A bit of context

Recently, I began dabbling more and more with continuous integration and deployment for my research projects. This also included the need to generate GitHub releases from a GitHub Actions script due to two reasons:

  • Zenodo, which I use to archive my work and make it citeable, can automatically archive every GitHub release of your project, but it must be a full release, not just a tag.
  • For some of my projects, I need to generate ZIP artifacts in order to make all data in subprojects available as a single download (which unfortunately does not work together with Zenodos GitHub integration due to zenodo/zenodo/#1235).

Fortunately, generating releases with GitHub Actions is quite easy with actions/create-release. However, I was left with one problem: What do I put in the release body?

The problem

The most obvious solution for releases targeted at Zenodo seemed to just include the README.md using the body_path parameter instead of adding the release text statically with the body parameter, since the Zenodo release might be the first impression of the project that a visitor gets. However, throwing copies of the whole README.md around each time a new release is created is both a bit verbose and also unhelpful, if you really just want to know what’s new in the current release.

I already do keep a changelog, but, again, using the whole CHANGELOG.md in body_path seems equally overkill. I also do not want to make the changelog layout any more complicated, as I barely keep up with maintaining the thing as it is.

So we are left with the following requirements for our automatically generated release body:

  • Include a brief explanation what the project is about.
  • Add the relevant sections from the CHANGELOG.md without changing anything about the layout of the file.
  • If possible, the solution should work for any repository, so that I can simply slap this on all of my projects without wasting much thought about it.

The solution

As you have probably guessed this is one of these instances where the answer lies in the ubiquitous question “Can’t we do that with sed or awk somehow?”. First, we need the static part that describes the project in a few sentences. You could probably extract this from the first paragraph of the README.md, but this is a little tricky, because if you only count newlines, you might get the status buttons instead of the first text paragraph, but you also cannot be sure that all of your repositories will have status buttons. Therefore, I chose the boring solution of just adding a RELEASE_HEAD.md to the repository, which contains the heading and project description.

The next step is to get the relevant part of the CHANGELOG.md. Fortunately, if you follow the proposed structure on keepachangelog.com, this part is quite easy to identify: It will start at a line starting with ## [X.Y.Z], where X.Y.Z is the version number of the current release, and end at the next line that starts with ## (notice the space after the hashes). Let’s call these lines start and end to make the sed command that we are concocting a little easier to understand.

The simplest version of the command that I stumbled upon through Google was

sed -ne "/start/,/end/ p" CHANGELOG.md

which just prints the lines between stard and end, but also includes the lines start and end themselves. Nice, so we just need to remove the last line—or actually the last two lines, since the second last line should be empty. Easy, right? Surprisingly, this is not that trivial with a single sed call, so we need to pipe the result into head -n -2. This opens up another problem, because the pipe output of our sed call is different from its print output. The p command prints all the lines we want, but in a pipe we just get the unchanged file as output, because we did not change anything in the file. Bash scripting: Gotta love it! The solution looks like this:

sed -e "/start/,/end/ ! d" CHANGELOG.md

We replaced p with ! d, which first inverts the selection and then deletes the selected lines, and drop the -n argument to see the actual output. The result can finally be piped into head -n -2 and then be appended to our content in RELEASE_HEAD.md. Of course, we also need to automatically find the current version tag, but fortunately this is available (with a little extra work) in the environment variable GITHUB_REF. The relevant parts of the resulting GitHub Actions script look as follows:

- name: Set env # required to get 'vX.Y.Z' instead of 'refs/tag/vX.Y.Z'
  run: echo "RELEASE_VERSION=${GITHUB_REF#refs/*/}" >> $GITHUB_ENV

- name: Extract changelog for release version
  run: |
    printf "\n" >> RELEASE.md
    sed -e "/^## \\[${RELEASE_VERSION:1}\\]/,/^## / ! d" CHANGELOG.md | head -n -2 >> RELEASE.md

- name: Create Release
  id: create_release
  uses: actions/create-release@v1
    GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} # provided by Actions
    tag_name: ${{ github.ref }}
    release_name: Release ${{ github.ref }}
    body_path: RELEASE.md
    draft: true
    prerelease: false

This script just makes the following assumptions:

  • Your headings in CHANGELOG.md will have the form ## [X.Y.Z] (optionally followed by something else)
  • Your version tags have the form vX.Y.Z.
  • Your repository contains a file called RELEASE_HEAD.md.

Otherwise, it should be pretty much universal.