sh

README

sh

A shell parser and formatter. Supports POSIX Shell and Bash.

For a quick overview, see the examples. Requires Go 1.7 or later.

shfmt

go get -u github.com/mvdan/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 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.

Packages are available for Arch, 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

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

Supporting some of these could be possible, but they would involve major drawbacks explained below.

• Bash associative arrays. Cannot be parsed statically as that depends on whether array was defined via declare -A.

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

• $(( and (( ambiguity. This means backtracking, which would greatly complicate the parser. In practice, the POSIX spec recommends to space the operands if $( ( is meant.

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

Related projects

• format-shell - Atom plugin for shfmt