# Haskell Dockerfile Linter

[![Build Status][github-actions-img]][github-actions]
[![GPL-3 licensed][license-img]][license]
[![GitHub release][release-img]][release]
![Github downloads][downloads-img]
<img align="right" alt="pipecat" width="150"
src="https://hadolint.github.io/hadolint/img/cat_container.png" />

A smarter Dockerfile linter that helps you build [best practice][] Docker
images. The linter parses the Dockerfile into an AST and performs rules on
top of the AST. It stands on the shoulders of [ShellCheck][] to lint
the Bash code inside `RUN` instructions.

[:globe_with_meridians: **Check the online version on
hadolint.github.io/hadolint**](https://hadolint.github.io/hadolint)
[![Screenshot](screenshot.png)](https://hadolint.github.io/hadolint)

## How to use

You can run `hadolint` locally to lint your Dockerfile.

```bash
hadolint <Dockerfile>
hadolint --ignore DL3003 --ignore DL3006 <Dockerfile> # exclude specific rules
hadolint --trusted-registry my-company.com:500 <Dockerfile> # Warn when using untrusted FROM images
```

Docker comes to the rescue, providing an easy way how to run `hadolint` on most
platforms.
Just pipe your `Dockerfile` to `docker run`:

```bash
docker run --rm -i hadolint/hadolint < Dockerfile
# OR
docker run --rm -i ghcr.io/hadolint/hadolint < Dockerfile
```

or using [Podman](https://podman.io/):

```bash
podman run --rm -i docker.io/hadolint/hadolint < Dockerfile
# OR
podman run --rm -i ghcr.io/hadolint/hadolint < Dockerfile
```

or using Windows PowerShell:

```powershell
cat .\Dockerfile | docker run --rm -i hadolint/hadolint
```

## Install

You can download prebuilt binaries for OSX, Windows and Linux from the latest
[release page][]. However, if this does not work for you, please fall back to
container (Docker), `brew` or source installation.

On OSX, you can use [brew](https://brew.sh/) to install `hadolint`.

```bash
brew install hadolint
```

On Windows, you can use [scoop](https://github.com/lukesampson/scoop) to
install `hadolint`.

```batch
scoop install hadolint
```

On distributions that have `nix` installed, you can use the `hadolint`
package to run ad-hoc shells or permanently install `hadolint` into
your environment.

As mentioned earlier, `hadolint` is available as a container image:

```bash
docker pull hadolint/hadolint
# OR
docker pull ghcr.io/hadolint/hadolint
```

If you need a container with shell access, use the Debian or Alpine
variants:

```bash
docker pull hadolint/hadolint:latest-debian
# OR
docker pull hadolint/hadolint:latest-alpine
# OR
docker pull ghcr.io/hadolint/hadolint:latest-debian
# OR
docker pull ghcr.io/hadolint/hadolint:latest-alpine
```

You can also build `hadolint` locally. You need [Haskell][] and the [stack][]
build tool to build the binary.

```bash
git clone https://github.com/hadolint/hadolint \
&& cd hadolint \
&& stack install
```

If you want the
[VS Code Hadolint](https://github.com/michaellzc/vscode-hadolint)
extension to use Hadolint in a container, you can use the following
[wrapper script](https://github.com/hadolint/hadolint/issues/691#issuecomment-932116329):

```bash
#!/bin/bash
dockerfile="$1"
shift
docker run --rm -i hadolint/hadolint hadolint "$@" - < "$dockerfile"
```

## CLI

```bash
hadolint --help
```

```text
hadolint - Dockerfile Linter written in Haskell

Usage: hadolint [-v|--version] [-c|--config FILENAME] [DOCKERFILE...]
                [--file-path-in-report FILEPATHINREPORT] [--no-fail]
                [--no-color] [-V|--verbose] [-f|--format ARG] [--error RULECODE]
                [--warning RULECODE] [--info RULECODE] [--style RULECODE]
                [--ignore RULECODE]
                [--trusted-registry REGISTRY (e.g. docker.io)]
                [--require-label LABELSCHEMA (e.g. maintainer:text)]
                [--strict-labels] [--disable-ignore-pragma]
                [-t|--failure-threshold THRESHOLD]
  Lint Dockerfile for errors and best practices

Available options:
  -h,--help                Show this help text
  -v,--version             Show version
  -c,--config FILENAME     Path to the configuration file
  --file-path-in-report FILEPATHINREPORT
                           The file path referenced in the generated report.
                           This only applies for the 'checkstyle' format and is
                           useful when running Hadolint with Docker to set the
                           correct file path.
  --no-fail                Don't exit with a failure status code when any rule
                           is violated
  --no-color               Don't colorize output
  -V,--verbose             Enables verbose logging of hadolint's output to
                           stderr
  -f,--format ARG          The output format for the results [tty | json |
                           checkstyle | codeclimate | gitlab_codeclimate | gnu |
                           codacy | sonarqube | sarif] (default: tty)
  --error RULECODE         Make the rule `RULECODE` have the level `error`
  --warning RULECODE       Make the rule `RULECODE` have the level `warning`
  --info RULECODE          Make the rule `RULECODE` have the level `info`
  --style RULECODE         Make the rule `RULECODE` have the level `style`
  --ignore RULECODE        A rule to ignore. If present, the ignore list in the
                           config file is ignored
  --trusted-registry REGISTRY (e.g. docker.io)
                           A docker registry to allow to appear in FROM
                           instructions
  --require-label LABELSCHEMA (e.g. maintainer:text)
                           The option --require-label=label:format makes
                           Hadolint check that the label `label` conforms to
                           format requirement `format`
  --strict-labels          Do not permit labels other than specified in
                           `label-schema`
  --disable-ignore-pragma  Disable inline ignore pragmas `# hadolint
                           ignore=DLxxxx`
  -t,--failure-threshold THRESHOLD
                           Exit with failure code only when rules with a
                           severity equal to or above THRESHOLD are violated.
                           Accepted values: [error | warning | info | style |
                           ignore | none] (default: info)
```

## Configure

Configuration files can be used globally or per project.
Hadolint looks for configuration files in the following locations or their
platform specific equivalents in this order and uses the first one exclusively:
- `$PWD/.hadolint.yaml`
- `$XDG_CONFIG_HOME/hadolint.yaml`
- `$HOME/.config/hadolint.yaml`
- `$HOME/.hadolint/hadolint.yaml or $HOME/hadolint/config.yaml`
- `$HOME/.hadolint.yaml`

In windows, the `%LOCALAPPDATA%` environment variable is used instead of 
`XDG_CONFIG_HOME`. Config files can have either `yaml` or `yml` extensions.

`hadolint` full `yaml` config file schema

```yaml
failure-threshold: string               # name of threshold level (error | warning | info | style | ignore | none)
format: string                          # Output format (tty | json | checkstyle | codeclimate | gitlab_codeclimate | gnu | codacy)
ignored: [string]                       # list of rules
label-schema:                           # See Linting Labels below for specific label-schema details
  author: string                        # Your name
  contact: string                       # email address
  created: timestamp                    # rfc3339 datetime
  version: string                       # semver
  documentation: string                 # url
  git-revision: string                  # hash
  license: string                       # spdx
no-color: boolean                       # true | false
no-fail: boolean                        # true | false
override:
  error: [string]                       # list of rules
  warning: [string]                     # list of rules
  info: [string]                        # list of rules
  style: [string]                       # list of rules
strict-labels: boolean                  # true | false
disable-ignore-pragma: boolean          # true | false
trustedRegistries: string | [string]    # registry or list of registries
```

`hadolint` supports specifying the ignored rules using a configuration
file. The configuration file should be in `yaml` format. This is one
valid configuration file as an example:

```yaml
ignored:
  - DL3000
  - SC1010
```

Additionally, `hadolint` can warn you when images from untrusted
repositories are being used in Dockerfiles, you can append the
`trustedRegistries` keys to the configuration file, as shown below:

```yaml
ignored:
  - DL3000
  - SC1010

trustedRegistries:
  - docker.io
  - my-company.com:5000
  - "*.gcr.io"
```

If you want to override the severity of specific rules, you can do that too:

```yaml
override:
  error:
    - DL3001
    - DL3002
  warning:
    - DL3042
    - DL3033
  info:
    - DL3032
  style:
    - DL3015
```

`failure-threshold` Exit with failure code only when rules with a
severity above THRESHOLD are violated (Available in v2.6.0+)

```yaml
failure-threshold: info
warning:
    - DL3042
    - DL3033
  info:
    - DL3032
```

Additionally, you can pass a custom configuration file in the command line with
the `--config` option

```bash
hadolint --config /path/to/config.yaml Dockerfile
```

To pass a custom configuration file (using relative or absolute path) to
a container, use the following command:

```bash
docker run --rm -i -v /your/path/to/hadolint.yaml:/.config/hadolint.yaml hadolint/hadolint < Dockerfile
# OR
docker run --rm -i -v /your/path/to/hadolint.yaml:/.config/hadolint.yaml ghcr.io/hadolint/hadolint < Dockerfile
```

In addition to config files, Hadolint can be configured with environment
variables.
```bash
NO_COLOR=1                               # Set or unset. See https://no-color.org
HADOLINT_NOFAIL=1                        # Truthy value e.g. 1, true or yes
HADOLINT_VERBOSE=1                       # Truthy value e.g. 1, true or yes
HADOLINT_FORMAT=json                     # Output format (tty | json | checkstyle | codeclimate | gitlab_codeclimate | gnu | codacy | sarif )
HADOLINT_FAILURE_THRESHOLD=info          # threshold level (error | warning | info | style | ignore | none)
HADOLINT_OVERRIDE_ERROR=DL3010,DL3020    # comma separated list of rule codes
HADOLINT_OVERRIDE_WARNING=DL3010,DL3020  # comma separated list of rule codes
HADOLINT_OVERRIDE_INFO=DL3010,DL3020     # comma separated list of rule codes
HADOLINT_OVERRIDE_STYLE=DL3010,DL3020    # comma separated list of rule codes
HADOLINT_IGNORE=DL3010,DL3020            # comma separated list of rule codes
HADOLINT_STRICT_LABELS=1                 # Truthy value e.g. 1, true or yes
HADOLINT_DISABLE_IGNORE_PRAGMA=1         # Truthy value e.g. 1, true or yes
HADOLINT_TRUSTED_REGISTRIES=docker.io    # comma separated list of registry urls
HADOLINT_REQUIRE_LABELS=maintainer:text  # comma separated list of label schema items
```

## Non-Posix Shells

When using base images with non-posix shells as default (e.g. Windows based
images) a special pragma `hadolint shell` can specify which shell the base image
uses, so that Hadolint can automatically ignore all shell-specific rules.

```Dockerfile
FROM mcr.microsoft.com/windows/servercore:ltsc2022
# hadolint shell=powershell
RUN Get-Process notepad | Stop-Process
```

## Inline ignores

It is also possible to ignore rules by adding a special comment directly
above the Dockerfile statement for which you want to make an exception for.
Such comments look like
`# hadolint ignore=DL3001,SC1081`. For example:

```dockerfile
# hadolint ignore=DL3006
FROM ubuntu

# hadolint ignore=DL3003,SC1035
RUN cd /tmp && echo "hello!"
```

The comment "inline ignores" applies only to the statement following it.

## Global ignores

Rules can also be ignored on a per-file basis using the global ignore pragma.
It works just like inline ignores, excep that it applies to the whole file
instead of just the next line.

```dockerfile
# hadolint global ignore=DL3003,DL3006,SC1035
FROM ubuntu

RUN cd /tmp && echo "foo"
```

## Linting Labels

Hadolint is able to check if specific labels are present and conform
to a predefined label schema.
First, a label schema must be defined either via the command line:

```bash
hadolint --require-label author:text --require-label version:semver Dockerfile
```

or via the config file:

```yaml
label-schema:
  author: text
  contact: email
  created: rfc3339
  version: semver
  documentation: url
  git-revision: hash
  license: spdx
```

The value of a label can be either of `text`, `url`, `semver`, `hash` or
`rfc3339`:
| Schema  | Description                                        |
|:--------|:---------------------------------------------------|
| text    | Anything                                           |
| rfc3339 | A time, formatted according to [RFC 3339][rfc3339] |
| semver  | A [semantic version][semver]                       |
| url     | A URI as described in [RFC 3986][rfc3986]          |
| hash    | Either a short or a long [Git hash][githash]       |
| spdx    | An [SPDX license identifier][spdxid]               |
| email   | An email address conforming to [RFC 5322][rfc5322] |

By default, Hadolint ignores any label that is not specified in the label schema. To
warn against such additional labels, turn on strict labels, using the command line:

```bash
hadolint --strict-labels --require-label version:semver Dockerfile
```

or the config file:

```yaml
strict-labels: true
```

When strict labels is enabled, but no label schema is specified, `hadolint`
will warn if any label is present.

### Note on dealing with variables in labels

It is a common pattern to fill the value of a label not statically, but rather
dynamically at build time by using a variable:

```dockerfile
FROM debian:buster
ARG VERSION="du-jour"
LABEL version="${VERSION}"
```

To allow this, the label schema must specify `text` as value for that label:

```yaml
label-schema:
  version: text
```

## Integrations

To get most of `hadolint`, it is useful to integrate it as a check in your CI
or into your editor, or as a pre-commit hook, to lint your `Dockerfile` as you
write it. See our [Integration][] docs.

- [Code Review Platform Integrations][]
- [Continuous Integrations][]
- [Editor Integrations][]
- [Version Control Integrations][]

## Rules

An incomplete list of implemented rules. Click on the error code to get more
detailed information.

-   Rules with the prefix `DL` are from `hadolint`. Have a look at
    `Rules.hs` to find the implementation of the rules.

-   Rules with the `SC` prefix are from **ShellCheck** (only the most
    common rules are listed, there are dozens more).

Please [create an issue][] if you have an idea for a good rule.

<!--lint disable maximum-line-length-->

| Rule                                                         | Default Severity | Description                                                                                                                                         |
| :----------------------------------------------------------- | :--------------- | :-------------------------------------------------------------------------------------------------------------------------------------------------- |
| [DL1001](https://github.com/hadolint/hadolint/wiki/DL1001)   | Ignore           | Please refrain from using inline ignore pragmas `# hadolint ignore=DLxxxx`.                                                                         |
| [DL3000](https://github.com/hadolint/hadolint/wiki/DL3000)   | Error            | Use absolute WORKDIR.                                                                                                                               |
| [DL3001](https://github.com/hadolint/hadolint/wiki/DL3001)   | Info             | For some bash commands it makes no sense running them in a Docker container like ssh, vim, shutdown, service, ps, free, top, kill, mount, ifconfig. |
| [DL3002](https://github.com/hadolint/hadolint/wiki/DL3002)   | Warning          | Last user should not be root.                                                                                                                       |
| [DL3003](https://github.com/hadolint/hadolint/wiki/DL3003)   | Warning          | Use WORKDIR to switch to a directory.                                                                                                               |
| [DL3004](https://github.com/hadolint/hadolint/wiki/DL3004)   | Error            | Do not use sudo as it leads to unpredictable behavior. Use a tool like gosu to enforce root.                                                        |
| [DL3005](https://github.com/hadolint/hadolint/wiki/DL3005)   | Error            | Do not use apt-get dist-upgrade.                                                                                                                    |
| [DL3006](https://github.com/hadolint/hadolint/wiki/DL3006)   | Warning          | Always tag the version of an image explicitly.                                                                                                      |
| [DL3007](https://github.com/hadolint/hadolint/wiki/DL3007)   | Warning          | Using latest is prone to errors if the image will ever update. Pin the version explicitly to a release tag.                                         |
| [DL3008](https://github.com/hadolint/hadolint/wiki/DL3008)   | Warning          | Pin versions in `apt-get install`.                                                                                                                  |
| [DL3009](https://github.com/hadolint/hadolint/wiki/DL3009)   | Info             | Delete the apt-get lists after installing something.                                                                                                |
| [DL3010](https://github.com/hadolint/hadolint/wiki/DL3010)   | Info             | Use ADD for extracting archives into an image.                                                                                                      |
| [DL3011](https://github.com/hadolint/hadolint/wiki/DL3011)   | Error            | Valid UNIX ports range from 0 to 65535.                                                                                                             |
| [DL3012](https://github.com/hadolint/hadolint/wiki/DL3012)   | Error            | Multiple `HEALTHCHECK` instructions.                                                                                                                |
| [DL3013](https://github.com/hadolint/hadolint/wiki/DL3013)   | Warning          | Pin versions in pip.                                                                                                                                |
| [DL3014](https://github.com/hadolint/hadolint/wiki/DL3014)   | Warning          | Use the `-y` switch.                                                                                                                                |
| [DL3015](https://github.com/hadolint/hadolint/wiki/DL3015)   | Info             | Avoid additional packages by specifying `--no-install-recommends`.                                                                                  |
| [DL3016](https://github.com/hadolint/hadolint/wiki/DL3016)   | Warning          | Pin versions in `npm`.                                                                                                                              |
| [DL3018](https://github.com/hadolint/hadolint/wiki/DL3018)   | Warning          | Pin versions in `apk add`. Instead of `apk add <package>` use `apk add <package>=<version>`.                                                        |
| [DL3019](https://github.com/hadolint/hadolint/wiki/DL3019)   | Info             | Use the `--no-cache` switch to avoid the need to use `--update` and remove `/var/cache/apk/*` when done installing packages.                        |
| [DL3020](https://github.com/hadolint/hadolint/wiki/DL3020)   | Error            | Use `COPY` instead of `ADD` for files and folders.                                                                                                  |
| [DL3021](https://github.com/hadolint/hadolint/wiki/DL3021)   | Error            | `COPY` with more than 2 arguments requires the last argument to end with `/`                                                                        |
| [DL3022](https://github.com/hadolint/hadolint/wiki/DL3022)   | Warning          | `COPY --from` should reference a previously defined `FROM` alias                                                                                    |
| [DL3023](https://github.com/hadolint/hadolint/wiki/DL3023)   | Error            | `COPY --from` cannot reference its own `FROM` alias                                                                                                 |
| [DL3024](https://github.com/hadolint/hadolint/wiki/DL3024)   | Error            | `FROM` aliases (stage names) must be unique                                                                                                         |
| [DL3025](https://github.com/hadolint/hadolint/wiki/DL3025)   | Warning          | Use arguments JSON notation for CMD and ENTRYPOINT arguments                                                                                        |
| [DL3026](https://github.com/hadolint/hadolint/wiki/DL3026)   | Error            | Use only an allowed registry in the `FROM image`                                                                                                    |
| [DL3027](https://github.com/hadolint/hadolint/wiki/DL3027)   | Warning          | Do not use `apt` as it is meant to be a end-user tool, use `apt-get` or `apt-cache` instead                                                         |
| [DL3028](https://github.com/hadolint/hadolint/wiki/DL3028)   | Warning          | Pin versions in gem install. Instead of `gem install <gem>` use `gem install <gem>:<version>`                                                       |
| [DL3029](https://github.com/hadolint/hadolint/wiki/DL3029)   | Warning          | Do not use --platform flag with FROM.                                                                                                               |
| [DL3030](https://github.com/hadolint/hadolint/wiki/DL3030)   | Warning          | Use the `-y` switch to avoid manual input `yum install -y <package>`                                                                                |
| [DL3032](https://github.com/hadolint/hadolint/wiki/DL3032)   | Warning          | `yum clean all` missing after yum command.                                                                                                          |
| [DL3033](https://github.com/hadolint/hadolint/wiki/DL3033)   | Warning          | Specify version with `yum install -y <package>-<version>`                                                                                           |
| [DL3034](https://github.com/hadolint/hadolint/wiki/DL3034)   | Warning          | Non-interactive switch missing from `zypper` command: `zypper install -y`                                                                           |
| [DL3035](https://github.com/hadolint/hadolint/wiki/DL3035)   | Warning          | Do not use `zypper dist-upgrade`.                                                                                                                   |
| [DL3036](https://github.com/hadolint/hadolint/wiki/DL3036)   | Warning          | `zypper clean` missing after zypper use.                                                                                                            |
| [DL3037](https://github.com/hadolint/hadolint/wiki/DL3037)   | Warning          | Specify version with `zypper install -y <package>[=]<version>`.                                                                                     |
| [DL3038](https://github.com/hadolint/hadolint/wiki/DL3038)   | Warning          | Use the `-y` switch to avoid manual input `dnf install -y <package>`                                                                                |
| [DL3040](https://github.com/hadolint/hadolint/wiki/DL3040)   | Warning          | `dnf clean all` missing after dnf command.                                                                                                          |
| [DL3041](https://github.com/hadolint/hadolint/wiki/DL3041)   | Warning          | Specify version with `dnf install -y <package>-<version>`                                                                                           |
| [DL3042](https://github.com/hadolint/hadolint/wiki/DL3042)   | Warning          | Avoid cache directory with `pip install --no-cache-dir <package>`.                                                                                  |
| [DL3043](https://github.com/hadolint/hadolint/wiki/DL3043)   | Error            | `ONBUILD`, `FROM` or `MAINTAINER` triggered from within `ONBUILD` instruction.                                                                      |
| [DL3044](https://github.com/hadolint/hadolint/wiki/DL3044)   | Error            | Do not refer to an environment variable within the same `ENV` statement where it is defined.                                                        |
| [DL3045](https://github.com/hadolint/hadolint/wiki/DL3045)   | Warning          | `COPY` to a relative destination without `WORKDIR` set.                                                                                             |
| [DL3046](https://github.com/hadolint/hadolint/wiki/DL3046)   | Warning          | `useradd` without flag `-l` and high UID will result in excessively large Image.                                                                    |
| [DL3047](https://github.com/hadolint/hadolint/wiki/DL3047)   | Info             | `wget` without flag `--progress` will result in excessively bloated build logs when downloading larger files.                                       |
| [DL3048](https://github.com/hadolint/hadolint/wiki/DL3048)   | Style            | Invalid Label Key                                                                                                                                   |
| [DL3049](https://github.com/hadolint/hadolint/wiki/DL3049)   | Info             | Label `<label>` is missing.                                                                                                                         |
| [DL3050](https://github.com/hadolint/hadolint/wiki/DL3050)   | Info             | Superfluous label(s) present.                                                                                                                       |
| [DL3051](https://github.com/hadolint/hadolint/wiki/DL3051)   | Warning          | Label `<label>` is empty.                                                                                                                           |
| [DL3052](https://github.com/hadolint/hadolint/wiki/DL3052)   | Warning          | Label `<label>` is not a valid URL.                                                                                                                 |
| [DL3053](https://github.com/hadolint/hadolint/wiki/DL3053)   | Warning          | Label `<label>` is not a valid time format - must be conform to RFC3339.                                                                            |
| [DL3054](https://github.com/hadolint/hadolint/wiki/DL3054)   | Warning          | Label `<label>` is not a valid SPDX license identifier.                                                                                             |
| [DL3055](https://github.com/hadolint/hadolint/wiki/DL3055)   | Warning          | Label `<label>` is not a valid git hash.                                                                                                            |
| [DL3056](https://github.com/hadolint/hadolint/wiki/DL3056)   | Warning          | Label `<label>` does not conform to semantic versioning.                                                                                            |
| [DL3057](https://github.com/hadolint/hadolint/wiki/DL3057)   | Ignore           | `HEALTHCHECK` instruction missing.                                                                                                                  |
| [DL3058](https://github.com/hadolint/hadolint/wiki/DL3058)   | Warning          | Label `<label>` is not a valid email format - must be conform to RFC5322.                                                                           |
| [DL3059](https://github.com/hadolint/hadolint/wiki/DL3059)   | Info             | Multiple consecutive `RUN` instructions. Consider consolidation.                                                                                    |
| [DL3060](https://github.com/hadolint/hadolint/wiki/DL3060)   | Info             | `yarn cache clean` missing after `yarn install` was run.                                                                                            |
| [DL3061](https://github.com/hadolint/hadolint/wiki/DL3061)   | Error            | Invalid instruction order. Dockerfile must begin with `FROM`, `ARG` or comment.                                                                     |
| [DL4000](https://github.com/hadolint/hadolint/wiki/DL4000)   | Error            | `MAINTAINER` is deprecated.                                                                                                                         |
| [DL4001](https://github.com/hadolint/hadolint/wiki/DL4001)   | Warning          | Either use Wget or Curl but not both.                                                                                                               |
| [DL4003](https://github.com/hadolint/hadolint/wiki/DL4003)   | Warning          | Multiple `CMD` instructions found.                                                                                                                  |
| [DL4004](https://github.com/hadolint/hadolint/wiki/DL4004)   | Error            | Multiple `ENTRYPOINT` instructions found.                                                                                                           |
| [DL4005](https://github.com/hadolint/hadolint/wiki/DL4005)   | Warning          | Use `SHELL` to change the default shell.                                                                                                            |
| [DL4006](https://github.com/hadolint/hadolint/wiki/DL4006)   | Warning          | Set the `SHELL` option -o pipefail before `RUN` with a pipe in it                                                                                   |
| [SC1000](https://github.com/koalaman/shellcheck/wiki/SC1000) |                  | `$` is not used specially and should therefore be escaped.                                                                                          |
| [SC1001](https://github.com/koalaman/shellcheck/wiki/SC1001) |                  | This `\c` will be a regular `'c'` in this context.                                                                                                  |
| [SC1007](https://github.com/koalaman/shellcheck/wiki/SC1007) |                  | Remove space after `=` if trying to assign a value (or for empty string, use `var='' ...`).                                                         |
| [SC1010](https://github.com/koalaman/shellcheck/wiki/SC1010) |                  | Use semicolon or linefeed before `done` (or quote to make it literal).                                                                              |
| [SC1018](https://github.com/koalaman/shellcheck/wiki/SC1018) |                  | This is a unicode non-breaking space. Delete it and retype as space.                                                                                |
| [SC1035](https://github.com/koalaman/shellcheck/wiki/SC1035) |                  | You need a space here                                                                                                                               |
| [SC1045](https://github.com/koalaman/shellcheck/wiki/SC1045) |                  | It's not `foo &; bar`, just `foo & bar`.                                                                                                            |
| [SC1065](https://github.com/koalaman/shellcheck/wiki/SC1065) |                  | Trying to declare parameters? Don't. Use `()` and refer to params as `$1`, `$2` etc.                                                                |
| [SC1066](https://github.com/koalaman/shellcheck/wiki/SC1066) |                  | Don't use $ on the left side of assignments.                                                                                                        |
| [SC1068](https://github.com/koalaman/shellcheck/wiki/SC1068) |                  | Don't put spaces around the `=` in assignments.                                                                                                     |
| [SC1077](https://github.com/koalaman/shellcheck/wiki/SC1077) |                  | For command expansion, the tick should slant left (\` vs ´).                                                                                        |
| [SC1078](https://github.com/koalaman/shellcheck/wiki/SC1078) |                  | Did you forget to close this double-quoted string?                                                                                                  |
| [SC1079](https://github.com/koalaman/shellcheck/wiki/SC1079) |                  | This is actually an end quote, but due to next char, it looks suspect.                                                                              |
| [SC1081](https://github.com/koalaman/shellcheck/wiki/SC1081) |                  | Scripts are case sensitive. Use `if`, not `If`.                                                                                                     |
| [SC1083](https://github.com/koalaman/shellcheck/wiki/SC1083) |                  | This `{/}` is literal. Check expression (missing `;/\n`?) or quote it.                                                                              |
| [SC1086](https://github.com/koalaman/shellcheck/wiki/SC1086) |                  | Don't use `$` on the iterator name in for loops.                                                                                                    |
| [SC1087](https://github.com/koalaman/shellcheck/wiki/SC1087) |                  | Braces are required when expanding arrays, as in `${array[idx]}`.                                                                                   |
| [SC1095](https://github.com/koalaman/shellcheck/wiki/SC1095) |                  | You need a space or linefeed between the function name and body.                                                                                    |
| [SC1097](https://github.com/koalaman/shellcheck/wiki/SC1097) |                  | Unexpected `==`. For assignment, use `=`. For comparison, use `[ .. ]` or `[[ .. ]]`.                                                               |
| [SC1098](https://github.com/koalaman/shellcheck/wiki/SC1098) |                  | Quote/escape special characters when using `eval`, e.g. `eval "a=(b)"`.                                                                             |
| [SC1099](https://github.com/koalaman/shellcheck/wiki/SC1099) |                  | You need a space before the `#`.                                                                                                                    |
| [SC2002](https://github.com/koalaman/shellcheck/wiki/SC2002) |                  | Useless cat. Consider <code>cmd < file &#124; ..</code> or <code>cmd file &#124; ..</code> instead.                                                 |
| [SC2015](https://github.com/koalaman/shellcheck/wiki/SC2015) |                  | Note that <code>A && B &#124;&#124; C</code> is not if-then-else. C may run when A is true.                                                         |
| [SC2026](https://github.com/koalaman/shellcheck/wiki/SC2026) |                  | This word is outside of quotes. Did you intend to 'nest '"'single quotes'"' instead'?                                                               |
| [SC2028](https://github.com/koalaman/shellcheck/wiki/SC2028) |                  | `echo` won't expand escape sequences. Consider `printf`.                                                                                            |
| [SC2035](https://github.com/koalaman/shellcheck/wiki/SC2035) |                  | Use `./*glob*` or `-- *glob*` so names with dashes won't become options.                                                                            |
| [SC2039](https://github.com/koalaman/shellcheck/wiki/SC2039) |                  | In POSIX sh, something is undefined.                                                                                                                |
| [SC2046](https://github.com/koalaman/shellcheck/wiki/SC2046) |                  | Quote this to prevent word splitting                                                                                                                |
| [SC2086](https://github.com/koalaman/shellcheck/wiki/SC2086) |                  | Double quote to prevent globbing and word splitting.                                                                                                |
| [SC2140](https://github.com/koalaman/shellcheck/wiki/SC2140) |                  | Word is in the form `"A"B"C"` (B indicated). Did you mean `"ABC"` or `"A\"B\"C"`?                                                                   |
| [SC2154](https://github.com/koalaman/shellcheck/wiki/SC2154) |                  | var is referenced but not assigned.                                                                                                                 |
| [SC2155](https://github.com/koalaman/shellcheck/wiki/SC2155) |                  | Declare and assign separately to avoid masking return values.                                                                                       |
| [SC2164](https://github.com/koalaman/shellcheck/wiki/SC2164) |                  | Use <code>cd ... &#124;&#124; exit</code> in case `cd` fails.                                                                                       |

<!--lint enable maximum-line-length-->

## Develop

If you are an experienced Haskeller, we would be very grateful if you would
tear our code apart in a review.

### Setup

1.  Clone repository

    ```bash
    git clone --recursive git@github.com:hadolint/hadolint.git
    ```

1.  Install the dependencies

    ```bash
    stack install
    ```

### REPL

The easiest way to try out the parser is using the REPL.

```bash
# start the repl
stack repl
# overload strings to be able to use Text
:set -XOverloadedStrings
# import parser library
import Language.Docker
# parse instruction and look at AST representation
parseText "FROM debian:jessie"
```

### Tests

Run unit tests:

```bash
stack test
```

Run integration tests:

```bash
./integration_test.sh
```

### AST

Dockerfile syntax is fully described in the [Dockerfile reference][].
Just take a look at [Syntax.hs][] in the `language-docker` project to see
the AST definition.

### Building against custom libraries

Hadolint uses many libraries to do the dirty work. In particular,
language-docker is used to parse Dockerfiles and produce an AST which then can
be analyzed. To build Hadolint against a custom version of such libraries, do
the following. This example uses language-docker, but it would work with any
other libaray as well.

 1) In the same directory (e.g. `/home/user/repos`) clone Hadolint and
    language-docker git repositories
```bash
cd /home/user/repos
git clone https://github.com/hadolint/hadolint.git
git clone https://github.com/hadolint/language-docker.git
```

 2) Make your modifications to language-docker

 3) In the Hadolint repo, edit the `stack.yaml` file, such that the `extra-deps`
    property points to the other repo
```yaml
[...]
extra-deps:
  - ../language-docker
[...]
```

 4) Recompile Hadolint and run the tests
```bash
cd /home/user/repos/hadolint
stack test
```

## Alternatives

-   replicatedhq/[dockerfilelint](https://github.com/replicatedhq/dockerfilelint),
    the other linter used by the [super-linter](https://github.com/github/super-linter/blob/main/README.md#supported-linters)

-   RedCoolBeans/[dockerlint](https://github.com/RedCoolBeans/dockerlint/)

-   projectatomic/[dockerfile_lint](https://github.com/projectatomic/dockerfile_lint/)

<!-- References -->

[github-actions-img]: https://github.com/hadolint/hadolint/workflows/Haskell%20Tests/badge.svg?branch=master
[github-actions]: https://travis-ci.org/hadolint/hadolint/actions
[license-img]: https://img.shields.io/badge/license-GPL--3-blue.svg
[license]: https://tldrlegal.com/l/gpl-3.0
[release-img]: https://img.shields.io/github/release/hadolint/hadolint.svg
[release]: https://github.com/hadolint/hadolint/releases/latest
[downloads-img]: https://img.shields.io/github/downloads/hadolint/hadolint/total.svg
[best practice]: https://docs.docker.com/engine/userguide/eng-image/dockerfile_best-practices
[shellcheck]: https://github.com/koalaman/shellcheck
[release page]: https://github.com/hadolint/hadolint/releases/latest
[haskell]: https://www.haskell.org/downloads/
[stack]: http://docs.haskellstack.org/en/stable/install_and_upgrade.html
[integration]: docs/INTEGRATION.md
[code review platform integrations]: docs/INTEGRATION.md#code-review
[continuous integrations]: docs/INTEGRATION.md#continuous-integration
[editor integrations]: docs/INTEGRATION.md#editors
[version control integrations]: docs/INTEGRATION.md#version-control
[create an issue]: https://github.com/hadolint/hadolint/issues/new
[dockerfile reference]: http://docs.docker.com/engine/reference/builder/
[syntax.hs]: https://www.stackage.org/haddock/nightly-2018-01-07/language-docker-2.0.1/Language-Docker-Syntax.html
[rfc3339]: https://www.ietf.org/rfc/rfc3339.txt
[semver]: https://semver.org/
[rfc3986]: https://www.ietf.org/rfc/rfc3986.txt
[githash]: https://git-scm.com/book/en/v2/Git-Tools-Revision-Selection
[spdxid]: https://spdx.org/licenses/
[rfc5322]: https://www.ietf.org/rfc/rfc5322.txt