Conditional evaluation

Like variables, conditional evaluation is one of the key concepts you'll come across in programming. It is used to execute a certain action based on matched conditions.

Bash gives you four conditional keywords if, elif, else and fi.

1. Conditional evaluations must start with an if and end with an fi

2. Conditional evaluations can contain zero or more elif

3. The base case or the fallback should be handled by in an else statement

Consider the following example, we will read the input from the user and check if it is a rainbow color.

#!/bin/bash

echo "Please input a color of the rainbow"
read color

if [ "$color" = "red" ]; then
    echo "Awesome! I love Red!"
elif [ "$color" = "orange" ]; then
    echo "Bright and cheerful! Orange is great!"
elif [ "$color" = "yellow" ]; then
    echo "Sunny! Yellow is wonderful!"
elif [ "$color" = "green" ]; then
    echo "So fresh! Green is amazing!"
elif [ "$color" = "blue" ]; then
    echo "Cool choice! Blue is calming!"
elif [ "$color" = "indigo" ]; then
    echo "Unique and deep! Indigo is awesome!"
elif [ "$color" = "violet" ]; then
    echo "Elegant! Violet is beautiful!"
else
    echo "Hmm, that doesn't seem to be a color of the rainbow!"
fi

Consider Another example

If my name is "adeoye", print "Hello boss you are welcome!", if not, print "oops! I'm not sure I know you"

#!/bin/bash 

echo "Hello What is your name"

read name 

if [  $name = 'adeoye' ]; then
    echo "Hello boss you are welcome!"
else 
    echo "Oops! I'm not sure I know you"
fi