Bash do-while

Introduction

In Bash scripting, the do-while loop is a control structure that executes a block of code repeatedly until a certain condition becomes false. It is similar to the while loop, but with a slight difference in the condition checking.

The do-while loop first executes the block of code, and then checks the condition. If the condition is true, the loop continues to execute. If the condition is false, the loop is terminated, and the program continues with the next statement after the loop.

Syntax

The general syntax of the do-while loop in Bash is as follows:

do
    # code block to be executed
done while [ condition ]

The do keyword marks the beginning of the loop, and the done keyword marks the end of the loop. The condition is checked after executing the code block.

Example

Let's see a simple example to understand how the do-while loop works:

#!/bin/bash

counter=1
sum=0

echo "Enter integers (enter 0 to terminate):"

# execute the code block at least once
while true; do
    read number

    # add the number to the sum
    ((sum+=number))

    # check if the number is 0 to terminate the loop
    if [ $number -eq 0 ]; then
        break
    fi
done

echo "Sum: $sum"

In this example, the program asks the user to enter integers. It continues to read and sum the numbers until the user enters 0. The while true condition ensures that the loop executes at least once.

Conclusion

The do-while loop in Bash is a useful control structure for repeating a set of commands until a specific condition is met. It guarantees the execution of the code block at least once. Understanding and utilizing this loop can help programmers write more robust and flexible Bash scripts.