Chapter 3. Command Line Utilities

IN THIS CHAPTER

Special Characters 42

Basic Utilities 43

less Is more: Displaying a Text File One Screen at a Time 45

Working with Files 45

lpr: Prints a File 47

| (Pipe): Communicates Between Processes 52

Compressing and Archiving Files 56

Obtaining User and System Information 63

When Linus Torvalds introduced Linux and for a long time thereafter, Linux did not have a graphical user interface: It ran on character-based terminals only. All the tools ran from a command line. Today the Linux GUI is important, but many people especially system administrators run many command line programs. Command line utilities are often faster, more powerful, or more complete than their GUI counterparts. Sometimes there is no GUI counterpart to a text-based utility; some people just prefer the hands-on feeling of the command line.

When you work with a command line interface, you are working with a shell. Before you start working with a shell, it is important to understand something about the characters that are special to the shell, so this chapter starts with a discussion of shell special characters. The chapter then describes four basic utilities you can use to create and manipulate files (ls, cat, rm, and less) and one utility that tells you the name of the system you are using (hostname). It continues with a section on additional file manipulation utilities (including lpr, which prints files), followed by a brief discussion of how you can use a pipe on the command line. This chapter then describes utilities that compress and decompress files, locate other utilities, obtain user and system information, and allow you to communicate with other users. It concludes with a section on email.

tip: Run these utilities from a command line

This chapter describes command line (i.e., text-based) utilities. You can experiment with these utilities from a terminal, a terminal emulator within a GUI, or a virtual console (page 36).