Andrew beat me to the punch but I’ll post what I was typing anyway:
If you’re talking about code in your build function introspecting on which top-level steps (note the plural; you can actually invoke multiple steps at once) were selected, then the answer is no, there’s no way to get any information about which steps are being invoked unless you manually parse the argv yourself (which you almost definitely shouldn’t do!).
The build system is logically divided up into a “configure” phase which calls your build function in order to construct the graph of steps and learn which top-level steps are available, and a “make” phase which invokes the steps. The “configure” phase is not intended to know about which steps the user selected.
You didn’t explain exactly why you need this information, but if you want to conditionally take a certain code path in your build function depending what the user specified, your best option is using b.option.