For system administrators, programmers, and end users, shell command or carefully crafted shell script can save you time and effort, or facilitate consistency and repeatability for a variety of common tasks. This cookbook provides more than 300 practical recipes for using bash, the popular Unix shell that enables you to harness and customize the power of any Unix or Linux system.
 

Ideal for new and experienced users alike—including proficient Windows users and sysadmins—this updated second edition helps you solve a wide range of problems. You’ll learn ways to handle input/output, file manipulation, program execution, administrative tasks, and many other challenges. Each recipe includes one or more scripting examples and a discussion of why the solution works.
 

You’ll find recipes for problems including:

• •  Standard output and input, and executing commands
• •  Shell variables, shell logic, and arithmetic
• •  Intermediate shell tools and advanced scripting
• •  Searching for files with find, locate, and slocate
• •  Working with dates and times
• •  Creating shell scripts for various end-user tasks
• •  Working with tasks that require parsing
• •  Writing secure shell scripts
• •  Configuring and customizing bash
  
  Every modern operating system has at least one shell, and some have many. Some shells are command line–oriented, such as the shell discussed in this book. Others are graphical, like Windows Explorer or the Macintosh Finder. Some users will interact with the shell only long enough to launch their favorite application, and then never emerge from that until they log off. But most users spend a significant amount of time using the shell. The more you know about your shell, the faster and more productive you can be.
   

Whether you are a system administrator, a programmer, or an end user, there are certainly occasions where a simple (or perhaps not so simple) shell script can save you time and effort, or facilitate consistency and repeatability for some important task. Even using an alias to change or shorten the name of a command you use often can have a significant effect. We’ll cover this and much more.

About This Book

This book covers bash, the GNU Bourne Again Shell, which is a member of the family of shells that includes the original Bourne shell, sh, the Korn shell, ksh, and the public domain Korn shell, pdksh. While these and other shells such as dash and zsh are not specifically covered, odds are that most of the scripts will work pretty well with them.
 

You should be able to read this book cover to cover, and also just pick it up and read anything that catches your eye. But perhaps most importantly, we hope that when you have a question about how to do something or you need a hint, you will be able to easily find the right answer—or something close enough—and save time and effort.
 

A great part of the Unix philosophy is to build simple tools that do one thing well, then combine them as needed. This combination of tools is often accomplished via a shell script because these commands, called pipelines, can be long or difficult to remember and type. Where appropriate, we’ll cover the use of many of these tools in the context of the shell script as the glue that holds the pieces together to achieve the goal.

Ideal readers include:

• •  New Unix or Linux users who don’t know much about the shell, but want to do more than point and click
• •  Experienced Unix or Linux users and system administrators looking for quick answers to shell scripting questions
• •  Programmers who work in a Unix or Linux (or even Windows) environment and want to be more productive
• •  New Unix or Linux sysadmins, or those coming from a Windows environment who need to come up to speed quickly
• •  Experienced Windows users and sysadmins who want a more powerful scripting environment

Who Should Read This Book

This book is for anyone who uses a Unix or Linux system, as well as system administrators who may use several systems on any given day. With it, you will be able to create scripts that allow you to accomplish more, in less time, more easily, consistently, and repeatably than ever before.

Anyone? Yes. New users will appreciate the sections on automating repetitive tasks, making simple substitutions, and customizing their environment to be more friendly and perhaps behave in more familiar ways. Power users and administrators will find new and different solutions to common tasks and challenges. Advanced users will have a collection of techniques they can use at a moment’s notice to put out the latest fire, without having to remember every little detail of syntax.
 

This book assumes you have access to a Unix or Linux system (or see Recipes 1.14 through 1.18, or Recipe 15.4) and are familiar with logging in, typing basic commands, and using a text editor. You do not have to be root to use the vast majority of the recipes, though there are a few, particularly dealing with installing bash, where root access will be needed.

For the second edition, we’ve switched to Asciidoc and Git on O’Reilly’s Atlas system, which worked very well.

About the Author

Carl Albing is currently a Distinguished Visiting Professor in the Department of Computer Science at the U.S. Naval Academy where he is teaching courses on programming languages and on High Performance Computing. Prior to this he was writing software for some of the biggest and fastest computers in the world as a software engineer for Cray, Inc. As an independent consultant, he is comfortable programming with C, Java, bash and much more. Carl is the coauthor of two books, one on Java development on Linux and his latest, the O'Reilly "bash Cookbook". A former software consultant, manager, analyst and programmer with an amazing breadth of software experience, Carl has worked with companies in the US, Canada and Europe. He has worked for large companies and small startups, in technical as well as in managerial and marketing roles. Carl's software projects, past and present, involve the design and development of distributed computing software, medical image processing applications, compilers, medical devices, web-based factory floor automation, and more. Carl's education includes a Ph.D. in Computer Science as well as a B.A. degree in Mathematics and an International MBA. He has spoken at conferences and training seminars in the US, Canada and Europe as well as local high schools and colleges. Carl enjoys speaking at user groups and seminars on Linux, C, Java, and bash topics.

JP Vossen has been working with computers since the early 80s and has been in the IT industry since the early 90s, specializing in Information Security since the late 90s. He's been fascinated with scripting and automation since he first understood what an autoexec.bat was, and was delighted to discover the power and flexibility of bash and GNU on Linux in the mid-90s. He has previously written for Information Security Magazine and SearchSecurity.com, among others. On those few occasion when he's not in front of a computer, he is usually taking something apart, putting something together, or both.