Improve README.md syntax

README.md

@@ -2,6 +2,7 @@
 [![Build Status](https://travis-ci.org/projectatomic/dockerfile_lint.svg?branch=master)](https://travis-ci.org/projectatomic/dockerfile_lint)
 
 # dockerfile-lint
+
 A rule based 'linter' for [Dockerfiles](https://docs.docker.com/engine/reference/builder/). The linter rules can be used  to check file syntax as well as arbitrary semantic and best practice attributes determined by the rule file writer.
 The linter can also be used to check LABEL rules against docker images.
 
@@ -21,56 +22,67 @@ The linter can also be used to check LABEL rules against docker images.
 - [License](#license)
 
 # Quickstart
+
 1. Change to directory where you have a Dockerfile
 2. run
-  * Atomic CLI
-
-            atomic run projectatomic/dockerfile-lint
 
-            atomic run projectatomic/dockerfile-lint image <imageid>
+- Atomic CLI
 
-  * Docker CLI
+```sh
+atomic run projectatomic/dockerfile-lint
 
-            docker run -it --rm -v $PWD:/root/ \
-                   projectatomic/dockerfile-lint \
-                   dockerfile_lint [-f Dockerfile]
+atomic run projectatomic/dockerfile-lint image <imageid>
+```
 
-            docker run -it --rm -v $PWD:/root/  \
-                   -v /var/run/docker.sock:/var/run/docker.sock \
-                   projectatomic/dockerfile-lint \
-                   dockerfile_lint  image <imageid>
+- Docker CLI
 
+```sh
+docker run -it --rm -v $PWD:/root/ \
+       projectatomic/dockerfile-lint \
+       dockerfile_lint [-f Dockerfile]
 
+docker run -it --rm -v $PWD:/root/  \
+       -v /var/run/docker.sock:/var/run/docker.sock \
+       projectatomic/dockerfile-lint \
+       dockerfile_lint image <imageid>
+```
 
 By default, the linter runs in strict mode (errors and/or warnings result in non-zero return code). Run the command with `-p`  or `--permissive` to
 run in permissive mode:
 
-            atomic run projectatomic/dockerfile-lint -p
+```sh
+atomic run projectatomic/dockerfile-lint -p
 
-            docker run -it --rm -v $PWD:/root/ \
-                               projectatomic/dockerfile-lint \
-                               dockerfile_lint -p -f Dockerfile
+docker run -it --rm -v $PWD:/root/ \
+       projectatomic/dockerfile-lint \
+       dockerfile_lint -p -f Dockerfile
+```
 
 # Extending and Customizing: Rule Files
+
 Rule files are written in [yaml](http://www.yaml.org/). See the example rule file **sample_rules.yaml** in the root folder of the project.
 The rules are implememented using regular expressions, run on one instruction of the dockerfile at a time.
 The rule file has 4 sections, a profile section, a general section, a line rule section and a required instruction section.
 
 ## Profile Section
+
 The profile section gives information about the rule file
 The information here is meant to help a user select a rule file that is appropriate for a given dockerfile. Example:
+
 ```yaml
 profile:
   name: "Default"
   description: "Default Profile. Checks basic syntax."
 ```
 
 ## General Section
+
 This section contains general syntax rules.
 
 ## Rule Attributes
 
 Here is an example of a line rule expressed in yaml:
+
 ```yaml
     label: "is_latest_tag"
     regex: /latest/
@@ -82,7 +94,9 @@ Here is an example of a line rule expressed in yaml:
 ```
 
 ## Line Rule Section
+
 This section contains rules that must be run on a given instruction in the dockerfile. There is a rule to check the syntax of each instruction and zero or more rules for semantic checks. The example below shows rules to run against the `FROM` instruction:
+
 ```yaml
 line_rules:
     FROM:
@@ -116,29 +130,37 @@ line_rules:
           description: "Base Image must be from Red Hat"
           reference_url:
 ```
+
 Note the (optional) `inverse_rule` attribute - this is just a convinient way to negate a regex rule - by default a rule is considered violated if it matches the regex pattern, but when 'inverse_rule' is set to 'true' the rule is violated if the line does not match the regex.
 
 ## Required Instruction Section
+
 This section includes a list of instructions that must exist in the dockerfile in order for it to be considered valid.
 
 ## Inline Ignore Instructions
-The user can tell dockerfile_lint to ignore a specific comand line inside a Dockerfile by placing a comment containing the word "dockerfile_lint" followed by the word "ignore", separated by a space, or a space and a dash/equals sign, above the command in the Dockerfile to be ignored. 
-```
+
+The user can tell dockerfile_lint to ignore a specific comand line inside a Dockerfile by placing a comment containing the word "dockerfile_lint" followed by the word "ignore", separated by a space, or a space and a dash/equals sign, above the command in the Dockerfile to be ignored.
+
+```Dockerfile
 # Add is required <for some previously approved reason documented here>
 # dockerfile_lint - ignore
 ADD http://example.com/big.tar.xz /usr/src/things/
 ```
+
 The above inline ignore would cause dockerfile_lint to skip processing the ADD command that follows it.  This allows the writing of strict rules in order to catch when best practices are not followed, while still being able to explicitly override the check on a case by case basis if a valid reason exists.  
 
 # Library Usage
 
 ## Node.js application use
+
 Install from github from your application root directory:
-```
+
+```sh
 npm install git+https://github.com/projectatomic/dockerfile_lint
 ```
 
 Import and use the validator:
+
 ```js
 var fs = require('fs');
 var rulefile = '/path/to/rulefile';
@@ -148,37 +170,46 @@ var result = validator.validate(dockerfile);
 ```
 
 ## Command Line use
+
 You can install the linter globally on your pc:
-```
+
+```sh
 sudo npm install -g dockerfile_lint
 ```
 
 Run the tool:
-```
+
+```sh
 dockerfile_lint  -f /path/to/dockerfile  [-f /path/to/second/dockerfile]  [-r /path/to/rule/file]
 ```
+
 A default rule file is used if no rule file is given.
 
 You can also run the tool without installing it - just clone the source repository and run the tool from the bin directory :
-```
+
+```sh
 git clone [email protected]:projectatomic/dockerfile_lint.git
 cd dockerfile_lint/bin
 chmod 555 dockerfile_lint
 dockerfile_lint  -f /path/to/dockerfile  [ -r /path/to/rule/file]
 ```
 
 To display results as JSON use the `-j` option:
-```
+
+```sh
 dockerfile_lint  -j -f /path/to/dockerfile  [ -r /path/to/rule/file]
 ```
 
 Command Help:
-```
+
+```sh
 dockerfile_lint  -h
 ```
 
 # Credits
-The linter is based on https://github.com/aweiteka/dockerfile_checker
+
+The linter is based on <https://github.com/aweiteka/dockerfile_checker>
 
 # License
+
 MIT