Bash Quick Start Guide

Using while loops

The while loop runs a command repeatedly, running the commands in the body of the loop each time the test command succeeds, and terminating the loop as soon as the command fails.

We could write the loop that prints the numbers from 1 to 10 that we implemented with for in the previous section like so:

#!/bin/bash
((i = 1))
while ((i < 10)) ; do
    printf '%u\n' "$i"
    ((i++))
done

Note the similarity to the C-style for loop here, with the difference that the first expression, i = 1, and the third expression, i++, have been moved out into separate statements.

A while loop also behaves much like a for loop in terms of flow control: an iteration of the loop can be skipped with continue, and the whole loop can be terminated with ...