Shell Script to Add Two Numbers

    RahulBy 2 Mins ReadUpdated:

    Calculating the sum of two integers (Numbers) in a shell script is pretty simple as in other programming languages. Bash shell provides a command-line utility called expr to evaluate expressions. The latest version of the Bash shell also includes the functionality to evaluate expressions directly with the shell.

    In this tutorial, we will discuss a few methods to calculate the sum of the two numbers in a bash script.

    Bash – Adding Two Numbers

    The expr is the command-line utility used for evaluating mathematical expressions. Bash shell also supports evaluating the mathematical expressions directly.

    Use the following syntax to calculate the sum of two integers in a shell script:

    • Using expr command with quotes
      sum=`expr $num1 + $num2`
    • Use expr command inclosed with brackets and start with dollar symbol.
      sum=$(expr $num1 + $num2)
    • This is my preferred way to directly with the shell.
      sum=$(($num1 + $num2))

    In the next few examples, we will discuss calculating the sum of numbers directly with a shell. You can also choose expr command to give the syntax above.

    Calculate Sum in Shell Script

    Bash shell also evaluates the mathematical expressions directly. You just need to write the expressions enclosed in double brackets with a dollar like $((...)).

    Write an example shell script to initialize two numeric variables. Then perform an addition operation on both values and store results in the third variable.

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    #!/bin/bash
    # Calculate the sum of two integers with pre initialize values
    # in a shell script
     
    a=10
    b=20
     
    sum=$(( $a + $b ))
     
    echo "Sum is: $sum"

    Output:

    Sum is: 30

    Calculate Sum with Command Line Arguments

    In this second example, the shell script reads two numbers as command line parameters and performs the addition operation.

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    #!/bin/bash
    # Calculate the sum via command-line arguments
    # $1 and $2 refers to the first and second argument passed as command-line arguments
     
    sum=$(( $1 + $2 ))
     
    echo "Sum is: $sum"  

    Let’s execute this script is a shell

    ./sum.sh 12 14        # Executing script 

Sum is: 26

    Calculate Sum with Run Time Input

    Here is another example of a shell script, which takes input from the user at run time. Then calculate the sum of given numbers and store to a variable and show the results.

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    #!/bin/bash
    # Take input from user and calculate sum.
    read -p "Enter first number: " num1
    read -p "Enter second number: " num2
    sum=$(( $num1 + $num2 ))
    echo "Sum is: $sum"  

    Output:

    Enter first number: 12
Enter second number: 15
Sum is: 27

    Conclusion

    In this tutorial, you have learned few methods to add two numbers in a shell script.

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    4 Comments

    3. dixit on

      code :
      echo -n “enter the num1 ==> ”
      read num1
      echo -n “enter the num2 ==> ”
      read num2
      sum =$(( $num1 + $num2 ))
      echo “the sum of $num1 and $num2 is ==> $sum”

      i have written this code but it shows me some errors so can you help me ?

      error :
      enter the num1 ==> 10
      enter the num2 ==> 20
      sum: ‘=30’: No such file or directory
      the sum of 10 and 20 is ==>

      Reply
      • Rahul on

        Hi Dixit,
        Remove space after “sum variable”

        sum=$(( $num1 + $num2 ))

        The full script should be

        echo -n "enter the num1 ==> "
read num1
echo -n "enter the num2 ==> "
read num2
sum=$(( $num1 + $num2 ))
echo "the sum of $num1 and $num2 is ==> $sum"
        Reply

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