Book Image

Bash Quick Start Guide

By : Tom Ryder
Book Image

Bash Quick Start Guide

By: Tom Ryder

Overview of this book

Bash and shell script programming is central to using Linux, but it has many peculiar properties that are hard to understand and unfamiliar to many programmers, with a lot of misleading and even risky information online. Bash Quick Start Guide tackles these problems head on, and shows you the best practices of shell script programming. This book teaches effective shell script programming with Bash, and is ideal for people who may have used its command line but never really learned it in depth. This book will show you how even simple programming constructs in the shell can speed up and automate any kind of daily command-line work. For people who need to use the command line regularly in their daily work, this book provides practical advice for using the command-line shell beyond merely typing or copy-pasting commands into the shell. Readers will learn techniques suitable for automating processes and controlling processes, on both servers and workstations, whether for single command lines or long and complex scripts. The book even includes information on configuring your own shell environment to suit your workflow, and provides a running start for interpreting Bash scripts written by others.
Table of Contents (10 chapters)

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:

((i = 1))
while ((i < 10)) ; do
    printf '%u\n' "$i"

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 break.