Working with the do – while loop

Similar to the for command, while is also the command for loop operations. The command next to while is evaluated. If it is successful or 0, then the commands inside do and done are executed.

The purpose of a loop is to test a certain condition or expression and execute a given command while the condition is true (the while loop) or until the condition becomes true (the until loop):

while condition do commands done	until condition do commands done

The following is the while_01.sh script in which we read a file and display its
content:

#!/bin/bash 
file=/etc/resolv.conf 
while IFS= read -r line    # IFS : inter field separator 
do 
   # echo line is stored in $line 
  echo $line 
done < "$file" 

Let's test the program:

    $ chmod +x while_01.sh
    $ ./while_01.sh
  

The following will be the output after executing...