When I installed 7zip via home brew (Formula sevenzip), i noticed that i cannot run it via sevenzip and even brew info sevenzip did not tell me the name of the binary.
Only after looking in the script file on Github I noticed a command 7zz but there must be an easier way to find out the binaries or commands associated with a homebrew package.
The simplest I know is:
brew ls PACKAGE
and you can normally see it pretty quickly. Personally, I use p7zip as PACKAGE.
Alternatively, as brew --prefix tells you where binaries are installed (via symlinks), you can find the newest installed binary with:
ls -lrt $(brew --prefix)/bin
and it's the last one listed.