About contexts
Contexts are a way to access information about workflow runs, variables, runner environments, jobs, and steps. Each context is an object that contains properties, which can be strings or other objects.
Contexts, objects, and properties will vary significantly under different workflow run conditions. For example, the matrix context is only populated for jobs in a matrix.
You can access contexts using the expression syntax. For more information, see Evaluate expressions in workflows and actions.
${{ <context> }}
Warning
When creating workflows and actions, you should always consider whether your code might execute untrusted input from possible attackers. Certain contexts should be treated as untrusted input, as an attacker could insert their own malicious content. For more information, see Secure use reference.
Determining when to use contexts
GitHub Actions includes a collection of variables called contexts and a similar collection of variables called default variables. These variables are intended for use at different points in the workflow:
- Default environment variables: These environment variables exist only on the runner that is executing your job. For more information, see Store information in variables.
- Contexts: You can use most contexts at any point in your workflow, including when default variables would be unavailable. For example, you can use contexts with expressions to perform initial processing before the job is routed to a runner for execution; this allows you to use a context with the conditional
ifkeyword to determine whether a step should run. Once the job is running, you can also retrieve context variables from the runner that is executing the job, such asrunner.os. For details of where you can use various contexts within a workflow, see Contexts reference.
The following example demonstrates how these different types of variables can be used together in a job:
name: CI
on: push
jobs:
prod-check:
if: ${{ github.ref == 'refs/heads/main' }}
runs-on: ubuntu-latest
steps:
- run: echo "Deploying to production server on branch $GITHUB_REF"
name: CI
on: push
jobs:
prod-check:
if: ${{ github.ref == 'refs/heads/main' }}
runs-on: ubuntu-latest
steps:
- run: echo "Deploying to production server on branch $GITHUB_REF"
In this example, the if statement checks the github.ref context to determine the current branch name; if the name is refs/heads/main, then the subsequent steps are executed. The if check is processed by GitHub Actions, and the job is only sent to the runner if the result is true. Once the job is sent to the runner, the step is executed and refers to the $GITHUB_REF variable from the runner.