sh

README

sh

A shell parser, formatter and interpreter. Supports POSIX Shell, Bash and mksh. Requires Go 1.10 or later.

Quick start

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

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

shfmt

go get -u mvdan.cc/sh/cmd/shfmt

shfmt formats shell programs. It can use tabs or any number of spaces to indent. See canonical.sh for a quick look at its default style.

You can feed it standard input, any number of files or any number of directories to recurse into. When recursing, it will operate on .sh and .bash files and ignore files starting with a period. It will also operate on files with no extension and a shell shebang.

shfmt -l -w script.sh

Typically, CI builds should use the command below, to error if any shell scripts in a project don't adhere to the format:

shfmt -d .

Use -i N to indent with a number of spaces instead of tabs. There are other formatting options - see shfmt -h. For example, to get the formatting appropriate for Google's Style guide, use shfmt -i 2 -ci.

Packages are available for Arch, CRUX, Homebrew, NixOS and Void.

Replacing bash -n

bash -n can be useful to check for syntax errors in shell scripts. However, shfmt >/dev/null can do a better job as it checks for invalid UTF-8 and does all parsing statically, including checking POSIX Shell validity:

$ echo '${foo:1 2}' | bash -n
$ echo '${foo:1 2}' | shfmt
1:9: not a valid arithmetic operator: 2
$ echo 'foo=(1 2)' | bash --posix -n
$ echo 'foo=(1 2)' | shfmt -p
1:5: arrays are a bash feature

gosh

go get -u mvdan.cc/sh/cmd/gosh

Experimental shell that uses interp. Work in progress, so don't expect stability just yet.

Fuzzing

This project makes use of go-fuzz to find crashes and hangs in both the parser and the printer. To get started, run:

git checkout fuzz
./fuzz

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
1:16: not a valid arithmetic operator: string
$ 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 ))

• Some builtins like export and let are parsed as keywords. This is to allow statically parsing them and building their syntax tree, as opposed to just keeping the arguments as a slice of arguments.

JavaScript

A subset of the Go packages are available as an npm package called mvdan-sh. See the _js directory for more information.

Related projects

• Docker images - by jamesmstone, PeterDaveHello
• format-shell - Atom plugin for shfmt
• micro - Editor with a built-in plugin for shfmt
• shell-format - VS Code plugin for shfmt
• vim-shfmt - Vim plugin for shfmt