Your pipeline can define its own environment variables and add them to the pipeline's run state. These will be available to all steps in the run of the pipeline.
Use the utility functions for run state management to add new environment variables to the current run state. For example, the following line in the execution block of a step:
add_run_variables hero="Superman" villain="Lex Luthor"
creates two environment variables available to the current and all future steps of the pipeline's run:
$ printenv hero Superman $ printenv villain Lex Luthor
For more information on run state, see Creating Stateful Pipelines.