Pro Bash programming : scripting the GNU/Linux shell

Considering the critical role Bash has in the installation and operation of Linux distributions and thereby its ubiquity, Bash as a programming language is frequently overlooked by programmers. The author of Pro Bash Programming has done a creditable job in providing the wherewithal for everyone from beginners to expert shell programmers to write more powerful and efficient scripts using Bash, as he takes you through a fast paced coverage of bash's capabilities. Along the way, many useful, well explained and commented practical scripts are provided, many of which can be used to build and test your own scripts. The author claims that while he used to use C when he needed extra speed, that was several years ago and he now does everything in the shell. This book shows how.The 230 page book is divided into the 15 chapters below, with each chapter ending with a summary of the commands covered and some well chosen exercises. 1 Hello, World! Your first Shell Program - how to create and run a script and establish good scripting habits 2 Input, Output and Throughput - echo, printf, read and IO streams 3 Looping and Branching - tests, conditional execution, looping constructs 4 Command-Line Parsing and Expansion - quoting, brace, tilde, parameter, variable arithmetic and pathname expansion, command and process substitution, word splitting and parsing with getops 5 Parameters and Variables - variable scope (essential reading), positional parameters and expansion using patterns, arrays - indexed and associative 6 Shell Functions - how to define, use and set exit codes, use of compound commands, creation and use of function libraries 7 String Manipulation - concatenation, processing character by character, case conversion, inserting, overlaying and trimming strings 8 File Operations and Commands - reading, use of external commands, regular expressions with grep, sed and awk, file name expansion options 9 Reserved Words and Builtin Commands - good coverage of builtin commands, particularly read (including into arrays) plus a very informative section on how to use builtin commands correctly 10 Writing Bug-Free Scripts and Debugging the Rest - good scripting programming recommendations for bug free code plus a test and debug example 11 Programming for the Command Line - manipulating the directory stack, filesystem and miscellaneous functions, managing man pages, games! 12 Runtime Configuration - command line options and arguments, menus, configuration files, scripts with several names, using environment variables 13 Data Processing - sorting and searching arrays, various ways of reading arrays into memory, grids (string and two dimensional), data file formats 14 Scripting the Screen - using the screen as a blackboard or canvas, rendition modes and colours, text scrolling - rolling dice example 15 Entry-Level Programming - single key entry, use of author's key-funcs library, sanity checking, form entry, reading the mouse!Appendix: Shell Variables - alphabetic listing of (1) variables set by bash and (2) variables used by bashOne of the strengths of this book is that the author explains the fastest way to accomplish many standard programming tasks through the appropriate choice of one of the many different bash methods available, including the choice between builtin bash commands and external commands. I found chapter 9 particularly interesting here. Chapter 7 shows how effective bash is at string manipulation with the right techniques - amazing! While the book covers bash 4.0 and often uses non POSIX extensions, those unable to use bash 4.0 or constrained to POSIX compliant code are not forgotten, with the author providing alternatives that work within these constraints.Where a subject is introduced in an early chapter and expanded on later, the author thoughtfully provides the forward reference. Source code for the included scripts is available from the publisher's webpage for this book at [...]The 10 page index works reasonably well, but you may find it worthwhile grabbing the companion eBook so you can directly search through the book to make the best use of it as a reference source. If you buy the dead tree version, the eBook is available on-line for $10 until April 2010 direct from the publisher.I can recommend this book to anyone that can benefit from automating repetitive shell based tasks in Linux but isn't sure how best to go about it. The included scripts and wealth of tips on how to avoid common bash coding problems will provide you with a quick return on your investment. Neil Matthews

The bash shell is a complete programming language, not merely a glue to combine external Linux commands. By taking full advantage of shell internals, shell programs can perform as snappily as utilities written in C or other compiled languages. And you will see how, without assuming Unix lore, you can write professional bash 4.0 programs through standard programming techniques.

• Complete bash coverage
• Teaches bash as a programming language
• Helps you master bash 4.0 features

What you’ll learn

• Use the shell to write new utilities and accomplish most programming tasks.
• Use shell parameter expansion to replace many external commands, making scripts very fast.
• Learn to avoid many common mistakes that cause scripts to fail.
• Learn how bash’s readline and history libraries can save typing when getting user input.
• Learn to use features new to bash 4.0.
• Build shell scripts that get information from the Web.

Who this book is for

Beginning Linux and Unix system administrators who want to be in full command of their systems.

Table of Contents

1. Hello, World! Your First Shell Program
2. Input, Output, and Throughput
3. Looping and Branching
4. Command-Line Parsing and Expansion
5. Parameters and Variables
6. Shell Functions
7. String Manipulation
8. File Operations and Commands
9. Reserved Words and Builtin Commands
10. Writing Bug-Free Scripts and Debugging the Rest
11. Programming for the Command Line
12. Runtime Configuration
13. Data Processing
14. Scripting the Screen
15. Entry-Level Programming

The shell is a programming language. Don’t let anyone tell you otherwise. The shell is not just glue that sticks bits together. The shell is a lot more than a tool that runs other tools. The shell is a complete programming language!When a Linux user asked me about membership databases, I asked him what he really needed. He wanted to store names and addresses for a couple of hundred members and print mailing labels for each of them. I recommended using a text editor to store the information in a text file, and I provided a shell script to create the labels in PostScript. (The script, ps-labels, appeared in my first book, Shell Scripting Recipes: A Problem-Solution Approach.) When the SWEN worm was dumping hundreds of megabytes of junk into my mailbox every few minutes, I wrote a shell script to filter them out on the mail server and download the remaining mail to my home computer. That script has been doing its job for several years. I used to tell people that I did most of my programming in the shell but switched to C for anything that needed the extra speed. It has been several years since I have needed to use C, so I no longer mention it. I do everything in the shell. A shell script is as much a program as anything written in C, Python, or any other language. Just because shell scripts are easier to write doesn’t mean they should take a backseat to compiled programs or other scripting languages. I use the terms script and program interchangeably when referring to tasks written in the shell. Front Cover......Page 1 About the Author......Page 17 About the Technical Reviewer......Page 18 Introduction......Page 20 Scripting the Screen......Page 202 Entry-Level Programming......Page 214 Contents at a Glance......Page 4 Contents......Page 6 ■Chapter 1: Hello, World! Your First Shell Program 1......Page 24 ■Chapter 2: Input, Output, and Throughput 7......Page 30 ■Chapter 3: Looping and Branching 19......Page 42 ■Chapter 4: Command-Line Parsing and Expansion 29......Page 52 ■Chapter 5: Parameters and Variables 43......Page 66 ■Chapter 6: Shell Functions 59......Page 82 ■Chapter 7: String Manipulation 67......Page 90 ■Chapter 9: Reserved Words and Builtin Commands 97......Page 10 ■Chapter 11: Programming for the Command Line 125......Page 11 ■Chapter 12: Runtime Configuration 141......Page 12 ■Chapter 15: Entry-Level Programming 191......Page 13 Shell Variables......Page 228 A......Page 244 C......Page 245 D......Page 246 E......Page 247 I......Page 248 N......Page 249 Q......Page 250 S......Page 251 T......Page 252 XYZ......Page 253