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.

Preface

Who this book is for

What this book covers

To get the most out of this book

Free Chapter

What is Bash?

What Bash is and is not

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

Bash Command Structure

Bash Command Structure

Using Bash interactively

Interactive key bindings

Simple commands

Shell metacharacters

Running commands in sequence

Stopping a command list on error

Running a command in the background

Essential Commands

Essential Commands

Distinguishing command types

Essential Bash builtin commands

Essential system commands

Input, Output, and Redirection

Input, Output, and Redirection

Redirecting output

Redirecting errors

Redirecting input

Variables and Patterns

Variables and Patterns

Using variables

Loops and Conditionals

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

Scripts, Functions, and Aliases

Scripts, Functions, and Aliases

Choosing between functions and scripts

Using functions in scripts

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

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Upgrading Bash on macOS X

There is a special case of Bash versions for macOS X. If you are using Bash on OS X, you might notice that the version of Bash installed by default is much older than the minimum of 4.0 discussed in this book:

bash$ declare -p BASH_VERSION
declare -- BASH_VERSION="3.2.57(1)-release"

This is due to licensing changes in Bash 4.0 that were not acceptable to the operating system vendor, which leaves the version of Bash included on the system stuck at the last acceptable version. This means that, by default, your system may not have Bash 4.0 or newer, even if the system is brand new.

Fortunately, there are other ways to install Bash 4.0 or newer on a macOS X computer. One popular method is to use the Homebrew package-management system, available here: http://brew.sh/.

Follow the instructions on the Homebrew website to install it. You can then install a new version of Bash with:

$ brew install bash

You may have to include the newly-installed Bash path in the allowed list of login shells in /etc/shells before you can apply chsh to change your login shell. You may also have to adjust your terminal emulator (e.g. iTerm) to run the new version of Bash. Consult your operating system and terminal emulator documentation to learn how to do this.