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)

Quoting correctly

It can't be over-emphasized how important it is to wrap expansions, such as $myvar, ${myvar[1]}, and ${myvar##*/}, in double quotes. Failing to do this will lead to bugs down the line when values contain characters that have special meaning to Bash, especially spaces. This is a common problem with code that has been cut and pasted from old documentation, or from bad advice posted on websites or in chat channels.

It only takes a few examples to realize how dangerous a failure to quote properly can be, especially in circumstances where files can be created by other users, and hence might include shell metacharacters. A file named *, for example, is legal, and if expanded incorrectly, can wreak havoc on your scripts:

$ cd ~/important
$ myfilename='*'
$ echo $myfilename
important-document  passwords-DO-NOT-DELETE  anniversary-plans
$ echo "$myfilename...