How to share a calculated value between job steps?

Is there a DRY way to calculate and share a value in multiple job steps with GitHub Actions?

In the below workflow, echo ${GITHUB_REF} | cut -d'/' -f3-${GITHUB_SHA}` is repeated in multiple steps.

name: Test, Build and Deploy
on:
  push:
    branches:
      - master
jobs:
  build_and_push:
    name: Build and Push
    runs-on: ubuntu-latest
    steps:
      - name: Docker Build
        uses: "actions/docker/cli@master"
        with:
          args: build . --file Dockerfile -t cflynnus/blog:`echo ${GITHUB_REF} | cut -d'/' -f3`-${GITHUB_SHA}
      - name: Docker Tag Latest
        uses: "actions/docker/cli@master"
        with:
          args: tag cflynnus/blog:`echo ${GITHUB_REF} | cut -d'/' -f3`-${GITHUB_SHA} cflynnus/blog:latest

set-output can be used to define outputs for steps. The outputs can then be used in later steps and evaluated in with and env input sections. Also, the step returning outputs should have an id, which is referred to by the step consuming the outputs.

The following is what that would look like for your example.

name: Test, Build and Deploy
on:
  push:
    branches:
      - master
jobs:
  build_and_push:
    name: Build and Push
    runs-on: ubuntu-latest
    steps:
      - name: Set tag var
        id: vars
        run: echo "docker_tag=$(echo ${GITHUB_REF} | cut -d'/' -f3)-${GITHUB_SHA}" >> $GITHUB_OUTPUT
      - name: Docker Build
        uses: "actions/docker/cli@master"
        with:
          args: build . --file Dockerfile -t cflynnus/blog:${{ steps.vars.outputs.docker_tag }}
      - name: Docker Tag Latest
        uses: "actions/docker/cli@master"
        with:
          args: tag cflynnus/blog:${{ steps.vars.outputs.docker_tag }} cflynnus/blog:latest

Here is another example showing how to dynamically set multiple variables to be used by an action.

      - name: Set output variables
        id: vars
        run: |
          pr_title="[Test] Add report file $(date +%d-%m-%Y)"
          pr_body="This PR was auto-generated on $(date +%d-%m-%Y) \
            by [create-pull-request](https://github.com/peter-evans/create-pull-request)."
          echo "pr_title=$pr_title" >> $GITHUB_OUTPUT
          echo "pr_body=$pr_body" >> $GITHUB_OUTPUT
      - name: Create Pull Request
        uses: peter-evans/create-pull-request@v4
        with:
          title: ${{ steps.vars.outputs.pr_title }}
          body: ${{ steps.vars.outputs.pr_body }}

Alternatively you can create environment variables.

      - name: Set environment variables
        run: |
          echo "PR_TITLE=[Test] Add report file $(date +%d-%m-%Y)" >> $GITHUB_ENV
          echo "PR_BODY=This PR was auto-generated on $(date +%d-%m-%Y) by [create-pull-request](https://github.com/peter-evans/create-pull-request)." >> $GITHUB_ENV
      - name: Create Pull Request
        uses: peter-evans/create-pull-request@v4
        with:
          title: ${{ env.PR_TITLE }}
          body: ${{ env.PR_BODY }}

Update: The docker actions in the first example are deprecated. Please see this answer for the latest way to work with docker in GitHub Actions.

Note: For sharing values between different jobs, see this question.