All about the VI editor

The default editor that comes with the UNIX operating system is called vi (visual editor). It has two modes of operation:

1. Command mode commands which cause action to be taken on the file.
In the command mode, every single character typed is a command that performs operation on the text file being edited.

2. Insert mode in which entered text is inserted into the file.
In the insert mode, every character typed is added to the text in the file; pressing the Escape key turns off the Insert mode.

Syntax

vi file_name
It will open an empty file if not present already.

Commands that switch the editor to insert mode

a	It moves the cursor one position to the right before switching to insert mode, basically it will append
i	Insert text at current cursor position.
I	Insert text at the beginning of the current line.
o	Insert a blank line under the current cursor position and move the cursor to that line.
O	Insert a blank line above the current cursor position and move the cursor to that line.

Basic operations

Some of the popular vi commands are:

Moving through the text

h	move the cursor to the left
l	move the cursor to the right
k	move the cursor up
j	move the cursor down
H	moves the cursor to the top line of the screen
M	moves the cursor to the middle line of the screen
L	moves the cursor to the last line of the screen
w	move the cursor forward one word
b	move the cursor backward one word (if you are in the middle of a word, b command will move you to the beginning of the current word)
e	move to the end of a word
(	move to beginning of current block
)	move to beginning of current block
0	move to the beginning of a line
$	move to the end of a line

Screen Movement

Ctrl-f	scrolls down one screen
Ctrl-b	scrolls up one screen
Ctrl-u	scrolls up half a screen
Ctrl-d	scrolls down a half a screen
SHIFT-G	put the prompt at the end of the file, Preceding G with a number will move you to a specific line in the file
1G	move to the beginning of the file

Delete

dw	deletes from the character selected to the end of the word
ndw	deletes n words at the right side of the cursor
dd	deletes the current line
ndd	deletes n lines starting from the current cursor position
D	deletes from the current character to the end of the line
x	deletes the character on which the cursor is positioned
nx	delete the character selected and the next (n-1) characters
X	deletes the character on left of your cursor
nX	deletes n character on left of your cursor
$-9,$d	deletes last ten lines

Copy, Paste, Replacement | Join and Undo

yw	copies a word into a buffer
nyw	copies n word into a buffer
yy	copies a line into a buffer
nyy	copies n line into a buffer
p	paste line or words copied earlier on the line below the cursor
p	paste line or words copied earlier on the line above the cursor
r	replaces the current character with the next character you type and returns to command mode
cw	Changes and replaces the current word with text that you type. Press ESC to get out of replacement mode
:1,$s/word/newword/g	word with newword throughout the file

J	join the line on which cursor is placed with another line
nJ	join n lines
:u	undoes the last change you made in the file. Using it again will "undo the undo"
U	undoes all recent changes to the current line

Display line number

:set number	shows the line numbers
:n	moves to line n of the file
:.=	returns line number of current line at bottom of screen
:=	returns the total number of lines at bottom of screen
^g	provides the current line number, along with the total number of lines, in the file at the bottom of the screen

Search

/pattern	search the string(pattern) in the file and position the cursor on the first match below its position
n	search in a forward direction
N	search in a backwards direction
?pattern	search backward for occurrence of the pattern

Save and Quit

:w	save the file
:q	exit the editor
:q!	forces the exit when you want to quit a file containing unsaved changes
:e!	reads the original file back in so that you can start over
:wq	save and exit
ZZ	save file and exit VI
:w newfile	save the text to newfile
:wq!	overrides read-only permission
:1,100w newfile	write lines 1 to 100 to newfile
:$-9,$w newfile	write the last ten lines to newfile (the dollar sign denotes last line)

Some more commands

:recover	recover a file after an unexpected interruption
vi –r filename
R	puts you in overtype mode until you press ESC
.	Repeats the last command executed
:! command	execute external command from VI
:sh	start a shell from VI, Return to VI by entering exit or ctrl d
:sp	horizontally split current file
:vsp	vertically split current file
:r! command	insert output of command to the file

script to print fibonacci series

echo "Enter n for Fibonacci series: - "

read n

echo "Fibonacci series is: - "

echo "0"

echo "1"

i=0

j=1

cnt=2

while [ $cnt -le $n ]

do

k=`expr $i + $j`

i=$j

j=$k

echo $k

cnt=`expr $cnt + 1`

done

$ ./fibonacci.ksh

Enter n for Fibonacci series: -

10

Fibonacci series is: -

0

1

1

2

3

5

8

13

21

34

55

script to print file type in a directory

for filename in `ls -l`

do          

if [ -d $filename ]

    then

           echo $filename   it is a directory

                    elif [  -h $filename ]

                          then

                     echo $filename  it is a link

                     elif [ -f  $filename ]

                           then

                      echo $filename it is a file

fi

done

$ ./filetypecheck.ksh

filetypecheck.ksh it is a file

flashpoint it is a directory

new it is a file

new1 it is a file

newres it is a file

newrestu it is a file

newworld it is a file

test it is a directory

$ ls -l

total 12

-rwxr-xr-x 1 flash  363 Oct 29 23:31 filetypecheck.ksh*

drwxrwxr-x 2 flash4096 Oct 29 23:33 flashpoint/

-rw-rw-r-- 1 flash   0 Oct 29 23:22 new

-rw-rw-r-- 1 flash   0 Oct 29 23:22 new1

-rw-rw-r-- 1 flash   0 Oct 29 23:22 newres

-rw-rw-r-- 1 flash   0 Oct 29 23:22 newrestu

-rw-rw-r-- 1 flash   0 Oct 29  2016 newworld

drwxrwxr-x 2 flash 4096 Oct 29 23:22 test/

script to print zero to ten number

#!/bin/bash

num=0

while [ "$num" -lt 10 ];

do

echo "$num"

num=$((num+1))

done

In the above script we have first assigned zero value to variable num.
Then we are using while loop to iterate until the condition specified is valid,
That is it will continue to the operation till the num value is less than Ten.
do will perform the task specified.
echo will print the current value of num.

Output

0

1

2

3

4

5

6

7

8

9

script to find prime number

#!/bin/bash

echo -n "Enter a number: "

readnum

expr $num + 1  &> /dev/null

if [ $? -ne 0 ]

then

echo "You did not supplied number value"

exit 1

fi

[ $num -lt 2 ] && echo "Values < 2 are not prime numbers" && exit 1

i=2

while [ $i -lt $num ]

do

if [ `expr $num % $i` -eq 0 ]

then

echo "$num is not a prime number"

echo "Since it is divisible by $i"

exit

fi

i=`expr $i + 1`

done

echo "$num is a prime number "

$ ./primecheck

Enter a number: 17

17 is a prime number

Script to delete files from particular path

$ vi delete

#!/bin/ksh

LOGFILE=/home/ flash /logs/delete.log

touch $LOGFILE

echo " ------Starting Time `date` --------------- ">>$LOGFILE

cd /home/flash/enemy/bad

echo " ------FILE COUNT-----">>$LOGFILE

ls -lR /home/flash/enemy/bad/* | wc -l >>$LOGFILE

ls -ltr *.bad | awk '{print $9}' | xargs \rm

·        Here delete is the script name.

·        Firstly we have created a LOGFILE variable to create logs and defined the path where the log is to be created.

·        Touch command will create and empty file.

·        Echo command output will be redirected (>>) to LOGFILE in which current date stamp is added.

·        When you want to print output of any command inside echo command use : `  at the beginning and end of command.

E.g.: `date`

·        cd will change directory and then write the current count of files into LOGFILE by wc-l command

ls -lR /home/flash/enemy/bad/* | wc -l >>$LOGFILE

·        Here * means alll the types of file. We can specify type of extension to delete specific file.

E.g.: *.bad, *.txt

·        Last command is to remove files from the directory.

·        Then chmod 755 to change permissions of the file.

·        Now  run the script by ./scriptname and will remove the files.