How does the "do while" loop work in Bash?

The "do while" loop in Bash is a control flow statement that executes a block of code at least once and then repeats the execution as long as a specified condition is true. It's a post-test loop, meaning the condition is checked after the loop body is executed.

Here's a breakdown of how it works:

1. Execution of the Loop Body: The code block within the "do" section is executed first, regardless of the initial state of the condition.

2. Condition Evaluation: After the "do" block is executed, the "while" condition is evaluated. If the condition is true, the loop goes back to step 1 and executes the "do" block again. If the condition is false, the loop terminates, and the script continues with the next statement after the loop.

Syntax:

The basic syntax of a "do while" loop in Bash is:

do
   # Code to be executed
done while [ condition ]

Example:

Here's a simple example that prints numbers from 1 to 5 using a "do while" loop:

#!/bin/bash

counter=1

do
   echo "Counter: $counter"
   counter=$((counter + 1))
done while [ $counter -le 5 ]

In this example:

- The `counter` variable is initialized to 1.

- The loop first executes the commands inside the `do` block: printing the current value of `counter` and incrementing it by 1.

- After the `do` block, the `while` condition `[ $counter -le 5 ]` is checked. If `counter` is less than or equal to 5, the loop continues; otherwise, it terminates.

Key Characteristics:

- Guaranteed One Execution: The code inside the "do" block always executes at least once.

- Post-Test Loop: The condition is checked after the execution of the loop body.

- Condition Syntax: The condition is enclosed in square brackets `[]`, and it should be a valid Bash conditional expression (e.g., using `-le`, `-ge`, `-eq`, `-ne`, etc.).

The "do while" loop is useful when you need to ensure that a block of code runs at least once, regardless of the initial state of the condition. This is particularly helpful in scenarios where you need to prompt a user for input and then validate it, or when you need to perform an initial action before checking a condition.

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