GitHub Actions: Expressions, Contexts, Variables, and Outputs

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Expressions, contexts, env vars, configuration variables, step outputs, job outputs, and dynamic workflow logic in GitHub Actions.

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Contexts and expressions

Read data from the workflow run and evaluate conditions dynamically.

Use a context value in a step

Read metadata from the current workflow run.

↗#

yamlANYgithub-contextexpressions

yaml

- run: echo "Ref is ${{ github.ref }}"

Contexts expose run metadata such as branch, actor, repository, event payload, and more.

Use repository or organization variables

Read configuration values from the `vars` context.

↗#

yamlANYvarsenv

yaml

env:
  APP_ENV: ${{ vars.APP_ENV }}

Use configuration variables for non-secret values shared across workflows.

Build a matrix from JSON

Convert JSON text into a matrix object.

↗#

yamlANYfromJsonmatrixneeds

yaml

strategy:
  matrix: ${{ fromJson(needs.prepare.outputs.matrix) }}

`fromJson()` is useful when one job computes dynamic matrix values for another.

Check if a label is present

Use `contains()` in workflow conditions.

↗#

yamlANYcontainsiflabels

yaml

if: contains(github.event.pull_request.labels.*.name, 'deploy-preview')

Functions like `contains`, `startsWith`, `endsWith`, and `format` are commonly used in conditions.

Env files, step outputs, and job outputs

Pass values safely between steps and jobs.

Set an environment variable for later steps

Append to `GITHUB_ENV` to persist a variable in the current job.

↗#

bashANYGITHUB_ENVenv-files

bash

echo "IMAGE_TAG=${GITHUB_SHA}" >> "$GITHUB_ENV"

This is the supported way to set environment variables for subsequent steps in the job.

Set a step output

Append to `GITHUB_OUTPUT` to expose a named output.

↗#

bashANYGITHUB_OUTPUToutputs

bash

echo "version=1.2.3" >> "$GITHUB_OUTPUT"

Use `GITHUB_OUTPUT` instead of the old deprecated `set-output` workflow command.

Read a previous step output

Use the `steps` context to consume a step output.

↗#

yamlANYstepsoutputs

yaml

- id: version
  run: echo "value=1.2.3" >> "$GITHUB_OUTPUT"

- run: echo "Version is ${{ steps.version.outputs.value }}"

Give the producing step an `id` so later steps can reference its outputs.

Promote a step output to a job output

Pass values between jobs through `needs`.

↗#

yamlANYjob-outputsneeds

yaml

jobs:
  prepare:
    runs-on: ubuntu-latest
    outputs:
      version: ${{ steps.meta.outputs.version }}
    steps:
      - id: meta
        run: echo "version=1.2.3" >> "$GITHUB_OUTPUT"

  deploy:
    needs: prepare
    runs-on: ubuntu-latest
    steps:
      - run: echo "Deploying ${{ needs.prepare.outputs.version }}"

Job outputs are the standard way to pass structured values between jobs.

Write a multiline value to GITHUB_OUTPUT

Preserve newlines in an output variable.

↗#

bashANYmultilineGITHUB_OUTPUT

bash

{
  echo 'notes<<EOF'
  cat CHANGELOG.md
  echo 'EOF'
} >> "$GITHUB_OUTPUT"

Use the heredoc-like delimiter format for multiline values in environment files.

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