# sh

[![Go Reference](https://pkg.go.dev/badge/mvdan.cc/sh/v3.svg)](https://pkg.go.dev/mvdan.cc/sh/v3)

A shell parser, formatter, and interpreter. Supports [POSIX Shell], [Bash], and
[mksh]. Requires Go 1.25 or later.

### Quick start

To parse shell scripts, inspect them, and print them out,
see the [syntax package](https://pkg.go.dev/mvdan.cc/sh/v3/syntax).

For high-level operations like performing shell expansions on strings,
see the [shell package](https://pkg.go.dev/mvdan.cc/sh/v3/shell).

To interpret or run shell scripts,
see the [interp package](https://pkg.go.dev/mvdan.cc/sh/v3/interp).

### shfmt

	go install mvdan.cc/sh/v3/cmd/shfmt@latest

`shfmt` formats shell programs. See [canonical.sh](syntax/canonical.sh) for a
quick look at its default style. For example:

	shfmt -l -w script.sh

For more information, see [its manpage](cmd/shfmt/shfmt.1.scd), which can be
viewed directly as Markdown or rendered with [scdoc].

Packages are available on [Alpine], [Arch], [Debian], [Docker], [Fedora], [FreeBSD],
[Homebrew], [MacPorts], [NixOS], [OpenSUSE], [Scoop], [Snapcraft], [Void] and [webi].

### gosh

	go install mvdan.cc/sh/v3/cmd/gosh@latest

Proof of concept shell that uses the `interp` package.

### Fuzzing

We use Go's native fuzzing support. For instance:

	cd syntax
	go test -run=- -fuzz=ParsePrint

### Caveats

* When indexing Bash associative arrays, always use quotes. The static parser
  will otherwise have to assume that the index is an arithmetic expression.

```sh
$ echo '${array[spaced string]}' | shfmt
<standard input>:1:16: not a valid arithmetic operator: string
$ echo '${array[weird!key]}' | shfmt
<standard input>:1:8: reached ! without matching [ with ]
$ echo '${array[dash-string]}' | shfmt
${array[dash - string]}
```

* `$((` and `((` ambiguity is not supported. Backtracking would complicate the
  parser and make streaming support via `io.Reader` impossible. The POSIX spec
  recommends to [space the operands][posix-ambiguity] if `$( (` is meant.

```sh
$ echo '$((foo); (bar))' | shfmt
1:1: reached ) without matching $(( with ))
```

* `export`, `let`, and `declare` are parsed as keywords.
  This allows statically building their syntax tree,
  as opposed to keeping the arguments as a slice of words.
  It is also required to support `declare foo=(bar)`.

* The entire library is written in pure Go, which limits how closely the
  interpreter can follow POSIX Shell and Bash semantics.
  For example, Go does not support forking its own process, so subshells
  use a goroutine instead, meaning that real PIDs and file descriptors
  cannot be used directly.

### Formatting FAQs

* The formatter cannot be disabled for ranges of lines; most users wanting this
  are working around a bug or they don't like how a piece of code is formatted.
  Instead, search the issue tracker and file a new issue if necessary.
  Formatting of partial files leads to lots of edge cases and complexity
  which this project has no resources for, nor interest in, getting into.

* We avoid adding more formatting options where possible. Each added flag interacts
  with all others, multiplying the human cost of development, maintenance, testing,
  and properly documenting the behavior for end users.

* The true value in a formatter is consistency, especially for teams of developers.
  We do not aim to satisfy every developer's personal choice of optimal formatting.

### JavaScript

The parser and formatter are available as a third party npm package called [sh-syntax],
which bundles a version of this library compiled to WASM.

Previously, we maintained an npm package called [mvdan-sh] which used GopherJS
to bundle a JS version of this library. That npm package is now archived
given its poor performance and GopherJS not being as actively developed.
Any existing or new users should look at [sh-syntax] instead.

### Docker

All release tags are published via [Docker], such as `v3.5.1`.
The latest stable release is currently published as `v3`,
and the latest development version as `latest`.
The images only include `shfmt`; `-alpine` variants exist on Alpine Linux.

To build a Docker image, run:

	docker build -t my:tag -f cmd/shfmt/Dockerfile .

To use a Docker image, run:

	docker run --rm -u "$(id -u):$(id -g)" -v "$PWD:/mnt" -w /mnt my:tag <shfmt arguments>

### Related projects

The following editor integrations wrap `shfmt`:

- [BashSupport-Pro] - Bash plugin for JetBrains IDEs
- [dockerfmt] - Dockerfile formatter using shfmt
- [intellij-shellscript] - Intellij Jetbrains `shell script` plugin
- [micro] - Editor with a built-in plugin
- [neoformat] - (Neo)Vim plugin
- [shell-format] - VS Code plugin
- [vscode-shfmt] - VS Code plugin
- [shfmt.el] - Emacs package
- [Sublime-Pretty-Shell] - Sublime Text 3 plugin
- [Trunk] - Universal linter, available as a CLI, VS Code plugin, and GitHub action
- [vim-shfmt] - Vim plugin

Other noteworthy integrations include:

- [modd] - A developer tool that responds to filesystem changes
- [prettier-plugin-sh] - [Prettier] plugin using [sh-syntax]
- [sh-checker] - A GitHub Action that performs static analysis for shell scripts
- [mdformat-shfmt] - [mdformat] plugin to format shell scripts embedded in Markdown with shfmt
- [pre-commit-shfmt] - [pre-commit] shfmt hook
- [tesh] - Run scripts with mocks, assertions, and coverage

[alpine]: https://pkgs.alpinelinux.org/packages?name=shfmt
[arch]: https://archlinux.org/packages/extra/x86_64/shfmt/
[bash]: https://www.gnu.org/software/bash/
[BashSupport-Pro]: https://www.bashsupport.com/manual/editor/formatter/
[debian]: https://tracker.debian.org/pkg/golang-mvdan-sh
[docker]: https://hub.docker.com/r/mvdan/shfmt/
[dockerfmt]: https://github.com/reteps/dockerfmt
[editorconfig]: https://editorconfig.org/
[examples]: https://pkg.go.dev/mvdan.cc/sh/v3/syntax#pkg-examples
[fedora]: https://packages.fedoraproject.org/pkgs/golang-mvdan-sh-3/shfmt/
[freebsd]: https://www.freshports.org/devel/shfmt
[homebrew]: https://formulae.brew.sh/formula/shfmt
[intellij-shellscript]: https://www.jetbrains.com/help/idea/shell-scripts.html
[macports]: https://ports.macports.org/port/shfmt/details/
[mdformat-shfmt]: https://github.com/hukkin/mdformat-shfmt
[mdformat]: https://github.com/executablebooks/mdformat
[micro]: https://micro-editor.github.io/
[mksh]: http://www.mirbsd.org/mksh.htm
[modd]: https://github.com/cortesi/modd
[mvdan-sh]: https://www.npmjs.com/package/mvdan-sh
[neoformat]: https://github.com/sbdchd/neoformat
[nixos]: https://github.com/NixOS/nixpkgs/blob/HEAD/pkgs/tools/text/shfmt/default.nix
[OpenSUSE]: https://build.opensuse.org/package/show/openSUSE:Factory/shfmt
[posix shell]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html
[posix-ambiguity]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_03
[pre-commit]: https://pre-commit.com
[pre-commit-shfmt]: https://github.com/scop/pre-commit-shfmt
[prettier-plugin-sh]: https://github.com/un-ts/prettier/tree/master/packages/sh
[prettier]: https://prettier.io
[scdoc]: https://sr.ht/~sircmpwn/scdoc/
[scoop]: https://github.com/ScoopInstaller/Main/blob/HEAD/bucket/shfmt.json
[sh-checker]: https://github.com/luizm/action-sh-checker
[sh-syntax]: https://github.com/un-ts/sh-syntax
[shell-format]: https://marketplace.visualstudio.com/items?itemName=foxundermoon.shell-format
[shfmt.el]: https://github.com/purcell/emacs-shfmt/
[snapcraft]: https://snapcraft.io/shfmt
[sublime-pretty-shell]: https://github.com/aerobounce/Sublime-Pretty-Shell
[tesh]: https://github.com/feloy/tesh
[trunk]: https://trunk.io/check
[vim-shfmt]: https://github.com/z0mbix/vim-shfmt
[void]: https://github.com/void-linux/void-packages/blob/HEAD/srcpkgs/shfmt/template
[vscode-shfmt]: https://marketplace.visualstudio.com/items?itemName=mkhl.shfmt
[webi]: https://webinstall.dev/shfmt/
