In some cases, you may need to combine several expressions to create conditions for the if and else sections of the code. When dealing with multiple conditions, Bash offers the logical AND operator. This operator connects two or more expressions in a way that the overall result depends on the individual expressions and the operator itself. So let’s learn a brief overview of the AND operator in bash scripting.
- Understand the functionality of the logical AND operator in the bash script.
- Getting familiar with the syntax and truth table for the AND operator.
- Learning to deploy conditional loop with AND operator.
What is the “&&” Command Separator in Bash?
The && operator in Bash also known as a logical AND operator, allows you to link two logical expressions or conditions. It evaluates to true only when both expressions are true. If either one or both of the conditions are false, the entire expression is considered false. It’s akin to saying, “Both conditions must be met for this to be true.”
Syntax and Truth Table of “AND (&&)” Operator
Following is the basic syntax of the AND logical operator in Bash scripting:
command_1 && command_2 && command_3
Here, If command_1 is successful, it leads to the execution of command_2, and if command_2 is also successful, command_3 is executed. Conversely, if command_1 fails, command_2 and command_3 will not be executed.
A general practice to evaluate the final output of multiple conditions is to learn the truth table. A truth table is a tabular representation used in logic and mathematics to show all possible combinations of values for a set of logical expressions or variables. It displays the resulting logical outcomes (usually true or false) for each combination of input values.
Let’s look at a truth table for three commands.
A key point to remember is that ‘&&‘ serves a dual purpose, not just for verifying tests or conditions but also for executing multiple commands. Consequently, the commands following ‘&&‘ will only be executed if the commands preceding ‘&&‘ yield a True result, as you can sense from the truth table given above.
4 Methods to Use “AND (&&)” Operator in Bash Script
In Bash scripting, the AND (&&) operator offers several versatile methods for controlling command execution. Here in this article, I am going to demonstrate 4 methods of using the AND operator in a bash script. So let’s see what those methods are.
Method 01: Using the “-a” Syntax with the IF Statement
In this first method, I will utilize the -a syntax to construct the code. It’s important to note that the use of -a syntax may seem a bit outdated nowadays. In contemporary Bash scripting, using double square brackets [[ ]] with && is not only more efficient but also provides better control.
Nevertheless, here I have written a code to give you a demonstration of the role of the -a syntax. The objective of the provided Bash code is to employ conditional statements and evaluate two conditions based on the values of value1 and value2. Depending on the results of these conditions, the code aims to provide appropriate feedback by displaying different messages.
- At first, launch an Ubuntu Terminal.
- Write the following command to open a file in Nano:
- Copy the script mentioned below:
#!/bin/bash # Example values value1=10 value2=20 if [ "$value1" -gt 5 -a "$value2" -lt 30 ]; then echo "Both conditions are true: value1 is greater than 5 and value2 is less than 30." else echo "At least one condition is false." fi
- Press CTRL+O and ENTER to save the file; CTRL+X to exit the nano editor.
- Use the following command to make the file executable:
chmod u+x a_options.sh
- Run the script by the following command:
Upon execution, the code successfully applies the and operator and returns the output as Both conditions are true: value1 is greater than 5 and value2 is less than 30.
Method 02: Using Double Square Brackets with “AND (&&)” Operator
Unlike the first code, I will use a double square bracket to enclose the AND operator. The use of [[ … ]] is generally considered more flexible and readable, and it provides additional capabilities for complex conditions compared to [ … ].
Script (double_square.sh) >
#!/bin/bash # Example values value1=10 value2=20 if [[ "$value1" -gt 5 && "$value2" -lt 30 ]]; then echo "Both conditions are true: value1 is greater than 5 and value2 is less than 30." else echo "At least one condition is false." fi
Now, run the script by using the following command.
The code returns the output line as Both conditions are true: value1 is greater than 5 and value2 is less than 30, reinforcing the idea that both conditions are true.
Method 03: Using Individual Single Square Brackets with “AND (&&)” Operator
You can deploy the AND operator in a different approach and that does not hurt the objective of the previously stated code. For instance, you can separate both conditions with the AND operator, enclosed by the single square bracket. Let’s see how it works.
Script (single.sh) >
#!/bin/bash # Example values value1=10 value2=20 if [ "$value1" -gt 5 ] && [ "$value2" -lt 30 ]; then echo "Both conditions are true: value1 is greater than 5 and value2 is less than 30." else echo "At least one condition is false." fi
Use the following command to execute the bash file
As you can see from the image given above, the code successfully declares both conditions to be true.
Method 04: Using Individual Double Square Brackets with Bash “AND (&&)” Operator
You can also separate multiple conditions by using the double square brackets ([[ ]]). Check the code provided below.
Script (double_individual.sh) >
#!/bin/bash # Example values value1=10 value2=20 if [[ "$value1" -gt 5 ]] && [[ "$value2" -lt 30 ]]; then echo "Both conditions are true: value1 is greater than 5 and value2 is less than 30." else echo "At least one condition is false." fi
Run the code using the following command.
As the image shows, the code returns Both conditions are true: value1 is greater than 5 and value2 is less than 30 to the command line.
What Approach Should You Use?
After exploring numerous ways of using the && operator, it leaves us contemplating the optimal choice. Each of these methods involves an expression that’s assessed, returning a status of 0 for true and a non-zero value for false.
Nevertheless, if you opt for double brackets, you gain the liberty to employ unquoted parameter expansions, unquoted parentheses, and compare strings using ‘<‘ and ‘>‘. Additionally, you can seamlessly combine regular expressions. Although, in a strictly POSIX-compliant environment, these results might be misleading.
Ultimately, the choice comes down to personal preference when working on a relatively recent Linux version, and you’re free to use the method that suits you best.
4 Practical Examples Using Logical “AND (&&)” Operator in Bash Script
Following the method described before, you will now explore some practical examples using the logical AND operator in the bash script.
Example 01: Bash “AND (&&)” Operator in IF Condition
In the first example, I will utilize the Bash AND logical operator to create a combined boolean expression for a Bash IF statement. Our goal is to determine whether the variable num is both an even number and divisible by 10. If both conditions satisfy each other, it will print a specific message to the console.
Script (if_and.sh) >
#!/bin/bash num=50 if [ $((num % 2)) -eq 0 ] && [ $((num % 10)) -eq 0 ]; then echo "$num is even and also divisible by 10." fi
Run the script by using the following command
As the image suggests above, the code declares 50 to be an even number and also divisible by 10.
Example 02: Using the Bash Logical “AND (&&)” Between Two Conditions
Moving onto our second code, I will employ two conditions connected with an AND operator. This Bash script aims to determine whether an individual is eligible for a tax deduction and calculate the income tax owed based on their income and a given tax threshold.
Script (example2.sh) >
#!/bin/bash # Define income and tax threshold income=$1 tax_threshold=$2 # Define eligibility for tax deduction eligible_for_deduction=true # Check if income exceeds the tax threshold and is eligible for a deduction if [ "$income" -gt "$tax_threshold" ] && [ "$eligible_for_deduction" == "true" ]; then # Calculate income tax (assuming a 20% tax rate) tax_rate=0.20 taxable_income=$((income - tax_threshold)) tax_owed=$(bc <<< "scale=2; $taxable_income * $tax_rate") echo "Your income of $income exceeds the tax threshold of $tax_threshold and you are eligible for a tax deduction." echo "You owe $tax_owed in income tax." else echo "Your income of $income does not exceed the tax threshold of $tax_threshold or you are not eligible for a tax deduction." fi
Using the following code, run the script in your command line.
./example2.sh 4000 5000
As 4000 is less than the threshold value of 5000, the code returns “Your income of 4000 does not exceed the tax threshold of 5000 or you are not eligible for a tax deduction.” in the command line.
Example 03: Using the Bash Logical “AND (&&)” Among Three Conditions
Following the previous code, I am going to employ three conditions in a bash script. The script evaluates if a student possesses qualities associated with being an ideal student based on their input responses.
Script (three _and.sh) >
#!/bin/bash # Take three input values from the user echo -n "Does the student obtain good grade? " read good_grades echo -n "Does the student attend the class regularly? " read good_attendance echo -n "Is the student attentive in the class? " read active_participation # Check if the student is ideal if [ "$good_grades" == "yes" ] && [ "$good_attendance" == "yes" ] && [ "$active_participation" == "yes" ]; then echo "This student is ideal." else echo "This student is not ideal." fi
Run the code using the following command.
As the image depicts above, the command line asks for different questions to determine whether the student is ideal or not. Based on the information given by the user, the code declares the student to be ideal.
Example 04: Bash “AND (&&)” Operator in While Loop Expression
You can also employ the bash AND operator in any loop construction to execute your conditional expression multiple times. For instance, Here in this code, I deploy a while loop along with an AND operator. The code’s goal is to determine, for each number in a specific range, whether it is both an even number and divisible by 3.
Script (and_while.sh) >
#!/bin/bash # Initialize a counter echo -n "Upto which number you want to check:" read n1 counter=1 # Continue the loop as long as the counter is less than or equal to 5 while [ $counter -le $n1 ]; do # Check if the counter is even and divisible by 3 if [ $((counter % 2)) -eq 0 ] && [ $((counter % 3)) -eq 0 ]; then echo "$counter is even and divisible by 3." else echo "$counter is not even and not divisible by 3." fi # Increment the counter ((counter++)) done
Now run the code using the following command.
As you can see from the above image, the user input 12 is iterated over multiple times and the command line declares 6 and 12 as even numbers and divisible by 3 simultaneously.
In conclusion, the AND (&&) operator is a fundamental element of Bash scripting, offering a range of powerful capabilities. Its ability to conditionally execute commands makes it an indispensable tool for building reliable and efficient Bash scripts. I hope, from the article described above, you have learned something new and effective that can add some plus to your arsenal. However, if you have any questions or queries related to this article, feel free to comment below. Thank you.