Applies to OS X 10.6 (Snow Leopard) and newer; tested through MacOS 10.13 (High Sierra)
The general advice for adding particular directories to your PATH
environment variable on MacOS is to add an export PATH
to your ~/.bashrc
or equivalent. This has some drawbacks. For one, it only affects that shell for that user.
Additionally, sometimes installed Applications modify the system's default PATH
in ways that you don't want.
Understanding how MacOS generates the PATH
environment variable is instructive.
TL;DR read man path_helper
and be enlightened