If Bash is your login shell, and you log in to the system from a terminal or terminal emulator, then it will start in interactive mode. In this mode, Bash will present a prompt when it's ready to accept a command from your terminal. This differs from non-interactive or batch mode, where commands are read from some other source, such as a script file. We will use interactive mode in this chapter to experiment with the basics of shell script command line grammar.
Nearly all of the features available to Bash in scripts are also available on the interactive command line, and they behave essentially the same way as if you ran them from a script. This allows you to treat the interactive command line as a live scripting environment: you can assign variables, create functions, and manage control flow and processes.