Below I have some useful commands to view/modify the shell in Mac or Linux.
View all available shells
$ cat /etc/shells
View the current shell
$ echo $SHELL
Change the current shell to zsh
$ chsh -s /bin/zsh
We should restart the terminal after executing the above command for the new shell to take effect. In the chsh -s we can pass any one of the available shells in the machine.
Restart the shell
$ exec -l $SHELL