In the next few chapters, we’ll introduce a number of popular applications for Linux. We’ll start here with text editing, which underlies nearly every activity on the system. (You need an editor to create a file of more than trivial size, whether it is a program to be compiled, a configuration file for your system, or a mail message to send to a friend.) On a related topic, we’ll show you some text formatters that can make attractive documents and utilities that manage printing.
In this section, we’re going to cover the use of the vi (pronounced “vee-eye”) text editor. vi was the first real screen-based editor for Unix systems. It is also simple, small, and sleek. If you’re a system administrator, learning vi can be invaluable; in many cases, larger editors, such as Emacs, won’t be available in emergency situations (for instance, when booting Linux from a maintenance disk).
vi is based on the same principles as many other Unix applications: that each program provide a small, specific function and be able to interact with other programs. For example, vi doesn’t include its own spellchecker or paragraph filler, but those features are provided by other programs that are easy to fire off from within vi. Therefore, vi itself is a bit limited, but is able to interact with other applications to provide virtually any functionality you might want.
At first, vi may appear to be somewhat complex and unwieldy. However, its single-letter commands are fast and powerful once you’ve learned them. In the next section, we’re going to describe Emacs, a more flexible editor (really an integrated work environment) with an easier learning curve. Do keep in mind that knowing vi may be essential to you if you are in a situation where Emacs is not available, so we encourage you to learn the basics, as odd as they may seem. It should also be added that a number of vi clones are now available that are much more comfortable to use than the original vi, the most popular of which is vim (vi improved). Chances are that your distribution has things set up so that when starting vi, you actually start one of those. We’ll stick to the basics here, though, so that you can use the information presented here no matter which version of vi you use. You can find coverage of the newer versions in the book Learning the vi Editor by Linda Lamb and Arnold Robbins (O’Reilly).
Let’s fire up vi and edit a file. The syntax for vi is:
vi filename
For example:
eggplant$ vi test
will edit the file test
. Your screen should look
like this:
The column of ~
characters indicates that you are
at the end of the file.
While using vi, at any one time you are in one of two (or three, depending on how you look at it) modes of operation. These modes are known as command mode, edit mode, and ex mode.
After starting vi, you are in command mode. This mode allows you to use a number of (usually single-letter) commands to modify text, as we’ll see soon. Text is actually inserted and modified within edit mode. To begin inserting text, press i (which will place you into edit mode) and begin typing:
While inserting text, you may type as many lines as you wish (pressing the Enter key after each, of course), and you may correct mistakes using the Backspace key. To end edit mode and return to command mode, press the Escape key.
While in command mode, you can use the arrow keys to move around the file. Alternatively, or when the arrow keys don’t work, you may use h, j, k, and l, which move the cursor left, down, up, and right, respectively.
There are several ways to insert text other than using the
i command. The a command (for
“append”) inserts text
after the current cursor position. For example,
use the left arrow key to move the cursor between the words
good
and men
:
Press a, type wo, and then press Escape to return to command mode:
To open a line below the current one and begin inserting text, use the o command. Press o and type another line or two:
Remember that at any time you’re either in command mode (where commands such as i, a, or o are valid) or in edit mode (where you’re inserting text, followed by Escape to return to command mode). If you’re not sure which mode you’re in, press Escape. This takes you out of edit mode, if you are in it, and does nothing except beep if you’re already in command mode.
From command mode, the x command deletes the character under the cursor. If you press x five times, you end up with the following:
Now press a
and insert some text, followed by
Escape:
You can delete entire lines using the command dd
(that is, press d
twice in a row). If your cursor
is on the second line, dd will produce the
following:
Text that is deleted may be reinserted using the p command (for “put”). Pressing p now will return the deleted line to the buffer after the current line. Using P (uppercase) instead will insert the text before the current line. By default, p and P insert text from the “undo buffer”; you can also yank and replace text from other buffers, as we’ll see later.
The u command undoes the latest change (in this case, pressing u after dd is equivalent to p). If you inserted a large amount of text using the i command, pressing u immediately after returning to command mode would undo it.
To delete the word beneath the cursor, use the dw
command. Place the cursor on the word Diet
and
type dw:
You can replace
text using the R command, which overwrites the
text beginning at the cursor. Place the cursor on the first letter in
pizza
, press R, and type:
The r command replaces the single character under the cursor. r does not place you in insert mode per se, so there is no reason to use Escape to return to command mode.
The ~ command changes the case of the letter under
the cursor from upper- to lowercase, and vice versa. If you place the
cursor on the o
in Now
in the
previous example, and repeatedly press ~, you end
up with the following:
Another useful command for changing words is the cw command, which lets you simply type in the new word and — after pressing Escape — removes anything that might be left over from the original word. If the new text is longer than the one being changed, the space is automatically expanded as needed.
You already know how to use the arrow keys
to move around the document. In addition, the w
command moves the cursor to the beginning of the next word, and
b
moves it to the beginning of the current word.
The 0
(that’s a zero) command
moves the cursor to the beginning of the current line, and the
$
command moves it to the end of the line.
When editing large files, you’ll want to move forward or backward through the file one screen at a time. Pressing Ctrl-F moves the cursor one screen forward, and Ctrl-B moves it one screen backward.
In order to move the cursor to the end of the file, type
G
. You can also move to an arbitrary line: the
command 10G
would move the cursor to line 10 in
the file. To move to the beginning of the file, use
1G
.
Typing /
followed by a pattern and the Enter key
causes you to jump to the first occurrence of that pattern in the
text following the cursor. For example, placing the cursor on the
first line of text in our example and typing /burg
moves the cursor to the beginning of the word
“burgers.” Using
?
instead of /
searches
backward through the file.
The pattern following a /
or ?
command is actually a regular expression.
Regular expressions are a powerful way to specify patterns for search
and replace operations and are used by many Unix utilities. You can
find more information about regular expressions in the upcoming
section, Section 9.2.9. Using
regular expressions, you could, for example, search for the next
uppercase letter, using the command:
/[A-Z]
Therefore, if the pattern you’re searching for is not a static string, regular expressions can be used to specify just what you want.
You can couple moving commands with other commands, such as deletion.
For example, the command d$
will delete everything
from the cursor to the end of the line; dG
will
delete everything from the cursor to the end of the file.
Most of the commands dealing with files within vi are invoked from ex mode. You enter ex mode when you press the : key from command mode. This places the cursor on the last line of the display, allowing you to enter various extended commands.
For example, to write the file being edited, use the command
:w
. Typing :
causes you to
enter ex mode, and typing w
followed by the Enter key completes the command. The command
:wq
writes the file and exits
vi. (The command ZZ
— from
command mode, without the
“:” — is similar to
:wq
, but checks first if the file has been
changed, and writes it only in this case.)
To quit vi without saving changes to the file, use
the command :q!
. Using :q
alone
will quit vi, but only if modifications to the
file have been saved. The !
in
:q!
means to quit vi — and
that you really mean it.
To edit another file, use the :e
command. For
example, to stop editing test
, and edit the file
foo
instead, use the command shown at the bottom
of the following box:
If you use :e
without writing the file first,
you’ll get the error message:
No write since last change (:edit! overrides)
At this point, you can use :w
to save the original
file, and then use :e
, or you can use the command
:e! foo
, which tells vi to edit
the new file without saving changes to the original. This can be
useful if you edit a file and realize that you have screwed up. You
can then use the :e!
command; if you
don’t specify a filename, vi
discards the changes and re-edits the current file.
If you
use the :r
command, you can include the contents
of another file in the vi buffer. For example, the
command:
:r foo.txt
inserts the contents of the file foo.txt
after
the current line.
The :!
command allows you to enter the name of a command, which is executed
within vi. For example, the command:
:!ls -F
executes the
ls
command and
displays the results on your screen.
The :r!
command is similar to
:!
, but includes the standard output of the
command in the buffer. The command:
:r!ls -F
produces the following:
If you need to execute a series of shell commands, it’s often easier to use the suspend key (usually Ctrl-Z), provided you’re using a shell that supports job control, such as tcsh or bash.
There are many more features of vi than are documented here; most of these features are implemented through combinations of the simple features we’ve seen. Here are one or two other tidbits most vi users find useful.
The command:
:[x,y]s/pattern/replacement/flags
searches for pattern
between lines
x
and y
in the buffer, and
replaces instances of pattern
with the
replacement
text. pattern
is a
regular expression; replacement
is literal text
but can contain several special characters to refer to elements in
the original pattern
. The following command
replaces the first occurrence of weeble
with
wobble
on lines 1 through 10, inclusive:
:1,10s/weeble/wobble
Instead of giving line-number specification, you can use the
%
symbol to refer to the entire file. Other
special symbols can be used in place of x
and
y
. $
refers to the last line of
the file. Leave x
or y
blank to
refer to the current line.
Among the flags you
can use are g
to replace all instances of
pattern
on each line, and c
to
ask for confirmation for each replacement. In most instances, you
will want to use the g
flag, unless you want to
replace only the first occurrence of pattern
on
each line.
You can also use
marks to refer to lines. Marks are just
single-letter names that are given to cursor locations within the
document. Moving the cursor to a location in the file and typing
ma
will set the mark a
at that
point. (Marks may be named any of the letters a-z or A-Z.) You can
move the cursor directly to the mark a
with the
command `a
(with a backquote). Using a regular
single quote (as in 'a
) will move the cursor to
the beginning of the line that the mark a
is on.
Marks allow you to “remember” cursor locations that denote a region of text. For example, if you want to search and replace a block of text, you can move the cursor to the beginning of the text, set a mark, move the cursor to the end of the text, and use the command:
:'a,.s/weeble/wobble/
where 'a
refers to the line containing mark
a
, and . refers to the current line.
One way to copy and move text is to delete
it (using the d
or dd
commands)
and then replace it with the P
command, as
described earlier. For example, if you want to delete 10 lines,
starting with the line that contains your cursor, and paste them
somewhere else, just use the command 10dd
(to
delete 10 lines), move the cursor to the new location for the text,
and type p
. You can copy text in this way as well:
typing 10dd
followed by P
(at
the same cursor location) deletes the text and immediately replaces
it. You can then paste the text elsewhere by moving the cursor and
using p
multiple times.
Similar to dd
is the yy
command, which “yanks” text without
deleting it. You use p
to paste the yanked text as
with dd
. But note that each yank operation will
delete the previously yanked text from the
“clipboard.”
The deletion and yank commands can be used on more general regions
than lines. Recall that the d
command deletes text
through a move command; for example, d$
deletes
text from the cursor to the end of the line. Similarly,
y$
yanks text from the cursor to the end of the
line.
Let’s say you want to yank (or delete) a region of
text. This can be done with marks as well. Move the cursor to the
beginning of the text to be yanked and set a mark, as in
ma
. Move the cursor to the end of the text to be
yanked and use the command y'a
. This yanks text
from the cursor position to the mark a
. (Remember
that the command 'a
moves the cursor to the mark
a
.) Using d
instead of
y
deletes the text from the cursor to the mark.
The most convenient way to cut, copy, and paste portions of text within vi is to use registers. A register is just a named temporary storage space for text you wish to copy between locations, cut and paste within the document, and so forth.
Registers are given single letter names; any of the characters
a
-z
or
A
-Z
are valid. The
" command (a quotation mark) specifies a register;
it is followed by the name of the register, as in
"a for register
a
. The lowercase letters and their uppercase
counterparts refer to the same registers: using the lowercase letter
overwrites the previous contents of the register and using the
uppercase letter appends to it.
For instance, if we move the cursor to the first line in our example:
and use the command "ayy
, the current line is
yanked into the register a
. We can then move the
cursor to the second line, and use the command "ap
to paste the text from register a
after the
current line:
Similarly, the command "ay'a
yanks text from the
cursor to mark a
into register
a
. Note that there is no correspondence between
mark and register names!
Using registers allows you to copy text between files. Just copy the
text to a register, use the :e
command to edit a
new file, and paste the text from the register.
vi
is extensible in many ways. Most of the commands
we’ve introduced can be generalized to arbitrary
regions of text. As we’ve already seen, commands
such as d
and y
operate on the
text from the cursor to a move operation, such as
$
or G
. (dG
deletes text from the cursor to the end of the file.) Many other
commands operate on text through a move command in the same way.
Using marks you can operate on any region of text.
As we mentioned before, vi is just a text editor; it doesn’t have facilities for spell checking text, compiling programs, and other such features. However, vi executes other programs that you can use to extend the editor. The command:
:x,y!command
executes the named command
with the text on lines
x
through y
as standard input,
and replaces the lines with the standard output of the command. As
with the s
(search and replace) command, other
specifications, such as %
and
$
, can be used for the line numbers.
For example, let’s say you want to prepend a quote
character (>
) to all the lines in a region of
text. One way to do this is to write a short shell or Perl script
(see Section 1.5.4) that reads lines of input and
outputs those same lines with the quote character prepended. (Or use
a sed command; there are many alternatives.) You
can then send lines of text through this filter, which replaces them
with the quoted text within vi. If the script is
called quote
, just use a command, such as:
:`a,.!quote
which quotes the region of text between the cursor location and the
mark a
.
Be familiar with the various ex commands that
are available. The :set
command allows you to set
various options; for example, :set ai
turns on
auto indentation of text. (:set noai
turns it
off.)
You can specify ex commands (such as
:set
) to execute when starting up
vi in the file .exrc
in your
home directory. (The name of this file can be changed with the
EXINIT
environment variable.) For example, your
.exrc
file might contain:
set ai
to turn on autoindentation. You don’t need the : before ex commands in this file.
A number of good tutorials and references for vi are available — both online as well as in print. Learning the vi Editor is a good place to look for more information. If you have Internet access, the comp.editors archives for vi contain a number of reference and tutorial documents, as well as interesting vi hacks. ftp://alf.uib.no:/pub/vi is the archive home site; it is mirrored at cs.uwp.edu and elsewhere. The home of vim on the Web is http://www.vim.org.