Working with WHILE Loop in Bash Shell Scripting

Similar to for loop, while loop is also entry restricted loop. It means condition is checked before executing while loop. Mostly it also can do all the works which for loop can do but in uses it has own benefit of use in programming.

While Loop Example in Bash

For example following loop will be executed 10 times and exited when value of i will be greater than 10.

#!/bin/bash

i=1
while [ $i -le 10 ]
do
   echo "This is looping number $i"
   let i++
done

Infinite While Loop in Bash

Infinite for loops can be also known as never ending loop. The following loop will execute continuously until stopped forcefully using CTRL+C.

#!/bin/bash

while true
do
  echo "Press CTRL+C to Exit"
done

But we can conditional statement like if to terminate loop on matching any specific condition. Read more about working with if-else in bash scripting.

#!/bin/bash

while true
do
   if [ condition ];do
      exit
   fi
done

C-Style while Loop

In bash script we can also write while loops pretty similar to c programming language.

#!/bin/bash

i=1
while((i <= 10))
do
   echo $i
   let i++
done

Reading File Content using While Loop

While also provide option’s to read file content line by line, which is an very useful uses of while loop while working with files.

#!/bin/bash

while read i
do
   echo $i
done < /tmp/filename.txt

In this while loop read one line from file in one loop iteration and store value in variable i.