unison/docs/github-actions-help.md

Some things I wish I'd known about Github Actions

You can't have an env: key defined in terms of another env key, but

You can't define a matrix at the top level, it has to be defined within a job's strategy.

Windows doesn't seem to honor the default: run: shell: setting, so you need to set the shell: on run: manually?

Don't hesitate to do a lot with run: blocks aka bash scripts — at least bash is mature and well documented.

e.g. echo "bar=whatever" >> $GITHUB_OUTPUT # access with steps.<name>.outputs.bar in yaml strings

echo "foo=whatever" >> $GITHUB_ENV
# access with `env.foo` in yaml strings, or `$foo` in bash

Default Environment Variables: https://docs.github.com/en/actions/learn-github-actions/variables#default-environment-variables