Linux Editors

As you read through this book (especially Chapter 8, "Network Services"), no doubt you have come to the conclusion that everything in Linux is configured using one or more text files. These text-based configuration files control how the system boots, what services to run, and even how Apache functions. You can modify many of these settings using the graphical YaST interface, but not all. And what if no GUI were installed on the server or if you needed to administrate the system remotely and a graphical interface was not feasible?

Recall from the first chapter of this book, "Installing SUSE LINUX Enterprise Server," for an SLES server to run efficiently, a GUI desktop should not be installed because the graphical overhead puts an unnecessary load on the system. Therefore, an effective Linux system administrator should be familiar with the operation of text editors. SLES 9 ships with the following text editors:

• ed The original Unix line-based editor. It is very useful in scripts.

• sed A stream-oriented (that is, noninteractive) line-based editor. You have to insert commands to be executed on the data at the command line or in a script to be processed; therefore, it is not a text editor in the traditional word processor sense of the term. The sed utility works by sequentially reading a file, line by line, and performing all actions specified for the line. The modified line is then sent to the terminal (that is, to stdout, which can be redirected) with the requested changes made. The process is repeated until the whole file is processed. As such, sed is ideally suited to performing repetitive edits that would take considerable time if done manually.

• Vim (Vi IMproved) and gVim An enhanced version of the classic Unix screen-based editor, vi. Vim works in text mode in every terminal, but it also has a graphical user interface (gVim) that has menus and mouse support. You can find the latest version of Vim at http://www.vim.org.

• gedit The official text editor of the GNOME desktop environment. Using the GTK+ and GNOME libraries, gedit supports most standard editing features and has a powerful plug-in system to support dynamic function addition. Visit http://www.gnome.org/projects/gedit for more information and the latest version.

• Emacs (Editor MACroS) Based on a dialect of the Lisp programming language, Emacs is a GNU editor that has a fully integrated user environment and can be invoked either in text mode or GUI mode. Visit http://www.gnu.org/software/emacs for the latest version and more information.

• Kate (KDE Advanced Text Editor) A native KDE application that is capable of working with multiple documents concurrently, but only a single instance of Kate is required. Visit http://kate.kde.org for more information.

• JOE (Joe's Own Editor) Created by Joseph Allen, this full-screen text editor has the look and feel of the once-famous Micro-Pro WordStar PC editor (where a majority of the commands are based on the Ctrl-K keys and a third key combination, such as Ctrl-K-D to save the document). Visit http://sourceforge.net/projects/joe-editor for more information.

You should keep in mind that some of the editors mentioned here, such as gedit and Kate, will do you little good if the server does not have a GUI desktop installed. And as discussed in Chapter 1, "Installing SUSE LINUX Enterprise Server," not all servers will have a GUI desktop installed because GUIs on a server consume system resources unnecessarily.

Perhaps we are from the old school, but we highly prefer the vi editor (pronounced vee eye). Many seasoned Linux/Unix system administrators and programmers echo this same preference because when you become familiar with vi's somewhat unique command syntax, you will find that it is one of the most versatilealthough not necessarily the most full-featuredtext editors available. The other reason vi is a favorite among the hard-core Linux/Unix users is its universal availability. Other than the fact that you can find an implementation of vi for most operating systems, it is probably the only screen-oriented text editor that you can count on to be "always there" among all the Linux and Unix distributions available today. Being able to use vi ensures that you will always have an editor available to you, no matter what version or distribution of Linux/Unix you use.

NOTE

Many modern Linux distributions include Vim in conjunction with or instead of vi. SLES 9 ships with Vim instead of vi. Because Vim falls into the category of being a "vi-clone," knowledge of vi will serve you well in administrating SLES systems.

vi (and thus Vim) has three different "modes" of operation:

• Visual command mode This mode is used to issue short commands (of one character or sometimes a couple of characters) that allow you to manipulate the text or editor environment in a number of ways. You enter it by typing one of the text-entering commands shown in Table B.1 to control how and where text is entered.

  Table B.1. vi Single-Character Commands

  TEXT COMMAND	DESCRIPTION
  a	Start appending text after the current cursor position.
  A	Append text to the end of the current line.
  i	Start inserting text to the left of the current cursor location.
  I	Insert text at beginning of the current line.
  o	Insert a new line below the current line.
  O	Insert a new line above the current line.
  r	Replace a single character at the present location.
  R	Replace text starting at the current position (in other words, start overwriting the remainder of the line).
  u	Undo the last change. Undo all the changes to the current line.

  
  

• Data-entry or input mode This mode is used for entering text into the editor's work buffer before it is committed to the disk through a save operation, initiated in one of the command modes.

• Status line command mode This mode is also referred to as the "Colon command mode" because you enter this mode from the visual command mode by typing a colon. This mode is used for issuing longer, more complex commands to the editor, such as to save files, quit the editor, set environment variables, and perform more global editor tasks. The commands are echoed back to the user in the status line of the editor (demarcated by a : at the bottom of the screen) and are executed when you press Enter.

NOTE

To switch out of the input mode into the visual command mode, simply press the Esc key. Entering the status line command mode from the input mode is a two-step process: First press the Esc key to enter the visual command mode and then type a colon (:).

vi does not offer you much feedback as to which mode it is currently in. For instance, you may not not realize that vi is currently in the visual command mode and you typed dd. Instead of adding two d's to your file, you just accidentally deleted the current line of text. (Fortunately, you can undo the change by using the u command; see Table B.1.) If you are unsure what mode vi is operating in, press the Esc key a few times to place vi in visual mode. Even if you are already in the visual mode, the worst you get is an error beep on the terminal.

TIP

Often new users have difficultly knowing which mode they're working in because vi doesn't really offer much feedback. In a worst-case scenario, press Esc a few times and know that you will be in visual mode. Even if you are already in visual mode, the worst you will get is an error beep.

CAUTION

vi commands are case sensitive.

There is a rather rich set of editing commands in vi. Many of them are two-character combinations, usually with the first character denoting the action (such as deleting) and the second character indicating the type of text object (such as a word or sentence) to be acted on. Table B.2 shows some of the most commonly used vi editing commands.

Table B.2. vi Editing Commands

TEXT COMMAND	DESCRIPTION
cw	Change the word at the current cursor position.
D	Delete from the current location to the end of the line.
dd	Delete the current line.
dw	Delete the word at the current cursor location.
x	Delete one character at the current cursor position.
.	Repeat last edit command.
yy	Copy the current line into the memory buffer (known as "yank").
yw	Yank the word under the cursor.
p	Paste the text in the memory buffer (the "yanked" text) at the current cursor position.
P	Paste the yanked text before the current cursor position.
ZZ	Save the changes to disk and exit vi. (You can use :w to write the modifications made so far to disk without exiting the editor.)

TIP

You can precede the editing commands with a number to indicate the command is to be repeated that number of times. For instance, instead of entering dd five times to delete five lines, you can use 5dd instead.

vi, which is a screen-oriented editor, uses the curses library for screen manipulation. That means it works with all supported terminal types, and you can navigate the cursor around the screen using the standard arrow keys. You can move up and down a full screen at a time by pressing Ctrl-B and Ctrl-F, respectively; or, to scroll half a screen up and down, you can press Ctrl-D and Ctrl-U, respectively. Because vi is text-based and does not depend on a mouse, it is most suited for remote management tasks, such as performing file edits over a Telnet or SSH link.

For more information about using vi, you can type :help inside the editor. Other resources include the website dubbed "The Vi Lovers Home page" (http://thomer.com/vi/vi.html) and the book Learning the vi Editor (ISBN 1-56592-426-6).

TIP

You can start vi in read-only mode (vi -R filename). This is useful for viewing long configuration files without the fear of accidentally changing them. vi also has a recovery mode (vi -r filename) that recovers recent edits after a crash. Vim automatically detects this and displays a message similar to the following:

 E325: ATTENTION Found a swap file by the name ".test.txt.swp"      owned by: tasha   dated: Sun Mar 13 13:20:37 2005     file name: ~tasha/test.txt      modified: no     user name: tasha   host name: Athena    process ID: 3250 While opening file "test.txt"         dated: Sun Mar 13 13:20:32 2005 (1) Another program may be editing the same file.     If this is the case, be careful not to end up with     Two different instances of the same file when making     changes.     Quit, or continue with caution. (2) An edit session for this file crashed.     If this is the case, use ":recover" or     "vim -r test.txt" to recover the changes (see     ":help recovery").     If you did this already, delete the swap file     ".test.txt.swp" to avoid this message. Swap file ".test.txt.swp" already exists! [O]pen Read-Only, (E)dit anyway, (R)ecover, (Q)uit, (D)elete it: