Github Workflow

Environment, Variables, Path

Variables in the env map cannot be defined in terms of other variables in the map
Multiple checkout
- No matter how many time you actions/checkout, the default working directory is always /home/runner/work/${{ github.event.repository.name }}/${{ github.event.repository.name }}, even checkout other repository. The only different in checkout other repository, are those repository files.

Reusable workflows

https://docs.github.com/en/actions/using-workflows/reusing-workflows

reusable workflows should be referenced at the top-level jobs.*.uses key, not within steps

virtual-environments preinstalled software

Workflow logs include a link to the preinstalled tools on the exact runner. To find this information in the workflow log,

expand the Set up job section.
Under that section, expand the Virtual Environment section.
The link following Included Software will tell you the the preinstalled tools on the runner that ran the workflow.

Or you can go to some readme collections in source.

Triggers

Manual events

workflow_dispatch to trigger specific workflows in a repository
- Detect default branch only: if you configure manual workflow from any branches other than default branch, it won't show workflow in left panel nor it will show "Run workflow" button to trigger.
repository_dispatch to trigger more than one workflow in a repository and create custom events and event types