Writing Justfiles

The below readme is pulled from: https://github.com/casey/just/blob/master/README.md

It fully documents the Justfile syntax and system.

just

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

This readme is also available as a book. The book reflects the latest release, whereas the readme on GitHub reflects latest master.

(中文文档在这里, 快看过来!)

Commands, called recipes, are stored in a file called

justfile

with syntax inspired by

make

You can then run them with

just RECIPE

console

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

just

has a ton of useful features, and many improvements over

make

```
just
```
is a command runner, not a build system, so it avoids much of
```
make
```
's complexity and idiosyncrasies
. No need for
```
.PHONY
```
recipes!
Linux, MacOS, Windows, and other reasonable unices 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!

Quick Start

See the installation section for how to install

just

on your computer. Try running

just --version

to make sure that it's installed correctly.

For an overview of the syntax, check out this cheatsheet.

Once

just

is installed and working, create a file named

justfile

in the root of your project with the following contents:

just

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

console

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

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

console

$ just another-recipe
This is another recipe.

just

prints each command to standard error before running it, which is why

echo 'This is a recipe!'

was printed. This is suppressed for lines starting with

, which is why

echo 'This is another recipe.'

was not printed.

Recipes stop running if a command fails. Here

cargo publish

will only run if

cargo test

succeeds:

just

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

just

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

test: build
  ./test

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

console

$ 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:

console

$ 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:

console

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

Recipes may depend on recipes in submodules:

justfile

mod foo

baz: foo::bar

Examples

A variety of

justfile

s can be found in the examples directory and on GitHub.

Features

The Default Recipe

When

just

is invoked without a recipe, it runs the recipe with the

[default]

attribute, or the first recipe in the

justfile

if no recipe has the

[default]

attribute.

This recipe might be the most frequently run command in the project, like running the tests:

just

test:
  cargo test

You can also use dependencies to run multiple recipes by default:

just

default: lint build test

build:
  echo Building…

test:
  echo Testing…

lint:
  echo Linting…

If no recipe makes sense as the default recipe, you can add a recipe to the beginning of your

justfile

that lists the available recipes:

just

default:
  just --list

Listing Available Recipes

Recipes can be listed in alphabetical order with

just --list

console

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

Recipes in submodules can be listed with

just --list PATH

, where

PATH

is a space- or

::

-separated module path:

$ cat justfile
mod foo
$ cat foo.just
mod bar
$ cat bar.just
baz:
$ just --list foo bar
Available recipes:
    baz
$ just --list foo::bar
Available recipes:
    baz

just --summary

is more concise:

console

$ just --summary
build test deploy lint

Pass

--unsorted

to print recipes in the order they appear in the

justfile

just

test:
  echo 'Testing!'

build:
  echo 'Building!'

console

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

console

$ 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:

just

default:
  @just --list

Note that you may need to add

--justfile {{justfile()}}

to the line above. Without it, if you executed

just -f /some/distant/justfile -d .

just -f ./non-standard-justfile

, the plain

just --list

inside the recipe would not necessarily use the file you provided. It would try to find a justfile in your current path, maybe even resulting in a

No justfile found

error.

The heading text can be customized with

--list-heading

console

$ just --list --list-heading $'Cool stuff…\n'
Cool stuff…
    test
    build

And the indentation can be customized with

--list-prefix

console

$ 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:

console

$ just --list --list-heading ''
    test
    build

Invoking Multiple Recipes

Multiple recipes may be invoked on the command line at once:

just

build:
  make web

serve:
  python3 -m http.server -d out 8000

console

$ just build serve
make web
python3 -m http.server -d out 8000

Keep in mind that recipes with parameters will swallow arguments, even if they match the names of other recipes:

just

build project:
  make {{project}}

serve:
  python3 -m http.server -d out 8000

console

$ just build serve
make: *** No rule to make target `serve'.  Stop.

The

--one

flag can be used to restrict command-line invocations to a single recipe:

console

$ just --one build serve
error: Expected 1 command-line recipe invocation but found 2.

Working Directory

By default, recipes run with the working directory set to the directory that contains the

justfile

The

[no-cd]

attribute can be used to make recipes run with the working directory set to directory in which

just

was invoked.

just

@foo:
  pwd

[no-cd]
@bar:
  pwd

console

$ cd subdir
$ just foo
/
$ just bar
/subdir

You can override the working directory for all recipes with

set working-directory := '…'

just

set working-directory := 'bar'

@foo:
  pwd

console

$ pwd
/home/bob
$ just foo
/home/bob/bar

You can override the working directory for a specific recipe with the

working-directory

attribute1.38.0:

just

[working-directory: 'bar']
@foo:
  pwd

console

$ pwd
/home/bob
$ just foo
/home/bob/bar

The argument to the

working-directory

setting or

working-directory

attribute may be absolute or relative. If it is relative it is interpreted relative to the default working directory.

Aliases

Aliases allow recipes to be invoked on the command line with alternative names:

just

alias b := build

build:
  echo 'Building!'

console

$ just b
echo 'Building!'
Building!

The target of an alias may be a recipe in a submodule:

justfile

mod foo

alias baz := foo::bar

Settings

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

justfile

For example:

just

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

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

Table of Settings

Name	Value	Default	Description
`allow-duplicate-recipes`	boolean	`false`	Allow recipes appearing later in a `justfile` to override earlier recipes with the same name.
`allow-duplicate-variables`	boolean	`false`	Allow variables appearing later in a `justfile` to override earlier variables with the same name.
`dotenv-filename`	string	-	Load a `.env` file with a custom name, if present.
`dotenv-load`	boolean	`false`	Load a `.env` file, if present.
`dotenv-override`	boolean	`false`	Override existing environment variables with values from the `.env` file.
`dotenv-path`	string	-	Load a `.env` file from a custom path and error if not present. Overrides `dotenv-filename` .
`dotenv-required`	boolean	`false`	Error if a `.env` file isn't found.
`export`	boolean	`false`	Export all variables as environment variables.
`fallback`	boolean	`false`	Search `justfile` in parent directory if the first recipe on the command line is not found.
`ignore-comments`	boolean	`false`	Ignore recipe lines beginning with `#` .
`positional-arguments`	boolean	`false`	Pass positional arguments.
`quiet`	boolean	`false`	Disable echoing recipe lines before executing.
`script-interpreter` <sup>1.33.0</sup>	`[COMMAND, ARGS…]`	`['sh', '-eu']`	Set command used to invoke recipes with empty `[script]` attribute.
`shell`	`[COMMAND, ARGS…]`	-	Set command used to invoke recipes and evaluate backticks.
`tempdir`	string	-	Create temporary directories in `tempdir` instead of the system default temporary directory.
`unstable` <sup>1.31.0</sup>	boolean	`false`	Enable unstable features.
`windows-powershell`	boolean	`false`	Use PowerShell on Windows as default shell. (Deprecated. Use `windows-shell` instead.
`windows-shell`	`[COMMAND, ARGS…]`	-	Set the command used to invoke recipes and evaluate backticks.
`working-directory` <sup>1.33.0</sup>	string	-	Set the working directory for recipes and backticks, relative to the default working directory.

Boolean settings can be written as:

justfile

set NAME

Which is equivalent to:

justfile

set NAME := true

Non-boolean settings can be set to both strings and expressions.1.46.0

However, because settings affect the behavior of backticks and many functions, those expressions may not contain backticks or function calls, directly or transitively via reference.

Allow Duplicate Recipes

allow-duplicate-recipes

is set to

true

, defining multiple recipes with the same name is not an error and the last definition is used. Defaults to

false

just

set allow-duplicate-recipes

@foo:
  echo foo

@foo:
  echo bar

console

$ just foo
bar

Allow Duplicate Variables

allow-duplicate-variables

is set to

true

, defining multiple variables with the same name is not an error and the last definition is used. Defaults to

false

just

set allow-duplicate-variables

a := "foo"
a := "bar"

@foo:
  echo {{a}}

console

$ just foo
bar

Dotenv Settings

If any of

dotenv-load

dotenv-filename

dotenv-override

dotenv-path

, or

dotenv-required

are set,

just

will try to load environment variables from a file.

dotenv-path

is set,

just

will look for a file at the given path, which may be absolute, or relative to the working directory.

The command-line option

--dotenv-path

, short form

-E

, can be used to set or override

dotenv-path

at runtime.

dotenv-filename

is set

just

will look for a file at the given path, relative to the working directory and each of its ancestors.

dotenv-filename

is not set, but

dotenv-load

dotenv-required

are set, just will look for a file named

.env

, relative to the working directory and each of its ancestors.

dotenv-filename

and

dotenv-path

are similar, but

dotenv-path

is only checked relative to the working directory, whereas

dotenv-filename

is checked relative to the working directory and each of its ancestors.

It is not an error if an environment file is not found, unless

dotenv-required

is set.

The loaded variables are environment variables, not

just

variables, and so must be accessed using

$VARIABLE_NAME

in recipes and backticks.

dotenv-override

is set, variables from the environment file will override existing environment variables.

For example, if your

.env

file contains:

console

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

And your

justfile

contains:

just

set dotenv-load

serve:
  @echo "Starting server with database $DATABASE_ADDRESS on port $SERVER_PORT…"
  ./server --database $DATABASE_ADDRESS --port $SERVER_PORT

just serve

will output:

console

$ just serve
Starting server with database localhost:6379 on port 1337…
./server --database $DATABASE_ADDRESS --port $SERVER_PORT

Export

The

export

setting causes all

just

variables to be exported as environment variables. Defaults to

false

just

set export

a := "hello"

@foo b:
  echo $a
  echo $b

console

$ just foo goodbye
hello
goodbye

Positional Arguments

positional-arguments

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:

just

set positional-arguments

@foo bar:
  echo $0
  echo $1

Will produce the following output:

console

$ just foo hello
foo
hello

When using an

sh

-compatible shell, such as

bash

zsh

$@

expands to the positional arguments given to the recipe, starting from one. When used within double quotes as

"$@"

, arguments including whitespace will be passed on as if they were double-quoted. That is,

"$@"

is equivalent to

"$1" "$2"

… When there are no positional parameters,

"$@"

and

$@

expand to nothing (i.e., they are removed).

This example recipe will print arguments one by one on separate lines:

just

set positional-arguments

@test *args='':
  bash -c 'while (( "$#" )); do echo - $1; shift; done' -- "$@"

Running it with two arguments:

console

$ just test foo "bar baz"
- foo
- bar baz

Positional arguments may also be turned on on a per-recipe basis with the

[positional-arguments]

attribute1.29.0:

just

[positional-arguments]
@foo bar:
  echo $0
  echo $1

Note that PowerShell does not handle positional arguments in the same way as other shells, so turning on positional arguments will likely break recipes that use PowerShell.

If using PowerShell 7.4 or better, the

-CommandWithArgs

flag will make positional arguments work as expected:

just

set shell := ['pwsh.exe', '-CommandWithArgs']
set positional-arguments

print-args a b c:
  Write-Output @($args[1..($args.Count - 1)])

Shell

The

shell

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

sh -cu

just

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

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

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

just

passes the command to be executed as an argument. Many shells will need an additional flag, often

-c

, to make them evaluate the first argument.

Windows Shell

just

uses

sh

on Windows by default. To use a different shell on Windows, use

windows-shell

just

set windows-shell := ["powershell.exe", "-NoLogo", "-Command"]

hello:
  Write-Host "Hello, world!"

See powershell.just for a justfile that uses PowerShell on all platforms.

Windows PowerShell

set windows-powershell
uses the legacy
powershell.exe
binary, and is no longer recommended. See the
windows-shell
setting above for a more flexible way to control which shell is used on Windows.

just

uses

sh

on Windows by default. To use

powershell.exe

instead, set

windows-powershell

to true.

just

set windows-powershell := true

hello:
  Write-Host "Hello, world!"

Python 3

just

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

Bash

just

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

Z Shell

just

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

Fish

just

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

Nushell

just

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

If you want to change the default table mode to

light

just

set shell := ['nu', '-m', 'light', '-c']

Nushell was written in Rust, and has cross-platform support for Windows / macOS and Linux.

Documentation Comments

Comments immediately preceding a recipe will appear in

just --list

just

# build stuff
build:
  ./bin/build

# test stuff
test:
  ./bin/test

console

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

The

[doc]

attribute can be used to set or suppress a recipe's doc comment:

just

# This comment won't appear
[doc('Build stuff')]
build:
  ./bin/build

# This one won't either
[doc]
test:
  ./bin/test

console

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

Expressions and Substitutions

Various operators and function calls are supported in expressions, which may be used in assignments, default recipe arguments, and inside recipe body

{{…}}

substitutions.

just

tmpdir  := `mktemp -d`
version := "0.2.7"
tardir  := tmpdir / "awesomesauce-" + version
tarball := tardir + ".tar.gz"
config  := quote(config_dir() / ".project-config")

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

Concatenation

The

operator returns the left-hand argument concatenated with the right-hand argument:

just

foobar := 'foo' + 'bar'

Logical Operators

The logical operators

&&

and

||

can be used to coalesce string values1.37.0, similar to Python's

and

and

or

. These operators consider the empty string

''

to be false, and all other strings to be true.

These operators are currently unstable.

The

&&

operator returns the empty string if the left-hand argument is the empty string, otherwise it returns the right-hand argument:

justfile

foo := '' && 'goodbye'      # ''
bar := 'hello' && 'goodbye' # 'goodbye'

The

||

operator returns the left-hand argument if it is non-empty, otherwise it returns the right-hand argument:

justfile

foo := '' || 'goodbye'      # 'goodbye'
bar := 'hello' || 'goodbye' # 'hello'

Joining Paths

The

operator can be used to join two strings with a slash:

just

foo := "a" / "b"

$ just --evaluate foo
a/b

Note that a

is added even if one is already present:

just

foo := "a/"
bar := foo / "b"

$ just --evaluate bar
a//b

Absolute paths can also be constructed1.5.0:

just

foo := / "b"

$ just --evaluate foo
/b

The

operator uses the

character, even on Windows. Thus, using the

operator should be avoided with paths that use universal naming convention (UNC), i.e., those that start with

\?

, since forward slashes are not supported with UNC paths.

Escaping

{{

To write a recipe containing

{{

, use

{{{{

just

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:

just

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

Yet another option is to use

{{ "{{" }}

just

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

Strings

'single'

"double"

, and

'''triple'''

quoted string literals are supported. Unlike in recipe bodies,

{{…}}

interpolations are not supported inside strings.

Double-quoted strings support escape sequences:

just

carriage-return   := "\r"
double-quote      := "\""
newline           := "\n"
no-newline        := "\
"
slash             := "\\"
tab               := "\t"
unicode-codepoint := "\u{1F916}"

console

$ just --evaluate
"arriage-return   := "
double-quote      := """
newline           := "
"
no-newline        := ""
slash             := "\"
tab               := "     "
unicode-codepoint := "🤖"

The unicode character escape sequence

\u{…}

1.36.0 accepts up to six hex digits.

Strings may contain line breaks:

just

single := '
hello
'

double := "
goodbye
"

Single-quoted strings do not recognize escape sequences:

just

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

console

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

Indented versions of both single- and double-quoted strings, delimited by triple single- or double-quotes, are supported. Indented string lines are stripped of a leading line break, and leading whitespace common to all non-blank lines:

just

# this string will evaluate to `foo\nbar\n`
x := '''
  foo
  bar
'''

# this string will evaluate to `abc\n  wuv\nxyz\n`
y := """
  abc
    wuv
  xyz
"""

Similar to unindented strings, indented double-quoted strings process escape sequences, and indented single-quoted strings ignore escape sequences. Escape sequence processing takes place after unindentation. The unindentation algorithm does not take escape-sequence produced whitespace or newlines into account.

Shell-expanded strings

Strings prefixed with

are shell expanded1.27.0:

justfile

foobar := x'~/$FOO/${BAR}'

Value	Replacement
`$VAR`	value of environment variable `VAR`
`${VAR}`	value of environment variable `VAR`
`${VAR:-DEFAULT}`	value of environment variable `VAR` , or `DEFAULT` if `VAR` is not set
Leading `~`	path to current user's home directory
Leading `~USER`	path to `USER` 's home directory

This expansion is performed at compile time, so variables from

.env

files and exported

just

variables cannot be used. However, this allows shell expanded strings to be used in places like settings and import paths, which cannot depend on

just

variables and

.env

files.

Format strings

Strings prefixed with

are format strings1.44.0:

justfile

name := "world"
message := f'Hello, {{name}}!'

Format strings may contain interpolations delimited with

{{…}}

that contain expressions. Format strings evaluate to the concatenated string fragments and evaluated expressions.

Use

{{{{

to include a literal

{{

in a format string:

justfile

foo := f'I {{{{LOVE} curly braces!'

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

just

foo:
  -cat foo
  echo 'Done!'

console

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

Functions

just

provides many built-in functions for use in expressions, including recipe body

{{…}}

substitutions, assignments, and default parameter values.

All functions ending in

_directory

can be abbreviated to

_dir

. So

home_directory()

can also be written as

home_dir()

. In addition,

invocation_directory_native()

can be abbreviated to

invocation_dir_native()

System Information

arch()

— Instruction set architecture. Possible values are:

"aarch64"

"arm"

"asmjs"

"hexagon"

"mips"

"msp430"

"powerpc"

"powerpc64"

"s390x"

"sparc"

"wasm32"

"x86"

"x86_64"

, and

"xcore"

```
num_cpus()
```
1.15.0 - Number of logical CPUs.

os()

— Operating system. Possible values are:

"android"

"bitrig"

"dragonfly"

"emscripten"

"freebsd"

"haiku"

"ios"

"linux"

"macos"

"netbsd"

"openbsd"

"solaris"

, and

"windows"

```
os_family()
```
— Operating system family; possible values are:
```
"unix"
```
and
```
"windows"
```
.

For example:

just

system-info:
  @echo "This is an {{arch()}} machine".

console

$ just system-info
This is an x86_64 machine

The

os_family()

function can be used to create cross-platform

justfile

s that work on various operating systems. For an example, see cross-platform.just file.

External Commands

```
shell(command, args...)
```
1.27.0 returns the standard output of shell script
```
command
```
with zero or more positional arguments
```
args
```
. The shell used to interpret
```
command
```
is the same shell that is used to evaluate recipe lines, and can be changed with
```
set shell := […]
```
.
```
command
```
is passed as the first argument, so if the command is
```
'echo $@'
```
, the full command line, with the default shell command
```
sh -cu
```
and
```
args
```
```
'foo'
```
and
```
'bar'
```
will be:
```
'sh' '-cu' 'echo $@' 'echo $@' 'foo' 'bar'
```
This is so that
```
$@
```
works as expected, and
```
$1
```
refers to the first argument.
```
$@
```
does not include the first positional argument, which is expected to be the name of the program being run.

just

# arguments can be variables or expressions
file := '/sys/class/power_supply/BAT0/status'
bat0stat := shell('cat $1', file)

# commands can be variables or expressions
command := 'wc -l'
output := shell(command + ' "$1"', 'main.c')

# arguments referenced by the shell command must be used
empty := shell('echo', 'foo')
full := shell('echo $1', 'foo')
error := shell('echo $1')

just

# Using python as the shell. Since `python -c` sets `sys.argv[0]` to `'-c'`,
# the first "real" positional argument will be `sys.argv[2]`.
set shell := ["python3", "-c"]
olleh := shell('import sys; print(sys.argv[2][::-1])', 'hello')

Environment Variables

```
env(key)
```
1.15.0 — Retrieves the environment variable with name
```
key
```
, aborting if it is not present.

just

home_dir := env('HOME')

test:
  echo "{{home_dir}}"

console

$ just
/home/user1

```
env(key, default)
```
1.15.0 — Retrieves the environment variable with name
```
key
```
, returning
```
default
```
if it is not present.
```
env_var(key)
```
— Deprecated alias for
```
env(key)
```
.

env_var_or_default(key, default)

— Deprecated alias for

env(key, default)

A default can be substituted for an empty environment variable value with the

||

operator, currently unstable:

just

set unstable

foo := env('FOO', '') || 'DEFAULT_VALUE'

Executables

```
require(name)
```
1.39.0 — Search directories in the
```
PATH
```
environment variable for the executable
```
name
```
and return its full path, or halt with an error if no executable with
```
name
```
exists.
just
```
bash := require("bash")

@test:
 echo "bash: '{{bash}}'"
```
console
```
$ just
bash: '/bin/bash'
```
```
which(name)
```
1.39.0 — Search directories in the
```
PATH
```
environment variable for the executable
```
name
```
and return its full path, or the empty string if no executable with
```
name
```
exists. Currently unstable.
just
```
set unstable

bosh := which("bosh")

@test:
 echo "bosh: '{{bosh}}'"
```
console
```
$ just
bosh: ''
```

Invocation Information

```
is_dependency()
```
- Returns the string
```
true
```
if the current recipe is being run as a dependency of another recipe, rather than being run directly, otherwise returns the string
```
false
```
.

Invocation Directory

```
invocation_directory()
```
- Retrieves the absolute path to the current directory when
```
just
```
was invoked, before
```
just
```
changed it (chdir'd) prior to executing commands. On Windows,
```
invocation_directory()
```
uses
```
cygpath
```
to convert the invocation directory to a Cygwin-compatible
```
/
```
-separated path. Use
```
invocation_directory_native()
```
to return the verbatim invocation directory on all platforms.

For example, to call

rustfmt

on files just under the "current directory" (from the user/invoker's perspective), use the following rule:

just

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.):

just

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

```
invocation_directory_native()
```
- Retrieves the absolute path to the current directory when
```
just
```
was invoked, before
```
just
```
changed it (chdir'd) prior to executing commands.

Justfile and Justfile Directory

```
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

just

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

Source and Source Directory

```
source_file()
```
1.27.0 - Retrieves the path of the current source file.
```
source_directory()
```
1.27.0 - Retrieves the path of the parent directory of the current source file.

source_file()

and

source_directory()

behave the same as

justfile()

and

justfile_directory()

in the root

justfile

, but will return the path and directory, respectively, of the current

import

mod

source file when called from within an import or submodule.

Just Executable

```
just_executable()
```
- Absolute path to the
```
just
```
executable.

For example:

just

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

console

$ just
The executable is at: /bin/just

Just Process ID

```
just_pid()
```
- Process ID of the
```
just
```
executable.

For example:

just

pid:
  @echo The process ID is: {{ just_pid() }}

console

$ just
The process ID is: 420

String Manipulation

append(suffix, s)

1.27.0 Append

suffix

to whitespace-separated strings in

append('/src', 'foo bar baz')

→

'foo/src bar/src baz/src'

prepend(prefix, s)

1.27.0 Prepend

prefix

to whitespace-separated strings in

prepend('src/', 'foo bar baz')

→

'src/foo src/bar src/baz'

```
encode_uri_component(s)
```
1.27.0 - Percent-encode characters in
```
s
```
except
```
[A-Za-z0-9_.!~*'()-]
```
, matching the behavior of the
JavaScript
```
encodeURIComponent
```
function
.
```
quote(s)
```
- Replace all single quotes with
```
'\''
```
and prepend and append single quotes to
```
s
```
. This is sufficient to escape special characters for many shells, including most Bourne shell descendants.
```
replace(s, from, to)
```
- Replace all occurrences of
```
from
```
in
```
s
```
to
```
to
```
.
```
replace_regex(s, regex, replacement)
```
- Replace all occurrences of
```
regex
```
in
```
s
```
to
```
replacement
```
. Regular expressions are provided by the
Rust
```
regex
```
crate
. See the syntax documentation for usage examples. Capture groups are supported. The
```
replacement
```
string uses Replacement string syntax.
```
trim(s)
```
- Remove leading and trailing whitespace from
```
s
```
.
```
trim_end(s)
```
- Remove trailing whitespace from
```
s
```
.
```
trim_end_match(s, substring)
```
- Remove suffix of
```
s
```
matching
```
substring
```
.

trim_end_matches(s, substring)

- Repeatedly remove suffixes of

matching

substring

```
trim_start(s)
```
- Remove leading whitespace from
```
s
```
.

trim_start_match(s, substring)

- Remove prefix of

matching

substring

trim_start_matches(s, substring)

- Repeatedly remove prefixes of

matching

substring

Case Conversion

```
capitalize(s)
```
1.7.0 - Convert first character of
```
s
```
to uppercase and the rest to lowercase.
```
kebabcase(s)
```
1.7.0 - Convert
```
s
```
to
```
kebab-case
```
.
```
lowercamelcase(s)
```
1.7.0 - Convert
```
s
```
to
```
lowerCamelCase
```
.
```
lowercase(s)
```
- Convert
```
s
```
to lowercase.
```
shoutykebabcase(s)
```
1.7.0 - Convert
```
s
```
to
```
SHOUTY-KEBAB-CASE
```
.
```
shoutysnakecase(s)
```
1.7.0 - Convert
```
s
```
to
```
SHOUTY_SNAKE_CASE
```
.
```
snakecase(s)
```
1.7.0 - Convert
```
s
```
to
```
snake_case
```
.
```
titlecase(s)
```
1.7.0 - Convert
```
s
```
to
```
Title Case
```
.
```
uppercamelcase(s)
```
1.7.0 - Convert
```
s
```
to
```
UpperCamelCase
```
.
```
uppercase(s)
```
- Convert
```
s
```
to uppercase.

Path Manipulation

Fallible

```
absolute_path(path)
```
- Absolute path to relative
```
path
```
in the working directory.
```
absolute_path("./bar.txt")
```
in directory
```
/foo
```
is
```
/foo/bar.txt
```
.
```
canonicalize(path)
```
1.24.0 - Canonicalize
```
path
```
by resolving symlinks and removing
```
.
```
,
```
..
```
, and extra
```
/
```
s where possible.

extension(path)

- Extension of

path

extension("/foo/bar.txt")

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")

bar

parent_directory(path)

- Parent directory of

path

parent_directory("/foo/bar.txt")

/foo

without_extension(path)

path

without extension.

without_extension("/foo/bar.txt")

/foo/bar

These functions can fail, for example if a path does not have an extension, which will halt execution.

Infallible

```
clean(path)
```
- Simplify
```
path
```
by removing extra path separators, intermediate
```
.
```
components, and
```
..
```
where possible.
```
clean("foo//bar")
```
is
```
foo/bar
```
,
```
clean("foo/..")
```
is
```
.
```
,
```
clean("foo/./bar")
```
is
```
foo/bar
```
.
```
join(a, b…)
```
- This function uses
/
on Unix and
\
on Windows, which can be lead to unwanted behavior. The
/
operator, e.g.,
a / b
, which always uses
/
, should be considered as a replacement unless
\
s are specifically desired on Windows. Join path
```
a
```
with path
```
b
```
.
```
join("foo/bar", "baz")
```
is
```
foo/bar/baz
```
. Accepts two or more arguments.

Filesystem Access

```
path_exists(path)
```
- Returns
```
true
```
if the path points at an existing entity and
```
false
```
otherwise. Traverses symbolic links, and returns
```
false
```
if the path is inaccessible or points to a broken symlink.
```
read(path)
```
1.39.0 - Returns the content of file at
```
path
```
as string.

Error Reporting

```
error(message)
```
- Abort execution and report error
```
message
```
to user.

UUID and Hash Generation

```
blake3(string)
```
1.25.0 - Return BLAKE3 hash of
```
string
```
as hexadecimal string.
```
blake3_file(path)
```
1.25.0 - Return BLAKE3 hash of file at
```
path
```
as hexadecimal string.
```
sha256(string)
```
- Return the SHA-256 hash of
```
string
```
as hexadecimal string.
```
sha256_file(path)
```
- Return SHA-256 hash of file at
```
path
```
as hexadecimal string.
```
uuid()
```
- Generate a random version 4 UUID.

Random

```
choose(n, alphabet)
```
1.27.0 - Generate a string of
```
n
```
randomly selected characters from
```
alphabet
```
, which may not contain repeated characters. For example,
```
choose('64', HEX)
```
will generate a random 64-character lowercase hex string.

Datetime

```
datetime(format)
```
1.30.0 - Return local time with
```
format
```
.
```
datetime_utc(format)
```
1.30.0 - Return UTC time with
```
format
```
.

The arguments to

datetime

and

datetime_utc

are

strftime

-style format strings, see the

chrono

library docs for details.

Semantic Versions

```
semver_matches(version, requirement)
```
1.16.0 - Check whether a
semantic
```
version
```
, e.g.,
```
"0.1.0"
```
matches a
```
requirement
```
, e.g.,
```
">=0.1.0"
```
, returning
```
"true"
```
if so and
```
"false"
```
otherwise.

Style

```
style(name)
```
1.37.0 - Return a named terminal display attribute escape sequence used by
```
just
```
. Unlike terminal display attribute escape sequence constants, which contain standard colors and styles,
```
style(name)
```
returns an escape sequence used by
```
just
```
itself, and can be used to make recipe output match
```
just
```
's own output.
Recognized values for
```
name
```
are
```
'command'
```
, for echoed recipe lines,
```
error
```
, and
```
warning
```
.
For example, to style an error message:
just
```
scary:
 @echo '{{ style("error") }}OH NO{{ NORMAL }}'
```

User Directories1.23.0

These functions return paths to user-specific directories for things like configuration, data, caches, executables, and the user's home directory.

On Unix, these functions follow the XDG Base Directory Specification.

On MacOS and Windows, these functions return the system-specified user-specific directories. For example,

cache_directory()

returns

~/Library/Caches

on MacOS and

{FOLDERID_LocalAppData}

on Windows.

See the

dirs

crate for more details.

```
cache_directory()
```
- The user-specific cache directory.
```
config_directory()
```
- The user-specific configuration directory.
```
config_local_directory()
```
- The local user-specific configuration directory.
```
data_directory()
```
- The user-specific data directory.
```
data_local_directory()
```
- The local user-specific data directory.
```
executable_directory()
```
- The user-specific executable directory.
```
home_directory()
```
- The user's home directory.

If you would like to use XDG base directories on all platforms you can use the

env(…)

function with the appropriate environment variable and fallback, although note that the XDG specification requires ignoring non-absolute paths, so for full compatibility with spec-compliant applications, you would need to do:

just

xdg_config_dir := if env('XDG_CONFIG_HOME', '') =~ '^/' {
  env('XDG_CONFIG_HOME')
} else {
  home_directory() / '.config'
}

Constants

A number of constants are predefined:

Name	Value	Value on Windows
`HEX` <sup>1.27.0</sup>	`"0123456789abcdef"`
`HEXLOWER` <sup>1.27.0</sup>	`"0123456789abcdef"`
`HEXUPPER` <sup>1.27.0</sup>	`"0123456789ABCDEF"`
`PATH_SEP` <sup>1.41.0</sup>	`"/"`	`"\"`
`PATH_VAR_SEP` <sup>1.41.0</sup>	`":"`	`";"`
`CLEAR` <sup>1.37.0</sup>	`"\ec"`
`NORMAL` <sup>1.37.0</sup>	`"\e[0m"`
`BOLD` <sup>1.37.0</sup>	`"\e[1m"`
`ITALIC` <sup>1.37.0</sup>	`"\e[3m"`
`UNDERLINE` <sup>1.37.0</sup>	`"\e[4m"`
`INVERT` <sup>1.37.0</sup>	`"\e[7m"`
`HIDE` <sup>1.37.0</sup>	`"\e[8m"`
`STRIKETHROUGH` <sup>1.37.0</sup>	`"\e[9m"`
`BLACK` <sup>1.37.0</sup>	`"\e[30m"`
`RED` <sup>1.37.0</sup>	`"\e[31m"`
`GREEN` <sup>1.37.0</sup>	`"\e[32m"`
`YELLOW` <sup>1.37.0</sup>	`"\e[33m"`
`BLUE` <sup>1.37.0</sup>	`"\e[34m"`
`MAGENTA` <sup>1.37.0</sup>	`"\e[35m"`
`CYAN` <sup>1.37.0</sup>	`"\e[36m"`
`WHITE` <sup>1.37.0</sup>	`"\e[37m"`
`BG_BLACK` <sup>1.37.0</sup>	`"\e[40m"`
`BG_RED` <sup>1.37.0</sup>	`"\e[41m"`
`BG_GREEN` <sup>1.37.0</sup>	`"\e[42m"`
`BG_YELLOW` <sup>1.37.0</sup>	`"\e[43m"`
`BG_BLUE` <sup>1.37.0</sup>	`"\e[44m"`
`BG_MAGENTA` <sup>1.37.0</sup>	`"\e[45m"`
`BG_CYAN` <sup>1.37.0</sup>	`"\e[46m"`
`BG_WHITE` <sup>1.37.0</sup>	`"\e[47m"`

just

@foo:
  echo {{HEX}}

console

$ just foo
0123456789abcdef

Constants starting with

\e

are ANSI escape sequences.

CLEAR

clears the screen, similar to the

clear

command. The rest are of the form

\e[Nm

, where

is an integer, and set terminal display attributes.

Terminal display attribute escape sequences can be combined, for example text weight

BOLD

, text style

STRIKETHROUGH

, foreground color

CYAN

, and background color

BG_BLUE

. They should be followed by

NORMAL

, to reset the terminal back to normal.

Escape sequences should be quoted, since

is treated as a special character by some shells.

just

@foo:
  echo '{{BOLD + STRIKETHROUGH + CYAN + BG_BLUE}}Hi!{{NORMAL}}'

Attributes

Recipes,

mod

statements, and aliases may be annotated with attributes that change their behavior.

Name	Type	Description
`[arg(ARG, help="HELP")]` <sup>1.46.0</sup>	recipe	Print help string `HELP` for `ARG` in usage messages.
`[arg(ARG, long="LONG")]` <sup>1.46.0</sup>	recipe	Require values of argument `ARG` to be passed as `--LONG` option.
`[arg(ARG, short="S")]` <sup>1.46.0</sup>	recipe	Require values of argument `ARG` to be passed as short `-S` option.
`[arg(ARG, value="VALUE")]` <sup>1.46.0</sup>	recipe	Makes option `ARG` a flag which does not take a value.
`[arg(ARG, pattern="PATTERN")]` <sup>1.45.0</sup>	recipe	Require values of argument `ARG` to match regular expression `PATTERN` .
`[confirm]` <sup>1.17.0</sup>	recipe	Require confirmation prior to executing recipe.
`[confirm(PROMPT)]` <sup>1.23.0</sup>	recipe	Require confirmation prior to executing recipe with a custom prompt.
`[default]` <sup>1.43.0</sup>	recipe	Use recipe as module's default recipe.
`[doc(DOC)]` <sup>1.27.0</sup>	module, recipe	Set recipe or module's documentation comment to `DOC` .
`[extension(EXT)]` <sup>1.32.0</sup>	recipe	Set shebang recipe script's file extension to `EXT` . `EXT` should include a period if one is desired.
`[group(NAME)]` <sup>1.27.0</sup>	module, recipe	Put recipe or module in in group `NAME` .
`[linux]` <sup>1.8.0</sup>	recipe	Enable recipe on Linux.
`[macos]` <sup>1.8.0</sup>	recipe	Enable recipe on MacOS.
`[metadata(METADATA)]` <sup>1.42.0</sup>	recipe	Attach `METADATA` to recipe.
`[no-cd]` <sup>1.9.0</sup>	recipe	Don't change directory before executing recipe.
`[no-exit-message]` <sup>1.7.0</sup>	recipe	Don't print an error message if recipe fails.
`[no-quiet]` <sup>1.23.0</sup>	recipe	Override globally quiet recipes and always echo out the recipe.
`[openbsd]` <sup>1.38.0</sup>	recipe	Enable recipe on OpenBSD.
`[parallel]` <sup>1.42.0</sup>	recipe	Run this recipe's dependencies in parallel.
`[positional-arguments]` <sup>1.29.0</sup>	recipe	Turn on positional arguments for this recipe.
`[private]` <sup>1.10.0</sup>	alias, recipe	Make recipe, alias, or variable private. See Private Recipes.
`[script]` <sup>1.33.0</sup>	recipe	Execute recipe as script. See script recipes for more details.
`[script(COMMAND)]` <sup>1.32.0</sup>	recipe	Execute recipe as a script interpreted by `COMMAND` . See script recipes for more details.
`[unix]` <sup>1.8.0</sup>	recipe	Enable recipe on Unixes. (Includes MacOS).
`[windows]` <sup>1.8.0</sup>	recipe	Enable recipe on Windows.
`[working-directory(PATH)]` <sup>1.38.0</sup>	recipe	Set recipe working directory. `PATH` may be relative or absolute. If relative, it is interpreted relative to the default working directory.

A recipe can have multiple attributes, either on multiple lines:

just

[no-cd]
[private]
foo:
    echo "foo"

Or separated by commas on a single line1.14.0:

just

[no-cd, private]
foo:
    echo "foo"

Attributes with a single argument may be written with a colon:

just

[group: 'bar']
foo:

Enabling and Disabling Recipes1.8.0

The

[linux]

[macos]

[unix]

, and

[windows]

attributes are configuration attributes. By default, recipes are always enabled. A recipe with one or more configuration attributes will only be enabled when one or more of those configurations is active.

This can be used to write

justfile

s that behave differently depending on which operating system they run on. The

run

recipe in this

justfile

will compile and run

main.c

, using a different C compiler and using the correct output binary name for that compiler depending on the operating system:

just

[unix]
run:
  cc main.c
  ./a.out

[windows]
run:
  cl main.c
  main.exe

Disabling Changing Directory1.9.0

just

normally executes recipes with the current directory set to the directory that contains the

justfile

. This can be disabled using the

[no-cd]

attribute. This can be used to create recipes which use paths relative to the invocation directory, or which operate on the current directory.

For example, this

commit

recipe:

just

[no-cd]
commit file:
  git add {{file}}
  git commit

Can be used with paths that are relative to the current directory, because

[no-cd]

prevents

just

from changing the current directory when executing

commit

Requiring Confirmation for Recipes1.17.0

just

normally executes all recipes unless there is an error. The

[confirm]

attribute allows recipes require confirmation in the terminal prior to running. This can be overridden by passing

--yes

just

, which will automatically confirm any recipes marked by this attribute.

Recipes dependent on a recipe that requires confirmation will not be run if the relied upon recipe is not confirmed, as well as recipes passed after any recipe that requires confirmation.

just

[confirm]
delete-all:
  rm -rf *

Custom Confirmation Prompt1.23.0

The default confirmation prompt can be overridden with

[confirm(PROMPT)]

just

[confirm("Are you sure you want to delete everything?")]
delete-everything:
  rm -rf *

Groups

Recipes and modules may be annotated with one or more group names:

just

[group('lint')]
js-lint:
    echo 'Running JS linter…'

[group('rust recipes')]
[group('lint')]
rust-lint:
    echo 'Running Rust linter…'

[group('lint')]
cpp-lint:
  echo 'Running C++ linter…'

# not in any group
email-everyone:
    echo 'Sending mass email…'

Recipes are listed by group:

$ just --list
Available recipes:
    email-everyone # not in any group

    [lint]
    cpp-lint
    js-lint
    rust-lint

    [rust recipes]
    rust-lint

just --list --unsorted

prints recipes in their justfile order within each group:

$ just --list --unsorted
Available recipes:
    (no group)
    email-everyone # not in any group

    [lint]
    js-lint
    rust-lint
    cpp-lint

    [rust recipes]
    rust-lint

Groups can be listed with

--groups

$ just --groups
Recipe groups:
  lint
  rust recipes

Use

just --groups --unsorted

to print groups in their justfile order.

Command Evaluation Using Backticks

Backticks can be used to store the result of commands:

just

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:

just

# 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](#strings) section for details on unindenting.

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

The [`shell(…)` function](#external-commands) provides a more general mechanism
to invoke external commands, including the ability to execute the contents of a
variable as a command, and to pass arguments to a command.

### Conditional Expressions

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

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

bar:
  @echo "{{foo}}"

console

$ just bar
Good!

It is also possible to test for inequality:

just

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

bar:
  @echo {{foo}}

console

$ just bar
xyz

And match against regular expressions:

just

foo := if "hello" =~ 'hel+o' { "match" } else { "mismatch" }

bar:
  @echo {{foo}}

console

$ just bar
match

Regular expressions are provided by the regex crate, whose syntax is documented on docs.rs. Since regular expressions commonly use backslash escape sequences, consider using single-quoted string literals, which will pass slashes to the regex parser unmolested.

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

just

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

Conditionals can be used inside of recipes:

just

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

Multiple conditionals can be chained:

just

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

bar:
  @echo {{foo}}

console

$ just bar
abc

Stopping execution with error

Execution can be halted with the

error

function. For example:

just

foo := if "hello" == "goodbye" {
  "xyz"
} else if "a" == "b" {
  "abc"
} else {
  error("123")
}

Which produce the following error when run:

error: Call to function `error` failed: 123
   |
16 |   error("123")

Setting Variables from the Command Line

Variables can be overridden from the command line.

just

os := "linux"

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

build:
  ./build {{os}}

console

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

Any number of arguments of the form

NAME=VALUE

can be passed before recipes:

console

$ just os=plan9
./build plan9
./test --test plan9

Or you can use the

--set

flag:

console

$ just --set os bsd
./build bsd
./test --test bsd

Getting and Setting Environment Variables

Exporting

just

Variables

Assignments prefixed with the

export

keyword will be exported to recipes as environment variables:

just

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:

just

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.

just

export WORLD := "world"
# This backtick will fail with "WORLD: unbound variable"
BAR := `echo hello $WORLD`

just

# Running `just a foo` will fail with "A: unbound variable"
a $A $B=`echo $A`:
  echo $A $B

When export is set, all

just

variables are exported as environment variables.

Unexporting Environment Variables1.29.0

Environment variables can be unexported with the

unexport keyword

just

unexport FOO

@foo:
  echo $FOO

$ export FOO=bar
$ just foo
sh: FOO: unbound variable

Getting Environment Variables from the environment

Environment variables from the environment are passed automatically to the recipes.

just

print_home_folder:
  echo "HOME is: '${HOME}'"

console

$ just
HOME is '/home/myuser'

Setting

just

Variables from Environment Variables

Environment variables can be propagated to

just

variables using the

env()

function. See environment-variables.

Recipe Parameters

Recipes may have parameters. Here recipe

build

has a parameter called

target

just

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

To pass arguments on the command line, put them after the recipe name:

console

$ 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:

just

default: (build "main")

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

Variables can also be passed as arguments to dependencies:

just

target := "main"

_build version:
  @echo 'Building {{version}}…'
  cd {{version}} && make

build: (_build target)

A command's arguments can be passed to dependency by putting the dependency in parentheses along with the arguments:

just

build target:
  @echo "Building {{target}}…"

push target: (build target)
  @echo 'Pushing {{target}}…'

Parameters may have default values:

just

default := 'all'

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

Parameters with default values may be omitted:

console

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

Or supplied:

console

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

Default values may be arbitrary expressions, but expressions containing the

&&

||

, or

operators must be parenthesized:

just

arch := "wasm"

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

The last parameter of a recipe may be variadic, indicated with either a

or a

before the argument name:

just

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:

console

$ 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:

just

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:

just

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

{{…}}

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

just

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

And you type:

console

$ just search "cat toupee"

just

will run the command

lynx https://www.google.com/?q=cat toupee

, which will get parsed by

sh

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:

just

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

Parameters prefixed with a

will be exported as environment variables:

just

foo $bar:
  echo $bar

Parameters may be constrained to match regular expression patterns using the

[arg("name", pattern="pattern")]

attribute1.45.0:

just

[arg('n', pattern='\d+')]
double n:
  echo $(({{n}} * 2))

A leading

and trailing

are added to the pattern, so it must match the entire argument value.

You may constrain the pattern to a number of alternatives using the

operator:

just

[arg('flag', pattern='--help|--version')]
info flag:
  just {{flag}}

Regular expressions are provided by the Rust

regex

crate. See the syntax documentation for usage examples.

Usage information for a recipe may be printed with the

--usage

subcommand1.46.0:

console

$ just --usage foo
Usage: just foo [OPTIONS] bar

Arguments:
  bar

Help strings may be added to arguments using the

[arg(ARG, help=HELP)]

attribute:

just

[arg("bar", help="hello")]
foo bar:

console

$ just --usage foo
Usage: just foo bar

Arguments:
  bar hello

Recipe Flags and Options

Recipe parameters are positional by default.

In this

justfile

just

@foo bar:
  echo bar={{bar}}

The parameter

bar

is positional:

console

$ just foo hello
bar=hello

The

[arg(ARG, long=OPTION)]

1.46.0 attribute can be used to make a parameter a long option.

In this

justfile

just

[arg("bar", long="bar")]
foo bar:

The parameter

bar

is given with the

--bar

option:

console

$ just foo --bar hello
bar=hello

Options may also be passed with

--name=value

syntax:

console

$ just foo --bar=hello
bar=hello

The value of

long

can be omitted, in which case the option defaults to the name of the parameter:

just

[arg("bar", long)]
foo bar:

The

[arg(ARG, short=OPTION)]

1.46.0 attribute can be used to make a parameter a short option.

In this

justfile

just

[arg("bar", short="b")]
foo bar:

The parameter

bar

is given with the

-b

option:

console

$ just foo -b hello
bar=hello

If a parameter has both a long and short option, it may be passed using either.

Variadic

and

parameters cannot be options.

The

[arg(ARG, value=VALUE, …)]

1.46.0 attribute can be used with

long

short

to make a parameter a flag which does not take a value.

In this

justfile

just

[arg("bar", long="bar", value="hello")]
foo bar:

The parameter

bar

is given with the

--bar

option, but does not take a value, and instead takes the value given in the

[arg]

attribute:

console

$ just foo --bar
bar=hello

This is useful for unconditionally requiring a flag like

--force

on dangerous commands.

A flag is optional if its parameter has a default:

just

[arg("bar", long="bar", value="hello")]
foo bar="goodbye":

Causing it to receive the default when not passed in the invocation:

console

$ just foo
bar=goodbye

Dependencies

Dependencies run before recipes that depend on them:

just

a: b
  @echo A

b:
  @echo B

$ just a
B
A

In a given invocation of

just

, a recipe with the same arguments will only run once, regardless of how many times it appears in the command-line invocation, or how many times it appears as a dependency:

just

a:
  @echo A

b: a
  @echo B

c: a
  @echo C

$ just a a a a a
A
$ just b c
A
B
C

Multiple recipes may depend on a recipe that performs some kind of setup, and when those recipes run, that setup will only be performed once:

just

build:
  cc main.c

test-foo: build
  ./a.out --test foo

test-bar: build
  ./a.out --test bar

$ just test-foo test-bar
cc main.c
./a.out --test foo
./a.out --test bar

Recipes in a given run are only skipped when they receive the same arguments:

just

build:
  cc main.c

test TEST: build
  ./a.out --test {{TEST}}

$ just test foo test bar
cc main.c
./a.out --test foo
./a.out --test bar

Running Recipes at the End of a Recipe

Normal dependencies of a 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 immediately after the recipe and are introduced with an

&&

just

a:
  echo 'A!'

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

c:
  echo 'C!'

d:
  echo 'D!'

…running b prints:

console

$ 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

just

a:
  echo 'A!'

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

c:
  echo 'C!'

…running b prints:

console

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

This has limitations, since recipe

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.

Shebang Recipes

Recipes that start with

#!

are called shebang recipes, and are executed by saving the recipe body to a file and running it. This lets you write recipes in different languages:

just

polyglot: python js perl sh ruby nu

python:
  #!/usr/bin/env python3
  print('Hello from python!')

js:
  #!/usr/bin/env node
  console.log('Greetings from JavaScript!')

perl:
  #!/usr/bin/env perl
  print "Larry Wall says Hi!\n";

sh:
  #!/usr/bin/env sh
  hello='Yo'
  echo "$hello from a shell script!"

nu:
  #!/usr/bin/env nu
  let hello = 'Hola'
  echo $"($hello) from a nushell script!"

ruby:
  #!/usr/bin/env ruby
  puts "Hello from ruby!"

console

$ just polyglot
Hello from python!
Greetings from JavaScript!
Larry Wall says Hi!
Yo from a shell script!
Hola from a nushell script!
Hello from ruby!

On Unix-like operating systems, including Linux and MacOS, shebang recipes are executed by saving the recipe body to a file in a temporary directory, marking the file as executable, and executing it. The OS then parses the shebang line into a command line and invokes it, including the path to the file. For example, if a recipe starts with

#!/usr/bin/env bash

, the final command that the OS runs will be something like

/usr/bin/env bash /tmp/PATH_TO_SAVED_RECIPE_BODY

Shebang line splitting is operating system dependent. When passing a command with arguments, you may need to tell

env

to split them explicitly by using the

-S

flag:

just

run:
  #!/usr/bin/env -S bash -x
  ls

Windows does not support shebang lines. On Windows,

just

splits the shebang line into a command and arguments, saves the recipe body to a file, and invokes the split command and arguments, adding the path to the saved recipe body as the final argument. For example, on Windows, if a recipe starts with

#! py

, the final command the OS runs will be something like

py C:\Temp\PATH_TO_SAVED_RECIPE_BODY

Script Recipes

Recipes with a

[script(COMMAND)]

1.32.0 attribute are run as scripts interpreted by

COMMAND

. This avoids some of the issues with shebang recipes, such as the use of

cygpath

on Windows, the need to use

/usr/bin/env

, inconsistencies in shebang line splitting across Unix OSs, and requiring a temporary directory from which files can be executed.

Recipes with an empty

[script]

attribute are executed with the value of

set script-interpreter := […]

1.33.0, defaulting to

sh -eu

, and not the value of

set shell

The body of the recipe is evaluated, written to disk in the temporary directory, and run by passing its path as an argument to

COMMAND

Script and Shebang Recipe Temporary Files

Both script and shebang recipes write the recipe body to a temporary file for execution. Script recipes execute that file by passing it to a command, while shebang recipes execute the file directly. Shebang recipe execution will fail if the filesystem containing the temporary file is mounted with

noexec

or is otherwise non-executable.

The directory that

just

writes temporary files to may be configured in a number of ways, from highest to lowest precedence:

Globally with the
```
--tempdir
```
command-line option or the
```
JUST_TEMPDIR
```
environment variable1.41.0.
On a per-module basis with the
```
tempdir
```
setting.
Globally on Linux with the
```
XDG_RUNTIME_DIR
```
environment variable.
Falling back to the directory returned by std::env::temp_dir.

Python Recipes with

uv

uv

is an excellent cross-platform python project manager, written in Rust.

Using the

[script]

attribute and

script-interpreter

setting,

just

can easily be configured to run Python recipes with

uv

just

set unstable

set script-interpreter := ['uv', 'run', '--script']

[script]
hello:
  print("Hello from Python!")

[script]
goodbye:
  # /// script
  # requires-python = ">=3.11"
  # dependencies=["sh"]
  # ///
  import sh
  print(sh.echo("Goodbye from Python!"), end='')

Of course, a shebang also works:

just

hello:
  #!/usr/bin/env -S uv run --script
  print("Hello from Python!")

Safer Bash Shebang Recipes

If you're writing a

bash

shebang recipe, consider adding

set -euxo pipefail

just

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. This is
```
bash
```
-specific, so isn't turned on in normal linewise
```
just
```
recipes.

Together, these avoid a lot of shell scripting gotchas.

Shebang Recipe Execution on Windows

On Windows, shebang interpreter paths containing a

are translated from Unix-style paths to Windows-style paths using

cygpath

, a utility that ships with Cygwin.

For example, to execute this recipe on Windows:

just

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:

justfile

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:

just

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:

just

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

Sharing Environment Variables Between Recipes

Each line of each recipe is executed by a fresh shell, so it is not possible to share environment variables between recipes.

Using Python Virtual Environments

Some tools, like Python's venv, require loading environment variables in order to work, making them challenging to use with

just

. As a workaround, you can execute the virtual environment binaries directly:

just

venv:
  [ -d foo ] || python3 -m venv foo

run: venv
  ./foo/bin/python3 main.py

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:

just

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:

just

foo:
  cd bar && pwd

The other is to use a shebang recipe. Shebang recipe bodies are extracted and run as scripts, so a single shell instance will run the whole thing, and thus a

cd

on one line will affect later lines, just like a shell script:

just

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

Indentation

Recipe lines can be indented with spaces or tabs, but not a mix of both. All of a recipe's lines must have the same type of indentation, but different recipes in the same

justfile

may use different indentation.

Each recipe must be indented at least one level from the

recipe-name

but after that may be further indented.

Here's a justfile with a recipe indented with spaces, represented as

·

, and tabs, represented as

→

justfile

set windows-shell := ["pwsh", "-NoLogo", "-NoProfileLoadTime", "-Command"]

set ignore-comments

list-space directory:
··#!pwsh
··foreach ($item in $(Get-ChildItem {{directory}} )) {
····echo $item.Name
··}
··echo ""

# indentation nesting works even when newlines are escaped
list-tab directory:
→ @foreach ($item in $(Get-ChildItem {{directory}} )) { \
→ → echo $item.Name \
→ }
→ @echo ""

pwsh

PS > just list-space ~
Desktop
Documents
Downloads

PS > just list-tab ~
Desktop
Documents
Downloads

Multi-Line Constructs

Recipes without an initial shebang are evaluated and run line-by-line, which means that multi-line constructs probably won't do what you want.

For example, with the following

justfile

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:

console

$ 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

just

conditional:
  if true; then echo 'True!'; fi

just

conditional:
  if true; then \
    echo 'True!'; \
  fi

just

conditional:
  #!/usr/bin/env sh
  if true; then
    echo 'True!'
  fi

for

loops

just

for:
  for file in `ls .`; do echo $file; done

just

for:
  for file in `ls .`; do \
    echo $file; \
  done

just

for:
  #!/usr/bin/env sh
  for file in `ls .`; do
    echo $file
  done

while

loops

just

while:
  while `server-is-dead`; do ping -c 1 server; done

just

while:
  while `server-is-dead`; do \
    ping -c 1 server; \
  done

just

while:
  #!/usr/bin/env sh
  while `server-is-dead`; do
    ping -c 1 server
  done

Outside Recipe Bodies

Parenthesized expressions can span multiple lines:

just

abc := ('a' +
        'b'
         + 'c')

abc2 := (
  'a' +
  'b' +
  'c'
)

foo param=('foo'
      + 'bar'
    ):
  echo {{param}}

bar: (foo
        'Foo'
     )
  echo 'Bar!'

Lines ending with a backslash continue on to the next line as if the lines were joined by whitespace1.15.0:

just

a := 'foo' + \
     'bar'

foo param1 \
  param2='foo' \
  *varparam='': dep1 \
                (dep2 'foo')
  echo {{param1}} {{param2}} {{varparam}}

dep1: \
    # this comment is not part of the recipe body
  echo 'dep1'

dep2 \
  param:
    echo 'Dependency with parameter {{param}}'

Backslash line continuations can also be used in interpolations. The line following the backslash must be indented.

just

recipe:
  echo '{{ \
  "This interpolation " + \
    "has a lot of text." \
  }}'
  echo 'back to recipe body'

Command-line Options

just

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

console

$ just --list
Available recipes:
  js
  perl
  polyglot
  python
  ruby
$ just --show perl
perl:
  #!/usr/bin/env perl
  print "Larry Wall says Hi!\n";
$ just --show polyglot
polyglot: python js perl sh ruby

Setting Command-line Options with Environment Variables

Some command-line options can be set with environment variables

For example, unstable features can be enabled either with the

--unstable

flag:

console

$ just --unstable

Or by setting the

JUST_UNSTABLE

environment variable:

console

$ export JUST_UNSTABLE=1
$ just

Since environment variables are inherited by child processes, command-line options set with environment variables are inherited by recursive invocations of

just

, where as command line options set with arguments are not.

Consult

just --help

for which options can be set with environment variables.

Private Recipes

Recipes and aliases whose name starts with a

are omitted from

just --list

just

test: _test-helper
  ./bin/test

_test-helper:
  ./bin/super-secret-test-helper-stuff

console

$ just --list
Available recipes:
    test

And from

just --summary

console

$ just --summary
test

The

[private]

attribute1.10.0 may also be used to hide recipes or aliases without needing to change the name:

just

[private]
foo:

[private]
alias b := bar

bar:

console

$ just --list
Available recipes:
    bar

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:

just

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

Now only the lines starting with

will be echoed:

console

$ just quiet
hello
goodbye
# all done!

All recipes in a Justfile can be made quiet with

set quiet

just

set quiet

foo:
  echo "This is quiet"

@foo2:
  echo "This is also quiet"

The

[no-quiet]

attribute overrides this setting:

just

set quiet

foo:
  echo "This is quiet"

[no-quiet]
foo2:
  echo "This is not quiet"

Shebang recipes are quiet by default:

just

foo:
  #!/usr/bin/env bash
  echo 'Foo!'

console

$ just foo
Foo!

Adding

to a shebang recipe name makes

just

print the recipe before executing it:

just

@bar:
  #!/usr/bin/env bash
  echo 'Bar!'

console

$ just bar
#!/usr/bin/env bash
echo 'Bar!'
Bar!

just

normally prints error messages when a recipe line fails. These error messages can be suppressed using the

[no-exit-message]

1.7.0 attribute. You may find this especially useful with a recipe that wraps a tool:

just

git *args:
    @git {{args}}

console

$ just git status
fatal: not a git repository (or any of the parent directories): .git
error: Recipe `git` failed on line 2 with exit code 128

Add the attribute to suppress the exit error message when the tool exits with a non-zero code:

just

[no-exit-message]
git *args:
    @git {{args}}

console

$ just git status
fatal: not a git repository (or any of the parent directories): .git

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:

just

default:
  @just --choose

Invoking

justfile

s 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:

console

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

Additional recipes after the first are sought in the same

justfile

. For example, the following are both equivalent:

console

$ just foo/a b
$ (cd foo && just a b)

And will both invoke recipes

and

foo/justfile

Imports

One

justfile

can include the contents of another using

import

statements.

If you have the following

justfile

justfile

import 'foo/bar.just'

a: b
  @echo A

And the following text in

foo/bar.just

just

b:
  @echo B

foo/bar.just

will be included in

justfile

and recipe

will be defined:

console

$ just b
B
$ just a
B
A

The

import

path can be absolute or relative to the location of the justfile containing it. A leading

~/

in the import path is replaced with the current users home directory.

Justfiles are insensitive to order, so included files can reference variables and recipes defined after the

import

statement.

Imported files can themselves contain

import

s, which are processed recursively.

allow-duplicate-recipes

and

allow-duplicate-variables

allow duplicate recipes and variables, respectively, to override each other, instead of producing an error.

Within a module, later definitions override earlier definitions:

just

set allow-duplicate-recipes

foo:

foo:
  echo 'yes'

When

import

s are involved, things unfortunately get much more complicated and hard to explain.

Shallower definitions always override deeper definitions, so recipes at the top level will override recipes in imports, and recipes in an import will override recipes in an import which itself imports those recipes.

When two duplicate definitions are imported and are at the same depth, the one from the earlier import will override the one from the later import.

This is because

just

uses a stack when processing imports, pushing imports onto the stack in source-order, and always processing the top of the stack next, so earlier imports are actually handled later by the compiler.

This is definitely a bug, but since

just

has very strong backwards compatibility guarantees and we take enormous pains not to break anyone's

justfile

, we have created issue #2540 to discuss whether or not we can actually fix it.

Imports may be made optional by putting a

after the

import

keyword:

just

import? 'foo/bar.just'

Importing the same source file multiple times is not an error1.37.0. This allows importing multiple justfiles, for example

foo.just

and

bar.just

, which both import a third justfile containing shared recipes, for example

baz.just

, without the duplicate import of

baz.just

being an error:

justfile

# justfile
import 'foo.just'
import 'bar.just'

justfile

# foo.just
import 'baz.just'
foo: baz

justfile

# bar.just
import 'baz.just'
bar: baz

just

# baz
baz:

Modules1.19.0

justfile

can declare modules using

mod

statements.

mod

statements were stabilized in

just

1.31.0. In earlier versions, you'll need to use the

--unstable

flag,

set unstable

, or set the

JUST_UNSTABLE

environment variable to use them.

If you have the following

justfile

justfile

mod bar

a:
  @echo A

And the following text in

bar.just

just

b:
  @echo B

bar.just

will be included in

justfile

as a submodule. Recipes, aliases, and variables defined in one submodule cannot be used in another, and each module uses its own settings.

Recipes in submodules can be invoked as subcommands:

console

$ just bar b
B

Or with path syntax:

console

$ just bar::b
B

If a module is named

foo

, just will search for the module file in

foo.just

foo/mod.just

foo/justfile

, and

foo/.justfile

. In the latter two cases, the module file may have any capitalization.

Module statements may be of the form:

justfile

mod foo 'PATH'

Which loads the module's source file from

PATH

, instead of from the usual locations. A leading

~/

PATH

is replaced with the current user's home directory.

PATH

may point to the module source file itself, or to a directory containing the module source file with the name

mod.just

justfile

, or

.justfile

. In the latter two cases, the module file may have any capitalization.

Environment files are only loaded for the root justfile, and loaded environment variables are available in submodules. Settings in submodules that affect environment file loading are ignored.

Recipes in submodules without the

[no-cd]

attribute run with the working directory set to the directory containing the submodule source file.

justfile()

and

justfile_directory()

always return the path to the root justfile and the directory that contains it, even when called from submodule recipes.

Modules may be made optional by putting a

after the

mod

keyword:

just

mod? foo

Missing source files for optional modules do not produce an error.

Optional modules with no source file do not conflict, so you can have multiple mod statements with the same name, but with different source file paths, as long as at most one source file exists:

just

mod? foo 'bar.just'
mod? foo 'baz.just'

Modules may be given doc comments which appear in

--list

output1.30.0:

justfile

# foo is a great module!
mod foo

console

$ just --list
Available recipes:
    foo ... # foo is a great module!

Modules are still missing a lot of features, for example, the ability to refer to variables in other modules. See the module improvement tracking issue for more information.

Hiding

justfile

just

looks for

justfile

s 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:

console

$ 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

just

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

default:
  echo foo

Formatting and dumping

justfile

Each

justfile

has a canonical formatting with respect to whitespace and newlines.

You can overwrite the current justfile with a canonically-formatted version using the currently-unstable

--fmt

flag:

console

$ cat justfile
# A lot of blank lines





some-recipe:
  echo "foo"
$ just --fmt --unstable
$ cat justfile
# A lot of blank lines

some-recipe:
    echo "foo"

Invoking

just --fmt --check --unstable

runs

--fmt

in check mode. Instead of overwriting the

justfile

just

will exit with an exit code of 0 if it is formatted correctly, and will exit with 1 and print a diff if it is not.

You can use the

--dump

command to output a formatted version of the

justfile

to stdout:

console

$ just --dump > formatted-justfile

The

--dump

command can be used with

--dump-format json

to print a JSON representation of a

justfile

Fallback to parent

justfile

If a recipe is not found in a

justfile

and the

fallback

setting is set,

just

will look for

justfile

s in the parent directory and up, until it reaches the root directory.

just

will stop after it reaches a

justfile

in which the

fallback

setting is

false

or unset.

As an example, suppose the current directory contains this

justfile

just

set fallback
foo:
  echo foo

And the parent directory contains this

justfile

just

bar:
  echo bar

console

$ just bar
Trying ../justfile
echo bar
bar

Avoiding Argument Splitting

Given this

justfile

just

foo argument:
  touch {{argument}}

The following command will create two files,

some

and

argument.txt

console

$ just foo "some argument.txt"

The user's shell will parse

"some argument.txt"

as a single argument, but when

just

replaces

touch {{argument}}

with

touch some argument.txt

, the quotes are not preserved, and

touch

will receive two arguments.

There are a few ways to avoid this: quoting, positional arguments, and exported arguments.

Quoting

Quotes can be added around the

{{argument}}

interpolation:

just

foo argument:
  touch '{{argument}}'

This preserves

just

's ability to catch variable name typos before running, for example if you were to write

{{argument}}

, but will not do what you want if the value of

argument

contains single quotes.

Positional Arguments

The

positional-arguments

setting causes all arguments to be passed as positional arguments, allowing them to be accessed with

$1

$2

, …, and

$@

, which can be then double-quoted to avoid further splitting by the shell:

just

set positional-arguments

foo argument:
  touch "$1"

This defeats

just

's ability to catch typos, for example if you type

$2

instead of

$1

, but works for all possible values of

argument

, including those with double quotes.

Exported Arguments

All arguments are exported when the

export

setting is set:

just

set export

foo argument:
  touch "$argument"

Or individual arguments may be exported by prefixing them with

just

foo $argument:
  touch "$argument"

This defeats

just

's ability to catch typos, for example if you type

$argument

, but works for all possible values of

argument

, including those with double quotes.

Configuring the Shell

There are a number of ways to configure the shell for linewise recipes, which are the default when a recipe does not start with a

#!

shebang. Their precedence, from highest to lowest, is:

The
```
--shell
```
and
```
--shell-arg
```
command line options. Passing either of these will cause
```
just
```
to ignore any settings in the current justfile.
```
set windows-shell := [...]
```
```
set windows-powershell
```
(deprecated)
```
set shell := [...]
```

Since

set windows-shell

has higher precedence than

set shell

, you can use

set windows-shell

to pick a shell on Windows, and

set shell

to pick a shell for all other platforms.

Timestamps

just

can print timestamps before each recipe commands:

just

recipe:
  echo one
  sleep 2
  echo two

$ just --timestamp recipe
[07:28:46] echo one
one
[07:28:46] sleep 2
[07:28:48] echo two
two

By default, timestamps are formatted as

HH:MM:SS

. The format can be changed with

--timestamp-format

$ just --timestamp recipe --timestamp-format '%H:%M:%S%.3f %Z'
[07:32:11:.349 UTC] echo one
one
[07:32:11:.350 UTC] sleep 2
[07:32:13:.352 UTC] echo two
two

The argument to

--timestamp-format

is a

strftime

-style format string, see the

chrono

library docs for details.

Signal Handling

Signals are messsages sent to running programs to trigger specific behavior. For example,

SIGINT

is sent to all processes in the terminal forground process group when

CTRL-C

is pressed.

just

tries to exit when requested by a signal, but it also tries to avoid leaving behind running child proccesses, two goals which are somewhat in conflict.

just

exits leaving behind child processes, the user will have no recourse but to

ps aux | grep

for the children and manually

kill

them, a tedious endevour.

Fatal Signals

SIGHUP

SIGINT

, and

SIGQUIT

are generated when the user closes the terminal, types

ctrl-c

, or types

ctrl-\

, respectively, and are sent to all processes in the foreground process group.

SIGTERM

is the default signal sent by the

kill

command, and is delivered only to its intended victim.

When a child process is not running,

just

will exit immediately on receipt of any of the above signals.

When a child process is running,

just

will wait until it terminates, to avoid leaving it behind.

Additionally, on receipt of

SIGTERM

just

will forward

SIGTERM

to any running children1.41.0, since unlike other fatal signals,

SIGTERM

, was likely sent to

just

alone.

Regardless of whether a child process terminates successfully after

just

receives a fatal signal,

just

halts execution.

SIGINFO

SIGINFO

is sent to all processes in the foreground process group when the user types

ctrl-t

on BSD-derived operating systems, including MacOS, but not Linux.

just

responds by printing a list of all child process IDs and commands1.41.0.

Windows

On Windows,

just

behaves as if it had received

SIGINT

when the user types

ctrl-c

. Other signals are unsupported.

justfile

NPX Install

Tags

SKILL.md Content

Writing Justfiles

Quick Start

Examples

Features

The Default Recipe

Listing Available Recipes

Invoking Multiple Recipes

Working Directory

Aliases

Settings

Table of Settings

Allow Duplicate Recipes

Allow Duplicate Variables

Dotenv Settings

Export

Positional Arguments

Shell

Windows Shell

Windows PowerShell

Python 3

Bash

Z Shell

Fish

Nushell

Documentation Comments

Expressions and Substitutions

Concatenation

Logical Operators

Joining Paths

Escaping {{

Strings

Shell-expanded strings

Format strings

Ignoring Errors

Functions

System Information

External Commands

Environment Variables

Executables

Invocation Information

Invocation Directory

Justfile and Justfile Directory

Source and Source Directory

Just Executable

Just Process ID

String Manipulation

Case Conversion

Path Manipulation

Fallible

Infallible

Filesystem Access

Error Reporting

UUID and Hash Generation

Random

Datetime

Semantic Versions

Style

User Directories<sup>1.23.0</sup>

Constants

Attributes

Enabling and Disabling Recipes<sup>1.8.0</sup>

Disabling Changing Directory<sup>1.9.0</sup>

Requiring Confirmation for Recipes<sup>1.17.0</sup>

Custom Confirmation Prompt<sup>1.23.0</sup>

Groups

Command Evaluation Using Backticks

Stopping execution with error

Setting Variables from the Command Line

Getting and Setting Environment Variables

Exporting just Variables

Unexporting Environment Variables<sup>1.29.0</sup>

Getting Environment Variables from the environment

Setting just Variables from Environment Variables

Recipe Parameters

Recipe Flags and Options

Dependencies

Escaping
`{{`

Exporting
`just`
Variables

Setting
`just`
Variables from Environment Variables

Python Recipes with
`uv`

`if`
statements

`for`
loops

`while`
loops

Invoking
`justfile`
s in Other Directories

Hiding
`justfile`
s

Formatting and dumping
`justfile`
s

Fallback to parent
`justfile`
s

`SIGINFO`