Usage of “OR” Operator in Bash Scripting [2 Cases]

Bash includes a range of logical operators that help to set multiple conditions within a bash script. Among these, the logical OR operator, denoted by “||” in Bash, executes Boolean OR operations. In this article, I will demonstrate an overall picture of the OR operator in bash scripts, including its syntax, different user cases, and examples. So let’s begin.

Key Takeaways

• Getting familiar with the OR operator and its syntax.
• Understanding the implication of if statement or while loop along with the OR operator in bash.

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“OR” Operator in Bash Scripting

In bash scripting, a developer can use OR operator to develop his code aiming to menu selection, file existence, error handling, verify the user data, etc. To begin with all of those effective applications, let’s understand the syntax and the mechanism of the bash OR operator first.

Syntax of “OR” Operator

Within the logical operators of the bash script, you’ll find the logical OR operator, which carries out a boolean OR operation. One single Bash boolean OR operator accepts two operands and yields a true outcome if either of them is true, otherwise, it results in a false. The syntax of the OR operator is as such.

operand_1 || operand_2

Here, operand_1 and operand_2 represent logical expressions or boolean conditions that produce either a true or false result. In Bash, the || operator performs the boolean OR operation.

Truth Table of Bash “OR” Operator

Following the syntax of the OR operator provided above, the OR operator in Bash assesses two logical expressions and yields a true outcome if either of them is true, otherwise, it produces a false result.  Below is a truth table for the Bash logical OR operator, serving as a helpful reference to grasp its behavior:

2 Practical Cases of Using “OR” Operator in Bash Scripting

Down below, I am going to discuss several practical cases with examples to demonstrate you the overall idea of the OR operator in bash. Check this out and don’t forget to run the code in your command line.

Case 01: Using Bash “OR” Operator in IF Condition

The Bash OR operator in an if condition allows for the execution of a code block when at least one of the provided conditions is true. This flexibility enables various scenarios where different conditions can trigger specific actions based on the outcome. Let’s have three examples to grasp the idea of it.

Example 01: Check If a Number is Between a Specific Range

The objective of the provided Bash script is to allow a user to input a number and determine whether that number falls within the range of 10 to 20. It uses conditional statements to check if the input number is either less than 10 or greater than 20, and based on the evaluation, it provides user feedback.

Steps to Follow >

1. At first, launch an Ubuntu Terminal.
2. Write the following command to open a file in Nano:

   nano number_check.sh

   EXPLANATION

   • nano: Opens a file in the Nano text editor.
   • number_check.sh : Name of the file.
3. Copy the script mentioned below:

   #!/bin/bash
   
   read -p "Enter a number: " number
   
   if [ $number -lt 10 ] || [ $number -gt 20 ]; then
       echo "The number is not between 10 and 20."
   else
       echo "The number is between 10 and 20."
   fi
   

   EXPLANATION

   This Bash script begins with the shebang #!/bin/bash, indicating that it should be executed using the Bash shell. It proceeds to ask the user to input a number using the read command, and the entered number is stored in the number variable. The script then uses an if statement to evaluate whether the value of number is less than 10 or greater than 20. If either condition is met, as denoted by the logical OR operator ||, the script displays the message “The number is not between 10 and 20.” Conversely, if neither condition is true, it prints “The number is between 10 and 20.”

4. Press CTRL+O and ENTER to save the file; CTRL+X to exit.
5. Use the following command to make the file executable:

   chmod u+x number_check.sh

   EXPLANATION

   • chmod: Changes the permissions of files and directories.
   • u+x: Here, u refers to the “user” or the owner of the file and +x specifies the permission being added, in this case, the “execute” permission. u+x grants the user (owner) permission to execute (run) the file.
   • number_check.sh : File name.
6. Run the script by the following command:

   ./number_check.sh

   While 35 is passed as the user input, the bash code evaluates it and returns The number is not between 10 and 20 to the command line. Subsequently, when the number 12 is provided, the code declares the value as a number that lies between 10 and 20.

Example 02: Check If a Number is Even or Divisible by 5

In a different scenario, I will now examine whether the provided number is divisible by 2 (making it even) or divisible by 5. To accomplish this, I’ve developed a Bash script given below.

Script (number_check2.sh) >

#!/bin/bash

read -p "Enter a number: " number

if [ $((number % 2)) -eq 0 ] || [ $((number % 5)) -eq 0 ]; then
    if [ $((number % 2)) -eq 0 ]; then
        echo "The number is even."
    fi

    if [ $((number % 5)) -eq 0 ]; then
        echo "The number is divisible by 5."
    fi
else
    echo "The number is neither even nor divisible by 5."
fi

To run the code, execute the following command to the command line.

./number_check2.sh

Upon giving 23 and 10 as user input, the command line returns 23 as neither even nor divisible by 5, 10 as an even number, and divisible by 5.

Example 03: Check Condition Using “-o” Operator

Other than using the OR (||) operator, you can accomplish the same using the -o Operator. Follow the code given below to understand it’s functionality.

Script (o_operator.sh) >

#!/bin/bash

read -p "Enter a number: " number

if [ $((number % 2)) -eq 0 -o $((number % 5)) -eq 0 ]; then
    echo "The number is either even or divisible by 5."
else
    echo "The number is neither even nor divisible by 5."
fi

Use the following command to run the code in the command line.

./o_operator.sh

Upon executing the bash file, as you can see from the image given above, the code returns 5 as a number either to be even or divisible by 5 and 9 as a number neither even nor divisible by 5.

Case 02: Bash “OR” Operator in “While Loop” Expression

In Bash, you can also use the OR operator (||) in the expression of a while loop to create a loop that continues running as long as either of the specified conditions is true. Here’s a sample code provided below. The objective of this Bash script is to present a simple menu to the user, allowing them to choose between starting a new game or quitting. The script uses a while loop with the OR operator to continue running until a valid choice of either 1 or 2 is made by the user.

Script (while_or.sh) >

#!/bin/bash

choice=""

while [ "$choice" != "1" ] || [ "$choice" != "2" ]; do
    echo "Choose an option:"
    echo "1. Start a new game"
    echo "2. Quit"

    read -p "Enter your choice (1 or 2): " choice

    if [ "$choice" == "1" ]; then
        echo "Starting a new game..."
        # Add game start logic here
    elif [ "$choice" == "2" ]; then
        echo "Goodbye!"
        break
    else
        echo "Invalid choice. Please enter 1 or 2."
    fi
done

Run the script using the following command:

./while_or.sh

As you can see from the image given above, the code starts a new game when the user presses 1 and ends the execution once the user gives 2 as the user input.

Assignment on Bash “OR” Operator

Here for your perusal, I have given to an assignment to asses your overall proficiency from today’s learning. Don’t forget to share with others in the comment section.

1. Write a Bash script that prompts the user to input their age and checks whether the user is elder or younger. If the age is less than 18 then the user will be regarded as younger, older otherwise. Provide appropriate messages based on the conditions.
2. Write a bash code to print a set of numbers using or operator in a loop.

Conclusion

In conclusion, this article delves into the effective utilization of the OR operator in Bash scripting. It thoroughly explains the syntax of the OR operator, emphasizing its role in performing logical OR operations. Then it returns a true result when either of the two operands is true. The article also provides valuable insights into the OR operator’s practical applications, with a focus on its use in IF conditions and within while loop expressions. However, if you have any questions or queries related to this article, feel free to comment below. Thank you.

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