Terminal.app: changing shell behavior problem? I'm having problems setting Terminal.app's default shell.  It appears to work using a command line utility which sets the shell for the account, however not in Terminal.app's dialog which is for each session.  I find that if I set the shell system with with 'chsh', the $SHELL variable in Terminal.app correctly reflects the shell.  If I change the shell in Terminal.app only, $SHELL does not correctly reflect the shell, however the shell appears to be the correct shell running.  I tried this on a temp account to rule out other interactions and it has the same behavior.

Here is a use case:
When I run in Terminal.app:

$ chsh -s /bin/ksh


and invoke Terminal.app, the shell is correctly changed:

$ echo $SHELL
/bin/ksh


The problem is if try similar through Terminal.app->Preferences->General->Shells open with->Command->/bin/ksh

$ echo $SHELL
/bin/bash


Yet when I try command completions with TAB, it reflects ksh behavior.

Therefore, my suspicion is there is something overriding the SHELL environment variable where it is always SHELL=/bin/bash, despite the shell being different than that.

Does anyone know if Apple has a bug here?
The following information is taken from


SHELL environment variable still points to zsh after using bash and
What sets the $SHELL environment variable?


on Unix &amp; Linux, which applies to macOS as well.

You are running the Korn shell if the Terminal preference is set to /bin/ksh. The output 

$ echo $SHELL
/bin/bash


is misleading because the SHELL variable is set by the login process to


  The user's shell, as specified by the password database.


(On macOS it is a user database and not the /etc/passwd file as on Linux, where that information is stored, but that does not matter.)

You can type

$ echo $0
-ksh


or

$ echo $KSH_VERSION
Version AJM 93u+ 2012-08-01


to verify that you are running the Korn shell.

Setting the shell via  

$ chsh -s /bin/ksh


sets the login shell in the user database, and then SHELL is set accordingly:

$ echo $SHELL
/bin/ksh