Customize your workflow with environment variables and artifact data

  • 12 minutes

Here, you'll learn how to use default and custom environment variables, custom scripts, cache dependencies, and pass artifact data between jobs. You'll also learn how to access the workflow logs from both the GitHub website and REST API endpoints.

Default environment variables and contexts

Within the GitHub Actions workflow, there are several default environment variables that are available for you to use, but only within the runner that's executing a job. These default variables are case-sensitive, and they refer to configuration values for the system and for the current user. We recommend that you use these default environment variables to reference the filesystem rather than using hard-coded file paths. To use a default environment variable, specify $ followed by the environment variable's name.

jobs:
  prod-check:
    steps:
      - run: echo "Deploying to production server on branch $GITHUB_REF"

In addition to default environment variables, you can use defined variables as contexts. Contexts and default variables are similar in that they both provide access to environment information, but they have some important differences. While default environment variables can only be used within the runner, context variables can be used at any point within the workflow. For example, context variables allow you to run an if statement to evaluate an expression before the runner is executed.

name: CI
on: push
jobs:
  prod-check:
    if: github.ref == 'refs/heads/main'
    runs-on: ubuntu-latest
    steps:
      - run: echo "Deploying to production server on branch $GITHUB_REF"

This example is using the github.ref context to check the branch that triggered the workflow. If the branch is main, the runner is executed and prints out "Deploying to production server on branch $GITHUB_REF". The default environment variable $GITHUB_REF is used in the runner to refer to the branch. Notice that default environment variables are all uppercase where context variables are all lowercase.

Custom environment variables

Similar to using default environment variables, you can use custom environment variables in your workflow file. To create a custom variable, you need to define it in your workflow file using the env context. If you want to use the value of an environment variable inside a runner, you can use the runner operating system's normal method for reading environment variables.

name: CI
on: push
jobs:
  prod-check:
    if: github.ref == 'refs/heads/main'
    runs-on: ubuntu-latest
    steps:
      - run: echo "Nice work, $First_Name. Deploying to production server on branch $GITHUB_REF"
        env:
          First_Name: Mona

Scripts in your workflow

In the preceding workflow snippet examples, the run keyword is used to print a string of text. Because the run keyword tells the job to execute a command on the runner, you use the run keyword to run actions or scripts.

jobs:
  example-job:
    steps:
      - run: npm install -g bats

In this example, you're using npm to install the bats software testing package by using the run keyword. You can also run a script as an action. You can store the script in your repository, often done in a .github/scripts/ directory, and then supply the path and shell type using the run keyword.

jobs:
  example-job:
    steps:
      - name: Run build script
        run: ./.github/scripts/build.sh
        shell: bash

Cache dependencies with the cache action

When building out a workflow, you'll often find the need to reuse the same outputs or download dependencies from one run to another. Instead of downloading these dependencies over and over again, you can cache them to make your workflow run faster and more efficiently. This can dramatically reduce the time it takes to run certain steps in a workflow, because jobs on GitHub-hosted runners start in a clean virtual environment each time. Caching dependencies will help speed up the time it takes to recreate these dependency files.

To cache dependencies for a job, use GitHub's cache action. This action retrieves a cache identified by a unique key that you provide. When the action finds the cache, it then retrieves the cached files to the path that you configure. To use the cache action, you'll need to set a few specific parameters:

Parameter Description Required
Key Refers to the key identifier created when saving and searching for a cache. Yes
Path Refers to the file path on the runner to cache or search. Yes
Restore-keys Consists of alternative existing keys to caches if the desired cache key isn't found. No 
steps:
  - uses: actions/checkout@v2

  - name: Cache NPM dependencies
    uses: actions/cache@v2
    with:
      path: ~/.npm
      key: ${{ runner.os }}-npm-cache-${{ hashFiles('**/package-lock.json') }}
      restore-keys: |
        ${{ runner.os }}-npm-cache-

In the preceding example, the path is set to ~/.npm and the key includes the runner's operating system and the SHA-256 hash of the package-lock.json file. Prefixing the key with an ID (npm-cache in this example) is useful when you're using the restore-keys fallback and have multiple caches.

Pass artifact data between jobs

Similar to the idea of caching dependencies within your workflow, you can pass data between jobs within the same workflow. You can do this by using the upload-artifact and download-artifact actions. Jobs that are dependent on a previous job's artifacts must wait for the previous job to complete successfully before they can run. This is useful if you have a series of jobs that need to run sequentially based on artifacts uploaded from a previous job. For example, job_2 requires job_1 by using the needs: job_1 syntax.

name: Share data between jobs
on: push
jobs:
  job_1:
    name: Upload File
    runs-on: ubuntu-latest
    steps:
      - run: echo "Hello World" > file.txt
      - uses: actions/upload-artifact@v2
        with:
          name: file
          path: file.txt

  job_2:
    name: Download File
    runs-on: ubuntu-latest
    needs: job_1
    steps:
      - uses: actions/download-artifact@v2
        with:
          name: file
      - run: cat file.txt

The preceding example has two jobs. job_1 writes some text into the file file.txt. Then it uses the actions/upload-artifact@v2 action to upload this artifact and store the data for future use within the workflow. job_2 requires job_1 to complete by using the needs: job_1 syntax. It then uses the actions/download-artifact@v2 action to download that artifact, and then print the contents of file.txt.

Enable step debug logging in a workflow

In some cases, the default workflow logs won't provide enough detail to diagnose why a specific workflow run, job, or step has failed. For these situations, you can enable additional debug logging for two options: runs and steps. Enable this diagnostic logging by setting two repository secrets that require admin access to the repository to true:

  • To enable runner diagnostic logging, set the ACTIONS_RUNNER_DEBUG secret in the repository that contains the workflow to true.
  • To enable step diagnostic logging, set the ACTIONS_STEP_DEBUG secret in the repository that contains the workflow to true.

Access the workflow logs from the user interface

When you think about successful automation, you aim to spend the least amount of time looking at what's automated so you can focus your attention on what's relevant. However, sometimes things don't go as planned, and you need to review what happened. That debugging process can be frustrating. GitHub provides a clear layout structure that enables a quick way to navigate between the jobs, while keeping the context of the currently debugging step. To view the logs of a workflow run in GitHub, you can follow these steps:

  1. Navigate to the Actions tab in your repository.
  2. In the left sidebar, click the desired workflow.
  3. From the list of workflow runs, select the desired run.
  4. Under Jobs, select the desired job.
  5. Read the log output.

If you have several runs within a workflow, you can also select the Status filter after choosing your workflow and set it to Failure to only display the failed runs within that workflow.

Access the workflow logs from the REST API

In addition to viewing logs using GitHub, you can also use GitHub's REST API to view logs for workflow runs, re-run workflows, or even cancel workflow runs. To view a workflow run's log using the API, you need to send a GET request to the logs endpoint. Keep in mind that anyone with read access to the repository can use this endpoint. If the repository is private, you must use an access token with the repo scope.

For example, a GET request to view a specific workflow run log would follow this path:

GET /repos/{owner}/{repo}/actions/runs/{run_id}/logs