sh/

sh

A shell parser, formatter and interpreter. Supports POSIX Shell, Bash and mksh. Requires Go 1.9 or later.

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

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.

Advantages over 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

• Bash index expressions must be an arithmetic expression or a quoted string. This is because the static parser can't know whether the array is an associative array (string keys) since that depends on having called or not declare -A.

 $ echo '${array[spaced string]}' | shfmt
1:16: not a valid arithmetic operator: string

• $(( and (( ambiguity is not suported. Backtracking would greatly complicate the parser and make stream support - io.Reader - impossible. In practice, 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 AST, as opposed to just keeping the arguments as a slice of arguments.

Related projects

• dockerised-shfmt - A docker image of shfmt
• 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