Switching from zsh to bash on OSX, and back again?

You can just use exec to replace your current shell with a new shell:

Switch to bash:

exec bash

Switch to zsh:

exec zsh

This won't affect new terminal windows or anything, but it's convenient.

you can try chsh -s /bin/bash to set the bash as the default, or chsh -s /bin/zsh to set the zsh as the default.

Terminal will need a restart to take effect.

I switch between zsh and bash somewhat frequently. For a while, I used to have to source my bash_profile every switch. Then I found out you can (typically) do

exec bash --login

or just

exec bash -l