Capture An Output Value For Use In A Later Step

GitHub Actions has a workflow command called set-output. This can be used to capture the output from a shell command in step. That output value can then be used in a later step.

A useful example of this is reading the version of a tool from a dot-file to tell a later step what version of that tool to install.

Here's the .tool-versions file included in my repository:

postgres 13.1
ruby 3.0.0
nodejs 15.4.0

Assuming I've already checked out my repo, I can find and read the nodejs version from my .tool-versions file with a step that uses set-output.

  - name: Read Node.js version to install from `.tool-versions`
    id: nodejs
    run: >-
      echo "::set-output name=NODE_VERSION::$(
        cat .tool-versions |
        grep nodejs |
        sed 's/nodejs \(.*\)$/\1/'
      )"

echo runs the command in the string which sets NODE_VERSION as an output value to what ends up being 15.4.0.

This output value can be referenced in a later step.

  - name: Install required Node.js version
    uses: actions/setup-node@v1
    with:
      node-version: "${{ steps.nodejs.outputs.NODE_VERSION }}"

steps has a reference to the nodejs step (note the id above) which then has outputs like the NODE_VERSION.

source