Bash While Loop

Bash While Loop is a loop statement used to execute a block of statements repeatedly based on the boolean result of an expression, for as long as the expression evaluates to TRUE.

Syntax – Bash While Loop

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while [ expression ]; do
	statement(s)
done

The expression can contain only one condition. If the expression should have multiple conditions, the syntax of while loop is as follows :

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while [[ expression ]]; do
	statement(s)
done

Example 1 – Bash While Loop

In this example, we are using while loop to execute a block of statements 10 times, and we print the iteration number in the while body.

Bash Script File

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#!/bin/bash

count=10
i=0

# while loop
while [ $i -lt $count ]; do
   echo "$i"
   let i++
done

When the above while loop script is run in terminal, we will get the following output.

Output

$ ./bash-while-loop-example 
0
1
2
3
4
5
6
7
8
9

Example 2 – Bash While Loop – Multiple Conditions

In this example, we will write while loop with a compound condition consisting of simple conditions. The simple conditions are joined by Logical Operators.

Bash Script File

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#!/bin/bash

count=10
a=0
b=0

# multiple conditions in the expression of while loop
while [[ $a -lt $count && $b -lt 4 ]]; do
   echo "$a"
   let a++
   let b++
done

Run the above while loop script in terminal, and we shall get the following output.

Output

$ ./bash-while-loop-example 
0
1
2
3

We can also use Bash For loop for looping.

Conclusion

In this Bash Tutorial – Bash While Loop, we have learnt about syntax of while loop statement in bash scripting for single and multiple conditions in expression with example scripts.