Github Actions

GitHub Actions

Create, edit, debug, and optimize GitHub Actions workflows and custom actions.

Trigger

Activate when working with:

• Files in .github/workflows/ (workflow YAML files)
• Files named action.yml or action.yaml (custom action definitions)
• Any task involving CI/CD pipeline configuration for GitHub repositories
• Debugging failed workflow runs or action errors

Workflow Fundamentals

File Location

All workflow files must be in .github/workflows/. Subdirectories are not supported.

Minimal Workflow Structure

name: CI
on: [push]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: echo "Hello"

Top-Level Keys

• name -- display name in Actions tab (optional)
• run-name -- names the run, supports github and inputs contexts (optional)
• on -- trigger event(s) (required)
• permissions -- GITHUB_TOKEN scopes
• env -- workflow-level environment variables
• defaults.run -- default shell and working-directory for run steps
• concurrency -- prevent duplicate runs
• jobs -- job definitions (required)

Events and Triggers

Common Trigger Patterns

# Branch and path filtering
on:
  push:
    branches: [main, 'releases/**']
    paths: ['src/**']
    paths-ignore: ['docs/**']
  pull_request:
    branches: [main]
    types: [opened, synchronize, reopened]

# Scheduled (cron)
on:
  schedule:
    - cron: '30 5 * * 1-5'

# Manual dispatch with typed inputs
on:
  workflow_dispatch:
    inputs:
      environment:
        type: choice
        options: [staging, production]
        required: true
      dry_run:
        type: boolean
        default: false

# API-triggered
on:
  repository_dispatch:
    types: [deploy]

# Chain workflows
on:
  workflow_run:
    workflows: ["Build"]
    types: [completed]
    branches: [main]

Input Types for workflow_dispatch

boolean, choice, number, environment, string. Max 25 inputs.

Filter Pattern Syntax

• * matches any character except /
• ** matches any character including /
• ! negation (must follow a positive pattern)
• Cannot mix branches with branches-ignore -- use ! negation instead

Key pull_request Activity Types

opened, synchronize, reopened, closed, ready_for_review, labeled, unlabeled, review_requested, converted_to_draft

For a full event and activity type reference, consult references/syntax-reference.md.

Jobs

Job Configuration

jobs:
  build:
    runs-on: ubuntu-latest
    needs: [lint, test]           # dependencies
    if: github.ref == 'refs/heads/main'
    timeout-minutes: 30           # default: 360
    continue-on-error: false
    permissions:
      contents: read
    environment:
      name: production
      url: https://myapp.example.com
    outputs:
      version: ${{ steps.ver.outputs.value }}
    env:
      NODE_ENV: production
    defaults:
      run:
        shell: bash
    steps:
      - uses: actions/checkout@v4

Steps

steps:
  - id: step1
    name: "Display Name"
    if: success()
    uses: actions/checkout@v4
    with:
      ref: main
    env:
      TOKEN: ${{ secrets.MY_TOKEN }}
    continue-on-error: true
    timeout-minutes: 10

  - name: Run commands
    run: |
      npm install
      npm test
    shell: bash
    working-directory: ./app

Setting Outputs

# Step output
- id: my_step
  run: echo "result=value" >> $GITHUB_OUTPUT

# Multiline output (use heredoc delimiters)
- run: |
    echo "json> "$GITHUB_OUTPUT"
    cat result.json >> "$GITHUB_OUTPUT"
    echo "EOF" >> "$GITHUB_OUTPUT"

# Job output (declared at job level, references step)
jobs:
  build:
    outputs:
      artifact-id: ${{ steps.upload.outputs.id }}

# Consume in dependent job
  deploy:
    needs: build
    steps:
      - run: echo "${{ needs.build.outputs.artifact-id }}"

Dynamic Environment Variables

- run: echo "MY_VAR=hello" >> $GITHUB_ENV
- run: echo "$MY_VAR"    # available in subsequent steps

Job Summaries

- run: echo "### Build Results :rocket:" >> $GITHUB_STEP_SUMMARY

Matrix Strategies

strategy:
  fail-fast: false
  max-parallel: 4
  matrix:
    os: [ubuntu-latest, windows-latest, macos-latest]
    node: [18, 20, 22]
    include:
      - os: ubuntu-latest
        node: 16
        experimental: true
    exclude:
      - os: macos-latest
        node: 18
runs-on: ${{ matrix.os }}
continue-on-error: ${{ matrix.experimental == true }}

Dynamic Matrix from Job Output

jobs:
  setup:
    outputs:
      matrix: ${{ steps.set.outputs.matrix }}
    steps:
      - id: set
        run: echo 'matrix=["a","b","c"]' >> "$GITHUB_OUTPUT"
  run:
    needs: setup
    strategy:
      matrix:
        value: ${{ fromJSON(needs.setup.outputs.matrix) }}

Expressions and Contexts

Status Check Functions (for if: conditionals)

• success() -- all previous steps succeeded (default)
• failure() -- any previous step failed
• always() -- runs even if cancelled
• cancelled() -- workflow was cancelled

Use if: success() || failure() to run on both outcomes but skip cancellation.

Common Patterns

if: github.ref == 'refs/heads/main'
if: github.event_name == 'pull_request'
if: contains(github.event.pull_request.labels.*.name, 'deploy')
if: startsWith(github.ref, 'refs/tags/')
if: always() && needs.build.result == 'success'

# Ternary-like
value: ${{ github.event_name == 'push' && 'production' || 'staging' }}

Key Contexts

• github.* -- workflow run info (ref, sha, actor, event, repository, etc.)
• env.* -- environment variables
• vars.* -- configuration variables (repo/org/environment level)
• secrets.* -- secret values
• steps..outputs.* -- step outputs
• needs..outputs.* -- dependent job outputs
• matrix.* -- current matrix values
• runner.* -- runner info (os, arch, temp)
• inputs.* -- workflowdispatch/workflowcall inputs

Built-in Functions

• contains(search, item), startsWith(), endsWith() -- case-insensitive
• format('{0} {1}', val0, val1) -- string formatting
• join(array, separator) -- default separator ,
• toJSON(value), fromJSON(value) -- JSON serialization
• hashFiles(pattern) -- SHA-256 of matching files
• success(), failure(), always(), cancelled() -- status checks

For complete context properties, consult references/syntax-reference.md.

Permissions

# Workflow-level (applies to all jobs by default)
permissions:
  contents: read
  pull-requests: write

# Job-level override
jobs:
  deploy:
    permissions:
      contents: read
      id-token: write

# Shorthand
permissions: read-all
permissions: {}    # disable all

Available scopes: actions, attestations, checks, contents, deployments, discussions, id-token, issues, models, packages, pages, pull-requests, security-events, statuses.

Access levels: read, write, none.

Concurrency

concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true

# For PRs (fallback when github.head_ref is undefined)
concurrency:
  group: ${{ github.head_ref || github.run_id }}
  cancel-in-progress: true

Always include github.workflow in the group name to avoid cross-workflow cancellation.

Caching

Prefer setup actions with built-in caching over raw actions/cache:

- uses: actions/setup-node@v4
  with:
    node-version: 20
    cache: npm

Manual caching:

- uses: actions/cache@v4
  with:
    path: ~/.npm
    key: ${{ runner.os }}-npm-${{ hashFiles('**/package-lock.json') }}
    restore-keys: |
      ${{ runner.os }}-npm-

Secrets

# Use as environment variable (preferred -- avoids leaking via process args)
- env:
    API_KEY: ${{ secrets.API_KEY }}
  run: curl -H "Authorization: Bearer $API_KEY" https://api.example.com

# Pass as action input
- uses: some/action@v1
  with:
    token: ${{ secrets.MY_TOKEN }}

Key rules:

• Always pass secrets via env:, never interpolate directly in run: scripts
• Secrets cannot be used in if: conditionals -- set as env var first
• Secrets are not passed to workflows triggered from forks
• Secrets must be explicitly passed to reusable workflows (or use secrets: inherit)
• GITHUB_TOKEN is automatic and scoped to the repo

Reusable Workflows

Define (workflow_call)

on:
  workflow_call:
    inputs:
      environment:
        required: true
        type: string
    secrets:
      deploy_key:
        required: true
    outputs:
      url:
        value: ${{ jobs.deploy.outputs.url }}

Call

jobs:
  deploy:
    uses: ./.github/workflows/reusable-deploy.yml
    with:
      environment: staging
    secrets:
      deploy_key: ${{ secrets.STAGING_KEY }}

  # Or pass all secrets
  deploy-alt:
    uses: org/repo/.github/workflows/deploy.yml@main
    secrets: inherit

Limitations: max 9 levels nesting, no loops, uses must be at job level (not in steps).

Custom Actions

Three Types

| Type | Platform | Speed | runs.using | |------|----------|-------|--------------| | Composite | All | Fast | composite | | JavaScript | All | Fast | node20 | | Docker | Linux only | Slower | docker |

Composite Action (action.yml)

name: 'My Action'
description: 'Does something useful'
inputs:
  name:
    required: true
outputs:
  result:
    value: ${{ steps.run.outputs.result }}
runs:
  using: composite
  steps:
    - id: run
      run: echo "result=done" >> $GITHUB_OUTPUT
      shell: bash    # shell is MANDATORY on every run step

Referencing Actions

- uses: actions/checkout@8e5e7e5ab8b370d2c5cb812c4b306480e4a84920  # SHA (most secure)
- uses: actions/checkout@v4          # tag
- uses: ./.github/actions/my-action  # local
- uses: docker://alpine:3.18        # Docker image

Deployment Environments

jobs:
  deploy:
    environment:
      name: production
      url: https://myapp.example.com
    runs-on: ubuntu-latest

Features (configured in repo Settings > Environments): required reviewers, wait timers, deployment branch restrictions, environment-scoped secrets and variables.

Security Hardening

Critical Rules

1. Pin actions to full SHA -- tags can be moved maliciously
2. Use least-privilege permissions -- start with permissions: {}, add back per-job
3. Never interpolate untrusted input in run: scripts -- use intermediate env vars

Script Injection Prevention

# VULNERABLE
- run: echo "Title: ${{ github.event.pull_request.title }}"

# SECURE
- env:
    TITLE: ${{ github.event.pull_request.title }}
  run: echo "Title: $TITLE"

Dangerous Contexts (always treat as untrusted)

github.event.pull_request.title, github.event.pull_request.body, github.event.comment.body, github.event.issue.title, github.event.issue.body, github.head_ref, github.event.head_commit.message

Additional Security Measures

• Use OIDC for cloud auth instead of long-lived credentials
• Protect .github/workflows/ with CODEOWNERS
• Enable Dependabot for action version updates
• Never use self-hosted runners for public repos
• Never store structured data (JSON/XML) as secrets -- redaction relies on exact string matching

Using gh CLI in Workflows

GitHub CLI is pre-installed on all runners. Set GH_TOKEN for auth:

- run: gh pr comment $PR --body "LGTM"
  env:
    GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
    PR: ${{ github.event.pull_request.number }}

References

For the complete syntax reference including all trigger events with activity types, all context properties, and detailed examples, consult references/syntax-reference.md.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: gokhanamal
• Source: gokhanamal/ai-context
• License: MIT

Install and usage instructions live in the source repository linked above.