just
is a handy way to save and run project-specific commands.
(éĺŽćšä¸ćć楣,čżé,忍çčżćĽ!)
Commands, called recipes, 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 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 Makeâs complexity and idiosyncrasies. No need for
.PHONY
recipes! -
Linux, MacOS, and Windows are supported with no additional dependencies. (Although if your system doesnât have an
sh
, youâll 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 theJustfile
. -
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
- Quick Start
- Examples
- Features
- Listing Available Recipes
- Aliases
- Settings
- Documentation Comments
- Variables and Substitution
- Strings
- Ignoring Errors
- Functions
- Command Evaluation Using Backticks
- Setting Variables from the Command Line
- Environment Variables
- Recipe Parameters
- Running recipes at the end of a recipe
- Writing Recipes in Other Languages
- Multi-line Constructs
- Command Line Options
- Private Recipes
- Quiet Recipes
- Selecting Recipes to Run With an Interactive Chooser
- Invoking Justfiles in Other Directories
- Just Scripts
- Miscellanea
- Contributing
- Frequently Asked Questions
- Further Ramblings
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 youâd 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
âŚor Powershell:
# use Powershell instead of sh:
set shell := ["powershell.exe", "-c"]
hello:
Write-Host "Hello, world!"
Operating System | Package Manager | Package | Command |
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just AUR |
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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 youâd like to put just
:
curl --proto '=https' --tlsv1.2 -sSf https://just.systems/install.sh | bash -s -- --to DEST
See Installation for how to install just
on your computer. Try running just --version
to make sure that itâs 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 theyâre 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!
A variety of example justfiles can be found in the examples directory.
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 youâd like just
to default to listing the recipes in the justfile, you can
use this as your default recipe:
default:
@just --list
Aliases allow recipes to be invoked with alternative names:
alias b := build
build:
echo 'Building!'
$ just b
build
echo 'Building!'
Building!
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
Name | Value | Description |
---|---|---|
|
|
Set the command used to invoke recipes and evaluate backticks. |
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}}")
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, strings, concatenation, and substitution using {{âŚâ}}
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}}
To write a recipe containing {{
, use {{ "{{" }}
:
braces:
echo 'I {{ "{{" }}LOVE}} curly braces!'
(An unmatched }}
is ignored, so it doesnât need to be escaped.)
Another option is to put all the text youâd like to escape inside of an interpolation:
braces:
echo '{{'I {{LOVE}} curly braces!'}}'
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!
"
Normally, if a command returns a nonzero 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!
Just provides a few built-in functions that might be useful when writing recipes.
-
arch()
â Instruction set architecture. Possible values are:"aarch64"
,"arm"
,"asmjs"
,"hexagon"
,"mips"
,"msp430"
,"powerpc"
,"powerpc64"
,"s390x"
,"sparc"
,"wasm32"
,"x86"
,"x86_64"
, and"xcore"
. -
os()
â Operating system. Possible values are:"android"
,"bitrig"
,"dragonfly"
,"emscripten"
,"freebsd"
,"haiku"
,"ios"
,"linux"
,"macos"
,"netbsd"
,"openbsd"
,"solaris"
, and"windows"
. -
os_family()
â 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
-
env_var(key)
â Retrieves the environment variable with namekey
, aborting if it is not present. -
env_var_or_default(key, default)
â Retrieves the environment variable with namekey
, returningdefault
if it is not present.
-
invocation_directory()
- Retrieves the path of the current working directory, beforejust
changed it (chdirâd) prior to executing commands.
For example, to call rustfmt
on files just under the "current directory" (from the user/invokerâs 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
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
Backticks can be used to store the result of commands:
localhost := `dumpinterfaces | cut -d: -f2 | sed 's/\/.*//' | sed 's/ //g'`
serve:
./serve {{localhost}} 8080
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
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
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}}
{{âŚâ}}
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}}'
Dependencies of a recipes always run before a recipe starts. That is to say, the dependee always runs before the depender.
You can call Just recursively to run a recipe after a recipe ends. Given the following justfile:
a:
echo 'A!'
b: a
echo 'B!'
just c
c:
echo 'C!'
âŚrunning 'b' prints:
$ just b
echo 'A!'
A!
echo 'B!'
B!
echo 'C!'
C!
This has some 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.
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!
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 use a Windows style path to the interpreter.
Recipes without an initial shebang are evaluated and run line-by-line, which means that multi-line constructs probably wonât 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.
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:
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
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.
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.
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!
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 currenly 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 isnât, 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 youâd like just
to default to selecting recipes with a chooser, you can
use this as your default recipe:
default:
@just --choose
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 itâs 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/
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 youâd rather leave the working directory unchanged, use #!/usr/bin/env just --working-directory . --justfile
.
Tools that pair nicely with just
include:
-
watchexec
â a simple tool that watches a path and runs a command whenever it detects modifications.
For lightning-fast command running, put alias j=just
in your shellâs configuration file.
Shell completion scripts for Bash, Zsh, Fish, PowerShell, and Elvish are available in the completions directory. Please refer to your shellâs 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
justfile
syntax is close enough to make
that you may want to tell your editor to use make syntax highlighting 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
Include the following in a justfile
to enable syntax highlighting in vim and emacs:
# Local Variables:
# mode: makefile
# End:
# vim: set ft=make :
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
A non-normative grammar of justfiles can be found in GRAMMAR.md.
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.
If you want some commands to be available everywhere, put them in ~/.justfile
and add the following to your shellâs initialization file:
alias .j='just --justfile ~/.justfile --working-directory ~'
Or, if youâd rather they run in the current directory:
alias .j='just --justfile ~/.justfile --working-directory .'
Iâm pretty sure that nobody actually uses this feature, but itâs there.
ÂŻ\_(ă)_/ÂŻ
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 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. Donât worry about running Janus yourself, Casey will happily run it for you on changes that need it.
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 wonât 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 doesnât 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 Makeâs 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 Makeâs 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.
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.
I personally find it very useful to write a justfile
for almost every project, big or small.
On a big project with multiple contributors, itâs 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, itâs likely that youâll come up with other useful things which are part of the projectâs collective wisdom, but which arenât written down anywhere, like the arcane commands needed for some part of your revision control workflow, install all your projectâs 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 itâs nice to be able to remember commands by name instead of ^Reverse searching your shell history, and itâs 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 projectâs justfile
, or some of the justfile
âs out in the wild.
Anyways, I think thatâs 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!
đ¸