How to embed code from repo in github markdown?

@Petros's answer is (still) correct, however I got annoyed enough with this that I've created a tool to automate the copying and keep your readme synchronised with the source - https://github.com/zakhenry/embedme

Example usage from the accepted answer

Insert a comment into the code fence

```rb
# path/to/your/file.rb
```

Run npx embedme README.md (this assumes you have Nodejs installed)

The README will be written in-place, with the content of the file following your comment

```rb
# path/to/your/file.rb
class MyClass
end
```

Note that as the comment is still there, you can happily re-run npx embedme README.md again and it won't make any change.

If you have CI, you can also run npx embedme --verify README.md which will return 1 if it detects a diff (this would mean that the source was updated without the readme being updated).

Github now supports rendering permalink in markdown files. example - https://github.com/stevemar/code-reference-in-readme

credit: https://www.stevemar.net/github-code-in-readme/

If you are willing to use github actions, I found Markdown autodocs on Github Marketplace to work for my project.

All you have to do is to add a line in your .github/workflows/your-workflow.yml file:

uses: dineshsonachalam/[email protected]

Then insert these snippets in your Markdown files:

<!-- MARKDOWN-AUTO-DOCS:START (CODE:src=./relative/path/to/code.js) -->
<!-- MARKDOWN-AUTO-DOCS:END -->

I also like the fact that it allows for remote files to be used:

<!-- MARKDOWN-AUTO-DOCS:START (CODE:src=https://raw.githubusercontent.com/username/project/master/path/to/file) -->
<!-- MARKDOWN-AUTO-DOCS:END -->

And also the fact that you can restrict the number of lines printed:

<!-- MARKDOWN-AUTO-DOCS:START (CODE:src=https://raw.githubusercontent.com/username/project/master/path/to/file&lines=1-42) -->
<!-- MARKDOWN-AUTO-DOCS:END -->

Not a direct answer, since GFM doesn't support includes, but I keep a list of projects I found that let you include things with a preprocessing step to produce the final markdown file: realazthat/snipinator: Related Projects.

Disclosure: I wrote snipinator.

Not complete, and not necessarily up to date. Make a PR to README.md.jinja, (see realazthat/snipinator/Contributions) to insert/modify the table, and edit this answer.

I created a tool that keeps your code snippets up to date in Readme:) it can be used either as 🪝 pre-commit hook or as a Github action, and it supports whole scripts, sections of scripts and 🐍 Python objects. It’s extremely easy to use, feel free to check it out! https://github.com/kvankova/code-embedder

You could write a script that will load the source code from a public repo and then show it within the container. Here is an example of an MD file which loads data from github and displays that within a container.

## Welcome to the Simple Alarm Server Example
This page will load and show a code example. 


<div id="code-element"></div>
<script src="https://unpkg.com/axios/dist/axios.min.js"></script>
<script>
      axios({
      method: 'get',
      url: 'https://raw.githubusercontent.com/iotify/nsim-examples/master/functional-testing/alarm-server.js'
       })
      .then(function (response) {
         document.getElementById("code-element").innerHTML = response.data;
      });
</script>