#! /bin/bash
number=1
while [ $number -le 15 ]; 
#if number is less than 15, loop will executed as below
do 
    echo "number is $number"
    number=$(( number + 4 ))
    #numnber will increase by 4, so 1,5,9,13
done
echo " bye "

## be careful!!!
## if the condition would never met example: 
## number =3 
## while [ $number -gt -5 ]; this condition was false from the beginning
## ctrl + c to exit