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Side Quest: Passing Data Between Steps with $GITHUB_OUTPUT

Optional: work through this deep-dive if you want to understand how data flows between steps, then return to Step 16.

GitHub Actions runs each step in its own shell process. That means a plain export MY_VAR=value in one step is invisible to the next step — the environment is thrown away when the step exits. $GITHUB_OUTPUT is the official mechanism for persisting data across steps.

Why export doesn't work across steps

# ❌ This looks reasonable but DOES NOT WORK
- name: Set a value
  run: export RESULT="hello"

- name: Use the value
  run: echo "$RESULT"   # prints nothing — RESULT is gone

Each step is a separate child process. Environment variables set with export only survive for the duration of that step.

Single-line values

Append a key=value pair to the file path stored in the $GITHUB_OUTPUT environment variable:

# ✅ Write a single-line value
echo "status=healthy" >> $GITHUB_OUTPUT

To read it back in a later step, reference ${{ steps.<id>.outputs.status }} — but first you need to give the writing step an id.

Giving steps an id

A step id is how you refer to its outputs elsewhere in the workflow. Add id: at the same level as name: and run::

- name: Check health
  id: health_check
  run: |
    echo "status=healthy" >> $GITHUB_OUTPUT

Now any later step (or the AI prompt) can reference:

${{ steps.health_check.outputs.status }}

Multi-line values with the <<EOF heredoc syntax

A single echo "key=value" won't work for multi-line content because the newlines would break the key=value format. Use a heredoc delimiter instead:

# ✅ Write a multi-line value
echo "commit_log<<EOF" >> $GITHUB_OUTPUT
echo "$COMMIT_LOG" >> $GITHUB_OUTPUT
echo "EOF" >> $GITHUB_OUTPUT

The three lines together tell GitHub Actions:

  1. commit_log<<EOF — start a multi-line value named commit_log, using EOF as the end marker.
  2. $COMMIT_LOG — the actual content (can span many lines).
  3. EOF — close the block.

You can use any unique string as the delimiter — EOF is just a convention.

Injecting outputs into an AI prompt

Once your data is in $GITHUB_OUTPUT, you reference it directly inside the workflow Markdown body — which is the AI prompt in gh-aw. There is no separate step to invoke the AI; the body text is sent to the model after all step outputs have been resolved.

Frontmatter (data-preparation step):

steps:
  - name: Fetch recent commits
    id: recent
    run: |
      echo "commit_log<<EOF" >> $GITHUB_OUTPUT
      git log --oneline -10 >> $GITHUB_OUTPUT
      echo "EOF" >> $GITHUB_OUTPUT

Workflow body (the prompt):

Here are the recent commits:
${{ steps.recent.outputs.commit_log }}

Write a one-paragraph summary of this activity.

The ${{ ... }} expression is resolved by GitHub Actions before the body is sent to the model, so the AI receives the fully expanded text.

✅ Checkpoint

  • You can explain why export does not pass values between steps
  • You can write a single-line value to $GITHUB_OUTPUT
  • You know how to give a step an id and reference its outputs
  • You can use the <<EOF heredoc syntax for multi-line values
  • You can reference step outputs inside an AI prompt

Return to Connect a Live Data Source to Your Workflow.