Before you begin, you should feel comfortable with what you have learned so far. You should know how to move from directory to directory, how to list files, and how to read a long file listing. You should know how to use mail, cat, and vi. You should know how to manage your files, and how to modify their permissions. Most importantly, you should be learning how tocombine commands together with pipes, and how to use redirectionto take input from, or put output into, a file. The commands you will learn in this chapter are powerful on theirown, but they can be much more powerfulwhen combined with some of the commands you have already learned.