tring-with-carriage-return := "
string-with-double-quote    := """
string-with-newline         := "
"
string-with-slash           := "\"
string-with-tab             := "     "

Single-quoted strings do not recognize escape sequences and may contain line breaks:

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

line-breaks := 'hello
this
is
  a
     raw
string!
'

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

line-breaks := "hello
this
is
  a
     raw
string!
"

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

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

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

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

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 a + before the argument name:

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

Variadic parameters 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

A variadic parameter with a default argument will accept zero or more arguments:

commit MESSAGE +FLAGS='':
  git commit {{FLAGS}} -m "{{MESSAGE}}"

{{…}} substitutions may need to be quoted if they contains 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}}'

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!

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!

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/

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.

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

Syntax Highlighting

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

Vim

For vim, 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

Vim and Emacs

Include the following in a justfile to enable syntax highlighting in vim and emacs:

# Local Variables:
# mode: makefile
# End:
# vim: set ft=make :

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.

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.

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 ~/.justfile and add the following to your shell’s initialization file:

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

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

alias .j='just --justfile ~/.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 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!

😸

BojanKogoj/just

just

Manual

Installation

Prerequisites

Packages

Pre-built Binaries

Quick Start

Features

Listing Available Recipes

Aliases

Settings

Table of Settings

Shell

Documentation Comments

Variables and Substitution

Escaping {{

Strings

Functions

System Information

Environment Variables

Invocation Directory

Dotenv Integration

Command Evaluation Using Backticks

Setting Variables from the Command Line

Environment Variables

Recipe Parameters

Writing Recipes in Other Languages

Multi-line Constructs

if statements

for loops

while loops

Command Line Options

Private Recipes

Quiet Recipes

Invoking Justfiles in Other Directories

Just Scripts

Miscellanea

Companion Tools

Shell Alias

Shell Completion Scripts

Syntax Highlighting

Vim

Vim and Emacs

Visual Studio Code

Kakoune

Other Editors

Grammar

just.sh

Non-Project Specific Justfile

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

`just`

Escaping `{{`

`if` statements

`for` loops

`while` loops