Creating a Basic Markdown Preview Tool

Working with files is one of the most frequent tasks we perform when building command-line tools. Programs pull data from files and also save results in them. This is particularly important when working with Linux or Unix because system resources are represented as files.

To get comfortable working with files in CLI apps, we’ll be developing a tool to preview Markdown files locally, using a web browser.

The tool we’ll write converts the Markdown source into HTML that can be viewed in a browser. To work with files in Go, we’ll use the packages os and io from the standard library. We’ll create and open files so that we can read data or save it to files using different methods. We’ll handle paths consistently across multiple platforms to make our code more flexible, ensuring our tool works in cross-platform scenarios. We’ll use the defer statement to effectively clean up used resources. In addition, we’ll apply the io.Writer interface, which is a powerful concept of the language. Finally, we’ll work with temporary files and templates.

Markdown preview tool

Let’s implement the initial version of the Markdown preview tool. We’ll call this tool mdp (for Markdown preview) and accept the file name of the Markdown file to be previewed as its argument. This tool will perform four main steps:

• Read the contents of the input Markdown file.
• Use some Go external libraries to parse Markdown and generate a valid HTML block.
• Wrap the results with an HTML header and footer.
• Save the buffer to an HTML file that can be viewed in a browser.

Below, we’ll go over how to use an external package called blackfriday to convert Markdown into HTML. But according to its documentation, it doesn’t sanitize the output to prevent malicious content. To ensure that our tool generates safe output, we’ll sanitize the content using another external package called bluemonday. For more information, check this package’s GitHub ...