# 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 is parsing the Dockerfile into an AST and performs rules on
top of the AST. It is standing 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 to provide 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 if you are 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 it doesn't work for you, please fall back to
Docker, `brew` or source installation.

If you are 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
```

As shown before, `hadolint` is available as a Docker container:

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

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

```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
```

## CLI

```bash
hadolint --help
```

```text
hadolint - Dockerfile Linter written in Haskell

Usage: hadolint [-v|--version] [--no-fail] [--no-color] [-c|--config FILENAME] 
                [-V|--verbose] [-f|--format ARG] [DOCKERFILE...] 
                [--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] [-t|--failure-theshold THRESHOLD]
  Lint Dockerfile for errors and best practices

Available options:
  -h,--help                Show this help text
  -v,--version             Show version
  --no-fail                Don't exit with a failure status code when any rule
                           is violated
  --no-color               Don't colorize output
  -c,--config FILENAME     Path to the configuration file
  -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 |
                           codacy] (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`
  -t,--failure-theshold THRESHOLD
                           Exit with failure code only when rules with a
                           severity above THRESHOLD are violated. Accepted
                           values: [error | warning | info | style | ignore |
                           none] (default: info)
```

## Configure

Configuration files can be used globally or per project. By default,
`hadolint` will look for a configuration file in the current directory
with the name `.hadolint.yaml` or `.hadolint.yml`

`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 | 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
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
```

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
```

The global configuration file should be placed in the folder
specified by `XDG_CONFIG_HOME`,
with the name `hadolint.yaml` or `hadolint.yml`. In summary, the
following locations are valid for the configuration file, in order
or preference:

- `$PWD/.hadolint.yaml`
- `$XDG_CONFIG_HOME/hadolint.yaml`
- `~/.config/hadolint.yaml`

In windows, the `%LOCALAPPDATA%` environment variable is used instead of `XDG_CONFIG_HOME`

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
```

## Inline ignores

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

```dockerfile
# hadolint ignore=DL3006
FROM ubuntu

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

Inline ignores will only work if place directly above the instruction.

## Linting Labels

Hadolint has the ability to check that specific labels be present and conform
to a predefined label schema.
First a label schema must be defined either via commandline:

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

or via 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 not specified in the label schema. To
warn on such additional labels, turn on strict labels:

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

or in the config file:

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

When strict labels is enabled, but no label schema has been 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 to your CI
or to 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` originate from `hadolint`. Take a look at
`Rules.hs` to find the implementation of the rules.

-   Rules with the `SC` prefix originate 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                                                                                                                                         |
|:-------------------------------------------------------------|:-----------------|:----------------------------------------------------------------------------------------------------------------------------------------------------|
| [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)   | IgnoreC          | `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.                                                                                            |
| [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 really thankful 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.

## Alternatives

- 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/platform/
[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