Using the expr command for arithmetic

We can use the expr command for arithmetic operations. The expr command is an external command; the binary of the expr command is stored in the folder called /usr/bin/expr.

Perform an addition operation as follows:

$ expr 40 + 2
42

Perform a subtraction operation as follows:

$ expr 42 - 2
40

Perform a division operation as follows:

$ expr 40 / 10
4

Perform a modulus (getting remainder) operation as follows:

$ expr 42 % 10
2
$ expr 4 * 10
expr: syntax error

With the expr command, we cannot use * for multiplication. We need to use \* for multiplication:

$ expr "4 * 10"
4 * 10
$ expr 4 \* 10
40

We will write a simple script to add two numbers. Write the Shell script called arithmetic_01.sh as follows:

#!/bin/bash
x=5
y=2
z=`expr $x + $y`
echo $z
Test the script as follows:
$ chmod +x arithmetic_01.sh
$ ./arithmetic_01.sh

The output is here:

Let's write a script to perform all the basic arithmetic operations. Write the Shell script called arithmetic_02.sh as follows:

#!/bin/bash
var1=30
var2=20
echo `expr $var1 + $var2`  # Arithmetic Addition
echo `expr $var1 - $var2`  # Arithmetic Subtraction
echo `expr $var1 \* $var2` # Arithmetic Multiplication
echo `expr $var1 / $var2`  # Arithmetic Division
echo `expr $var1 % $var2`  # Arithmetic Modular Division
                           # (Remainder)

Let us test the script:

$ chmod +x arithmetic_02.sh
$ ./arithmetic_02.sh

The output is here:

Using an arithmetic expansion

We can use two different ways for evaluating arithmetic expressions:

$(( expression ))
$[ expression ]

Learn arithmetic operations using the preceding mentioned arithmetic expansion:

$ a=10
$ b=20
$ c=$((a + b))
$ echo $c

During arithmetic operations, we may need to find square or cube of any given number. These operations are called as exponent operations. We can perform exponent operations as follows:

$ a=5
$ b=3
$ expo=$[ $a ** $b ]# This is equivalent to a^b
$ echo $expo
125

This is the result of the 5³ operations.

Another way of arithmetic expansions is as follows:

$ B=10
$ A=$[B + 10]
$ echo $A
20
$ echo $[ 3 + 4 - 5 ]
2

$ echo $[ 3 + 4 * 5]
23

Arithmetic multiplication has more precedence over addition. Therefore, 4*5 was performed first, and the addition of 3+20 was performed later on:

$ echo $[(3 + 4) * 5]
35

$ echo $(( 3 + 4 ))
7

$ echo $(( 6 / 0 ))
bash: 6/0: division by 0 ( error token is "0")

We will use many of the preceding arithmetic techniques for doing the same addition operation and check the result.

Let's write an interactive script called arithmetic_03.sh as follows:

#!/bin/bash
echo "Enter  first value"
read number_1
echo "Enter  secondvalue"
read number_2
total=`expr $number_1 + $number_2`
echo $total
sum=$(($number_1 + $number_2))
echo "sum is "$sum
echo "Sum is $[ $number_1+$number_2 ]"

Let us test the script:

$ chmod +x arithmetic_03.sh
$ ./arithmetic_03.sh

Output:

Enter  first value
10
Enter  second  value
5
15
Sum is 15
Sum is 15

The preceding Shell script shows that even if we use any of the previous techniques, the result remains the same.

Let's write the shell called script arithmetic_04.sh as follows:

#!/bin/bash
# Interactive Shell Script Demonstrating Arithmetic Operators
echo "Enter First value"
read number_1
echo "Enter Second value"
read number_2
echo $(($number_1 + $number_2))
echo $(($number_1 / $number_2)) # Division of two numbers

Let's test the program as follows:

$ chmod +x arithmetic_04.sh
$ ./arithmetic_04.sh

Output:

Enter First value
10
Enter Second value
5
15
2

We will write one more script with a different technique. Let's write the Shell script arithmetic_05.sh as follows:

#!/bin/bash
# Script is For Demonstrating Arithmetic
var1=10
var2=20
echo $(($var1+$var2))  # Adding Two Values
echo $(($var1-$var2))  # Subtract Two Values
echo $(($var1*$var2))  # Multiply Two Values
echo $(($var1%$var2))  # Remainder

Let's test the program here:

$ chmod +x arithmetic_05.sh
$ ./arithmetic_05.sh

Output:

We will write a script to add five numbers that are passed from a command line. Let's write the Shell script arithmetic_06.sh as follows:

#!/bin/bash
# Write a shell script which will receive 5 numbers from command line # and print their sum.
echo "Sum of Five Numbers is:" $(($1 + $2 + $3 + $4 + $5))

Let's test the program:

$ chmod +x arithmetic_06.sh
$ ./arithmetic_06.sh 10 20 30 40 50

Output:

Sum of Five Numbers is: 150

Let's write the Shell script arithmetic_07.sh as follows for finding cube, quotient, and remainder:

#!/bin/bash

x=99

(( cube = x * x * x ))
(( quotient = x / 5 ))
(( remainder = x % 5 ))

echo "The cube of $x is $cube."
echo "The quotient of $x divided by 5 is $quotient."
echo "The remainder of $x divided by 5 is $remainder."

# Note the use of parenthesis to controlling arithmetic operator
# precedence evaluation.
(( y = 2 * (quotient * 5 + remainder) ))
echo "Two times $x is $y."

Let's test the program:

$ chmod +x arithmetic_07.sh
$ ./arithmetic_07.sh

Output:

The cube of 99 is 970299.
The quotient of 99 divided by 5 is 19.
The remainder of 99 divided by 5 is 4.
Two times 99 is 198.

Previous Chapter

Using the let command for arithmetic

Next Chapter

Binary, octal, and hex arithmetic operations

Table of Contents for Learning Linux Shell Scripting

Using the expr command for arithmetic

Using an arithmetic expansion

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Learning Linux Shell Scripting