shell features enable you to gather data input and direct data output between commands and Linux filesystems. To save on typing, you can find, edit, and repeat commands from your shell history. Many power users hardly touch a graphical interface, doing most of their work from a shell.
You can gather commands into a file using programming constructs such as conditional tests, loops, and case statements to perform complex operations quickly, which would be difficult to retype over and over. Programs consisting of commands that are stored and run from a file are referred to as shell scripts. Many Linux system administrators use shell scripts to automate tasks such as backing up data, monitoring log files, or checking system health.
The shell is a command language interpreter. If you have used Microsoft operating systems, you'll see that using a shell in Linux is similar to, but generally much more powerful than, the PowerShell interpreter used to run commands. You can happily use Linux from a graphical desktop interface, but as you grow into Linux you will surely need to use the shell at some point to track down a problem or administer some features.
How to use the shell isn't obvious at first, but with the right help you can quickly learn many of the most important shell features. This chapter is your guide to working with the Linux system commands, processes, and filesystem from the shell. It describes the shell environment and helps you tailor it to your needs.
About Shells and Terminal Windows
There are several ways to get to a shell interface in Linux. Three of the most common are the shell prompt, Terminal window, and virtual console, which you learn more about in the following sections.
To start, boot up your Linux system. On your screen, you should see either a graphical login screen or a plain-text login prompt similar to the following:
Red Hat Enterprise Linux Server release 8.0 (Ootpa) Kernel 4.18.0-42.el8.x86_64 on an X86 mylinuxhost login:
In either case, you should log in with a regular user account. If you have a plain-text login prompt, continue to the next section, “Using the shell prompt.” If you log in through a graphical screen, go to the section “Using a Terminal window” to see how to access a shell from the desktop. In either case, you can access more shells as described in the section “Using virtual consoles,” which appears shortly in this chapter.
Using the shell prompt
If your Linux system has no graphical user interface (or one that isn't working at the moment), you will most likely see a shell prompt after you log in. Typing commands from the shell will probably be your primary means of using the Linux system.
The default prompt for a regular user is simply a dollar sign:
$
The default prompt for the root user is a pound sign (also called a number sign or a hash tag):
#
In most Linux systems, the $ and # prompts are preceded by your username, system name, and current directory name. For example, a login prompt for the user named jake on a computer named pine with /usr/share/ as the current working directory would appear as follows:
[jake@pine share]$
You can change the prompt to display any characters you like and even read in pieces of information about your system. For example, you can use the current working directory, the date, the local computer name, or any string of characters as your prompt. To configure your prompt, see the section “Setting your prompt” later in this chapter.
Although a tremendous number of features are available with the shell, it's easy to begin by just entering a few commands. Try some of the commands shown in the remaining sections to become familiar with your current shell environment.
In the examples that follow, the dollar ($) and pound (#) symbols indicate a prompt. A $ indicates that the command can be run by any user, but a # typically means that you should run the command as the root user; that is, many administrative tools require root permission to be able to run them. The prompt is followed by the command that you type (and then press Enter). The lines that follow show the output resulting from the command.
NOTE
Although we use # to indicate that a command be run as the root user, you do not need to log in as the root user to run a command as root. In fact, the most common way to run a command as a root user is to use the sudo command. See Chapter 8, “Learning System Administration,” for further information about the sudo command.
Using a Terminal window
With the desktop GUI running, you can open a Terminal emulator program (sometimes referred to as a Terminal window) to start a shell. Most Linux distributions make it easy for you to get to a shell from the GUI. Here are two common ways to launch a Terminal window from a Linux desktop:
Right-click the desktop. In the context menu that appears, if you see Open in Terminal, Shells, New Terminal, Terminal Window, Xterm, or some similar item, select it to start a Terminal window. (Some distributions have disabled this feature.)
Click the panel menu. Many Linux desktops include a panel at the top or bottom of the screen from which you can launch applications. For example, in some systems that use the GNOME 2 desktop, you can select Applications ➪ System Tools ➪ Terminal to open a Terminal window. In GNOME 3, click the Activities menu, type Terminal, and press Enter.
In all cases, you should be able to type a command as you would from a shell with no GUI. Different Terminal emulators are available with Linux. In Fedora, Red Hat Enterprise Linux (RHEL), and other Linux distributions that use the GNOME desktop, the default Terminal emulator window is the GNOME Terminal (started by the gnome-terminal command).
GNOME Terminal supports many features beyond the basic shell. For example, you can cut and paste text to or from a GNOME Terminal window, change fonts, set a title, choose colors or images to use as background, and set how much text to save when text scrolls off the screen.
To try some GNOME Terminal features, start up a Fedora or RHEL system and log in to the desktop. Then follow this procedure:
1 Select Applications ➪ Utilities ➪ Terminal (or click on the Activities menu and type Terminal). A Terminal window should open on your desktop.
2 Select Edit ➪ Profile Preferences or Preferences.
3 On the General tab or current profile (depending on your version of GNOME), check the “Custom font” box.
4 Select the Font field, try a different font and size, and then click Select. The new font appears in the Terminal window.
5 Unselect the “Custom font” box. This takes you back to the original font.
6 On the Colors tab, clear the “Use colors from system theme” check box. From here, you can try some different font and background colors.
7 Re-select
