VI quick reference

Introduction
vi  pronounced as ” vee eye ” is a unix editor available on almost all the unix  operating systems , solaris , bsd ,aix , hpux etc.
This document is a quick reference to vi editor and will be of help if your are new to unix , learning unix  or just refreshing your vi knowledge after a few years.

Requirements:
In order to work correctly the vi need  correct terminal type (TERM) setting  .The TERM setting depends on the   type of terminal you have . Commonly used TERM types are vt100 , vt220 and ansi .  In most cases vt100 will  work  fine . In case  vi is not able to understand the TERM you have given, it starts in open mode   giving you a line by line display .
Generally TERM is taken from .profile or  /etc/profile  but can be set at the command line as :

$TERM=vt100
$export TERM

echo $TERM will display the current TERM set.

Create new file or  Open existing file in vi
vi without any file name will open a   new file where you can enter the text and edit but while coming out you will  be asked to enter a valid file name to save the text.  vi with a  file name as argument will  open that file for editing  if the file already exists it opens it  otherwise it creates a new file by the argument.
Example :  $vi  testfile
Creates or opens the existing file called testfile

Modes in vi

vi operates in following  two modes :
i. ) Command Mode : After a file is opened it is opened  in command
mode ,that is , input from the keyboard will be treated as vi commands
and you will not see the words you are typing on the screen .

ii.) Insert Mode: To enter the text you have to put vi in insert  by pressing ‘i’ or ‘a’  after  which you can add the text and whatever is being type will be seen on the  screen. . To switch between these mode Esc key is used .   Esc i
(text mode)  Esc (command mode)

Saving  & Exiting  vi editor
You can exit vi in different ways :

1.) Quit without saving : If you don’t  want to save the work :q  will take you out without saving  your editing in vi.
2.) Write & quit : . Simple :w saves the current file but don’t exit. For save and quit  :wq is  used in vi.
3.) Forced Quite : An ! (Exclamation  sign at the end of  exit commands ( :q! , :wq! )  causes a forced  quit from vi  after ignoring editing (for :q!)  or writing (for :wq!)  all the change