mvdan/sh

sh

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

Quick start

To parse shell scripts, inspect them, and print them out, see the syntax package.

For high-level operations like performing shell expansions on strings, see the shell package.

To interpret or run shell scripts, see the interp package.

shfmt

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

shfmt formats shell programs. See canonical.sh for a quick look at its default style. For example:

shfmt -l -w script.sh

For more information, see its manpage, 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.

$ 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 if $( ( is meant.

$ 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
• vscode-shfmt - VS Code plugin
• shfmt.el - Emacs package
• Trunk - Universal linter, available as a CLI, VS Code plugin, and GitHub action

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