No idea, but I am interested to see how you get there.
I'm not sure why do you want to avoid curl. It is there as like as java.
This is not helpful for you, but I found a way for Windows.
wmic datafile where name="C:\\Program Files\\FileMaker\\FileMaker Server\\Database Server\\fmsadmin.exe" get version
What's the reason for wanting to know the console version? It does not necessarily mean that FMS as a whole is at that exact subversion as each component may be patched differently.
I found similar command "mdls" on OSX, but the file doesn't have version information in Finder Info, mdls also can't show it.