Quickref

Variable	Description	Example
CI	Always set to true
GITHUB_ACTION	The name of the action currently running
GITHUB_ACTION_PATH	The path where an action is located, only supported in composite actions.	/home/runner/work/_actions/repo-owner/name-of-action-repo/v1
GITHUB_ACTION_REPOSITORY	The owner and repository name of the action.	actions/checkout
GITHUB_ACTIONS	Always set to true when GitHub Actions is running the workflow.
GITHUB_ACTOR	The name of the person or app that initiated the workflow.	octocat
GITHUB_ACTOR_ID	The account ID of the person or app that triggered the initial workflow run.	1234567
GITHUB_API_URL	Returns the API URL.	https://api.github.com
GITHUB_BASE_REF	The name of the base ref or target branch of the pull request in a workflow run.	main
GITHUB_ENV	The path on the runner to the file that sets variables from workflow commands	/home/runner/work/_temp/_runner_file_commands/set_env_87406d6e-4979-4d42-98e1-3dab1f48b13a
GITHUB_EVENT_NAME	The name of the event that triggered the workflow.	workflow_dispatch
GITHUB_EVENT_PATH	The path to the file on the runner that contains the full event webhook payload.	/github/workflow/event.json
GITHUB_GRAPHQL_URL	Returns the GraphQL API URL.	https://api.github.com/graphql
GITHUB_HEAD_REF	The head ref or source branch of the pull request in a workflow run	feature-branch-1
GITHUB_JOB	The job_id of the current job.	greeting_job
GITHUB_OUTPUT	The path on the runner to the file that sets the current step's outputs from workflow commands	/home/runner/work/_temp/_runner_file_commands/set_output_a50ef383-b063-46d9-9157-57953fc9f3f0
GITHUB_PATH	The path on the runner to the file that sets system PATH variables from workflow commands	/home/runner/work/_temp/_runner_file_commands/add_path_899b9445-ad4a-400c-aa89-249f18632cf5
GITHUB_REF
The fully-formed ref of the branch or tag that triggered the workflow run.	refs/heads/feature-branch-1
GITHUB_REF_NAME	The short ref name of the branch or tag that triggered the workflow run	feature-branch-1
GITHUB_REF_PROTECTED	true if branch protections or rulesets are configured for the ref that triggered the workflow run	true
GITHUB_REF_TYPE	The type of ref that triggered the workflow run	branch or tag
GITHUB_REPOSITORY	The owner and repository name	octocat/Hello-World
GITHUB_REPOSITORY_ID	The ID of the repository.	123456789
GITHUB_REPOSITORY_OWNER	The repository owner's name.	octocat
GITHUB_REPOSITORY_OWNER_ID	The repository owner's account ID	1234567
GITHUB_RETENTION_DAYS	The number of days that workflow run logs and artifacts are kept	90
GITHUB_RUN_ATTEMPT	A unique number for each attempt of a particular workflow run in a repository	3
GITHUB_RUN_ID	A unique number for each workflow run within a repository	1658821493
GITHUB_RUN_NUMBER	A unique number for each run of a particular workflow in a repository	3
GITHUB_SERVER_URL	The URL of the GitHub server.	https://github.com
GITHUB_SHA	The commit SHA that triggered the workflow	ffac537e6cbbf934b08745a378932722df287a53
GITHUB_STEP_SUMMARY	The path on the runner to the file that contains job summaries from workflow commands	/home/runner/_layout/_work/_temp/_runner_file_commands/step_summary_1cb22d7f-5663-41a8-9ffc-13472605c76c
GITHUB_TRIGGERING_ACTOR	The username of the user that initiated the workflow run
GITHUB_WORKFLOW	The name of the workflow.	My test workflow
GITHUB_WORKFLOW_REF	The ref path to the workflow.	octocat/hello-world/.github/workflows/my-workflow.yml@refs/heads/my_branch
GITHUB_WORKFLOW_SHA	The commit SHA for the workflow file	b16dc47deadbeefdeafbeefbeefdeadbeebaad0d
GITHUB_WORKSPACE	The default working directory on the runner when using actions/checkout	/home/runner/work/my-repo-name/my-repo-name
RUNNER_ARCH	The architecture of the runner executing the job	X86
RUNNER_DEBUG	This is set only if debug logging is enabled	1
RUNNER_NAME	The name of the runner executing the job	Hosted Agent
RUNNER_OS	The operating system of the runner executing the job	Linux
RUNNER_TEMP	The path to a temporary directory on the runner	D:\a\_temp
RUNNER_TOOL_CACHE	The path to the directory containing preinstalled tools for GitHub-hosted runners	C:\hostedtoolcache\windows

Source

https://docs.github.com/en/actions/learn-github-actions/variables#default-environment-variables