Ubuntu Unleashed 2013 Edition: Covering 12.10 and 13.04, Eighth Edition

The while Statement

You can use the while statement to execute a series of commands while a specified condition is true. The loop terminates as soon as the specified condition evaluates to false. It is possible that the loop will not execute at all if the specified condition initially evaluates to false. You should be careful with the while command because the loop never terminates if the specified condition never evaluates to false.

Endless Loops Have Their Place in Shell Programs

Endless loops can sometimes be useful. For example, you can easily construct a simple command that constantly monitors the 802.11b link quality of a network interface by using a few lines of script:

#!/bin/shwhile :  do   /sbin/iwconfig eth0 |  grep Link | tr '\n' ...