Shell Programming - Arithmetic Operators

In this tutorial we will learn about Arithmetic Operators in Shell Programming.

We will be covering the following math operations in this tutorial.

• Addition +
• Subtraction -
• Multiplication *
• Division /
• Modulus % to get remainder

expr command

In shell script all variables hold string value even if they are numbers. So, to perform arithmetic operations we use the expr command.

The expr command can only work with integer values. For floating point numbers we use the bc command.

To compute the result we enclose the expression in backticks ` `.

Addition

We use the + symbol to perform addition.

In the following example we are taking two integer value from the user and showing the result after addition.

#!/bin/sh

# take two integers from the user
echo "Enter two integers: "
read a b

# perform addition
result=`expr $a + $b`

# show result
echo "Result: $result"

In the above script `expr $a + $b` means we are adding values stored in variable a and b and evaluating the expression using the expr command. We are then saving the result of the addition operation in the variable result.

Output:

$ sh add.sh
Enter two integers: 
10 20
Result: 30

In the following example we are enclosing the variables in double quotes and using bc to handle floating point numbers.

#!/bin/sh
  
# take two numbers from the user
echo "Enter two numbers: "
read a b

# perform addition
result=`expr "$a + $b" | bc`

# show result
echo "Result: $result"

Output:

$ sh add2.sh 
Enter two numbers: 
1.2 3.4 
Result: 4.6

Subtraction

To perform subtraction we use the - symbol.

In the following example we will take two numbers from the user and print the subtraction result.

#!/bin/sh

# take two numbers from user
echo "Enter two numbers: "
read a b

# compute subtraction result
result=`expr "$a - $b" | bc`

# print output
echo "Result: $result"

Output:

$ sh subtract.sh 
Enter two numbers: 
10 9
Result: 1

$ sh subtract.sh 
Enter two numbers: 
9 10
Result: -1

$ sh subtract.sh 
Enter two numbers: 
10.5 9.1
Result: 1.4

Multiplication

To perform multiplication we use the * symbol.

In the following example we will multiply two numbers.

#!/bin/sh

# take two numbers from user
echo "Enter two numbers: "
read a b

# compute multiplication result
result=`expr "$a * $b" | bc`

# print output
echo "Result: $result"

Output:

$ sh multiplication.sh 
Enter two numbers: 
2 3
Result: 6

$ sh multiplication.sh 
Enter two numbers: 
-2 3
Result: -6

$ sh multiplication.sh 
Enter two numbers: 
1.5 4
Result: 6.0

Division

To perform division we use the / symbol.

In the following example we will divide two numbers.

#!/bin/sh

# take two numbers from user
echo "Enter two numbers: "
read a b

# compute division result
result=`expr "$a / $b" | bc -l`

# print output
echo "Result: $result"

Output:

$ sh division.sh 
Enter two numbers: 
4 2
Result: 2

$ sh division.sh 
Enter two numbers: 
5 2
Result: 2.50000000000000000000

The -l option loads the standard math library with default scale set to 20.

Modulus

To perform modulus operations we use the % symbol.

In the following example we will get the remainder by dividing two numbers.

#!/bin/sh

# take two numbers from user
echo "Enter two numbers: "
read a b

# compute modulus result
result=`expr "$a % $b" | bc`

# print output
echo "Result: $result"

Output:

$ sh modulus.sh 
Enter two numbers: 
5 2
Result: 1

$ sh modulus.sh 
Enter two numbers: 
5.1 2
Result: 1.1