16.1 The Korn Shell or POSIX Shell

16.2 Bourne Shell

The Bourne shell is an interactive command interpreter and command programming language. The bsh command runs the Bourne shell.

The Bourne shell can be run either as a login shell or as a subshell under the login shell. Only the login command can call the Bourne shell as a login shell. It does this by using a special form of the bsh command name: -bsh. When called with an initial - (hyphen), the shell first reads and runs commands found in the system /etc/profile file and your $HOME/.profile, if one exists.

The /etc/profile file sets variables needed by all users. Finally, the shell is ready to read commands from your standard input.

16.3 C Shell