Calculating Mathematical Expressions in Shell Scripting Language – Part V

You People would be feeling comfortable, understanding Shell Scripts and writing them fluently, as per your need. This is the last post of this tutorial series, where we will be carrying out a bit complex Mathematical Operations using scripting language. The last four articles of Shell Scripting series which are chronologically.

Lets start with Fibonacci Series

A pattern of numbers where each number is the sum of two preceding numbers. The series is 0, 1, 1, 2, 3, 5, 8…… By definition, the first two numbers in the Fibonccai sequence are 0 and 1.

Script 1: Fibonacci.sh

#!/bin/bash

echo "How many numbers do you want of Fibonacci series ?" 

read total 

x=0 

y=1 

i=2 

echo "Fibonacci Series up to $total terms :: " 

echo "$x" 

echo "$y" 

while [ $i -lt $total ] 

do 

i=`expr $i + 1 ` 

z=`expr $x + $y ` 

echo "$z" 

x=$y 

y=$z 

done

Sample Output

[root@localhost ~]# chmod 755 Fibonacci.sh

[root@localhost ~]# ./Fibonacci.sh

How many numbers do you want of Fibonacci series ? 

10 

Fibonacci Series up to 10 terms :: 

0 

1 

1 

2 

3 

5 

8 

13 

21 

34

You are Familiar with the fact that computer understand only in the Binary Format, i.e., ‘0‘ and ‘1‘ and most of us have enjoyed learning the conversion of Decimal to Binary. How about writing a simple script for this complex operation.

Script 2: Decimal2Binary.sh

#!/bin/bash 

for ((i=32;i>=0;i--)); do 

r=$(( 2**$i)) 

Probablity+=( $r  ) 

done 

[[ $# -eq 0 ]] &echo -en "Decimal\t\tBinary\n" 

for input_int in $@; do 

s=0 

test ${#input_int} -gt 11 &printf "%-10s\t" "$input_int" 

for n in ${Probablity[@]}; do 

if [[ $input_int -lt ${n} ]]; then 

[[ $s = 1 ]] && printf "%d" 0 

else 

printf "%d" 1 ; s=1 

input_int=$(( $input_int - ${n} )) 

fi 

done 

echo -e 

done

Sample Output

[root@localhost ~]# chmod 755 Decimal2Binary.sh

[root@localhost ~]# ./Decimal2Binary.sh 1121

Decimal        Binary 

1121           10001100001

Note: The above script accept Input at run time, which obviously is an aid.

Well the inbuilt ‘bc‘ command can convert a decimal to binary in a script of single line. Run, at your terminal.

[root@localhost ~]# echo "obase=2; NUM" | bc

Replace ‘NUM‘ with the number, which you want to convert from Decimal to Binary. For example,

[root@localhost ~]# echo "obase=2; 121" | bc 

1111001

Next we will be writing a script which function just opposite of the above script, Converting Binary Values to Decimal.

Script 3: Binary2Decimal.sh

#!/bin/bash 

echo "Enter a number :" 

read Binary 

if [ $Binary -eq 0 ] 

then 

echo "Enter a valid number " 

else 

while [ $Binary -ne 0 ] 

do 

Bnumber=$Binary 

Decimal=0 

power=1 

while [ $Binary -ne 0 ] 

do 

rem=$(expr $Binary % 10 ) 

Decimal=$((Decimal+(rem*power))) 

power=$((power*2)) 

Binary=$(expr $Binary / 10) 

done 

echo  " $Decimal" 

done 

fi

Sample Output

[root@localhost ~]# chmod 755 Binary2Decimal.sh

[root@localhost ~]# ./Binary2Decimal.sh

Enter a number : 

11 

3

Note: The above function can be performed in terminal using ‘bc‘ command as.

[root@localhost ~]# echo "ibase=2; BINARY" | bc

Replace ‘BINARY‘ with the Binary number, viz.,

[root@localhost ~]# echo "ibase=2; 11010101" | bc 

213

Similarly you can write conversion from octal, hexadecimal to decimal and vice-versa yourself. Accomplishing the above result in terminal using ‘bc‘ command is.

Decimal to Octal

[root@localhost ~]# echo "obase=8; Decimal" | bc

Decimal to Hexadecimal

[root@localhost ~]# echo "obase=16; Decimal" | bc

Octal to Decimal

[root@localhost ~]# echo "ibase=8; Octal" | bc

Hexadecimal to Decimal

[root@localhost ~]# echo "ibase=16; Hexadecimal" | bc

Binary to Octal

[root@localhost ~]# echo "ibase=2;obase=8 Binary" | bc

Some of the Common Numeric tests used in shell scripting language with description is.

Test : INTEGER1 -eq INTEGER2

Meaning: INTEGER1 is equal to INTEGER2

Test : INTEGER1 -ge INTEGER2

Meaning: INTEGER1 is greater than or equal to INTEGER2

Test: INTEGER1 -gt INTEGER2

Meaning: INTEGER1 is greater than INTEGER2

Test:INTEGER1 -le INTEGER2

Meaning: INTEGER1 is less than or equal to INTEGER2

Test: INTEGER1 -lt INTEGER2

Meaning: INTEGER1 is less than INTEGER2

Test: INTEGER1 -ne INTEGER2

Meaning: INTEGER1 is not equal to INTEGER2

That’s all for this article, and the article series. This is the last article of Shell Script Series and it does not means that no article on Scripting language will be here again, it only means the shell scripting tutorial is over and whenever we find an interesting topic worth knowing or a query from you people, we will be happy to continue the series from here.