As can be seen:
mactex was installed successfully:
==> Installing Cask mactex ==> Running installer for mactex; your password may be necessary. ==> Package installers may write to any location; options such as --appdir are ignored. Password: ==> installer: Package name is MacTeX-2017 ==> installer: Upgrading at base path / ==> installer: The upgrade was successful. 🍺 mactex was successfully installed!
Where is it however..
21:22:37/hw6 $which tex 21:23:35/hw6 $which mactex