Using output from a previous job in a new one in a GitHub Action

Update: It's now possible to set job outputs that can be used to transfer string values to downstream jobs. See this answer.

What follows is the original answer. These techniques might still be useful for some use cases.

1. Write the data to file and use actions/upload-artifact and actions/download-artifact. A bit awkward, but it works.
2. Create a repository dispatch event and send the data to a second workflow. I prefer this method personally, but the downside is that it needs a repo scoped PAT.

Here is an example of how the second way could work. It uses repository-dispatch action.

name: "We 🎔 Perl"
on:
  issues:
    types: [opened, edited, milestoned]

jobs:
  seasonal_greetings:
    runs-on: windows-latest
    steps:
      - name: Maybe greet
        id: maybe-greet
        env:
          HEY: "Hey you!"
          GREETING: "Merry Xmas to you too!"
          BODY: ${{ github.event.issue.body }}
        run: |
          $output=(perl -e 'print ($ENV{BODY} =~ /Merry/)?$ENV{GREETING}:$ENV{HEY};')
          Write-Output "::set-output name=GREET::$output"
      - name: Repository Dispatch
        uses: peter-evans/repository-dispatch@v1
        with:
          token: ${{ secrets.REPO_ACCESS_TOKEN }}
          event-type: my-event
          client-payload: '{"greet": "${{ steps.maybe-greet.outputs.GREET }}"}'

This triggers a repository dispatch workflow in the same repository.

name: Repository Dispatch
on:
  repository_dispatch:
    types: [my-event]
jobs:
  myEvent:
    runs-on: ubuntu-latest
    steps:
      - run: echo ${{ github.event.client_payload.greet }}

In my case I wanted to pass an entire build/artifact, not just a string:

name: Build something on Ubuntu then use it on MacOS

on:
  workflow_dispatch:
    # Allows for manual build trigger

jobs:
  buildUbuntuProject:
    name: Builds the project on Ubuntu (Put your stuff here)
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: some/compile-action@v99
      - uses: actions/upload-artifact@v2
        # Upload the artifact so the MacOS runner do something with it
        with:
          name: CompiledProject
          path: pathToCompiledProject
  doSomethingOnMacOS:
    name: Runs the program on MacOS or something
    runs-on: macos-latest
    needs: buildUbuntuProject # Needed so the job waits for the Ubuntu job to finish
    steps:
      - uses: actions/download-artifact@master
        with:
          name: CompiledProject
          path: somewhereToPutItOnMacOSRunner
      - run: ls somewhereToPutItOnMacOSRunner # See the artifact on the MacOS runner

It is possible to capture the entire output (and return code) of a command within a run step, which I've written up here to hopefully save someone else the headache. Fair warning, it requires a lot of shell trickery and a multiline run to ensure everything happens within a single shell instance.

In my case, I needed to invoke a script and capture the entirety of its stdout for use in a later step, as well as preserve its outcome for error checking:

# capture stdout from script 
SCRIPT_OUTPUT=$(./do-something.sh)

# capture exit code as well
SCRIPT_RC=$?

# FYI, this would get stdout AND stderr
SCRIPT_ALL_OUTPUT=$(./do-something.sh 2>&1)

Since Github's job outputs only seem to be able to capture a single line of text, I also had to escape any newlines for the output:

echo "::set-output name=stdout::${SCRIPT_OUTPUT//$'\n'/\\n}"

Additionally, I needed to ultimately return the script's exit code to correctly indicate whether it failed. The whole shebang ends up looking like this:

- name: A run step with stdout as a captured output
  id: myscript
  run: |
    # run in subshell, capturiing stdout to var
    SCRIPT_OUTPUT=$(./do-something.sh)
    # capture exit code too
    SCRIPT_RC=$?
    # print a single line output for github
    echo "::set-output name=stdout::${SCRIPT_OUTPUT//$'\n'/\\n}"
    # exit with the script status
    exit $SCRIPT_RC
  continue-on-error: true
- name: Add above outcome and output as an issue comment
  uses: actions/github-script@v5
  env:
    STEP_OUTPUT: ${{ steps.myscript.outputs.stdout }}
  with:
    github-token: ${{ secrets.GITHUB_TOKEN }}
    script: |
      // indicates whather script succeeded or not
      let comment = `Script finished with \`${{ steps.myscript.outcome }}\`\n`;

      // adds stdout, unescaping newlines again to make it readable
      comment += `<details><summary>Show Output</summary>

      \`\`\`
      ${process.env.STEP_OUTPUT.replace(/\\n/g, '\n')}
      \`\`\`

      </details>`;

      // add the whole damn thing as an issue comment
      github.rest.issues.createComment({
        issue_number: context.issue.number,
        owner: context.repo.owner,
        repo: context.repo.repo,
        body: comment
      })

Edit: there is also an action to accomplish this with much less bootstrapping, which I only just found.

2022 October update: GitHub is deprecating set-output and recommends to use GITHUB_OUTPUT instead. The syntax for defining the outputs and referencing them in other steps, jobs.

An example from the docs:

- name: Set color
  id: random-color-generator
  run: echo "SELECTED_COLOR=green" >> $GITHUB_OUTPUT
- name: Get color
  run: echo "The selected color is ${{ steps.random-color-generator.outputs.SELECTED_COLOR }}"

To update @vonc https://stackoverflow.com/a/61236803/667767 on multiline output.

Here is the way to do it

      echo 'RESULT<<EOF' >> $GITHUB_OUTPUT
      echo $multiLine >> $GITHUB_OUTPUT
      echo 'EOF' >> $GITHUB_OUTPUT

I managed to do it simply by setting up output. I did some processes in job_1, if things go ok I can set the output as custom something, I used true. So the next job will not run even if job_1 returned success, it has to return true. Then deploy job runs, else it gets skipped.

jobs:
  job_1:
    runs-on: [ ubuntu-latest ]
    outputs:
      run_next: ${{ steps.job1.outputs.run_next }}
    steps:
      - name: check commit message
        id: job1
        run: |
          echo "your if else logic here, if all ok, set the output to true"
          echo "run_next=true" >> $GITHUB_OUTPUT
    
  deploy:
    if: contains(needs.job_1.outputs.run_next, 'true')
    needs: job_1
    runs-on: [ ubuntu-latest ]
    steps:
      - name: Checkout
        uses: actions/checkout@v3
     ....
     ......

This met my needs.