In the command line interface, you enter commands to tell the operating system which task you want to perform. The login shell refers to the shell that is loaded when you log in to the computer system. Initially, the Korn shell is set up as the login shell. Although some commands can be entered by simply typing one word, other commands use flags and parameters. Each command has a syntax that designates the required and optional flags, files, and parameters.
Flags modify the way the command runs.
The operating system runs the commands sequentially. Commands are case-sensitive. The shell distinguishes between uppercase and lowercase letters. A backslash signifies line continuation to the shell. The following example is one command that spans two lines.