This document provides examples of various BASH scripting concepts like arrays, command line arguments, loops, functions, conditionals, input/output etc. It contains 16 programs demonstrating features such as array manipulation, looping constructs, taking user input, reading/writing files and more. The programs are intended to help learn BASH scripting through examples.

1. BASH ­ Learning by Examples
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Program (1) ~ array.sh
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#!/bin/bash
echo "=============="
declare ­a myarr[0]="Arun"
declare ­a myarr1
myarr1=(arun bagul bangalore mumbai raju santhosh)
myarr[1]="Bagul"
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}
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Program (2) ~ command_line_arguments.sh
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#!/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 ­ $name"
read n
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2. Program (3) ~ default_value.sh
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#!/bin/bash
#start='123'
#start=${1:­$start}
start=${1:­'123'}
echo "Value of 'start' variable is ==> $start"
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Program (4) ~ echo_example.sh
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#!/bin/bash
name="Arun"
echo ­e "My Name is $name_arun and n"
echo ­e "My Name is ${name}_arun and n"
echo ­e 'My Name is $name and n'
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Program (5) ~ elif.sh
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#! /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
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Program (6) ~ for_loop_example­1.sh
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#!/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

3. ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
Program (7) ~ for_loop_example­2.sh
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#!/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"
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Program (8) ~ for_loop_example­3.sh
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#!/bin/bash
for i in {1..9}
do
echo $i
done
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Program (9) ~ function.sh
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#!/bin/bash
function my_function()
{
name="Arun Bagul"
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

4. echo ­e "n end of program"
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Program (10) ~ how_to_pass_argument_to_function.sh
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#!/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 arun bagul 1234
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Program (11) ~ how_to_take_hidden_input.sh
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#!/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 ­ $mypwd"
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Program (12) ~ how_to_take_input_from_user.sh
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#!/bin/bash
echo ­ne "Enter the Name:­ "
read name
echo ­n ­e "Enter the Number:­ "
read num
echo "­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­"
add=$(expr $num + 10)
echo "Name is ~ $name"
echo "Number is ~ $add"
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Program (13) ~ ifthen.sh
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#!/bin/bash

5. if [ "arun" == "arun" ];then
echo "true!"
else
echo "false"
fi
echo "­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­"
if [ 2 == 2 ];then
echo "true!"
else
echo "false"
fi
echo "­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­"
if [ "arun" = "arun" ];then
echo "true!"
else
echo "false"
fi
echo "­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­"
if [ 2 ­eq 2 ];then
echo "true!"
else
echo "false"
fi
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Program (14) ~ non­interactive.sh
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#!/usr/bin/expect ­f
spawn ssh arun@192.168.0.1
expect "password:"
sleep 1
send "pwdr"
interact
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Program (15) ~ read_file_line_by_line.sh
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#!/bin/bash
file_name="/etc/hosts"
while read myvar
do
echo "Line => $myvar"
done < $file_name
echo "#################################################"
for myvar1 in $(cat $file_name)
do

6. echo "Line => $myvar1"
done
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Program (16) ~ reverse­number.sh
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#!/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[*]}
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Program (17) ~ string­operation.sh
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#! /bin/bash
echo "Arun Bagul:­"
string="/root/arun/bagul/image.gif"
echo "string=> $string"
echo "String=> ${string##/*/}"
echo "String=> ${string#/*/}"
echo "String=> ${string%.*}"
echo "String=> ${string%%.*}"
#str="/home/y/conf/arunbagul/daily_market_0.conf"
str="${str##/*conf/}"
echo "String=> ${str%/*}"
#done
mystr="keyword_summary_exact_arunsb"
echo $mystr
echo ${mystr%_*}
echo "$*"
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Program (18) ~ switch.sh
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#!/bin/bash

7. echo " Switch program | arg1 => $1"
echo " ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­"
case $1 in
123)
echo "Case is 123"
;;
arun)
echo "Case is 'arun'"
;;
pri*)
echo "Case is 'pri*'"
;;
*)
echo " * Usage: $0 "
echo " Default case (nothing is matched)"
exit 0;
;;
esac
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Program (19) ~ while_loop_example­1.sh
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#!/bin/bash
mywait=wait
while [ "${mywait}" = "wait" ]
do
echo "arun"
done
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Program (20) ~ while_loop_example­2.sh
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#! /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
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Regards,
Arun