Tried to install gromacs 5.1.1 via homebrew, all commands are not found
I figured it out myself, so I'm posting the answer in case anyone else has this problem.

The answer was that gromacs has changed since the version I used most recently, and the commands I was used to no longer exist.  For example, the g_energy command now runs as gmx energy.

If you are also having this problem, gmx help commands should give you a list of what the commands are now.

Thanks for reading this!