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
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 :
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
#!/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
#!/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.