Bash Scripting – Else If Statement

When working with Bash and shell scripting, you might need to use conditions in your script. In programming, conditions are crucial: they are used to assert whether some conditions are true or not.

In this article, we will learn one of the conditional statements that is if, elseif, else along with a few examples. In several other languages, the elif is written as “elseif” or “else if”. The elif statement helps us to make decisions among different choices.

It's crucial that you comprehend the fundamentals of BASH logical operators before you begin. Just look over the list below:

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Bash If Else Statement

In order to execute a Bash “if else” statement, you have to use four different keywords: if, then, else:

• if : represents the condition that you want to check;

• then : if the previous condition is true, then execute a specific command;

• else : if the previous condition is false, then execute another command (note that the “ELSE” statement is optional, if you omit it, nothing will be executed if the condition evaluates to false.)

• fi : closes the “if, then, else” statement.

When using the “if else” statement, you will need to enclose conditions in single or double squared brackets.

if [[ condition ]]
then
  <execute command>
else
  <execute another command>
fi

if Statement

Bash if conditionals can have different forms. The most basic if statement takes the following form:

if TEST-COMMAND
then
  STATEMENTS
fi

The if statement starts with the if keyword followed by the conditional expression and the then keyword. The statement ends with the fi keyword. If the TEST-COMMAND evaluates to True, the STATEMENTS get executed. If TEST-COMMAND returns False, nothing happens; the STATEMENTS get ignored.

Let’s look at the following example script that checks whether a given number is greater than 100:

#!/bin/bash

echo -n "Enter a number: "
read VAR

if [[ $VAR -gt 100 ]]
then
  echo "The variable is greater than 100."
fi

if..else Statement

The Bash if..else statement takes the following form:

if TEST-COMMAND
then
  STATEMENTS1
else
  STATEMENTS2
fi

If the TEST-COMMAND evaluates to True, the STATEMENTS1 will be executed. Otherwise, if TEST-COMMAND returns False, the STATEMENTS2 will be executed. You can have only one else clause in the statement.

Let’s add an else clause to the previous example script:

#!/bin/bash

read -p "Enter a number: " NUM
echo

if [ $NUM -gt 100 ]
then
   echo "We have entered in IF block."
   sleep 3
   echo "Your Number is greater than 100"
   echo
   date
else
  echo "You have entered number less than 100."
fi

echo "Script execution completed successfully."

If you run the code and enter a number, the script will print a different message based on whether the number is greater or less/equal to 100.

ELIF (ELSE IF) statement

ELIF is the keyword used for the ELSE IF statement in bash scripting. If in a loop if more than two conditions exist which can not be solved only by using IF-ELSE statement then ELIF is used. Multiple ELIF conditions can be defined inside one if-else loop.

if [ condition1 ]
then
       statement1
 elif [ condition2 ]
then
       statement2
 elif [condition3 ]
then
       statement3
else
      statement_n
fi

Example:

Let’s add an elif clause to the previous script:

#!/bin/bash
echo -n "Enter a number: "
read VAR
if [ $VAR -gt 10 ]
then  
echo "The variable is greater than 10."
elif [ $VAR -eq 10 ]
then  
echo "The variable is equal to 10."
else  
echo "The variable is less than 10."
fi

We will count the number of network interfaces here:

#!/bin/bash

value=$(ip addr show | grep -v LOOPBACK | grep -ic mtu)

if [ $value -eq 1 ]
then
  echo "1 Active Network Interface found."
elif [ $value -gt 1 ]
then
  echo "Found Multiple active Interface."
else
  echo "No Active interface found."
fi