In the bash script, the expressions “(()),” and “$(())” are utilized for the calculation of the various expressions containing more than one argument. The only difference between “(())” and “$(())” is, the “(())” doesn’t return the output while the “$(())” returns the results and stores it in the defined variable.
This post will briefly demonstrate the usage of expressions “$(())” and “(())” in the bash script.
- Expression “$(())” and “(())” in Bash
- Perform Arithmetic Operations Using “$(())”
- Check whether the Number is Even or Odd Using “(())”
- Expression “$(())” and “(())” in a Loop
Expression “$(())” and “(())” in Bash
If the user uses the “(())” expression in the echo statement, it will print nothing while “$(())” prints the result value. To make it clear, the subsequent examples are performed are as below:
Example 1: Perform Arithmetic Operations Using “$(())” Expression
An example is considered to perform the arithmetic operations such as addition, subtraction, multiplication, and division using the “$(())” expression in the following script:
#!/bin/bash
a=4;
b=2;
echo "The Addition is $((a+b))"
echo "The Subtraction is $((a-b))"
echo "The Multiplication is $((a*b))"
echo "The Division is $((a/b))"
The description of the script is given below:
- Firstly, two variables “a” and “b” are initialized with values 4 and 2.
- After that, the echo statements are performed in addition to the variable “a” and “b” using “$((a+b))” and printing it on the screen.
- This way, subtraction, multiplication, and division operations are performed and printed on the screen.
Save the script file by pressing “Ctrl+O” and exit from the file by pressing “Ctrl+X” in the text editor.
Run the script file (script.sh) with the “bash” keyword to obtain the results in the terminal:
$ bash script.sh
The addition of two variables “a” and “b” is 6, subtraction is 2, multiplication is 8, and division is “2”.
Example 2: Check if the Number is Even or Odd Using “(())” Expression
As the “(())” expression doesn’t return the calculation results but can be used as a conditional statement to perform other tasks. The following script shows the usage of the “(())” expression in which even and odd numbers are calculated:
#!/bin/bash
read -p "Enter Number to Check: " num
((num%2==0)) && echo "The Number is Even"
The script is defined as below:
- The “read” property with a “p” flag is used to get the numbers from the user and store it in the “num” variable.
- The “((num%2==0))” expression is utilized to check if the number is even or odd. After that, the “echo” command is separated by “&&” to print the message in the terminal.
Save the script file and exit.
Run the “script.sh” file in the terminal:
$ bash script.sh
The entered number 6 is even, and it displays the “The Number is Even” in the terminal.
Example 3: Print Numbers Using “$(())” and “(())” in a Loop
The following code prints the first numbers from 1 to 10 using the “$(())” and “(())” expressions:
#!/bin/bash
a=1
while ((a<=10)) #(()) Expression to Check the Condition
do
echo "$a"
a=$((a+1)) #$(()) Expression incrementing and storing in variable a.
done
The description of the script is mentioned below:
- The “a” variable is initialized with 1.
- The while loop with the expression “((a<=10))” is utilized to check the number is less than and equal to 10.
- After that, the “do” statement prints the “a” variable.
- The “a=$((a+1))” expression is utilized to increment the variable “a” to continue the loop.
Save the file and exit the text editor.
Run the script file to retrieve the results:
$ bash script.sh
The output shows that the numbers from 1 to 10 have been printed on the screen.
Conclusion
To perform calculations in bash the expression “(())” and “$(())” are used, the “$(())” returns the results while “(())” doesn’t and is applied on conditions. The “$(())” is considered for storing the results in a variable or printing it on the screen. On the other side, the “(())” expression is used to check the conditional statement.
This write-up has illustrated the usage of expressions “$(())” and “(())” in the bash script.
