Shell Script Examples (Problem & Solution)

Problem : How to write shell script that will add two nos, which are supplied as command line argument, and if this two nos are not given show error and its usage.

Solution :


if [ $# -ne 2 ]
then
echo "Usage - $0 x y"
echo " Where x and y are two nos for which I will print sum"
exit 1
fi
echo "Sum of $1 and $2 is `expr $1 + $2`"

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Problem : Write Script to find out biggest number from given three nos. Nos are supplies as command line argument. Print error if sufficient arguments are not supplied.

Solution : 

#
# Algo:
# 1) START: Take three nos as n1,n2,n3.
# 2) Is n1 is greater than n2 and n3, if yes
# print n1 is bigest no goto step 5, otherwise goto next step
# 3) Is n2 is greater than n1 and n3, if yes
# print n2 is bigest no goto step 5, otherwise goto next step
# 4) Is n3 is greater than n1 and n2, if yes
# print n3 is bigest no goto step 5, otherwise goto next step
# 5) END
#
#

if [ $# -ne 3 ]
then
echo "$0: number1 number2 number3 are not given" >&2
exit 1
fi
n1=$1
n2=$2
n3=$3
if [ $n1 -gt $n2 ] && [ $n1 -gt $n3 ]
then
echo "$n1 is Bigest number"
elif [ $n2 -gt $n1 ] && [ $n2 -gt $n3 ]
then
echo "$n2 is Bigest number"
elif [ $n3 -gt $n1 ] && [ $n3 -gt $n2 ]
then
echo "$n3 is Bigest number"
elif [ $1 -eq $2 ] && [ $1 -eq $3 ] && [ $2 -eq $3 ]
then
echo "All the three numbers are equal"
else
echo "I can not figure out which number is biger"
fi

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Problem : Write script to print nos as 5,4,3,2,1 using while loop.


Solution : 

# Algo:
# 1) START: set value of i to 5 (since we want to start from 5, if you
# want to start from other value put that value)
# 2) Start While Loop
# 3) Chechk, Is value of i is zero, If yes goto step 5 else
# continue with next step
# 4) print i, decement i by 1 (i.e. i=i-1 to goto zero) and
# goto step 3
# 5) END
#
i=5
while test $i != 0
do
echo "$i
"
i=`expr $i - 1`
done

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Problem : Write Script, using case statement to perform basic math operation as
follows
+ addition
- subtraction
x multiplication
/ division
The name of script must be 'q4' which works as follows
$ ./q4 20 / 3, Also check for sufficient command line arguments

Solution : 

if test $# = 3
then
case $2 in
+) let z=$1+$3;;
-) let z=$1-$3;;
/) let z=$1/$3;;
x|X) let z=$1*$3;;
*) echo Warning - $2 invalied operator, only +,-,x,/ operator allowed
exit;;
esac
echo Answer is $z
else
echo "Usage - $0 value1 operator value2"
echo " Where, value1 and value2 are numeric values"
echo " operator can be +,-,/,x (For Multiplication)"
fi
Write Script to see current date, time, username, and current directory.
echo "Hello, $LOGNAME"
echo "Current date is `date`"
echo "User is `who i am`"
echo "Current direcotry `pwd`"

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Problem : Write script to print given number in reverse order, for eg. If no is 123 it must print as 321.


Solution : 


# Algo:
# 1) Input number n
# 2) Set rev=0, sd=0
# 3) Find single digit in sd as n % 10 it will give (left most digit)
# 4) Construct revrse no as rev * 10 + sd
# 5) Decrment n by 1
# 6) Is n is greater than zero, if yes goto step 3, otherwise next step
# 7) Print rev
#
if [ $# -ne 1 ]
then
echo "Usage: $0 number"
echo " I will find reverse of given number"
echo " For eg. $0 123, I will print 321"
exit 1
fi

n=$1
rev=0
sd=0

while [ $n -gt 0 ]
do
sd=`expr $n % 10`
rev=`expr $rev \* 10 + $sd`
n=`expr $n / 10`
done
echo "Reverse number is $rev"

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Problem : Write script to print given numbers sum of all digit, For eg. If no is 123 it's sum of all digit will be 1+2+3 = 6.


Solution :


# Algo:
# 1) Input number n
# 2) Set sum=0, sd=0
# 3) Find single digit in sd as n % 10 it will give (left most digit)
# 4) Construct sum no as sum=sum+sd
# 5) Decrment n by 1
# 6) Is n is greater than zero, if yes goto step 3, otherwise next step
# 7) Print sum
#
if [ $# -ne 1 ]
then
echo "Usage: $0 number"
echo " I will find sum of all digit for given number"
echo " For eg. $0 123, I will print 6 as sum of all digit (1+2+3)"
exit 1
fi

n=$1
sum=0
sd=0
while [ $n -gt 0 ]
do
sd=`expr $n % 10`
sum=`expr $sum + $sd`
n=`expr $n / 10`
done
echo "Sum of digit for numner is $sum"

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Problem : How to perform real number calculation in shell script and store result to
third variable , lets say a=5.66, b=8.67, c=a+b?

Solution :


a=5.66
b=8.67
c=`echo $a + $b | bc`
echo "$a + $b = $c"
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Problem : Write script to determine whether given file exist or not, file name is supplied as command line argument, also check for sufficient number of command line argument.


Solution : 


if [ $# -ne 1 ]
then
echo "Usage - $0 file-name"
exit 1
fi

if [ -f $1 ]
then
echo "$1 file exist"
else
echo "Sorry, $1 file does not exist"
fi

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Problem : Write script to print contains of file from given line number to next given number of lines. For e.g. If we called this script as Q13 and run as
$ Q13 5 5 myf , Here print contains of 'myf' file from line number 5 to next 5 line of that file.


Solution : 

if [ $# -eq 0 ]
then
echo "$0:Error command arguments missing!"
echo "Usage: $0 start_line uptoline filename"
echo "Where start_line is line number from which you would like to print file"
echo "uptoline is line number upto which would like to print"
echo "For eg. $0 5 5 myfile"
echo "Here from myfile total 5 lines printed starting from line no. 5 to"
echo "line no 10."
exit 1
fi

#
# Look for sufficent arg's
#

if [ $# -eq 3 ]; then
if [ -e $3 ]; then
tail +$1 $3 | head -n$2
else
echo "$0: Error opening file $3"
exit 2
fi
else
echo "Missing arguments!"
fi

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Problem : Write script called sayHello, put this script into your startup file called .bash_profile, the script should run as soon as you logon to system, and it print any one of the following message in infobox using dialog utility, if installed in your system, If dialog utility is not installed then use echo statement to print message : -
Good Morning
Good Afternoon
Good Evening , according to system time.


Solution : 


temph=`date | cut -c12-13`
dat=`date +"%A %d in %B of %Y (%r)"`

if [ $temph -lt 12 ]
then
mess="Good Morning $LOGNAME, Have nice day!"
fi

if [ $temph -gt 12 -a $temph -le 16 ]
then
mess="Good Afternoon $LOGNAME"
fi

if [ $temph -gt 16 -a $temph -le 18 ]
then
mess="Good Evening $LOGNAME"
fi

if which dialog > /dev/null
then
dialog --backtitle "Linux Shell Script Tutorial"\
--title "(-: Welcome to Linux :-)"\
--infobox "\n$mess\nThis is $dat" 6 60
echo -n " Press a key to continue. . . "
read
clear
else
echo -e "$mess\nThis is $dat"
fi

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Problem : How to write script, that will print, Message "Hello World" , in Bold and Blink effect, and in different colors like red, brown etc using echo command.

Solution : 


# Syntax: echo -e "escape-code your message, var1, var2 etc"
# For eg. echo -e "\033[1m Hello World"
#                               |                  |
#                               |                  |
#                       Escape code    Message
#

clear
echo -e "\033[1m Hello World"
# bold effect
echo -e "\033[5m Blink"
# blink effect
echo -e "\033[0m Hello World"
# back to noraml

echo -e "\033[31m Hello World"
# Red color
echo -e "\033[32m Hello World"
# Green color
echo -e "\033[33m Hello World"
# See remaing on screen
echo -e "\033[34m Hello World"
echo -e "\033[35m Hello World"
echo -e "\033[36m Hello World"

echo -e -n "\033[0m "
# back to noraml

echo -e "\033[41m Hello World"
echo -e "\033[42m Hello World"
echo -e "\033[43m Hello World"
echo -e "\033[44m Hello World"
echo -e "\033[45m Hello World"
echo -e "\033[46m Hello World"


echo -e "\033[0m Hello World"
# back to noraml

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Problem : Write script to implement background process that will continually print current time in upper right corner of the screen , while user can do his/her normal job at $ prompt.

Solution : 

echo
echo "Digital Clock for Linux"
echo "To stop this clock use command kill pid, see above for pid"
echo "Press a key to continue. . ."

while :
do
ti=`date +"%r"`
echo -e -n "\033[7s" #save current screen postion & attributes
#
# Show the clock
#

tput cup 0 69 # row 0 and column 69 is used to show clock

echo -n $ti # put clock on screen

echo -e -n "\033[8u" #restore current screen postion & attributs
#
#Delay fro 1 second
#
sleep 1
done