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Bash Quick Start Guide

By : Tom Ryder

5 (2)

Buy this Book

Bash Quick Start Guide

5 (2)

By: Tom Ryder

Buy this Book

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.

Preface

Who this book is for

What this book covers

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Free Chapter

What is Bash?

What Bash is and is not

Getting Bash

Checking Bash is running

Identifying the Bash version number

Upgrading Bash on macOS X

Understanding Bash features

Choosing when to apply Bash

Choosing when to avoid Bash

Getting help with Bash

Summary

Bash Command Structure

Using Bash interactively

Interactive key bindings

Simple commands

Shell metacharacters

Quoting

Running commands in sequence

Exit values

Stopping a command list on error

Running a command in the background

Summary

Essential Commands

Distinguishing command types

Essential Bash builtin commands

Essential system commands

Summary

Input, Output, and Redirection

Redirecting output

Redirecting errors

Redirecting input

Using pipes

Summary

Variables and Patterns

Using variables

Using globs

Using arrays

Summary

Loops and Conditionals

Using the if keyword

Switching with the case keyword

Looping over shell words with for

Using Bash's C-style for loops

Using while loops

Summary

Scripts, Functions, and Aliases

Aliases

Functions

Scripts

Choosing between functions and scripts

Using functions in scripts

Summary

Best Practices

Quoting correctly

Handling filenames starting with dashes

Separating output and diagnostics

Keeping scripts brief and simple

Keeping scripts flexible

Respecting and applying the user's configuration

Allowing scripts to run without user input

Limiting the scope of shell state changes

Avoiding path anti-patterns

Avoiding Bash for untrusted user input

Documenting scripts

Using temporary files cleanly

Cleaning up after a script

Tools to check shell scripts for problems

Summary

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Using temporary files cleanly

If you need a temporary file in your script to store data for the script's run, it can be tempting to assume a fixed path for the file in /tmp:

# Store the current date for later
# Requires GNU/BSD `date` with non-POSIX %s format
date +%s > /tmp/myscript-timestamp

/tmp exists on virtually all Unix systems, which makes it a popular choice. However, this approach has some risks:

There may be a safer or more suitable location for temporary files specified by the system, or preferred by the user, such as /var/tmp. The /tmp directory might be very strictly locked down in some environments, especially PCI-DSS-compliant systems.
If the temporary filename name is not unique, and more than one instance of the script runs at once, the behavior can be unpredictable and hard to debug.
Because /tmp is world-writable, if an attacker can write to and predict...