Chapter 8
Editors
This chapter does not provide an in-depth discussion of the ed
and vi editors. There are already books specific
to that subject, and there's information in every introductory UNIX book
on the market. This chapter concentrates on telling you why you should use these
editors and how you can best use them as an administrator to take full advantage
of their capabilities to make your job a little easier.
It is often said that if you can drive a car with manual transmission
then you can drive any car on the road. The same can be said about the oldest
editors of UNIX. There are other editors that are freely available on the Internet
and some user-friendly GUI editors are supplied by vendors as part of their
UNIX flavors. So why cover these two editors in this book? Administrators should
know all this already. The reality is that there are UNIX administrators with
two or more years' experience who have never really used these editors.
If you want to be a guru, here's a hint: You have to learn
the tools of the trade. Don't be surprised if you are even asked questions
in a job interview pertaining to editors and asked how fluent you are in them.
If you don't know the basics, you might not get the job. You might even
be asked what keys, other than the arrow keys, move the cursor around. You would
be amazed at the number of administrators who don't know the right answer.
Some interviewers believe this can help determine the level of experience or
devotion to the UNIX operating system. I have found that a lot of administrators
who have learned UNIX since 1989 use the arrows. If they have to think about
the letters ( h, j,
k, and l) they probably
haven't been using UNIX for more than seven years.
As much as you might hate these editors for their cryptic command
structure or because you cannot use a mouse or even the arrow keys sometimes,
learning the minimum requirements for the editors will be enough to get you
by. All you have to do is learn the six basic steps for editing:
-
Move the
cursor up, down, and through a line in the file.
-
Switch to insert mode and make additions or modifications
to the file.
-
Switch to command mode to manipulate, move, save, or exit
the file.
-
Delete characters, words, and lines from the file.
-
Write to a file and exit.
-
Exit or quit without writing to the file.
Mastering these six simple steps takes only 30 minutes for each
editor, if you sit down and take the time to learn. After you are hooked, you
might not accept any substitutes.
8.1 The Anatomy of ed & vi
8.1.1 Description
If you want to know UNIX, you've got to know ed
and vi. No matter what the flavor of UNIX, these
two editors are always there for you. Some editors other than ed
and vi might be excellent for everyday use, but
when push comes to shove and there isn't enough memory, disk space, or
the system is in bad shape, you can usually still count on ed
or vi to save the day.
Editors
can be installed anywhere on your system--in /usr, /usr/local, /opt, or some
partition other than the root partition. The ed
editor, however, remains installed in the root partition and is part of the
operating system when you need to boot into miniroot. So you see, when a worst-case
scenario takes place, you will still have access to ed.
The ed and vi
editors are made up of several parts that enable you to navigate in and manipulate
the system files in a pinch. Knowing the basic parts helps you to better understand
these editors.
ed
ed is a standard text editor. No frills;
it is as basic as they get. Do you need to learn this editor? Yes! You
don't need to know everything, just the basics. Startup, adding, deleting,
saving, and exiting are all you should need. The ed
editor is used primarily in extreme emergencies when all other editors are inaccessible.
Can this happen? Yes! If the system crashes hard enough, this definitely can
happen.
When you use ed, remember that only
one command at a time can appear on a line. ed runs
in two modes: insert and command.
-
Insert mode --In this mode, text is placed in the
buffer until a write command is issued. No commands
are recognized in this mode. To leave the input mode type a period ( .)
on a line by itself followed by the Enter key.
-
Command mode --In command mode, single-letter commands
are preceded by zero, one, or two addresses. These addresses specify one
or more lines in the buffer that the command uses. Only one command per
line is allowed.
vi
vi is actually the visual part of
the text editor ex, which in turn is a superset
of the ed editor. Although a lot of the vi
commands originate from ex, I will still reference
vi for these commands. For those who are not aware
of this, the vi editor was originally designed with
three modes: insert, command, and last line. Don't be confused about the
third mode. Many admins say there are only two modes: insert and command. The
last line mode is sometimes considered part of the command mode, because it
is used for entering various commands.
-
Insert mode --In this mode, keys that the user types
are displayed on the screen (except for the Esc key). This mode is also
known as the input mode.
-
Command mode --In this mode, every key that the user
types is interpreted as a command. Some keys do not have functions associated
with them. If one of these keys is entered, nothing happens to the text,
but the editor might beep. As you enter commands in this mode, you will
not see an echo of your keystroke, however you will see the results of the
command from that keystroke.
-
Last line mode --This mode enables you to edit and
issue a line of commands to the editor or to the system. The input line
appears at the bottom of screen or window when you type a colon ( :).
In this mode, you see the keystrokes echoed back onto the screen, unlike
in the command mode. The last line mode is also referred to by many people
as the command line mode or even the command mode.
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