Bash Scripting with Add Numbers via Expr and let cmd

Bash Scripting

 
In Linux, all tasks from execution of services to loading and unloading of modules are carried out by programs and all programs need to be executed. You use the commands to access all the basic features of kernel. Shell scripting is a way to automate such tasks, and bash is one of the language, that has capabilities enough to be called as scripting as well as a language that can be used for programming on the POSIX platform, for small tasks.  Bash Scripting else if statement

 

Add Two Numbers

You can do the arithmetical operations in bash in different ways. How you can add two integer numbers in bash using double brackets is shown in the following script. Create a file named ‘add_two_numbers.sh’ with the following code. Two integer values will be taken from the user and printed the result of addition. Bash Scripting with Add Two Numbers via variables

#!/bin/bash
echo "Enter first number"
read x
echo "Enter second number"
read y
(( sum=x+y ))
echo "The result of addition=$sum"

Run the file with bash command.
 

 

 

Example – 1: Using ‘expr’ command

The oldest command for doing arithmetic operations in bash is ‘expr’. This command can work with integer values only and prints the output directly in the terminal. You have to use space with each operand when you want to use ‘expr’ command to do any mathematical operations. Create a bash file and add the various ‘expr’ commands to check how the ‘expr’ command works. Bash Scripting with Add Numbers via Expr and let cmd

#!/bin/bash
# Works as string
expr '10 + 30'
# Works as string
expr 10+30
#Perform the addition
expr 10 + 30
#Find out the remainder value
expr 30 % 9
#Using expr with backtick
myVal1=`expr 30 / 10`
echo $myVal1
#Using expr within command substitute
myVal2=$( expr 30 - 10 )
echo $myVal2

Run the file arithmetic.sh
 

 

 

Explain

The output shows that arithmetic operators worked only when space is used with each numeric value and no single quotation is used with expr command. You can also assign the output of expr command into a variable and print the variable later by using backtick or command substitute. 30/10 is calculated by using backtick and 30-10 is calculated by using command substitute.

 

Example – 2: Using ‘let’ command

‘let’ is another built-in command to do arithmetic operations in bash. ‘let’ command can’t print the output to the terminal without storing the value in a variable. But ‘let’ command can be used to remove the other limitations of the ‘expr’ command. Create a bash file and add the following code for seeing how the ‘let’ command works.

#!/bin/bash
# Multiplying 9 by 8
let val1=9*3
echo $val1
# Dividing 8 by 3y
let "val2 = 8 / 3"
echo $val2
# Subtracting 3 from 9
let val3=9-3
echo $val3
# Applying increment
let val4=7
let val4++
echo $val4
# Using argument value in arithmetic operation
let "val5=50+$1"
echo $val5

Run the file arithmetic2.sh
 

 

Explain

The output shows that arithmetic operators worked only when space is used with each numeric value and no single quotation is used with expr command. You can also assign the output of expr command into a variable and print the variable later by using backtick or command substitute. 30/10 is calculated by using backtick and 30-10 is calculated by using command substitute.

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