“A nearly impenetrable thicket of geekitude…”

zsh: Not Yet

In macOS 10.15 Catalina, Apple have decided to change the default shell from an antediluvian version of bash to a very recent version of zsh.

One reason for this appears to be bash switching to GPL V3 a while back. Whatever the reason, though, they are flagging this change up pretty heavily every time you open a shell:

The default interactive shell is now zsh.
To update your account to use zsh, please run `chsh -s /bin/zsh`.
For more details, please visit https://support.apple.com/kb/HT208050.

Switching to a new shell will be something of a major project, so although I will probably do that at some point I was delighted to find that you can disable the warning by adding the following to your .bash_profile: