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)

Limiting the scope of shell state changes

If you are going to change properties of the shell as a whole in part of your script, consider limiting the scope of that change only to the needed part of the script to avoid unexpected effects on the rest of it. Watch for these in particular:

  • The working directory
  • The positional parameters ($1, $2 ... )
  • Environment variables, especially PATH
  • Shell-local variables, especially IFS
  • Shell options with set (such as -x) or shopt (such as dotglob)
  • Shell resource limits set with ulimit

We already saw one effective means of limiting the scope of variables in Chapter 5, Variables and Patterns, by applying them as prefixes to a command:

IFS=: read -r name address

This limits the scope of the IFS change to the read command only.

For other types of shell state change, we have to get a bit more creative:

  • Keeping the script itself so short that...