Chapter 1. The vi Text Editor

Unix1 has a number of editors that can process the contents of text files, whether those files contain data, source code, or sentences. There are line editors, such as ed and ex, which display a line of the file on the screen; and there are screen editors, such as vi and Emacs, which display a part of the file on your terminal screen. Text editors based on the X Window System are also commonly available and popular. GNU Emacs provides multiple X windows, as does Vim through its gvim version.

vi is the most useful standard text editor on your system. Unlike Emacs, it is available in nearly identical form on every modern Unix system, thus providing a kind of text-editing lingua franca.2 The same might be said of ed and ex, but screen editors are generally much easier to use. (So much so, in fact, that line editors have generally fallen into disuse.) With a screen editor, you can scroll the page, move the cursor, delete lines, insert characters, and more, while seeing the results of your edits as you make them. Screen editors are very popular, since they allow you to make changes as you read through a file, like you would edit a printed copy, only faster.

Note

vi is short for visual editor and is pronounced “vee-eye.” This is illustrated graphically in Figure 1-1.

vive 0101
Figure 1-1. Correct pronunciation of vi

To many beginners, vi looks unintuitive and cumbersome—instead of using special control keys for word processing functions and just letting you type normally, it uses all of the regular keyboard keys for issuing commands. When the keyboard keys are issuing commands, vi is said to be in command mode. You must be in a special insert mode before you can type actual text on the screen. In addition, there seem to be so many commands.

Once you start learning, however, you realize that vi is well designed. You need only a few keystrokes to tell vi to do complex tasks. As you learn vi, you learn shortcuts that transfer more and more of the editing work to the computer—where it belongs.

vi (like any text editor) is not a “what you see is what you get” word processor. If you want to produce formatted documents, you must type in codes that are used by another formatting program to control the appearance of the printed copy. If you want to indent several paragraphs, for instance, you put a code where the indent begins and ends. Formatting codes allow you to experiment with or change the appearance of your printed files, and, in many ways, they give you much more control over the appearance of your documents than a word processor. Unix supports the troff formatting package.3 The TeX and LaTeX formatters are popular, commonly available alternatives.4 In recent years, so-called mark up languages have seen a resurgence in popularity. Of note are MarkDown and AsciiDoc5, although there are others as well.

Note

vi does support some simple formatting mechanisms. For example, you can tell it to automatically wrap when you come to the end of a line, or to automatically indent new lines. In addition, Vim provides automatic spellchecking.

As with any skill, the more editing you do, the easier the basics become, and the more you can accomplish. Once you are used to all the powers you have while editing with vi, you may never want to return to any “simpler” editor.

What are the components of editing? First, you want to insert text (a forgotten word or a new or missing sentence), and you want to delete text (a stray character or an entire paragraph). You also need to change letters and words (to correct misspellings or to reflect a change of mind about a term). You might want to move text from one place to another part of your file. And, on occasion, you want to copy text to duplicate it in another part of your file.

Unlike many word processors, vi’s command mode is the initial or “default” mode. Complex, interactive edits can be performed with only a few keystrokes. (And to insert raw text, you simply give any of the several “insert” commands and then type away.)

One or two characters are used for the basic commands. For example:

i

Insert

cw

Change word

Using letters as commands, you can edit a file with great speed. You don’t have to memorize banks of function keys or stretch your fingers to reach awkward combinations of keys. You never have to remove your hands from the keyboard, or mess around with multiple levels of menus! Most of the commands can be remembered by the letters that perform them, and nearly all commands follow similar patterns and are related to each other.

In general, vi commands:

  • Are case-sensitive (uppercase and lowercase keystrokes mean different things; I is different from i).

  • Are not shown (or “echoed”) on the screen when you type them.

  • Do not require an ENTER after the command.

There is also a group of commands that echo on the bottom line of the screen. Bottom-line commands are preceded by different symbols. The slash (/) and the question mark (?) begin search commands, and are discussed in Chapter 3. A colon (:) begins all ex commands. ex commands are those used by the ex line editor. The ex editor is available to you when you use vi, because ex is the underlying editor and vi is really just its “visual” mode. ex commands and concepts are discussed fully in Chapter 5, but this chapter introduces you to the ex commands to quit a file without saving edits.

A Brief Historical Perspective

Before diving into all the ins and outs of vi, it will help to understand vi’s worldview of your environment. In particular, this will help you make sense of many of vi’s otherwise more obscure error messages, and also appreciate how Vim has evolved beyond the original vi.

vi dates back to a time when computer users worked on terminals connected via serial lines to central mini-computers. Hundreds of different kinds of terminals existed and were in use worldwide. Each one did the same kind of actions (clear the screen, move the cursor, etc.), but the commands needed to make them do these actions were different. In addition, the Unix system let you choose the characters to use for backspace, generating an interrupt signal, and other commands useful on serial terminals, such as suspending and resuming output. These facilities were (and still are) managed with the stty command.

The original UCB version of vi abstracted out the terminal control information from the code (which was hard to change) into a text-file database of terminal capabilities (which was easy to change), managed by the termcap library. In the early 1980s, System V introduced a binary terminal information database and terminfo library. The two libraries were largely functionally equivalent. In order to tell vi which terminal you had, you had to set the TERM environment variable. This was typically done in a shell startup file, such as .profile or .login.

The termcap library is no longer used. GNU/Linux and BSD systems use the ncurses library, which provides a compatible superset of the System V terminfo library’s database and capabilities.

Today, everyone uses terminal emulators in a graphical environment (such as Gnome Terminal). The system almost always takes care of setting TERM for you.

Note

You can use vi from a PC non-GUI console too, of course. This is very useful when doing system recovery work in single-user mode. There aren’t too many people left who would want to work this way on a regular basis, though.

For day-to-day use, it is likely that you will want to use a GUI version of vi, such as Vim. On a Microsoft Windows or Mac OS system, this will probably be the default. However, when you run vi (or some other screen editor of the same vintage) inside a terminal emulator, it still uses TERM and terminfo and pays attention to the stty settings. And using it inside a terminal emulator is just as easy a way to learn vi as any other.

Another important fact to understand about vi is that it was developed at a time when Unix systems were considerably less stable than they are today. The vi user of yesteryear had to be prepared for the system to crash at arbitrary times, and so vi included support for recovering files that were in the middle of being edited when the system crashed.6 So, as you learn vi and see the descriptions of various problems that might occur, bear these historical developments in mind.

Opening and Closing Files

You can use vi to edit any text file. vi copies the file to be edited into a buffer (an area temporarily set aside in memory), displays the buffer (though you can see only one screenful at a time), and lets you add, delete, and change text. When you save your edits, vi copies the edited buffer back into a permanent file, replacing the old file of the same name. Remember that you are always working on a copy of your file in the buffer, and that your edits do not affect your original file until you save the buffer. Saving your edits is also called “writing the buffer,” or more commonly, “writing your file.”

Opening a File

vi is the Unix command that invokes the vi editor for an existing file or for a brand new file. The syntax for the vi command is:

$ vi [filename]

The brackets shown on the above command line indicate that the filename is optional. The brackets should not be typed. The $ is the shell prompt. If the filename is omitted, vi opens an unnamed buffer. You can assign the name when you write the buffer into a file. For right now, though, let’s stick to naming the file on the command line.

A filename must be unique inside its directory.

A filename can include any 8-bit character except a slash (/), which is reserved as the separator between files and directories in a pathname, and ASCII NUL, the character with all zero bits. You can even include spaces in a filename by typing a backslash () before the space. In practice, though, filenames generally consist of any combination of uppercase and lowercase letters, numbers, and the characters dot (.) and underscore (_). Remember that Unix is case-sensitive: lowercase letters are distinct from uppercase letters. Also remember that you must press ENTER to tell Unix that you are finished issuing your command.

When you want to open a new file in a directory, give a new filename with the vi command. For example, if you want to open a new file called practice in the current directory, you would enter:

$ vi practice

Since this is a new file, the buffer is empty and the screen appears as follows:

~
~
~
"practice" [New file]

The tildes (~) down the left-hand column of the screen indicate that there is no text in the file, not even blank lines. The prompt line (also called the status line) at the bottom of the screen echoes the name and status of the file.

You can also edit any existing text file in a directory by specifying its filename. Suppose that there is a Unix file with the pathname /home/john/letter. If you are already in the /home/john directory, use the relative pathname. For example:

$ vi letter

brings a copy of the file letter to the screen.

If you are in another directory, give the full pathname to begin editing:

$ vi /home/john/letter

Problems Opening Files

  • When you invoke vi , the message [open mode] appears.

    Your terminal type is probably incorrectly identified. Quit the editing session immediately by typing :q. Check the environment variable $TERM. It should be set to the name of your terminal. Or ask your system administrator to provide an adequate terminal type setting.

  • You see one of the following messages:

    Visual needs addressable cursor or upline capability
    terminal: Unknown terminal type
    Block device required
    Not a typewriter

    Your terminal type is either undefined, or there’s probably something wrong with your terminfo entry. Enter :q to quit. Check your $TERM environment variable, or ask your system administrator to select a terminal type for your environment.

  • A [new file] message appears when you think a file already exists.

    Check that you have used correct case in the filename (Unix filenames are case-sensitive). If you have, then you are probably in the wrong directory. Enter :q to quit. Then check to see that you are in the correct directory for that file (enter pwd at the Unix prompt). If you are in the right directory, check the list of files in the directory (with ls) to see whether the file exists under a slightly different name.

  • You invoke vi , but you get a colon prompt (indicating that you’re in ex line-editing mode).

    You probably typed an interrupt before vi could draw the screen. Enter vi by typing vi at the ex prompt (:).

  • One of the following messages appears:

    [Read only]
    File is read only
    Permission denied

    “Read only” means that you can only look at the file; you cannot save any changes you make. You may have invoked vi in view mode (with view or vi -R), or you do not have write permission for the file. See the section “Problems Saving Files”.

  • One of the following messages appears:

    Bad file number
    Block special file
    Character special file
    Directory
    Executable
    Non-ascii file
    file non-ASCII

    The file you’ve called up to edit is not a regular text file. Type :q! to quit, then check the file you wish to edit, perhaps with the file command.

  • When you type :q because of one of the previously mentioned difficulties, this message appears:

    No write since last change (:quit! overrides).

    You have modified the file without realizing it. Type :q! to leave vi. Your changes from this session are not saved in the file.

Modus Operandi

As mentioned earlier, the concept of the current “mode” is fundamental to the way vi works. There are two modes, command mode and insert mode. You start out in command mode, where every keystroke represents a command. In insert mode, everything you type becomes text in your file.

Sometimes, you can accidentally enter insert mode, or conversely, leave insert mode accidentally. In either case, what you type will likely affect your files in ways you did not intend.

Press the ESC key to force vi to enter command mode. If you are already in command mode, vi beeps at you when you press the ESC key. (Command mode is thus sometimes referred to as “beep mode.”)

Once you are safely in command mode, you can proceed to repair any accidental changes, and then continue editing your text.

Saving and Quitting a File

You can quit working on a file at any time, save your edits, and return to the Unix prompt. The vi command to quit and save edits is ZZ. Note that ZZ is capitalized.

Let’s assume that you do create a file called practice to practice vi commands, and that you type in six lines of text. To save the file, first check that you are in command mode by pressing ESC, and then enter ZZ.

Keystrokes Results

ZZ

"practice" [New file] 6 lines, 320 characters

Give the write and save command, ZZ. Your file is saved as a regular Unix file.

ls

ch01 ch02 practice

Listing the files in the directory shows the new file practice that you created.

You can also save your edits with ex commands. Type :w to save (write) your file but not quit vi; type :q to quit if you haven’t made any edits; and type :wq to both save your edits and quit. (:wq is equivalent to ZZ.) We’ll explain fully how to use ex commands in Chapter 5; for now, you should just memorize a few commands for writing and saving files.

Quitting Without Saving Edits

When you are first learning vi, especially if you are an intrepid experimenter, there are two other ex commands that are handy for getting out of any mess that you might create.

What if you want to wipe out all of the edits you have made in a session and then return to the original file? The command:

:e! ENTER

returns you to the last saved version of the file, so you can start over.

Suppose, however, that you want to wipe out your edits and then just quit vi? The command:

:q! ENTER

quits the file you’re editing and returns you to the Unix prompt. With both of these commands, you lose all edits made in the buffer since the last time you saved the file. vi normally won’t let you throw away your edits. The exclamation point added to the :e or :q command causes vi to override this prohibition, performing the operation even though the buffer has been modified.

Problems Saving Files

  • You try to write your file, but you get one of the following messages:

    File exists
    File file exists - use w!
    [Existing file]
    File is read only

    Type :w! file to overwrite the existing file, or type :w newfile to save the edited version in a new file.

  • You want to write a file, but you don’t have write permission for it. You get the message “Permission denied.”

    Use :w newfile to write out the buffer into a new file. If you have write permission for the directory, you can use mv to replace the original version with your copy of it. If you don’t have write permission for the directory, type :w pathname/file to write out the buffer to a directory in which you do have write permission (such as your home directory, or /tmp).

  • You try to write your file, but you get a message telling you that the file system is full.

    Type :!rm junkfile to delete a (large) unneeded file and free some space. (Starting an ex command with an exclamation point gives you access to Unix.)

    Or type :!df to see whether there’s any space on another file system. If there is, choose a directory on that file system and write your file to it with :w pathname. (df is the Unix command to check a disk’s free space.)

  • The system puts you into open mode and tells you that the file system is full.

    The disk with vi’s temporary files is filled up. Type :!ls /tmp to see whether there are any files you can remove to gain some disk space.7 If there are, create a temporary Unix shell from which you can remove files or issue other Unix commands. You can create a shell by typing :sh; type CTRL-D or exit to terminate the shell and return to vi. (All modern shells provide job-control, so you can simply type CTRL-Z to suspend vi and return to the Unix prompt; type fg to return to vi.) Once you’ve freed up some space, write your file with :w!.

  • You try to write your file, but you get a message telling you that your disk quota has been reached.

    Try to force the system to save your buffer with the ex command :pre (short for :preserve). If that doesn’t work, look for some files to remove. Use :sh (or CTRL-Z) to move out of vi and remove files. Use CTRL-D (or fg) to return to vi when you’re done. Then write your file with :w!.

Exercises

The only way to learn vi is to practice. You now know enough to create a new file and to return to the Unix prompt. Create a file called practice, insert some text, and then save and quit the file.

Open a file called practice in the current directory:

vi practice

Insert text:

iany text you like

Return to command mode:

ESC

Quit vi, saving edits:

ZZ

1 These days, the term “Unix” includes both commercial systems derived from the original Unix code base, and Unix work-alikes whose source code is available. Solaris, AIX, and HP-UX are examples of the former, and GNU/Linux and the various BSD-derived systems are examples of the latter. Also included are Mac OS’s terminal environment, Windows Subsystem for Linux (WSL) on Windows 10, and Cygwin and other similar environments for Windows. Unless otherwise noted, everything in this book applies across the board to all those systems.

2 GNU Emacs has become the universal version of Emacs. The only problem is that it doesn’t come standard with most commercial Unix systems; you must retrieve and install it yourself.

3 troff is for laser printers and typesetters. Its “twin brother” is nroff, for line printers and terminals. Both accept the same input language. Following common Unix convention, we refer to both with the name troff. Today, anyone using troff uses the GNU version, groff. See http://www.gnu.org/software/groff/ for more information.

4 See http://www.ctan.org and http://www.latex-project.org for information on TeX and LaTeX, respectively.

5 For more information on these, see https://en.wikipedia.org/wiki/Markdown and http://asciidoc.org/, respectively.

6 Thankfully, this kind of thing is much less common, although systems can still crash due to external circumstances, such as a power outage.

7 Your vi may keep its temporary files in /usr/tmp, /var/tmp, or your current directory; you may need to poke around a bit to figure out where exactly you’ve run out of room. Vim generally keeps its temporary file in the same directory as the file being edited.

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset
3.237.0.123