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Operators in Linux

1. Arithmetic Operators

  • + → Addition
  • - → Subtraction
  • * → Multiplication (use \* as * is a wildcard character)
  • / → Division
  • % → Modulo Operator

2. Relational Operators (Numeric Comparison)

  • -gt → Greater than
  • -ge → Greater than or equal to
  • -lt → Less than
  • -le → Less than or equal to
  • -eq → Equal to
  • -ne → Not equal to

These operators return boolean values (true/false).

3. Logical Operators

  • -a → Logical AND
  • -o → Logical OR
  • ! → Logical NOT

4. Assignment Operator

  • =

Note:

  • Except for the assignment operator, spaces are mandatory before and after other operators.

Performing Mathematical Operations in UNIX/Linux

There are multiple ways to perform mathematical operations:

1. Using expr Keyword

expr stands for expression.

#!/bin/bash
read -p "Enter First Number: " a
read -p "Enter Second Number: " b

sum=`expr $a + $b`
echo "The Sum: $sum"

sum=$(expr $a + $b)
echo "The Sum: $sum"

Notes:

  • $ symbol is mandatory.
  • Space is required before and after the + symbol.

2. Using let Keyword

let sum=a+b
echo "The Sum: $sum"

let sum=$a+$b
echo "The Sum: $sum"

Notes:

  • $ symbol is optional.
  • Do not use spaces before and after the +.

3. Using (())

sum=$((a+b))
echo "The Sum: $sum"

sum=$(($a+$b))
echo "The Sum: $sum"

Notes:

  • Space and $ symbol are optional.

4. Using []

sum=$[a+b]
echo "The Sum: $sum"

sum=$[$a+$b]
echo "The Sum: $sum"

Notes:

  • Space and $ symbol are optional.

Floating-Point Arithmetic with bc

bc (Binary Calculator) is used to perform both integer and floating-point arithmetic. Start bc by typing bc in the terminal:

durgasoft@durgasoft:~/scripts$ bc
bc 1.07.1
10.5+30.6
41.1
10.2^2
104.0
10.5*3.6
37.8
ctrl+d  # Exit bc

Script for Floating-Point Arithmetic

#!/bin/bash
read -p "Enter First Number: " a
read -p "Enter Second Number: " b

sum=$(echo $a+$b | bc)
echo "The Sum: $sum"

echo "The Difference: $(echo $a-$b | bc)"
echo "The Product: $(echo $a*$b | bc)"

Output:

durgasoft@durgasoft:~/scripts$ ./test.sh
Enter First Number: 10.5
Enter Second Number: 5.3
The Sum: 15.8
The Difference: 5.2
The Product: 55.6

Examples and Exercises

Q1: Write a Script to Read Two Integer Numbers and Print Their Sum

#!/bin/bash
read -p "Enter First Number: " a
read -p "Enter Second Number: " b
sum=$[a+b]
echo "The Sum: $sum"

Q2: Write a Script to Read a 4-Digit Integer and Print the Sum of Its Digits

#!/bin/bash
read -p "Enter Any 4-Digit Integer Number: " n

a=$(echo $n | cut -c 1)
b=$(echo $n | cut -c 2)
c=$(echo $n | cut -c 3)
d=$(echo $n | cut -c 4)

echo "The Sum of 4 Digits: $[a+b+c+d]"

Output:

durgasoft@durgasoft:~/scripts$ ./test.sh
Enter Any 4-Digit Integer Number: 1234
The Sum of 4 Digits: 10

durgasoft@durgasoft:~/scripts$ ./test.sh
Enter Any 4-Digit Integer Number: 3456
The Sum of 4 Digits: 18

Q3: Write a Script to Calculate Bonus as 25% of Annual Salary

#!/bin/bash
read -p "Enter Employee Monthly Salary: " salary

annual_salary=$[salary*12]
bonus=$[annual_salary*25/100]

echo "The Bonus: $bonus"

Output:

durgasoft@durgasoft:~/scripts$ ./test.sh
Enter Employee Monthly Salary: 10000
The Bonus: 30000