reg existed on 10.8 and lower as documented here - https://developer.apple.com/library/prerelease/mac/documentation/Darwin/Reference/ManPages/man1/reg.1.html
However, in OS X 10.9 I only find man page but not the command. My requirement is to passively monitor the processor registers (dump them). It looks like 'reg' does that.
Is there an equivalent utility that I download somewhere for MAC OS X >= 10.9.