While Loop in Bash

Similar to the for loop, while loop is also entry restricted loop. It means the condition is checked before executing the while loop. While a loop is also capable of doing all the work a for loop can do.

Syntax:

while [condition]
do
  //programme to execute
done

1. Bash – While Loop Example

For example, the following loop will be executed 5 times and terminated when the value of variable num will be greater than 5.

Shell

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#!/bin/bash num=1 while [ $num -le 5 ] do    echo "$num"    let num++ done

2. Bash – Infinite While Loop

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

Shell

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#!/bin/bash while true do   echo "Press CTRL+C to Exit" done

You can also terminate this loop by adding some conditional exit in the script. So whenever the condition goes true, the loop will exit.

Shell

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#!/bin/bash while true do    if [condition];then       exit    fi done

3. Bash – C-Style While Loop

You can also write while loop in bash scripts similar to while loop c programming language.

Shell

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#!/bin/bash num=1 while((num <= 5)) do    echo $num    let num++ done

4. Bash – While Loop Read File Content

This is a useful feature provided by the while loop to read file content line by line. Using this we can read files line by line and perform some tasks.

Shell

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#!/bin/bash while read myvar do    echo $myvar done < /tmp/filename.txt

The while loop reads one line from the file in one iteration and assigns the value to the variable myvar.