Usage of Logical “AND (&&)” Operator in Bash Scripting

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.

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.

See a truth table for three commands with “&” operator:

Command1 Command2 Command3  Result
true true true true
true true false false
true false true false
true false false false
false true true false
false true false false
false false true false
false false false false

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.

1. 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.

To employ the logical “&&” operator using “-a” syntax, follow the script given 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
EXPLANATION

The provided Bash script sets two example values, value1 and value2, to 10 and 20, respectively. It then employs an if statement to check two conditions. The first condition verifies if the value of value1 is greater than 5, and the second condition checks if the value of value2 is less than 30, using the -gt and -lt comparison operators, respectively. If both of these conditions are true, the script displays the message “Both conditions are true: value1 is greater than 5 and value2 is less than 30.” On the other hand, if at least one of these conditions is false, the script outputs the message “At least one condition is false.” using the echo command.

Using -a Syntax with the if StatementUpon 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.

2. Using Double Square Brackets with “AND (&&)” Operator

Unlike the first code, this code 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 [ … ].

To use logical “&&” operator using double square brackets, follow the code given below:

#!/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
EXPLANATION

The script starts by setting example values: value1 is set to 10, and value2 is set to 20. It then uses an if statement with the [[ … ]] construct. Within this construct, it checks two conditions. First, it checks if the value of value1 is greater than 5 using the -gt operator, and second, it checks if the value of value2 is less than 30 using the -lt operator. If both of these conditions are true, the script displays the message “Both conditions are true: value1 is greater than 5 and value2 is less than 30.” However, if at least one of these conditions is false, it will output the message “At least one condition is false.”

 Using Double Square Brackets with AND (&&) OperatorThe 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.

3. 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 code. For instance, you can separate both conditions with the AND operator, enclosed by the single square bracket.

To understand how a logical “&&” operator operates using a single square bracket, see the code given below:

#!/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
EXPLANATION

The provided Bash script sets two example values, value1 and value2, to 10 and 20, respectively. It then uses an if statement with basic [ … ] conditional constructs to check two conditions. First, it checks if the value of value1 is greater than 5 using the -gt operator, and then it checks if the value of value2 is less than 30 using the -lt operator. If both of these conditions are true, the script displays the message “Both conditions are true: value1 is greater than 5 and value2 is less than 30.” However, if at least one of these conditions is false, it outputs the message “At least one condition is false.”

Using Individual Single Square Brackets with AND (&&) OperatorAs you can see from the image given above, the code successfully declares both conditions to be true.

4. Using Individual Double Square Brackets with Bash “AND (&&)” Operator

You can separate multiple conditions by using the double square brackets ([[ ]]). Check the code provided below:

#!/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
EXPLANATION

The provided Bash script sets example values for value1 and value2, checks two conditions using [[ … ]], and then outputs a message. If both conditions are true, it displays “Both conditions are true: value1 is greater than 5 and value2 is less than 30,” otherwise it shows “At least one condition is false.”

Using Individual Double Square Brackets with Bash AND (&&) OperatorAs 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.

1. 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.

To employ “&&” operator with IF condition, see the code given below:

#!/bin/bash

num=50

if [ $((num % 2)) -eq 0 ] && [ $((num % 10)) -eq 0 ]; then
  echo "$num is even and also divisible by 10."
fi
EXPLANATION

This Bash script begins by setting the variable num to the value 50. It then enters an if statement, which checks two conditions. First, it evaluates whether num modulo 2 is equal to 0 (i.e., it’s even), and secondly, it checks if num modulo 10 is also equal to 0 (i.e., it’s divisible by 10). If both conditions are met, the script displays the message “$num is even and also divisible by 10.”

Bash AND Operator (&&) in IF ConditionAs the image suggests above, the code declares 50 to be an even number and also divisible by 10.

2. 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.

To calculate tax using the logical “&&” operator, use the following code:

#!/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
EXPLANATION

The code begins by taking two command-line arguments: income and tax_threshold. It defines the eligibility for a tax deduction as true.

The script then enters an if statement, where it checks if the income is greater than the tax_threshold and if eligible_for_deduction is set to true. If both conditions are met, it calculates the taxable income by subtracting the tax_threshold from the income. It assumes a 20% tax rate to calculate the tax_owed and prints a message indicating that the income exceeds the tax threshold and the amount of income tax owed.

If the conditions are not met, it prints a message stating that the income does not exceed the tax threshold or that the individual is not eligible for a tax deduction.

Using the Bash Logical AND (&&) Between Two ConditionsAs 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.

3. 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. See the code construction below:

#!/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
EXPLANATION

This Bash script solicits three input values from the user regarding a student’s performance in school. It first asks if the student obtains good grades, then if the student attends classes regularly, and finally, if the student is attentive in class.

Subsequently, the script enters an if statement, where it checks if all three conditions are met. It verifies whether good_grades is yes, good_attendance is yes, and active_participation is yes. If all these conditions are true, it prints the message “This student is ideal.” However, if any of the conditions are not met, it prints “This student is not ideal.”

Using the Bash Logical AND (&&) Among Three ConditionsAs 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.

4. 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.

To use the logical “&” operator with the While loop, see the code given below:

#!/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
EXPLANATION

This Bash script starts by initializing a counter, which counts from 1 up to a specified number n1 obtained from user input. It employs a while loop to continue executing as long as the counter is less than or equal to n1.

Within the loop, it checks whether the counter is both even and divisible by 3. If both conditions are met, it prints “$counter is even and divisible by 3.” If not, it prints “$counter is not even and not divisible by 3.” This code helps identify numbers within the specified range that meet these criteria. The counter is then incremented with each iteration of the loop until it exceeds the user-defined n1, at which point the loop terminates.

 Bash AND (&&) Operator in While Loop ExpressionAs 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.

Conclusion

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.

People Also Ask

What is the difference between && and || in bash script?

&& is the logical AND operator, which executes the second command only if the first command succeeds. || is the logical OR operator, which executes the second command only if the first command fails (returns a non-zero exit status).

What does 2>&1 do in bash?

2>&1 in Bash redirects the standard error (file descriptor 2) to the same location as the standard output (file descriptor 1). It combines error output with standard output, so both standard output and standard error messages are displayed in the same place.

Why is bash better than CMD?

Bash is more powerful and versatile than CMD due to its extensive command-line capabilities, support for scripting, and compatibility with Unix-based systems.

What is the difference between $() and () in Bash?

$() is used for command substitution. It captures the output of a command and assigns it to a variable or uses it in another command. () creates a subshell, where commands run in a separate shell environment. It’s often used for grouping commands or running commands in a subshell without affecting the parent shell.


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Mohammad Shah Miran

Hey, I'm Mohammad Shah Miran, previously worked as a VBA and Excel Content Developer at SOFTEKO, and for now working as a Linux Content Developer Executive in LinuxSimply Project. I completed my graduation from Bangladesh University of Engineering and Technology (BUET). As a part of my job, i communicate with Linux operating system, without letting the GUI to intervene and try to pass it to our audience.

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