I know that $SHELL is an environment-variable, which refers to the current default-shell. echo $SHELL
prints the path to stdout.
Here the use of it for keeping the terminal window open: How to run a script without closing the terminal?
What does $SHELL do, when it is entered like a some command?
exit
the shell, the window will be closed. – choroba Feb 07 '20 at 10:32