The step event occurs when the first instruction of a source line is executed. For example, you can get simple tracing with:
when step { echo $lineno: $line; }; cont |
When enabling a step event, you instruct dbx to single step automatically next time the contcommand is used.
The step (and next) events do not occur upon the termination of the step command. The step command is implemented in terms of the step event roughly as follows: alias step="when step -temp { whereami; stop; }; cont"