= `just`
:toc: macro
:toc-title:
image:https://img.shields.io/crates/v/just.svg[crates.io version,link=https://crates.io/crates/just]
image:https://github.com/casey/just/workflows/Build/badge.svg[build status,link=https://github.com/casey/just/actions]
image:https://img.shields.io/github/downloads/casey/just/total.svg[downloads,link=https://github.com/casey/just/releases]
image:https://img.shields.io/discord/695580069837406228?logo=discord[chat on discord,link=https://discord.gg/ezYScXR]
image:https://img.shields.io/badge/Say%20Thanks-!-1EAEDB.svg[say thanks,link=https://saythanks.io/to/casey]
`just` is a handy way to save and run project-specific commands.
(非官方中文文档,link:https://github.com/chinanf-boy/just-zh[这里],快看过来!)
Commands, called recipes, are stored in a file called `justfile` with syntax inspired by `make`:
```make
build:
cc *.c -o main
# test everything
test-all: build
./test --all
# run a specific test
test TEST: build
./test --test {{TEST}}
```
You can then run them with `just RECIPE`:
```sh
$ 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
link:https://github.com/casey/just#what-are-the-idiosyncrasies-of-make-that-just-avoids[Make's
complexity and idiosyncrasies]. No need for `.PHONY` recipes!
- Errors are specific and informative, and syntax errors are reported along with their source context.
- Recipes can accept
link:https://github.com/casey/just#recipe-parameters[command line arguments].
- Wherever possible, errors are resolved statically. Unknown recipes and
circular dependencies are reported before anything runs.
- Just link:https://github.com/casey/just#dotenv-integration[loads `.env`
files], making it easy to populate environment variables.
- Recipes can be
link:https://github.com/casey/just#listing-available-recipes[listed from the
command line].
- Command line completion scripts are
link:https://github.com/casey/just#shell-completion-scripts[available for
most popular shells].
- Recipes can be written in
link:https://github.com/casey/just#writing-recipes-in-other-languages[arbitrary
languages], like Python or NodeJS.
- `just` can be invoked from any subdirectory, not just the directory that contains the `Justfile`.
- And link:https://github.com/casey/just#manual[much more]!
If you need help with `just` please feel free to open an issue or ping me on link:https://discord.gg/ezYScXR[discord]. Feature requests and bug reports are always welcome!
[discrete]
== Manual
toc::[]
== Installation
=== Prerequisites
`just` should run on any system with a reasonable `sh`, including Linux, MacOS, and the BSDs.
On Windows, `just` works with the `sh` provided by https://git-scm.com[Git for Windows], https://desktop.github.com[GitHub Desktop], and http://www.cygwin.com[Cygwin].
If you'd rather not install `sh`, you can use the `shell` setting to use the shell of your choice.
Like `cmd.exe`:
```make
# use cmd.exe instead of sh:
set shell := ["cmd.exe", "/c"]
list:
dir
```
…or Powershell:
```make
# use Powershell instead of sh:
set shell := ["powershell.exe", "-c"]
hello:
Write-Host "Hello, world!"
```
=== Packages
[options="header"]
|===================================================================================================================================================================================================================================================================================================================================================
| Operating System | Package Manager | Package | Command
| https://forge.rust-lang.org/release/platform-support.html[Various] | https://www.rust-lang.org[Cargo] | https://crates.io/crates/just[just] | `cargo install just`
| https://en.wikipedia.org/wiki/Microsoft_Windows[Microsoft Windows] | https://scoop.sh[Scoop] | https://github.com/ScoopInstaller/Main/blob/master/bucket/just.json[just] | `scoop install just`
| https://en.wikipedia.org/wiki/MacOS[macOS] | https://brew.sh[Homebrew] | https://formulae.brew.sh/formula/just[just] | `brew install just`
| https://en.wikipedia.org/wiki/MacOS[macOS] | https://www.macports.org[MacPorts] | https://ports.macports.org/port/just/summary[just] | `port install just`
| https://www.archlinux.org[Arch Linux] | https://github.com/Jguer/yay[Yay] | https://aur.archlinux.org/packages/just/[just] ^AUR^ | `yay -S just`
| https://nixos.org/nixos/[NixOS], https://nixos.org/nix/manual/#ch-supported-platforms[Linux], https://nixos.org/nix/manual/#ch-supported-platforms[macOS] | https://nixos.org/nix/[Nix] | https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/tools/just/default.nix[just] | `nix-env -iA nixos.just`
| https://voidlinux.org[Void Linux] | https://wiki.voidlinux.org/XBPS[XBPS] | https://github.com/void-linux/void-packages/blob/master/srcpkgs/just/template[just] | `xbps-install -S just`
| https://getsol.us/[Solus] | https://getsol.us/articles/package-management/basics/en[eopkg] | https://dev.getsol.us/source/just/[just] | `eopkg install just`
|===================================================================================================================================================================================================================================================================================================================================================
=== Pre-built Binaries
Pre-built binaries for Linux, MacOS, and Windows can be found on https://github.com/casey/just/releases[the releases page].
You can use the following command on Linux, MacOS, or Windows to download the latest release, just replace `DEST` with the directory where you'd like to put `just`:
```sh
curl --proto '=https' --tlsv1.2 -sSf https://just.systems/install.sh | bash -s -- --to DEST
```
== Quick Start
See xref:Installation[] for how to install `just` on your computer. Try running `just --version` to make sure that it's installed correctly.
Once `just` is installed and working, create a file named `justfile` in the root of your project with the following contents:
```make
recipe-name:
echo 'This is a recipe!'
# this is a comment
another-recipe:
@echo 'This is another recipe.'
```
When you invoke `just` it looks for file `justfile` in the current directory and upwards, so you can invoke it from any subdirectory of your project.
The search for a `justfile` is case insensitive, so any case, like `Justfile`, `JUSTFILE`, or `JuStFiLe`, will work.
Running `just` with no arguments runs the first recipe in the `justfile`:
```sh
$ just
echo 'This is a recipe!'
This is a recipe!
```
One or more arguments specify the recipe(s) to run:
```sh
$ just another-recipe
This is another recipe.
```
`just` prints each command to standard error before running it, which is why `echo 'This is a recipe!'` was printed. This is suppressed for lines starting with `@`, which is why `echo 'Another recipe.'` was not printed.
Recipes stop running if a command fails. Here `cargo publish` will only run if `cargo test` succeeds:
```make
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`:
```make
build:
cc main.c foo.c bar.c -o main
test: build
./test
sloc:
@echo "`wc -l *.c` lines of code"
```
```sh
$ 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:
```sh
$ 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:
```sh
$ just test build
cc main.c foo.c bar.c -o main
./test
testing... all tests passed!
```
== Examples
A variety of example justfiles can be found in the link:examples[examples directory].
== Features
=== Listing Available Recipes
Recipes can be listed with `just --list` :
```sh
$ just --list
Available recipes:
build
test
deploy
lint
```
`just --summary` is more concise:
```sh
$ just --summary
build test deploy lint
```
=== Aliases
Aliases allow recipes to be invoked with alternative names:
```make
alias b := build
build:
echo 'Building!'
```
```sh
$ just b
build
echo 'Building!'
Building!
```
=== Settings
Settings control interpretation and execution. Each setting may be specified at most once, anywhere in the justfile.
For example:
```make
set shell := ["zsh", "-cu"]
foo:
# this line will be run as `zsh -cu 'ls **/*.txt'`
ls **/*.txt
```
==== Table of Settings
[options="header"]
|=================
| Name | Value | Description
|`shell` | `[COMMAND, ARGS...]` | Set the command used to invoke recipes and evaluate backticks.
|=================
==== Shell
The `shell` setting controls the command used to invoke recipe lines and backticks. Shebang recipes are unaffected.
```make
# use python3 to execute recipe lines and backticks
set shell := ["python3", "-c"]
# use print to capture result of evaluation
foos := `print("foo" * 4)`
foo:
print("Snake snake snake snake.")
print("{{foos}}")
```
=== Documentation Comments
Comments immediately preceding a recipe will appear in `just --list`:
```make
# build stuff
build:
./bin/build
# test stuff
test:
./bin/test
```
```sh
$ just --list
Available recipes:
build # build stuff
test # test stuff
```
=== Variables and Substitution
Variables, strings, concatenation, and substitution using `{{...}}` are supported:
```make
version := "0.2.7"
tardir := "awesomesauce-" + version
tarball := tardir + ".tar.gz"
publish:
rm -f {{tarball}}
mkdir {{tardir}}
cp README.md *.c {{tardir}}
tar zcvf {{tarball}} {{tardir}}
scp {{tarball}} me@server.com:release/
rm -rf {{tarball}} {{tardir}}
```
==== Escaping `{{`
To write a recipe containing `{{`, use `{{ "{{" }}`:
```make
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:
```make
braces:
echo '{{'I {{LOVE}} curly braces!'}}'
```
=== Strings
Double-quoted strings support escape sequences:
```make
string-with-tab := "\t"
string-with-newline := "\n"
string-with-carriage-return := "\r"
string-with-double-quote := "\""
string-with-slash := "\\"
```
```sh
$ just --evaluate
"tring-with-carriage-return := "
string-with-double-quote := """
string-with-newline := "
"
string-with-slash := "\"
string-with-tab := " "
```
Single-quoted strings do not recognize escape sequences and may contain line breaks:
```make
escapes := '\t\n\r\"\\'
line-breaks := 'hello
this
is
a
raw
string!
'
```
```sh
$ just --evaluate
escapes := "\t\n\r\"\\"
line-breaks := "hello
this
is
a
raw
string!
"
```
=== Functions
Just provides a few built-in functions that might be useful when writing recipes.
==== System Information
- `arch()` – Instruction set architecture. Possible values are: `"aarch64"`, `"arm"`, `"asmjs"`, `"hexagon"`, `"mips"`, `"msp430"`, `"powerpc"`, `"powerpc64"`, `"s390x"`, `"sparc"`, `"wasm32"`, `"x86"`, `"x86_64"`, and `"xcore"`.
- `os()` – Operating system. Possible values are: `"android"`, `"bitrig"`, `"dragonfly"`, `"emscripten"`, `"freebsd"`, `"haiku"`, `"ios"`, `"linux"`, `"macos"`, `"netbsd"`, `"openbsd"`, `"solaris"`, and `"windows"`.
- `os_family()` – Operating system family; possible values are: `"unix"` and `"windows"`.
For example:
```make
system-info:
@echo "This is an {{arch()}} machine".
```
```
$ just system-info
This is an x86_64 machine
```
==== Environment Variables
- `env_var(key)` – Retrieves the environment variable with name `key`, aborting if it is not present.
- `env_var_or_default(key, default)` – Retrieves the environment variable with name `key`, returning `default` if it is not present.
==== Invocation Directory
- `invocation_directory()` - Retrieves the path of the current working directory, before `just` changed it (chdir'd) prior to executing commands.
For example, to call `rustfmt` on files just under the "current directory" (from the user/invoker's perspective), use the following rule:
```
rustfmt:
find {{invocation_directory()}} -name \*.rs -exec rustfmt {} \;
```
Alternatively, if your command needs to be run from the current directory, you could use (e.g.):
```
build:
cd {{invocation_directory()}}; ./some_script_that_needs_to_be_run_from_here
```
==== Dotenv Integration
`just` will load environment variables from a file named `.env`. This file can be located in the same directory as your justfile or in a parent directory. These variables are environment variables, not `just` variables, and so must be accessed using `$VARIABLE_NAME` in recipes and backticks.
For example, if your `.env` file contains:
```
# a comment, will be ignored
DATABASE_ADDRESS=localhost:6379
SERVER_PORT=1337
```
And your justfile contains:
```make
serve:
@echo "Starting server with database $DATABASE_ADDRESS on port $SERVER_PORT..."
./server --database $DATABASE_ADDRESS --port $SERVER_PORT
```
`just serve` will output:
```sh
$ just serve
Starting server with database localhost:6379 on port 1337...
./server --database $DATABASE_ADDRESS --port $SERVER_PORT
```
=== Command Evaluation Using Backticks
Backticks can be used to store the result of commands:
```make
localhost := `dumpinterfaces | cut -d: -f2 | sed 's/\/.*//' | sed 's/ //g'`
serve:
./serve {{localhost}} 8080
```
=== Setting Variables from the Command Line
Variables can be overridden from the command line.
```make
os := "linux"
test: build
./test --test {{os}}
build:
./build {{os}}
```
```sh
$ just
./build linux
./test --test linux
```
Any number of arguments of the form `NAME=VALUE` can be passed before recipes:
```sh
$ just os=plan9
./build plan9
./test --test plan9
```
Or you can use the `--set` flag:
```sh
$ just --set os bsd
./build bsd
./test --test bsd
```
=== Environment Variables
Assignments prefixed with the `export` keyword will be exported to recipes as environment variables:
```make
export RUST_BACKTRACE := "1"
test:
# will print a stack trace if it crashes
cargo test
```
=== Recipe Parameters
Recipes may have parameters. Here recipe `build` has a parameter called `target`:
```make
build target:
@echo 'Building {{target}}...'
cd {{target}} && make
```
To pass arguments on the command line, put them after the recipe name:
```sh
$ 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:
```make
default: (build "main")
build target:
@echo 'Building {{target}}...'
cd {{target}} && make
```
Parameters may have default values:
```make
default := 'all'
test target tests=default:
@echo 'Testing {{target}}:{{tests}}...'
./test --tests {{tests}} {{target}}
```
Parameters with default values may be omitted:
```sh
$ just test server
Testing server:all...
./test --tests all server
```
Or supplied:
```sh
$ just test server unit
Testing server:unit...
./test --tests unit server
```
Default values may be arbitrary expressions, but concatenations must be parenthesized:
```make
arch := "wasm"
test triple=(arch + "-unknown-unknown"):
./test {{triple}}
```
The last parameter of a recipe may be variadic, indicated with either a `+` or a `*` before the argument name:
```make
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:
```sh
$ 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:
```make
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:
```make
test +FLAGS='-q':
cargo test {{FLAGS}}
```
`{{...}}` substitutions may need to be quoted if they contains spaces. For example, if you have the following recipe:
```make
search QUERY:
lynx https://www.google.com/?q={{QUERY}}
```
And you type:
```sh
$ 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:
```make
search QUERY:
lynx 'https://www.google.com/?q={{QUERY}}'
```
=== Running recipes at the end of a recipe
Dependencies of a recipes always run before a recipe starts. That is to say, the dependee always runs before the depender.
You can call Just recursively to run a recipe after a recipe ends. Given the following justfile:
```make
a:
echo 'A!'
b: a
echo 'B!'
just c
c:
echo 'C!'
```
…running 'b' prints:
```sh
$ just b
echo 'A!'
A!
echo 'B!'
B!
echo 'C!'
C!
```
This has some limitations, since recipe `c` is run with an entirely new invocation of Just: Assignments will be recalculated, dependencies might run twice, and command line arguments will not be propagated to the child Just process.
=== Writing Recipes in Other Languages
Recipes that start with a `#!` are executed as scripts, so you can write recipes in other languages:
```make
polyglot: python js perl sh ruby
python:
#!/usr/bin/env python3
print('Hello from python!')
js:
#!/usr/bin/env node
console.log('Greetings from JavaScript!')
perl:
#!/usr/bin/env perl
print "Larry Wall says Hi!\n";
sh:
#!/usr/bin/env sh
hello='Yo'
echo "$hello from a shell script!"
ruby:
#!/usr/bin/env ruby
puts "Hello from ruby!"
```
```sh
$ just polyglot
Hello from python!
Greetings from JavaScript!
Larry Wall says Hi!
Yo from a shell script!
Hello from ruby!
```
==== 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 http://www.cygwin.com[Cygwin].
For example, to execute this recipe on Windows:
```make
echo:
#!/bin/sh
echo "Hello!"
```
The interpreter path `/bin/sh` will be translated to a Windows-style path using
`cygpath` before being executed.
If the interpreter path does not contain a `/` it will be executed without being translated. This is useful if `cygpath` is not available, or you wish to use a Windows style path to the interpreter.
=== 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
```make
conditional:
if true; then echo 'True!'; fi
```
```make
conditional:
if true; then \
echo 'True!'; \
fi
```
```make
conditional:
#!/usr/bin/env sh
if true; then
echo 'True!'
fi
```
==== `for` loops
```make
for:
for file in `ls .`; do echo $file; done
```
```make
for:
for file in `ls .`; do \
echo $file; \
done
```
```make
for:
#!/usr/bin/env sh
for file in `ls .`; do
echo $file
done
```
==== `while` loops
```make
while:
while `server-is-dead`; do ping -c 1 server; done
```
```make
while:
while `server-is-dead`; do \
ping -c 1 server; \
done
```
```make
while:
#!/usr/bin/env sh
while `server-is-dead`; do
do ping -c 1 server
done
```
=== Command Line Options
`just` supports a number of useful command line options for listing, dumping, and debugging recipes and variable:
```sh
$ just --list
Available recipes:
js
perl
polyglot
python
ruby
$ just --show perl
perl:
#!/usr/bin/env perl
print "Larry Wall says Hi!\n";
$ just --show polyglot
polyglot: python js perl sh ruby
```
Run `just --help` to see all the options.
=== Private Recipes
Recipes and aliases whose name starts with a `_` are omitted from `just --list`:
```make
test: _test-helper
./bin/test
_test-helper:
./bin/super-secret-test-helper-stuff
```
```sh
$ just --list
Available recipes:
test
```
And from `just --summary`:
```sh
$ just --summary
test
```
This is useful for helper recipes which are only meant to be used as dependencies of other recipes.
=== Quiet Recipes
A recipe name may be prefixed with '@' to invert the meaning of '@' before each line:
```make
@quiet:
echo hello
echo goodbye
@# all done!
```
Now only the lines starting with '@' will be echoed:
```sh
$ j quiet
hello
goodbye
# all done!
```
Shebang recipes are quiet by default:
```make
foo:
#!/usr/bin/env bash
echo 'Foo!'
```
```sh
$ just foo
Foo!
```
Adding `@` to a shebang recipe name makes `just` print the recipe before executing it:
```make
@bar:
#!/usr/bin/env bash
echo 'Bar!'
```
```sh
$ just bar ~/src/just
#!/usr/bin/env bash
echo 'Bar!'
Bar!
```
=== Invoking Justfiles in Other Directories
If the first argument passed to `just` contains a `/`, then the following occurs:
1. The argument is split at the last `/`.
2. 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.
3. 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:
```sh
$ (cd foo && just build)
$ just foo/build
$ just foo/
```
=== Just Scripts
By adding a shebang line to the top of a justfile and making it executable, `just` can be used as an interpreter for scripts:
```sh
$ cat > script <<EOF
#!/usr/bin/env just --justfile
foo:
echo foo
EOF
$ chmod +x script
$ ./script foo
echo foo
foo
```
When a script with a shebang is executed, the system supplies the path to the script as an argument to the command in the shebang. So, with a shebang of `#!/usr/bin/env just --justfile`, the command will be `/usr/bin/env just --justfile PATH_TO_SCRIPT`.
With the above shebang, `just` will change its working directory to the location of the script. If you'd rather leave the working directory unchanged, use `#!/usr/bin/env just --working-directory . --justfile`.
== Miscellanea
=== Companion Tools
Tools that pair nicely with `just` include:
- https://github.com/mattgreen/watchexec[`watchexec`] — a simple tool that watches a path and runs a command whenever it detects modifications.
=== Shell Alias
For lightning-fast command running, put `alias j=just` in your shell's configuration file.
=== Shell Completion Scripts
Shell completion scripts for Bash, Zsh, Fish, PowerShell, and Elvish are available in the link:completions[] directory. Please refer to your shell's documentation for how to install them.
The `just` binary can also generate the same completion scripts at runtime, using the `--completions` command:
```sh
$ just --completions zsh > just.zsh
```
=== Syntax Highlighting
`justfile` syntax is close enough to `make` that you may want to tell your editor to use make syntax highlighting for just.
==== Vim
For vim, you can put the following in `~/.vim/filetype.vim`:
```vimscript
if exists("did_load_filetypes")
finish
endif
augroup filetypedetect
au BufNewFile,BufRead justfile setf make
augroup END
```
==== Vim and Emacs
Include the following in a `justfile` to enable syntax highlighting in vim and emacs:
```
# Local Variables:
# mode: makefile
# End:
# vim: set ft=make :
```
==== Visual Studio Code
An extension for VS Code by https://github.com/skellock[skellock] is https://marketplace.visualstudio.com/items?itemName=skellock.just[available here]. (https://github.com/skellock/vscode-just[repository])
You can install it from the command line by running:
```
code --install-extension skellock.just
```
==== Kakoune
Kakoune supports `justfile` syntax highlighting out of the box, thanks to TeddyDD.
==== Other Editors
Feel free to send me the commands necessary to get syntax highlighting working in your editor of choice so that I may include them here.
=== Grammar
A non-normative grammar of justfiles can be found in link:GRAMMAR.md[].
=== just.sh
Before `just` was a fancy rust program it was a tiny shell script that called `make`. You can find the old version in link:extras/just.sh[].
=== Non-Project Specific Justfile
If you want some commands to be available everywhere, put them in `~/.justfile` and add the following to your shell's initialization file:
```sh
alias .j='just --justfile ~/.justfile --working-directory ~'
```
Or, if you'd rather they run in the current directory:
```sh
alias .j='just --justfile ~/.justfile --working-directory .'
```
I'm pretty sure that nobody actually uses this feature, but it's there.
¯\\_(ツ)_/¯
== Contributing
`just` welcomes your contributions! `just` is released under the maximally permissive https://creativecommons.org/publicdomain/zero/1.0/legalcode.txt[CC0] public domain dedication and fallback license, so your changes must also released under this license.
=== Janus
https://github.com/casey/janus[Janus] is a tool that collects and analyzes justfiles, and can determine if a new version of `just` breaks or changes the interpretation of existing justfiles.
Before merging a particularly large or gruesome change, Janus should be run to make sure that nothing breaks. Don't worry about running Janus yourself, Casey will happily run it for you on changes that need it.
== Frequently Asked Questions
=== What are the idiosyncrasies of Make that Just avoids?
Make has some behaviors which are confusing, complicated, or make it unsuitable for use as a general command runner.
One example is that under some circumstances, Make won't actually run the commands in a recipe. For example, if you have a file called `test` and the following makefile:
```make
test:
./test
```
Make will refuse to run your tests:
```sh
$ make test
make: `test' is up to date.
```
Make assumes that the `test` recipe produces a file called `test`. Since this file exists and the recipe has no other dependencies, Make thinks that it doesn't have anything to do and exits.
To be fair, this behavior is desirable when using Make as a build system, but not when using it as a command runner. You can disable this behavior for specific targets using Make's built-in link:https://www.gnu.org/software/make/manual/html_node/Phony-Targets.html[`.PHONY` target name], but the syntax is verbose and can be hard to remember. The explicit list of phony targets, written separately from the recipe definitions, also introduces the risk of accidentally defining a new non-phony target. In `just`, all recipes are treated as if they were phony.
Other examples of Make’s idiosyncrasies include the difference between `=` and `:=` in assignments, the confusing error messages that are produced if you mess up your makefile, needing `$$` to use environment variables in recipes, and incompatibilities between different flavors of Make.
=== What's the relationship between just and cargo build scripts?
http://doc.crates.io/build-script.html[Cargo build scripts] have a pretty specific use, which is to control how cargo builds your rust project. This might include adding flags to `rustc` invocations, building an external dependency, or running some kind of codegen step.
`just`, on the other hand, is for all the other miscellaneous commands you might run as part of development. Things like running tests in different configurations, linting your code, pushing build artifacts to a server, removing temporary files, and the like.
Also, although `just` is written in rust, it can be used regardless of the language or build system your project uses.
== Further Ramblings
I personally find it very useful to write a `justfile` for almost every project, big or small.
On a big project with multiple contributors, it's very useful to have a file with all the commands needed to work on the project close at hand.
There are probably different commands to test, build, lint, deploy, and the like, and having them all in one place is useful and cuts down on the time you have to spend telling people which commands to run and how to type them.
And, with an easy place to put commands, it's likely that you'll come up with other useful things which are part of the project's collective wisdom, but which aren't written down anywhere, like the arcane commands needed for some part of your revision control workflow, install all your project's dependencies, or all the random flags you might need to pass to the build system.
Some ideas for recipes:
* Deploying/publishing the project
* Building in release mode vs debug mode
* Running in debug mode or with logging enabled
* Complex git workflows
* Updating dependencies
* Running different sets of tests, for example fast tests vs slow tests, or running them with verbose output
* Any complex set of commands that you really should write down somewhere, if only to be able to remember them
Even for small, personal projects it's nice to be able to remember commands by name instead of ^Reverse searching your shell history, and it's a huge boon to be able to go into an old project written in a random language with a mysterious build system and know that all the commands you need to do whatever you need to do are in the `justfile`, and that if you type `just` something useful (or at least interesting!) will probably happen.
For ideas for recipes, check out link:justfile[this project's `justfile`], or some of the `justfile`{zwsp}s https://github.com/search?o=desc&q=filename%3Ajustfile&s=indexed&type=Code[out in the wild].
Anyways, I think that's about it for this incredibly long-winded README.
I hope you enjoy using `just` and find great success and satisfaction in all your computational endeavors!
😸
5e2b51e83e