At the command line, enter the following command:

$ awk ‘{ print }’ /etc/passwd

You should see the contents of your /etc/passwd file appear before
your eyes.Now, for an explanation of what awk did. When we called awk,we specified /etc/passwd as our input file. When we executed awk, it evaluated the print command for each line in /etc/passwd, in order.All output is sent to stdout, and we get a result identical to catting /etc/passwd. Now, for an explanation of the { print } code block. In awk, curly braces are used to group blocks of code together, similar to C. Inside our block of code,we have a single print command. In awk, when a print command appears by itself, the full contents of the curr-ent line are printed.

Here is another awk example that does exactly the same thing:

$ awk ‘{ print $0 }’ /etc/passwd

In awk, the $0 variable represents the entire current line, so print
and print $0 do exactly the same thing. Now is a good time for an
example.
#!/bin/bash #SCRIPT: method4.sh #PURPOSE: Process a file line by line with awk FILENAME=$1 awk ‘{kount++;print kount, $0} END{print “\nTotal ” kount ” lines read”}’ $FILENAME

Output:
[root@www blog]# sh method4.sh file_passwd 1 venu:x:500:500:venu madhav:/home/venu:/bin/bash 2 padmin:x:501:501:Project Admin:/home/project:/bin/bash 3 king:x:502:503:king:/home/project:/bin/bash 4 user1:x:503:501::/home/project/:/bin/bash 5 user2:x:504:501::/home/project/:/bin/bash Total 5 lines read

Awk is really good at handling text that has been broken into multiple
logical fields, and allows you to effortlessly reference each individ-
ual field from inside your awk script. The following script will print
out a list of all user accounts on your system:

awk -F”:” ‘{ print $1 “\t ” $3 }’ /etc/passwd

Above, when we called awk, we use the -F option to specify “:” as the
field separator. By default white space (blank line) act as filed sep-
arator. You can set new filed separator with -F option. When awk proc-
esses the print $1 “\t ” $3 command, it will print out the first and
third fields that appears on each line in the input file. “\t” is used
to separate field with tab.

—————————————–
Program (1) ~ array.sh
—————————————–

#!/bin/bash
echo “==============”
declare -a myarr[0]=”Manoj”
declare -a myarr1
myarr1=(Manoj Chauhan bangalore mumbai pune delhi)
myarr[1]=”Chauhan”

echo “my name is ${myarr[0]} ${myarr[1]}”
echo “————————–”
echo “${myarr1[*]}”
echo ${myarr1[2]}
echo ${myarr1[@]}
echo “————————–”
echo “Total no of elements in array – ${#myarr1[*]}”
echo “Total no of elements in array – ${#myarr1[@]}”
echo “Size of word ‘${myarr1[2]}’ is – ${#myarr1[2]}”
echo ${#myarr1[1]}
echo ${#myarr1[0]}

echo “————————–”

#how to delete element in array
unset myarr[1]
echo “myarr is – ${myarr[*]}”

#how to assign element in array
myarr[1]=”- System Engineer!”
echo “myarr is – ${myarr[*]}”

echo ${myarr}

————————————————————-
Program (2) ~ command_line_arguments.sh
————————————————————-

#!/bin/bash

echo “Script/command name => $0″
echo “arg1 => $1″
echo “arg2 => $2″
echo “arg3 => $3″
echo “Total No of argument = $#”

echo “Script PID is => $$”
echo “Status of previous command – $?”

name=$myname
echo “Name – $name”

—————————————–
Program (3) ~ default_value.sh
—————————————–

#!/bin/bash

#start=’123′
#start=${1:-$start}

start=${1:-’123′}

echo “Value of ’start’ variable is ==> $start”

—————————————–
Program (4) ~ echo_example.sh
—————————————–

#!/bin/bash

name=”Manoj”

echo -e “My Name is $name_Manoj and \n”
echo -e “My Name is ${name}_Manoj and \n”

echo -e ‘My Name is $name and \n’

—————————————–
Program (5) ~ elif.sh
—————————————–

#! /bin/bash

if [ $1 -eq $2 ];then
echo “good”
elif [ $2 -eq $3 ];then
echo “Fine”
elif [ $1 -eq $3 ];then
echo “OK”
else
echo “NO”
fi

—————————————————
Program (6) ~ for_loop_example-1.sh
—————————————————

#!/bin/bash

i=1
while [ $i -le 512 ]
do
temp=$i
echo “What is => $i | $temp”
i=$(expr $i + 32)
for (( j=$temp; $j<=$i; j++ ))
do
echo -n ” $j”
done
done

—————————————————
Program (7) ~ for_loop_example-2.sh
————————————————–

#!/bin/bash
#for val in $(ls -1 /tmp)
sum=0
#for val in {1..5}
#for val in {$1..$2}
for((val=$1;$val<=$2;val++))
do
#echo “$val”
sum=$(expr $sum + $val )
#sum=`expr $sum + $val`
done

echo “$0 # Sum of $1 to $2 => $sum”

—————————————————–
Program (8) ~ for_loop_example-3.sh
—————————————————–

#!/bin/bash

for i in {1..9}
do
echo $i
done

—————————————–
Program (9) ~ function.sh
—————————————–

#!/bin/bash

function my_function()
{
name=”Manoj Chauhan”
echo “‘my_function’ body ~ $name”
return 1;
}
##########

myfunc()
{
echo “Another way of defining the function”
}

##########################

echo “Starting function program”
echo “——————————”

#calling function here
my_function
##
myfunc

echo -e “\n end of program”

—————————————————————————-
Program (10) ~ how_to_pass_argument_to_function.sh
—————————————————————————-

#!/bin/bash

function my_function()
{
echo “Total number of argument ~ $#”
echo “Arg1 => $1″
echo “Arg2 => $2″
echo “Arg3 => $3″
return 0;
}
##########

echo “Starting function program”
echo “——————————”

#calling function here
my_function Manoj Chauhan 1234

—————————————————————
Program (11) ~ how_to_take_hidden_input.sh
—————————————————————

#!/bin/bash

echo -n “Enter User Name :”
read username
echo -n “Enter Password :”
read -s mypwd

echo -e “\nI am $username and my password is – $mypwd”

——————————————————————–
Program (12) ~ how_to_take_input_from_user.sh
——————————————————————–

#!/bin/bash

echo -ne “Enter the Name:- ”
read name
echo -n -e “Enter the Number:- ”
read num

echo “——————————”

add=$(expr $num + 10)

echo “Name is ~ $name”
echo “Number is ~ $add”

—————————————–
Program (13) ~ ifthen.sh
—————————————–

#!/bin/bash

if [ "Manoj" == "Manoj" ];then
echo “true!”
else
echo “false”
fi

echo “———————————-”

if [ 2 == 2 ];then
echo “true!”
else
echo “false”
fi

echo “———————————-”

if [ "Manoj" = "Manoj" ];then
echo “true!”
else
echo “false”
fi

echo “———————————-”

if [ 2 -eq 2 ];then
echo “true!”
else
echo “false”
fi

———————————————-
Program (14) ~ non-interactive.sh
———————————————

#!/usr/bin/expect -f
spawn ssh Manoj@192.168.0.1
expect “password:”
sleep 1
send “pwd\r”
interact

——————————————————–
Program (15) ~ read_file_line_by_line.sh
——————————————————-

#!/bin/bash

file_name=”/etc/hosts”

while read myvar
do
echo “Line => $myvar”
done < $file_name

echo “##########################”

for myvar1 in $(cat $file_name)
do
echo “Line => $myvar1″
done

———————————————–
Program (16) ~ reverse-number.sh
———————————————–

#!/bin/bash

declare -a date_array
num=$1
i=$(expr $(echo $num | wc -c) – 1 )

while [ $num -gt 10 ]
do
temp=$( expr $num % 10 )
num=$( expr $num / 10);
echo “Digit($i) => $temp”
date_array[$i]=”${temp}”
i=$(expr $i – 1)
done
echo “Digit($i) => $num”
date_array[$i]=”${num}”

echo ${date_array[*]}

———————————————–
Program (17) ~ string-operation.sh
———————————————–

#! /bin/bash

echo “Manoj Chauhan:-”
string=”/root/Manoj/Chauhan/image.gif”
echo “string=> $string”
echo “String=> ${string##/*/}”
echo “String=> ${string#/*/}”

echo “String=> ${string%.*}”
echo “String=> ${string%%.*}”
#str=”/home/y/conf/ManojChauhan/daily_market_0.conf”
str=”${str##/*conf/}”
echo “String=> ${str%/*}”

#done

mystr=”keyword_summary_exact_Manojsb”
echo $mystr
echo ${mystr%_*}

echo “$*”

—————————————–
Program (18) ~ switch.sh
—————————————–

#!/bin/bash

echo ” Switch program | arg1 => $1″
echo ” ——————————-”
case $1 in

123)
echo “Case is 123″
;;

Manoj)
echo “Case is ‘Manoj’”
;;

pri*)

echo “Case is ‘pri*’”
;;

*)
echo ” * Usage: $0 ”
echo “ Default case (nothing is matched)”
exit 0;
;;
esac

——————————————————-
Program (19) ~ while_loop_example-1.sh
——————————————————-

#!/bin/bash

mywait=wait

while [ "${mywait}" = "wait" ]
do
echo “Manoj”
done

——————————————————–
Program (20) ~ while_loop_example-2.sh
——————————————————–

#! /bin/bash

## on command line -> i=0 && while [ $i -le 10 ] ; do echo $i; i=$(expr $i + 1); done

i=0
while [ $i -le 10 ]
do
echo $i
i=$(expr $i + 1)
done

#!/bin/bash
# Varnish Process Monitor
# Written By: Manoj Chauhan
# Email ID: mchauhan75@gmail.com
# Dated: 31-07-2009
# Restart Varnish Server When It Goes Down
LOG=/usr/bin/logger
RESTART=”/usr/bin/sudo /etc/init.d/varnishncsa restart”
STATUS=”/etc/init.d/varnishncsa status”
# Path to pgrep command
PGREP=”/usr/bin/pgrep”
VARNISHPID=”varnishncsa”
Hostname=`hostname`
STATE_OK=0
STATE_WARNING=1
STATE_CRITICAL=2
STATE_UNKNOWN=3
STATE_DEPENDENT=4
FLAG=0
/etc/init.d/varnishncsa status >/dev/null 2>&1
if [ $? -ne "0" ];then
{
#Nagios restart varnish service
$LOG “Critical:- $Hostname – Varnish service is down, restarted by nagios”
$RESTART >/dev/null 2>&1
}
fi
# Find varnish pid
PID=`$PGREP ${VARNISHPID} | wc -l`
if [ $PID -eq 0 ];then
{
#Nagios restart varnish service
$LOG “Critical:- $Hostname – Varnish PID is down, restarted by nagios”
$RESTART >/dev/null 2>&1
}
fi
/etc/init.d/varnishncsa status >/dev/null 2>&1
if [ $? -ne "0" ];then
{
$LOG “Critical:- $Hostname – Varnish service is down, please check…”
echo “CRITICAL – $Hostname -  Varnish service is down or not restarting, please check”
exit $STATE_CRITICAL;
}
else
{
FLAG=1
echo “OK – $Hostname -  Varnish service is running”
}
fi
if [ $FLAG -eq 0 ];then
{
# Find varnish pid
PID=`$PGREP ${VARNISHPID} | wc -l`
if [ $PID -eq 0 ];then
{
$LOG “Critical:- Varnish service is down, please check…”
echo “CRITICAL – $Hostname -  Varnish service is down or not restarting, please check”
exit $STATE_CRITICAL;
}
else
{
echo “OK – $Hostname -  Varnish service is running”
}
fi
}
fi