Configure vscode to autoformat file when press ctrl + s

vscode_autoformat.md

How to Auto-Format Dockerfiles and docker-compose in VS Code

This guide helps you automatically format your Dockerfile every time you press Ctrl+S in Visual Studio Code – no manual steps required! Debian/Ubuntu Edition

It also includes optional setup for Hadolint (a popular Dockerfile linter) to highlight best practices, security issues, and inefficiencies in real time.

Step 1: Install dockerfmt (Formatter) on Debian/Ubuntu

dockerfmt is the tool that formats your Dockerfile (indentation, multi-line RUN commands, etc.).

Manual binary install dockerfmt

1. Download the latest Linux x86_64 binary:

   wget https://github.com/reteps/dockerfmt/releases/latest/download/dockerfmt-Linux-x86_64 -O dockerfmt

2. Make it executable and move to a system directory:

   chmod +x dockerfmt
   sudo mv dockerfmt /usr/local/bin/

Verify installation:

dockerfmt --version

Step 2: Install hadolint (Linter) on Debian/Ubuntu

Hadolint scans your Dockerfile for best practices (e.g., unpinned versions, unnecessary packages) and security risks.

Direct binary install (fast and reliable)

sudo wget -O /usr/local/bin/hadolint https://github.com/hadolint/hadolint/releases/download/v2.12.0/hadolint-Linux-x86_64
sudo chmod +x /usr/local/bin/hadolint

Verify:

hadolint --version

Install yamlint

Linux / Windows (Go required)

go install github.com/google/yamlfmt@latest

Make sure it’s on your PATH:

yamlfmt --version

Step 3: Install Required VS Code Extensions

1. Open VS Code → Extensions view (Ctrl+Shift+X).
2. Install Run on Save by emeraldwalk (ID: emeraldwalk.runonsave) – this enables auto-formatting on save.
3. (Optional) Install hadolint by exiasr (ID: exiasr.hadolint) – provides real-time linting with underlines and a Problems panel.

Step 4: Configure VS Code Settings

Open your user settings.json:

• Press Ctrl+Shift+P → type Preferences: Open User Settings (JSON)

Add or merge this configuration:

{

    "files.autoSave": "afterDelay",
    // add with run on save, after that if I press ctrl + s in dockerfile, run dockerfmt
    "emeraldwalk.runonsave": {
        "commands": [
            {
                "match": "Dockerfile*",
                // "cmd": "dockerfmt --write --indent=4 --space-redirects --newline ${file}"
                "cmd": "dockerfmt --write --indent=4 --space-redirects ${file}"
            },
            {
                "match": "(docker-compose\\.ya?ml|compose\\.ya?ml|.*\\.ya?ml)",
                "cmd": "yamlfmt ${file}"
            }
        ]
    },
    "makefile.configureOnOpen": true,
    "editor.minimap.enabled": false,
    "git.confirmSync": false,
    "editor.formatOnSaveMode": "modificationsIfAvailable",
    "editor.formatOnSave": true,
    "notebook.formatOnSave.enabled": true,
    "mbake.formatOnSave": true,
    "files.autoSaveWhenNoErrors": true,
    "files.autoSaveWorkspaceFilesOnly": true,
}

Customization options

• Add --newline for a trailing newline:
  "cmd": "dockerfmt --write --indent=4 --space-redirects --newline ${file}"
• For 2-space indentation:
  "cmd": "dockerfmt --write --indent=2 --space-redirects ${file}"

Step 5: Test It!

1. Open or create a Dockerfile.
2. Add some intentionally messy multi-line commands (e.g., unindented RUN instructions).
3. Press Ctrl+S – the file should auto-format perfectly!
4. (If Hadolint is installed) Check the Problems panel for any linting warnings or suggestions.