GitHub Actions by Example: Context Expressions

As seen in Context Variables, you can inject variables into the workflow by using the ${{ <context variable> }} syntax. Workflows support evaluating expressions as well such as comparisons and simple functions. For more information see the docs.

name: expressions-example
on:
  push:
  pull:
jobs:
  use-expressions:
    strategy:
      matrix:
        greeting: [Hello, Howdy, Hey]
    runs-on: ubuntu-latest
    steps:
      -
        name: Print if 'Hello'

Use equality operators to get a boolean result; in this case we are only running the step when the greeting is “Hello”. Note the use of single quotes for the string literal. You can use ==, !=, <, <=, >, >=, &&, ||, and ( ... ). Learn more about operators here

        if: ${{ matrix.greeting == 'Hello' }}
        run: echo "greeting is Hello"
      -
        name: Print if starts with 'He'
        if: ${{ startsWith(matrix.greeting, 'He') }}
        run: echo "greeting starts with He"
      -
        name: Print if ends with 'y'
        if: ${{ endsWith(matrix.greeting, 'y') }}
        run: echo "greeting ends with y"          
      -
        name: Print if contains 'ow'
        if: ${{ contains(matrix.greeting, 'ow') }}
        run: echo "greeting contains ow"
      -
        name: Print formatted greeting
        run: |
                    echo "${{ format('{0} says {1}', github.actor, matrix.greeting) }}"
      -
        name: To JSON

toJSON() converts things to a pretty-printed JSON string

        run: echo 'Job context is ${{ toJSON(job) }}'
      -
        name: From JSON

fromJSON() converts a string into a JSON object or value

        env: ${{ fromJSON('{"FAVORITE_FRUIT": "APPLE", "FAVORITE_COLOR": "BLUE"}') }}
        run: echo "I would like a ${FAVORITE_COLOR} ${FAVORITE_FRUIT}"
      - 
        name: Success

success() returns true if no previous steps have failed or have been canceled.

        if: ${{ success() }}
        run: echo "Still running..."
      -
        name: Always

always() returns true no matter if a step failed or the workflow was cancelled.

        if: ${{ always() }}
        run: echo "You will always see this"
      -
        name: Canceled

canceled() returns true if the workflow was canceled.

        if: ${{ canceled() }}
        run: echo "You canceled the workflow"
      -
        name: Failure

failure() returns true if any previous step failed.

        if: ${{ failure() }}
        run: echo "Something went wrong..."