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

this is a comment

another-recipe: @echo 'This is another recipe.' When you invoke just it looks for file justfile in the current directory and upwards, so you can invoke it from any subdirectory of your project. The search for a justfile is case insensitive, so any case, like Justfile , JUSTFILE , or JuStFiLe , will work. just will also look for files with the name .justfile , in case you'd like to hide a justfile . Running just with no arguments runs the first recipe in the justfile : $ just echo 'This is a recipe!' This is a recipe! One or more arguments specify the recipe(s) to run: $ just another-recipe This is another recipe. just prints each command to standard error before running it, which is why echo 'This is a recipe!' was printed. This is suppressed for lines starting with @ , which is why echo 'This is another recipe.' was not printed. Recipes stop running if a command fails. Here cargo publish will only run if cargo test succeeds: publish: cargo test

tests passed, time to publish!

cargo publish Recipes can depend on other recipes. Here the test recipe depends on the build recipe, so build will run before test : build: cc main.c foo.c bar.c -o main test: build ./test sloc: @echo "wc -l *.c lines of code" $ just test cc main.c foo.c bar.c -o main ./test testing… all tests passed! Recipes without dependencies will run in the order they're given on the command line: $ just build sloc cc main.c foo.c bar.c -o main 1337 lines of code Dependencies will always run first, even if they are passed after a recipe that depends on them: $ just test build cc main.c foo.c bar.c -o main ./test testing… all tests passed! Recipes may depend on recipes in submodules: 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: test: cargo test You can also use dependencies to run multiple recipes by default: 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: default: just --list Listing Available Recipes Recipes can be listed in alphabetical order with just --list : $ 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: $ just --summary build test deploy lint Pass --unsorted to print recipes in the order they appear in the justfile : test: echo 'Testing!' build: echo 'Building!' $ just --list --unsorted Available recipes: test build $ just --summary --unsorted test build If you'd like just to default to listing the recipes in the justfile , you can use this as your default recipe: default: @just --list Note that you may need to add --justfile {{justfile()}} to the line above. Without it, if you executed just -f /some/distant/justfile -d . or 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 : $ just --list --list-heading $'Cool stuff…\n' Cool stuff… test build And the indentation can be customized with --list-prefix : $ just --list --list-prefix ···· Available recipes: ····test ····build The argument to --list-heading replaces both the heading and the newline following it, so it should contain a newline if non-empty. It works this way so you can suppress the heading line entirely by passing the empty string: $ just --list --list-heading '' test build Invoking Multiple Recipes Multiple recipes may be invoked on the command line at once: build: make web serve: python3 -m http.server -d out 8000 $ 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: build project: make {{project}} serve: python3 -m http.server -d out 8000 $ 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: $ 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. @foo: pwd [no-cd] @bar: pwd $ cd subdir $ just foo / $ just bar /subdir You can override the working directory for all recipes with set working-directory := '…' : set working-directory := 'bar' @foo: pwd $ 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: [working-directory: 'bar'] @foo: pwd $ 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: alias b := build build: echo 'Building!' $ just b echo 'Building!' Building! The target of an alias may be a recipe in a submodule: 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: 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 1.33.0 [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 1.31.0 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 1.33.0 string - Set the working directory for recipes and backticks, relative to the default working directory. Boolean settings can be written as: set NAME Which is equivalent to: 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 If 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 . set allow-duplicate-recipes @foo: echo foo @foo: echo bar $ just foo bar Allow Duplicate Variables If 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 . set allow-duplicate-variables a := "foo" a := "bar" @foo: echo {{a}} $ 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. If 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. If dotenv-filename is set just will look for a file at the given path, relative to the working directory and each of its ancestors. If dotenv-filename is not set, but dotenv-load or 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. If dotenv-override is set, variables from the environment file will override existing environment variables. For example, if your .env file contains:

a comment, will be ignored

DATABASE_ADDRESS=localhost:6379 SERVER_PORT=1337 And your justfile contains: 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: $ 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 . set export a := "hello" @foo b: echo $a echo $b $ just foo goodbye hello goodbye Positional Arguments If positional-arguments is true , recipe arguments will be passed as positional arguments to commands. For linewise recipes, argument $0 will be the name of the recipe. For example, running this recipe: set positional-arguments @foo bar: echo $0 echo $1 Will produce the following output: $ just foo hello foo hello When using an sh -compatible shell, such as bash or 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 $@ expand to nothing (i.e., they are removed). This example recipe will print arguments one by one on separate lines: set positional-arguments @test *args='': bash -c 'while (( "$#" )); do echo - $1; shift; done' -- "$@" Running it with two arguments: $ 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: [positional-arguments] @foo bar: echo $0 echo $1 Note that PowerShell does not handle positional arguments in the same way as other shells, so turning on positional arguments will likely break recipes that use PowerShell. If using PowerShell 7.4 or better, the -CommandWithArgs flag will make positional arguments work as expected: set shell := ['pwsh.exe', '-CommandWithArgs'] set positional-arguments print-args a b c: Write-Output @($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 .

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 : 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. set windows-powershell := true hello: Write-Host "Hello, world!" Python 3 set shell := ["python3", "-c"] Bash set shell := ["bash", "-uc"] Z Shell set shell := ["zsh", "-uc"] Fish set shell := ["fish", "-c"] Nushell set shell := ["nu", "-c"] If you want to change the default table mode to light : 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 :

build stuff

build: ./bin/build

test stuff

test: ./bin/test $ 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:

This comment won't appear

[doc('Build stuff')] build: ./bin/build

This one won't either

[doc] test: ./bin/test $ 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. 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: 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: 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: foo := '' || 'goodbye' # 'goodbye' bar := 'hello' || 'goodbye' # 'hello' Joining Paths The / operator can be used to join two strings with a slash: foo := "a" / "b" $ just --evaluate foo a/b Note that a / is added even if one is already present: foo := "a/" bar := foo / "b" $ just --evaluate bar a//b Absolute paths can also be constructed1.5.0: 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 {{{{ : braces: echo 'I {{{{LOVE}} curly braces!' (An unmatched }} is ignored, so it doesn't need to be escaped.) Another option is to put all the text you'd like to escape inside of an interpolation: braces: echo '{{'I {{LOVE}} curly braces!'}}' Yet another option is to use {{ "{{" }} : braces: echo 'I {{ "{{" }}LOVE}} curly braces!' Strings '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: carriage-return := "\r" double-quote := "\"" newline := "\n" no-newline := "\ " slash := "\" tab := "\t" unicode-codepoint := "\u{1F916}" $ 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: single := ' hello ' double := " goodbye " Single-quoted strings do not recognize escape sequences: escapes := '\t\n\r\"\' $ just --evaluate escapes := "\t\n\r\"\" Indented versions of both single- and double-quoted strings, delimited by triple single- or double-quotes, are supported. Indented string lines are stripped of a leading line break, and leading whitespace common to all non-blank lines:

this string will evaluate to foo\nbar\n

x := ''' foo bar '''

this string will evaluate to abc\n wuv\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 x are shell expanded1.27.0: 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 f are format strings1.44.0: 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: 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 - : foo: -cat foo echo 'Done!' $ 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: system-info: @echo "This is an {{arch()}} machine". $ 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.

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')

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. home_dir := env('HOME') test: echo "{{home_dir}}" $ 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: 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. bash := require("bash") @test: echo "bash: '{{bash}}'" $ 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. set unstable bosh := which("bosh") @test: echo "bosh: '{{bosh}}'" $ 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: 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 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 : 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 or mod source file when called from within an import or submodule. Just Executable just_executable() - Absolute path to the just executable. For example: executable: @echo The executable is at: {{just_executable()}} $ just The executable is at: /bin/just Just Process ID just_pid() - Process ID of the just executable. For example: pid: @echo The process ID is: {{ just_pid() }} $ just The process ID is: 420 String Manipulation append(suffix, s) 1.27.0 Append suffix to whitespace-separated strings in s . append('/src', 'foo bar baz') → 'foo/src bar/src baz/src' prepend(prefix, s) 1.27.0 Prepend prefix to whitespace-separated strings in s . 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 s matching substring . trim_start(s) - Remove leading whitespace from s . trim_start_match(s, substring) - Remove prefix of s matching substring . trim_start_matches(s, substring) - Repeatedly remove prefixes of s 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") is txt . file_name(path) - File name of path with any leading directory components removed. file_name("/foo/bar.txt") is bar.txt . file_stem(path) - File name of path without extension. file_stem("/foo/bar.txt") is bar . parent_directory(path) - Parent directory of path . parent_directory("/foo/bar.txt") is /foo . without_extension(path) - path without extension. without_extension("/foo/bar.txt") is /foo/bar . These functions can fail, for example if a path does not have an extension, which will halt execution. Infallible 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: 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: 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 1.27.0 "0123456789abcdef" HEXLOWER 1.27.0 "0123456789abcdef" HEXUPPER 1.27.0 "0123456789ABCDEF" PATH_SEP 1.41.0 "/" "\" PATH_VAR_SEP 1.41.0 ":" ";" CLEAR 1.37.0 "\ec" NORMAL 1.37.0 "\e[0m" BOLD 1.37.0 "\e[1m" ITALIC 1.37.0 "\e[3m" UNDERLINE 1.37.0 "\e[4m" INVERT 1.37.0 "\e[7m" HIDE 1.37.0 "\e[8m" STRIKETHROUGH 1.37.0 "\e[9m" BLACK 1.37.0 "\e[30m" RED 1.37.0 "\e[31m" GREEN 1.37.0 "\e[32m" YELLOW 1.37.0 "\e[33m" BLUE 1.37.0 "\e[34m" MAGENTA 1.37.0 "\e[35m" CYAN 1.37.0 "\e[36m" WHITE 1.37.0 "\e[37m" BG_BLACK 1.37.0 "\e[40m" BG_RED 1.37.0 "\e[41m" BG_GREEN 1.37.0 "\e[42m" BG_YELLOW 1.37.0 "\e[43m" BG_BLUE 1.37.0 "\e[44m" BG_MAGENTA 1.37.0 "\e[45m" BG_CYAN 1.37.0 "\e[46m" BG_WHITE 1.37.0 "\e[47m" @foo: echo {{HEX}} $ 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 N 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. @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")] 1.46.0 recipe Print help string HELP for ARG in usage messages. [arg(ARG, long="LONG")] 1.46.0 recipe Require values of argument ARG to be passed as --LONG option. [arg(ARG, short="S")] 1.46.0 recipe Require values of argument ARG to be passed as short -S option. [arg(ARG, value="VALUE")] 1.46.0 recipe Makes option ARG a flag which does not take a value. [arg(ARG, pattern="PATTERN")] 1.45.0 recipe Require values of argument ARG to match regular expression PATTERN . [confirm] 1.17.0 recipe Require confirmation prior to executing recipe. [confirm(PROMPT)] 1.23.0 recipe Require confirmation prior to executing recipe with a custom prompt. [default] 1.43.0 recipe Use recipe as module's default recipe. [doc(DOC)] 1.27.0 module, recipe Set recipe or module's documentation comment to DOC . [extension(EXT)] 1.32.0 recipe Set shebang recipe script's file extension to EXT . EXT should include a period if one is desired. [group(NAME)] 1.27.0 module, recipe Put recipe or module in in group NAME . [linux] 1.8.0 recipe Enable recipe on Linux. [macos] 1.8.0 recipe Enable recipe on MacOS. [metadata(METADATA)] 1.42.0 recipe Attach METADATA to recipe. [no-cd] 1.9.0 recipe Don't change directory before executing recipe. [no-exit-message] 1.7.0 recipe Don't print an error message if recipe fails. [no-quiet] 1.23.0 recipe Override globally quiet recipes and always echo out the recipe. [openbsd] 1.38.0 recipe Enable recipe on OpenBSD. [parallel] 1.42.0 recipe Run this recipe's dependencies in parallel. [positional-arguments] 1.29.0 recipe Turn on positional arguments for this recipe. [private] 1.10.0 alias, recipe Make recipe, alias, or variable private. See Private Recipes . [script] 1.33.0 recipe Execute recipe as script. See script recipes for more details. [script(COMMAND)] 1.32.0 recipe Execute recipe as a script interpreted by COMMAND . See script recipes for more details. [unix] 1.8.0 recipe Enable recipe on Unixes. (Includes MacOS). [windows] 1.8.0 recipe Enable recipe on Windows. [working-directory(PATH)] 1.38.0 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: [no-cd] [private] foo: echo "foo" Or separated by commas on a single line1.14.0: [no-cd, private] foo: echo "foo" Attributes with a single argument may be written with a colon: [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: [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: [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 to 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. [confirm] delete-all: rm -rf * Custom Confirmation Prompt1.23.0 The default confirmation prompt can be overridden with [confirm(PROMPT)] : [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: [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: localhost := dumpinterfaces | cut -d: -f2 | sed 's/\/.*//' | sed 's/ //g' serve: ./serve {{localhost}} 8080 Indented backticks, delimited by three backticks, are de-indented in the same manner as indented strings:

This backtick evaluates the command echo foo\necho bar\n, which produces the value foo\nbar\n.

stuff := `` echo foo echo bar See the [Strings](#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}}" $ just bar Good! It is also possible to test for inequality: foo := if "hello" != "goodbye" { "xyz" } else { "abc" } bar: @echo {{foo}} $ just bar xyz And match against regular expressions: foo := if "hello" =~ 'hel+o' { "match" } else { "mismatch" } bar: @echo {{foo}} $ 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. foo := if env_var("RELEASE") == "true" {get-something-from-release-database} else { "dummy-value" } Conditionals can be used inside of recipes: bar foo: echo {{ if foo == "bar" { "hello" } else { "goodbye" } }} Multiple conditionals can be chained: foo := if "hello" == "goodbye" { "xyz" } else if "a" == "a" { "abc" } else { "123" } bar: @echo {{foo}} $ just bar abc Stopping execution with error Execution can be halted with the error function. For example: foo := if "hello" == "goodbye" { "xyz" } else if "a" == "b" { "abc" } else { error("123") } Which produce the following error when run: error: Call to functionerror` failed: 123 | 16 | error("123") Setting Variables from the Command Line Variables can be overridden from the command line. os := "linux" test: build ./test --test {{os}} build: ./build {{os}} $ just ./build linux ./test --test linux Any number of arguments of the form NAME=VALUE can be passed before recipes: $ just os=plan9 ./build plan9 ./test --test plan9 Or you can use the --set flag: $ just --set os bsd ./build bsd ./test --test bsd Getting and Setting Environment Variables Exporting just Variables Assignments prefixed with the export keyword will be exported to recipes as environment variables: export RUST_BACKTRACE := "1" test:

will print a stack trace if it crashes

cargo test Parameters prefixed with a $ will be exported as environment variables: test $RUST_BACKTRACE="1":

will print a stack trace if it crashes

cargo test Exported variables and parameters are not exported to backticks in the same scope. export WORLD := "world"

This backtick will fail with "WORLD: unbound variable"

BAR := echo hello $WORLD

Running just a foo will fail with "A: unbound variable"

a $A $B=echo $A:

echo $A $B

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

:

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.

print_home_folder:

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

$ 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

:

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

Variables can also be passed as arguments to dependencies:

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:

build target:

@echo "Building {{target}}…"

push target: (build target)

@echo 'Pushing {{target}}…'

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 expressions containing the

+

,

&&

,

||

, or

/

operators must be parenthesized:

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:

backup +FILES:

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

Variadic parameters prefixed with

+

accept

one or more

arguments and expand

to a string containing those arguments separated by spaces:

$ just backup FAQ.md GRAMMAR.md

scp FAQ.md GRAMMAR.md me@server.com:

FAQ.md 100% 1831 1.8KB/s 00:00

GRAMMAR.md 100% 1666 1.6KB/s 00:00

Variadic parameters prefixed with

*

accept

zero or more

arguments and

expand to a string containing those arguments separated by spaces, or an empty

string if no arguments are present:

commit MESSAGE *FLAGS:

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

Variadic parameters can be assigned default values. These are overridden by

arguments passed on the command line:

test +FLAGS='-q':

cargo test {{FLAGS}}

{{…}}

substitutions may need to be quoted if they contain spaces. For

example, if you have the following recipe:

search QUERY:

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

And you type:

$ just search "cat toupee"

just

will run the command

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

, which

will get parsed by

sh

as

lynx

,

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

, and

toupee

, and not the intended

lynx

and

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

.

You can fix this by adding quotes:

search QUERY:

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

Parameters prefixed with a

$

will be exported as environment variables:

foo $bar:

echo $bar

Parameters may be constrained to match regular expression patterns using the

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

attribute1.45.0:

[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:

[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:

$ just --usage foo

Usage: just foo [OPTIONS] bar

Arguments:

bar

Help strings may be added to arguments using the

[arg(ARG, help=HELP)]

attribute:

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

foo bar:

$ just --usage foo

Usage: just foo bar

Arguments:

bar hello

Recipe Flags and Options

Recipe parameters are positional by default.

In this

justfile

:

@foo bar:

echo bar={{bar}}

The parameter

bar

is positional:

$ 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

:

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

foo bar:

The parameter

bar

is given with the

--bar

option:

$ just foo --bar hello

bar=hello

Options may also be passed with

--name=value

syntax:

$ 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:

[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

:

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

foo bar:

The parameter

bar

is given with the

-b

option:

$ 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

or

short

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

In this

justfile

:

[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:

$ 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:

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

foo bar="goodbye":

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

$ just foo

bar=goodbye

Dependencies

Dependencies run before recipes that depend on them:

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:

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:

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:

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

&&

:

a:

echo 'A!'

b: a && c d

echo 'B!'

c:

echo 'C!'

d:

echo 'D!'

…running

b

prints:

$ just b

echo 'A!'

A!

echo 'B!'

B!

echo 'C!'

C!

echo 'D!'

D!

Running Recipes in the Middle of a Recipe

just

doesn't support running recipes in the middle of another recipe, but you

can call

just

recursively in the middle of a recipe. Given the following

justfile

:

a:

echo 'A!'

b: a

echo 'B start!'

just c

echo 'B end!'

c:

echo 'C!'

…running

b

prints:

$ just b

echo 'A!'

A!

echo 'B start!'

B start!

echo 'C!'

C!

echo 'B end!'

B end!

This has limitations, since recipe

c

is run with an entirely new invocation

of

just

Assignments will be recalculated, dependencies might run twice, and command line arguments will not be propagated to the child just process. 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: 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!" $ 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: 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 : 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: 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 : 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: echo:

!/bin/sh

echo "Hello!" The interpreter path /bin/sh will be translated to a Windows-style path using cygpath before being executed. If the interpreter path does not contain a / it will be executed without being translated. This is useful if cygpath is not available, or you wish to pass a Windows-style path to the interpreter. Setting Variables in a Recipe Recipe lines are interpreted by the shell, not just , so it's not possible to set just variables in the middle of a recipe: foo: x := "hello" # This doesn't work! echo {{x}} It is possible to use shell variables, but there's another problem. Every recipe line is run by a new shell instance, so variables set in one line won't be set in the next: foo: x=hello && echo $x # This works! y=bye echo $y # This doesn't, y is undefined here! The best way to work around this is to use a shebang recipe. Shebang recipe bodies are extracted and run as scripts, so a single shell instance will run the whole thing: foo:

!/usr/bin/env bash

set -euxo pipefail x=hello echo $x 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: 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: foo: pwd # This pwd will print the same directory… cd bar pwd # …as this pwd! There are a couple ways around this. One is to call cd on the same line as the command you want to run: foo: cd bar && pwd The other is to use a shebang recipe. Shebang recipe bodies are extracted and run as scripts, so a single shell instance will run the whole thing, and thus a cd on one line will affect later lines, just like a shell script: 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 → . 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 "" 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 : conditional: if true; then echo 'True!' fi The extra leading whitespace before the second line of the conditional recipe will produce a parse error: $ just conditional error: Recipe line has extra leading whitespace | 3 | echo 'True!' | ^^^^^^^^^^^^^^^^ To work around this, you can write conditionals on one line, escape newlines with slashes, or add a shebang to your recipe. Some examples of multi-line constructs are provided for reference. if statements conditional: if true; then echo 'True!'; fi conditional: if true; then \ echo 'True!'; \ fi conditional:

!/usr/bin/env sh

if true; then echo 'True!' fi for loops for: for file in ls .; do echo $file; done for: for file in ls .; do \ echo $file; \ done for:

!/usr/bin/env sh

for file in ls .; do echo $file done while loops while: while server-is-dead; do ping -c 1 server; done while: while server-is-dead; do \ ping -c 1 server; \ done while:

!/usr/bin/env sh

while server-is-dead; do ping -c 1 server done Outside Recipe Bodies Parenthesized expressions can span multiple lines: 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: 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. 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: $ 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: $ just --unstable Or by setting the JUST_UNSTABLE environment variable: $ 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 : 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 The [private] attribute1.10.0 may also be used to hide recipes or aliases without needing to change the name: [private] foo: [private] alias b := bar bar: $ 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: @quiet: echo hello echo goodbye @# all done! Now only the lines starting with @ will be echoed: $ just quiet hello goodbye

all done!

All recipes in a Justfile can be made quiet with set quiet : set quiet foo: echo "This is quiet" @foo2: echo "This is also quiet" The [no-quiet] attribute overrides this setting: set quiet foo: echo "This is quiet" [no-quiet] foo2: echo "This is not quiet" 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

!/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: git args: @git {{args}} $ 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: [no-exit-message] git args: @git {{args}} $ 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: 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: $ (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: $ just foo/a b $ (cd foo && just a b) And will both invoke recipes a and b in foo/justfile . Imports One justfile can include the contents of another using import statements. If you have the following justfile : import 'foo/bar.just' a: b @echo A And the following text in foo/bar.just : b: @echo B foo/bar.just will be included in justfile and recipe b will be defined: $ 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: 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: 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

import 'foo.just' import 'bar.just'

foo.just

import 'baz.just' foo: baz

bar.just

import 'baz.just' bar: baz

baz

baz: Modules1.19.0 A 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 : mod bar a: @echo A And the following text in bar.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: $ just bar b B Or with path syntax: $ 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: mod foo 'PATH' Which loads the module's source file from PATH , instead of from the usual locations. A leading ~/ in 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: 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: mod? foo 'bar.just' mod? foo 'baz.just' Modules may be given doc comments which appear in --list output1.30.0:

foo is a great module!

mod foo $ 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 s 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: $ cat > script <<EOF

!/usr/bin/env just --justfile

foo: echo foo EOF $ chmod +x script $ ./script foo echo foo foo When a script with a shebang is executed, the system supplies the path to the script as an argument to the command in the shebang. So, with a shebang of

!/usr/bin/env just --justfile

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

!/usr/bin/env just --working-directory . --justfile

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

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

default: echo foo Formatting and dumping justfile s 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: $ 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: $ 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 s 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 : set fallback foo: echo foo And the parent directory contains this justfile : bar: echo bar $ just bar Trying ../justfile echo bar bar Avoiding Argument Splitting Given this justfile : foo argument: touch {{argument}} The following command will create two files, some and argument.txt : $ 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: 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: set positional-arguments foo argument: touch "$1" This defeats just 's ability to catch typos, for example if you type $2 instead of $1 , but works for all possible values of argument , including those with double quotes. Exported Arguments All arguments are exported when the export setting is set: set export foo argument: touch "$argument" Or individual arguments may be exported by prefixing them with $ : 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: 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. If 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.