Up until now, each time you have entered a command, you have been using the shell. The shell also controls your environment and contains a programming language. Most Unix computers, including Uniform Access computers, run several shells, allowing you to choose the one you prefer. By default, on Uniform Access computers, you start in the C-shell . The C-shell offers a number of special commands known as control codes.
Control codes define commands specific to the operating system.
Typically, standard input is from the keyboard, and standard output is displayed to the screen. The routing of standard input and output can be changed by using redirection and piping . Redirection and piping let you connect commands together. You can then use this file as you would any other file. You can use output redirect to save information such as a help note into a file.