dockerfmt

Dockerfile formatter, and a modern version of dockfmt. Built on top of the internal buildkit parser.

Installation

Binaries

Binaries are available from the releases page.

go install

go install github.com/reteps/dockerfmt@latest

Usage

A updated version of the dockfmt. Uses the dockerfile parser from moby/buildkit and the shell formatter from mvdan/sh.

Usage:
  dockerfmt [Dockerfile...] [flags]
  dockerfmt [command]

Available Commands:
  completion  Generate the autocompletion script for the specified shell
  help        Help about any command
  version     Print the version number of dockerfmt

Flags:
  -c, --check             Check if the file(s) are formatted
  -h, --help              help for dockerfmt
  -i, --indent uint       Number of spaces to use for indentation (default 4)
  -n, --newline           End the file with a trailing newline
  -s, --space-redirects   Redirect operators will be followed by a space
  -w, --write             Write the formatted output back to the file(s)

Use "dockerfmt [command] --help" for more information about a command.

Pre-commit

You can add the following entry to your .pre-commit-config.yaml file to use dockerfmt as a pre-commit hook:

repos:
  - repo: https://github.com/reteps/dockerfmt
    # run `pre-commit autoupdate` to pin the version
    rev: main
    hooks:
      - id: dockerfmt
        args:
          # optional: add additional arguments here
          - --indent=4

Limitations

• The RUN parser currently doesn't support grouping or semicolons in commands. Adding semicolon support is a non-trivial task.

• No line wrapping is performed for long JSON commands

• The # escape=X directive is not supported

Contributions are welcome!

Issues

• This is not production software until the 1.0.0 release, please treat it as such.
• Please file issues for any bugs or feature requests!

Features

• Format RUN steps with https://github.com/mvdan/sh
• Support for basic heredocs:

RUN <<EOF
echo "hello"
echo "world"
EOF

• Support for basic inline comments in run steps:

RUN echo "hello" \
    # this is a comment
    && echo "world"

RUN echo "hello" \
    # this is a comment
    # that spans multiple lines
    && echo "world"

This is surprisingly non-trivial as we want to attach the comments to their position in the formatted output, but they are stripped by the parser beforehand.

JS Bindings

The JS bindings are available in the js directory. More information on how to use them can be found in the README file.