GitHub Actions, Hook, Cron, YAML

The three often appear together, but they are distinct concepts.

GitHub Actions

This system runs automated tasks when events occur within GitHub.

flowchart LR
    E[Event] --> W[Workflow YAML]
    W --> J[Job]
    J --> R[Runner]
    R --> S[Steps]

Example:

name: PR Check

on:
  pull_request:
    branches: [stable]

jobs:
  build:
    runs-on: windows-latest
    steps:
      - uses: actions/checkout@v4
      - run: cmake --build build

The Most Common Triggers

Hook

A hook is a local script that runs before or after a specific Git action.

Example: pre-push hook

git push
↓
pre-push hook
↓
Local Build / Test
↓
Push if successful

A hook is not YAML. It can be an executable script written in Shell, Python, or another language.

Cron

Cron is a time-scheduling expression.

Minute Hour Day Month Day-of-week
0  3  *  *  *

→ Every day at 03:00

Cron can be used inside GitHub Actions YAML.

on:
  schedule:
    - cron: '0 18 * * *'

In other words:

YAML
└─ schedule
   └─ cron expression

Are Builds Before Push Also Used?

Frequently. They are usually local builds, rather than GitHub Actions.

Implementation
↓
Local Incremental Build / Test
↓
Commit
↓
Push
↓
GitHub Actions Clean Build / Test
↓
PR Review

For large C++ projects, instead of requiring a full build on every push:

• Local: fast incremental builds
• CI: Clean Build
• Nightly: extensive regression tests

Dividing verification into these stages is more efficient.

Recommended Workflows

.github/workflows/
├─ pr-check.yml
├─ stable-check.yml
├─ manual-build.yml
└─ nightly.yml

PR Check

Fast compilation/tests

Stable Check

Check integration after merging

Manual Build

Full builds only when needed

Nightly

Heavy checks such as full regression, import/export, and performance

Actions does not judge “whether a feature is good for users.” It is the layer that automates mechanically verifiable conditions.