Linux provides a lot of different type of shells. There are shells like bash, ksh, csh. But what non of them exist in a Linux or Unix system. The default shell for Linux and Unix systems is
sh . This shell is called also dash because of its maintainers those works for Debian. We will call this as
sh from now.
Sh is by default installed and exist most of the Linux distributions and Unix. Sh is compact shell which have limited capabilities compared to bash, ksh, csh .
Sh have less library dependency and needs less memory. Embedded systems like modem, router, wireless uses sh because of its simplicity. It is fast but have limited capabilities like not having shell programming.
As said before sh is installed by default but most of the Linux distributions use bash as default shell. Current working shell can be changed to the sh like below just calling
/bin/sh shell executable.
In the last line of the screen shot it can be seen that
/bin/sh is the default shell and assigned to
_ shell variable.
As running the
sh executable starts new shell we want to exit this shell. To exit current sh shell just issue
exit command like below.