Hello Github Actions | Eka’s Notes

Official documentation:

https://docs.github.com/en/actions/learn-github-actions/introduction-to-github-actions

Basic examples:

Part I: Terminology and minimal file content

Good TL;DR from the docs:

An event automatically triggers the workflow, which contains a job. The job then uses steps to control the order in which actions are run.

"Github Actions" is the feature name. The smallest unit we can create is a workflow, represented by a file called .github/workflows/any-name-you-want.yml.
The workflow file uses the YAML syntax.
Required fields: on and jobs (which contains at least 1 job).
- Each job is required to have runs-on and steps (which contains at least 1 step).
- Each step is required to have run.
- I've never seen anything other than runs-on: ubuntu-latest in examples or existing actions, but we can choose other runners.
Optional name string field:
- A workflow may have a name. If present, it's shown in the repo Actions tab. If not, the workflow file name is shown.
- A step may also have a name. If present, it's shown as a heading in the job logs. If not, the command/step is shown.
- Unlike workflows and steps, a job has a required job_id string field. The job ID is shown in the single action screen (example). More info: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#jobsjob_id
Example of the most minimal workflow file possible: workflow-one.yml

on: [push, workflow_dispatch]
jobs:
  my-first-job:
    runs-on: ubuntu-latest
    steps:
      - run: echo "hello world"

Part II: multiple files & jobs, on

We can have multiple workflow files, eg. .github/workflows/one.yml, .github/workflows/two.yml, etc.
- If they have the same trigger event (eg. on: [push]), they start one after another immediately (ie. two does not wait for one to finish).
Trigger the workflow with on, which contains string, array, or YAML list.
- Docs: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#on
- Example: on: push runs every time there is a push to the repo.
- Example: on: [push, workflow_dispatch] runs on every push and can also be triggered manually from the Actions tab.
- More examples:
  - https://github.com/ekafyi/hello-gh-actions/actions/runs/845296148/workflow#L6-L8
  - https://github.com/ekafyi/hello-gh-actions/actions/runs/845299958/workflow#L6-L10 (only runs on push to foo-branch)
- See: List of events that trigger workflows
We can have multiple jobs. Like workflows, they start one after another immediately. Example: first-job ran from 16:50:21 to 16:50:26; second-job ran from 16:50:21 to 16:50:22.
- https://github.com/ekafyi/hello-gh-actions/runs/2585692781
- https://github.com/ekafyi/hello-gh-actions/runs/2585692722
The syntax used in workflow files is not JS (but rather similar). We print variables surrounded by quote marks, eg. echo "${{ foo }}". This syntax has its own functions, such as toJSON and fromJSON, which correspond to stringify and parse.
Contexts are built-in objects containing information about the repo, run, environment, jobs, and steps. Example: We can access our Github repo information with echo "${{ toJSON(github) }}".
- ⚠️ Sensitive information like tokens are replaced with asterisks in the action log, but always be careful about passing/sending such data.

[!question] Thought I'm not sure in which cases I will ever need multiple workflows or multiple jobs.

Further read: List of contexts, literals, operators, functions, filters

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