Andrew Hudson - Fedora™ Unleashed, 2008 edition

To experiment with the environment variables, you can modify the PS1variable to manipulate the appearance of your shell prompt. If you are working with bash,you can use its built-in exportcommand to change the shell prompt. For example, if your default shell prompt looks like

[andrew@teletran ~]$

you can change its appearance by using the PS1 variable like this:

$ PS1='$OSTYPE r001z ->'

After you press Enter, you see the following:

linux-gnu r001z ->

See the bashman page for other variables you can use for prompt settings.

Linux distributions include a number of applications known as text editors that you can use to create text files or edit system configuration files. Text editors are similar to word processing programs, but generally have fewer features, work only with text files, and might or might not support spell checking or formatting. The text editors range in features and ease of use, but are found on nearly every Linux distribution. The number of editors installed on your system depends on what software packages you've installed on the system.

Some of the console-based text editors are as follows:

► emacs — The comprehensive GNU emacsediting environment, which is much more than an editor; see the section "Working with emacs"later in this chapter

► joe — Joe's Own Editor, a text editor, which can be used to emulate other editors

► nano — A simple text editor similar to the picotext editor included with the pineemail program

► vim —An improved, compatible version of the vitext editor (which we call viin the rest of this chapter because it has a symbolic link named viand a symbolically linked manual page)

Note that not all text editors described here are screen oriented. Some of the text editors for the X Window System, which provide a graphical interface, such as menu bars, buttons, scrollbars and so on, are the following:

► gedit — A GUI text editor for GNOME

► kate — A simple KDE text editor

► kedit — Another simple KDE text editor

A good reason to learn how to use a text-based editor, such as vi,is that system maintenance and recovery operations generally never take place during X Window sessions (negating the use of a GUI editor). Many larger, more complex and capable editors do not work when Linux is booted to its single-user or maintenance mode. See Chapter 11 for more information about how Fedora boots. If anything does go wrong with your system, you probably won't be able to get into the X Window System, making knowledge and experience of using both the command line and text editors such as vi important. Make a point of opening some of the editors and playing around with them; you never know — you might just thank me someday!

Another reason to learn how to use a text-based editor under the Linux console mode is so that you can edit text files through dialup or network shell sessions because many servers do not host graphical desktops.

The editor found on nearly every UNIX and Linux system is, without a doubt, the vieditor, originally written by Bill Joy. This simple-to-use but incredibly capable editor features a somewhat cryptic command set, but you can put it to use with only a few commands. Although more experienced UNIX and Linux users continue to use viextensively during computing sessions, many newer users might prefer learning an easier-to-use text editor such as picoor GNU nano.Diehard GNU fans and programmers definitely use emacs.

That said, learning how to use viis a good idea. You might need to edit files on a Linux system with a minimal install, or a remote server without a more extensive offering of installed text editors. Chances are better than good that viwill be available.

You can start an editing session by using the vicommand like this:

$ vi file.txt

The vicommand works by using an insert (or editing) mode, and a viewing (or command) mode.

When you first start editing, you are in the viewing mode. You can use your cursor or other navigation keys (as shown later) to scroll through the text. To start editing, press the i key to insert text or the a key to append text. When finished, use the Esc key to toggle out of the insert or append modes and into the viewing (or command) mode. To enter a command, type a colon ( : ), followed by the command, such as w to write the file, and press Enter.

Although visupports many complex editing operations and numerous commands, you can accomplish work by using a few basic commands. These basic vicommands are the following:

► Cursor movement— h, j, k, l(left, down, up, and right)

► Delete character— x

► Delete line— dd

► Mode toggle— Esc, Insert(or i)

► Quit— :q

► Quit without saving— :q!

► Run a shell command— :sh(use 'exit'to return)

► Save file— :w

► Text search— /

Use the vimtutorcommand to quickly learn how to use vi's keyboard commands. The tutorial takes less than 30 minutes, and it teaches new users how to start or stop the editor; navigate files; insert and delete text; and perform search, replace, and insert operations.

Richard M. Stallman's GNU emacseditor, like vi, is included with Linux and nearly every other Linux distribution. Unlike other UNIX and Linux text editors, emacsis much more than a simple text editor — it is an editing environment and can be used to compile and build programs, act as an electronic diary, appointment book and calendar, compose and send electronic mail, read Usenet news, and even play games. The reason for this capability is that emacscontains a built-in language interpreter that uses the Elisp (emacsLISP) programming language.

The GNU version of this editor requires more than 30MB of hard drive space. However, there are versions with fewer resource requirements, and at least one other text editor included with Linux, named joe,can be used as an emacsclone (albeit with fewer features).

You can start an emacsediting session like this:

$ emacs file.txt

If you start emacswhen using X11, the editor launches in its own floating window. To force emacsto display inside a terminal window rather than its own window (which can be useful if the window is a login at a remote computer), use the -nwcommand-line option like this: emacs -nw file.txt .