Looping over multiple files with GitHub Actions

Question

I have multiple .md files in several subdirectories of my repository. They all have the same naming convention, e.g. seminar1/slides.md, seminar2/slides.md, etc. These *.md files need to be processed using pandoc. I would like to do this automatically every time I commit to the repository, and decided to implement this as an action that runs on Github.

I have created the following workflow as a .yml file, which GitHub recognises as an action. It works if I have a single subdirectory, e.g., /seminar1/*.md, but fails with more subdirectories.

name: Make slides

on: push

jobs:
  convert_via_pandoc:
    runs-on: ubuntu-18.04
    steps:
      - uses: actions/checkout@v2
        with:
          ref: slides
      - run: |
          echo "::set-env name=FILELIST::$(printf '"%s"' seminar*/*.md)"
      - uses: docker://pandoc/latex:2.9
        with:
          args: -t beamer --output=${{env.FILELIST}}.pdf ${{env.FILELIST}}
      - uses: actions/upload-artifact@v2
        with:
          name: seminar-slides
          path: seminar*/*.md.pdf        

How can I make a script detect all of the seminar*/*.md files and act on them?

Also, I need some help with general usability:

1. All of the scripts run from the root directory. This means I have to modify the content of the .md file to include the directory, e.g. seminar1/bridge.jpg rather than just including bridge.jpg. How can I change the working directory for each $env.FILELIST?
2. How can I strip the extension from the filename and use this in $env.FILELIST?

Answer 1

GitHub Actions supports 'matrix' for iterating in jobs, but it's hard to use and I could not get it to work with a list from a string. The only working solution I found was splitting the string myself and just using bash.

Here is my solution. It does not use docker://pandoc/latex:2.9 but is more to make the concepts clear.

• Iterating in GitHub Actions

  You have a string of comma-separated-values, like "a,b,c". You will need to parse it to a real array in every step and iterate over the values.

  IFS stands for "internal field separator". It is used by the shell to determine how to do word splitting, i. e. how to recognise word boundaries. We use the read command and feed it with our array-as-string. Afterwards we just iterate over the real array.

  name: Looping over values in Github Actions
  
  env:
    VALUE_ARRAY_AS_STRING: 'a.md,b.md,c.md'
  
  jobs:
    run-my-stuff:
      name: Iterating over comma-separated-values
      runs-on: ubuntu-latest
      steps:
        - name: Echo values from ENV
            run: |
              IFS="," read -a myarray <<< ${{ env.VALUE_ARRAY_AS_STRING }}
              for i in "${myarray[@]}"; do
                echo "Value: ${i}"
                echo "Value: ${i%.*}"
              done
  
        - name: Finding files and store to output
          id: finding-files
          run: |
            echo "::set-output name=FILELIST::$(find . -name '*.md' -print)"
  
        - name: Processing my found files from output
          run: |
            IFS="," read -a myarray <<< ${{ steps.finding-files.outputs.FILELIST }}
            for i in "${myarray[@]}"; do
              file_path=$(dirname "${i}")
              file_name=$(basename "${i}")
              cd file_path
              cat file_name
            done
  

• Finding all *.md files

  find . -name '*.md' -print
  

• Stripping file extensions

  From https://stackoverflow.com/a/125340/2467954 or How to extract directory path from file path?

  x="filename.md"
  echo ${x%.*} 
  

• Changing the working directory

  You can do this per step or with cd if you just run a command. I didn't look into it, but I would guess docker://pandoc/latex:2.9 has an argument for the working directory too. You will need to check the documentation.