just

just is a handy way to save and run commands.

Commands are stored in a file called justfile or 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}}

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 send me an email. Feature requests and bug reports are also always welcome!

getting started

just should run on any system with a reasonable sh and can be installed with cargo, the rust language package manager:

1. Install rust and cargo by following the instructions at rustup.rs
2. Run cargo install just
3. Add ~/.cargo/bin to your PATH

Optionally, you can also alias j=just for lighting fast command running.

How do I just?

Once just is working, create a file called justfile in the root of your project and start adding recipes to it.

Recipes look like this:

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

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

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

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

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

One or more arguments specify the recipes to run:

$ just another-recipe
Another recipe.

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

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!

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!

Assignment, strings, concatination, and substitution with {{...}} 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}}

{{...}} 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}}'

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!
"

Recipes may have parameters. Here recipe build has a parameter called target:

build target:
    @echo 'Building {{target}}...'
    cd {{target}} && make

Recipes with parameters have limitations. Other recipes may not depend on them, and only one recipe with parameters may be given on the command line.

To pass arguments, put them after the recipe name:

$ just build my-awesome-project
Building my-awesome-project...
cd my-awesome-project && make

Parameters may have default values:

test target tests='all':
    @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

Variables can be exported to recipes as environment variables:

export RUST_BACKTRACE = "1"

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

Variables can also be overridden from the command line:

os = "linux"

test: build
    ./test --test {{os}}

build:
    ./build {{os}}

$ just
./build linux
./test --test linux

You can pass any number of arguments of the form NAME=VALUE 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

Backticks can be used to store the result of commands:

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

serve:
    ./serve {{localhost}} 8080

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!

just also 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.

miscellanea

syntax hilighting

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

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

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

justfile grammar

A description of the grammar of justfiles can be found in GRAMMAR.md.

just.sh

Before just was a bloated rust program it was a tiny shell script that called make. If you can't or would rather not install rust you can find the old version in extras/just.sh.

non-project specific justfile

If you want some commands to be available everwhere, 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 .'

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 contributers, 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!

😸