Bash Scripting: Nested if statement

An if statement in a Bash script is the most basic way to use a conditional statement.

In simple terms, these conditional statements define “if a condition is true, then do that, otherwise do this instead.” The if statements become more complex when you nest them together, or in other words put one if statement inside of another if statement. You can make the nest as deep as you want, though it will continue to grow in complexity.

In this tutorial, you will learn how to use nested if statements in a Bash script on a Linux system. Check some of the examples below to see how nested if statements work.

In this tutorial you will learn:

• How to structure a nested if statement in a Bash script
• Real example of nested if statements to try on your own system

Software Requirements and Linux Command Line Conventions

Category	Requirements, Conventions or Software Version Used
System	Any Linux distro
Software	Bash shell (installed by default)
Other	Privileged access to your Linux system as root or via the sudo command.
Conventions	# – requires given linux commands to be executed with root privileges either directly as a root user or by use of sudo command $ – requires given linux commands to be executed as a regular non-privileged user

Structure of a nested if statement

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First, let’s go over how a nested if statement is structured in a Bash script. This will familiarize you with the syntax so you can easily interpret the coming examples, and eventually write your own from scratch.

#!/bin/bash

if EXPRESSION1; then
    STATEMENT1
	
    if EXPRESSION2; then
        STATEMENT2
	fi

fi

This is the most basic form of a nested if statement. Let’s go over what is happening here:

• The first if statement checks if an expression is true. If it is, it proceeds with the first statement.
• After the first statement, the script then checks if yet another expression is true. If it is, it proceeds with the second statement.
• But if the condition is not matched for the second if statement, only the first statement is executed and then the script escapes from the entire nested if.
• If the first expression does not match, then there is no chance of entering into the nested if statement to check for the second condition or any other subsequent conditions.
• Remember that the second if statement needs to be terminated before the first one, since it is nested

If any of this does not make sense at first, do not worry. Looking at the example below will help you visualize the process better.

Bash Scripting: Nested if statement example

Check out the example below to see how to use nested if statements within a Bash script.

The script below will first check to see if it is a weekday (Mon-Fri). If it is, it will then check to see if it is morning or night time (AM or PM). But, if the first if statement is not met because it is the weekend (Sat or Sun), then the second if statement will not get executed at all.

#!/bin/bash

# Determine the day of week and store it inside the $day variable
day=$(date +"%u")
# Determine if it is morning or night and store it in the $time variable
time=$(date +"%p")

# Check if the day of the week is between 1-5 (Mon-Fri)
if [ $day -le 5 ]; then
        # if it is a weekday, echo the text below
        echo "today is a weekday"
        # now determine if it is morning or night time
        if [ $time == "AM" ]; then
                echo "it is morning"
        else
                echo "it is night"
        fi
else
        # if the first condition was not met, execute the following command
        echo "today is the weekend!"
fi

Here is the output when we execute the script:

$ date
Fri 25 Feb 2022 09:55:14 PM EST

$ ./test.sh 
today is a weekday
it is night

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The point of a nested if is that the second if statement is only used if the first if statement is true. In this case, our script only checks the time of day if it first determined that the day of the week is Mon-Fri. We have left comments in the script to make this easier to digest.

Closing Thoughts

In this tutorial, you learned how to use a nested if statement in Bash scripting on a Linux system. This type of conditional statement has a niche use, since usually it is better to use case statements. If your nest is only two if statements deep, then this it is usually easy to maintain and understand what is going on, as we showed in the example here.