Shell if-elif-else Statement

Syntax

if [ expression 1 ]
then
   Statement(s) to be executed if expression 1 is true
elif [ expression 2 ]
then
   Statement(s) to be executed if expression 2 is true
elif [ expression 3 ]
then
   Statement(s) to be executed if expression 3 is true
else
   Statement(s) to be executed if no expression is true
fi

Example

#!/bin/sh

a=10
b=20

if [ $a == $b ]
then
   echo "a is equal to b"
elif [ $a -gt $b ]
then
   echo "a is greater than b"
elif [ $a -lt $b ]
then
   echo "a is less than b"
else
   echo "None of the condition met"
fi

Taking input from the user

!/bin/bash

read -p “Enter value of i :” i
if [ $i -eq 5 ]
then
echo “Value of i is 5”
elif [ $i -eq 10 ]
then
echo “Value of i is 10”
else
echo “Value of i is not equal to 5 or 10”
fi

Taking Input in Command Line $1 is the first argument. To run ./script 5

!/bin/bash

i=$1
if [ $i -eq 5 ]
then
echo “Value of i is 5”
elif [ $i -eq 10 ]
then
echo “Value of i is 10”
else
echo “Value of i is not equal to 5 or 10”
fi