An essential skill for Unix users and system administrators, shell scripts let you easily crunch data and automate repetitive tasks, offering a way to quickly harness the full power of any Unix system. This book provides the tips, tricks, and organized knowledge you need to create excellent scripts, as well as warnings of the traps that can turn your best efforts into bad shell scripts.
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Copyright
Foreword
Preface
Intended Audience
What You Should Already Know
Chapter Summary
Conventions Used in This Book
Code Examples
Unix Tools for Windows Systems
Safari Enabled
We d Like to Hear from You
Acknowledgments
Chapter 1. Background
Section 1.1. Unix History
Section 1.2. Software Tools Principles
Section 1.3. Summary
Chapter 2. Getting Started
Section 2.1. Scripting Languages Versus Compiled Languages
Section 2.2. Why Use a Shell Script?
Section 2.3. A Simple Script
Section 2.4. Self-Contained Scripts: The #! First Line
Section 2.5. Basic Shell Constructs
Section 2.6. Accessing Shell Script Arguments
Section 2.7. Simple Execution Tracing
Section 2.8. Internationalization and Localization
Section 2.9. Summary
Chapter 3. Searching and Substitutions
Section 3.1. Searching for Text
Section 3.2. Regular Expressions
Section 3.3. Working with Fields
Section 3.4. Summary
Chapter 4. Text Processing Tools
Section 4.1. Sorting Text
Section 4.2. Removing Duplicates
Section 4.3. Reformatting Paragraphs
Section 4.4. Counting Lines, Words, and Characters
Section 4.5. Printing
Section 4.6. Extracting the First and Last Lines
Section 4.7. Summary
Chapter 5. Pipelines Can Do Amazing Things
Section 5.1. Extracting Data from Structured Text Files
Section 5.2. Structured Data for the Web
Section 5.3. Cheating at Word Puzzles
Section 5.4. Word Lists
Section 5.5. Tag Lists
Section 5.6. Summary
Chapter 6. Variables, Making Decisions, and Repeating Actions
Section 6.1. Variables and Arithmetic
Section 6.2. Exit Statuses
Section 6.3. The case Statement
Section 6.4. Looping
Section 6.5. Functions
Section 6.6. Summary
Chapter 7. Input and Output, Files, and Command Evaluation
Section 7.1. Standard Input, Output, and Error
Section 7.2. Reading Lines with read
Section 7.3. More About Redirections
Section 7.4. The Full Story on printf
Section 7.5. Tilde Expansion and Wildcards
Section 7.6. Command Substitution
Section 7.7. Quoting
Section 7.8. Evaluation Order and eval
Section 7.9. Built-in Commands
Section 7.10. Summary
Chapter 8. Production Scripts
Section 8.1. Path Searching
Section 8.2. Automating Software Builds
Section 8.3. Summary
Chapter 9. Enough awk to Be Dangerous
Section 9.1. The awk Command Line
Section 9.2. The awk Programming Model
Section 9.3. Program Elements
Section 9.4. Records and Fields
Section 9.5. Patterns and Actions
Section 9.6. One-Line Programs in awk
Section 9.7. Statements
Section 9.8. User-Defined Functions
Section 9.9. String Functions
Section 9.10. Numeric Functions
Section 9.11. Summary
Chapter 10. Working with Files
Section 10.1. Listing Files
Section 10.2. Updating Modification Times with touch
Section 10.3. Creating and Using Temporary Files
Section 10.4. Finding Files
Section 10.5. Running Commands: xargs
Section 10.6. Filesystem Space Information
Section 10.7. Comparing Files
Section 10.8. Summary
Chapter 11. Extended Example: Merging User Databases
Section 11.1. The Problem
Section 11.2. The Password Files
Section 11.3. Merging Password Files
Section 11.4. Changing File Ownership
Section 11.5. Other Real-World Issues
Section 11.6. Summary
Chapter 12. Spellchecking
Section 12.1. The spell Program
Section 12.2. The Original Unix Spellchecking Prototype
Section 12.3. Improving ispell and aspell
Section 12.4. A Spellchecker in awk
Section 12.5. Summary
Chapter 13. Processes
Section 13.1. Process Creation
Section 13.2. Process Listing
Section 13.3. Process Control and Deletion
Section 13.4. Process System-Call Tracing
Section 13.5. Process Accounting
Section 13.6. Delayed Scheduling of Processes
Section 13.7. The /proc Filesystem
Section 13.8. Summary
Chapter 14. Shell Portability Issues and Extensions
Section 14.1. Gotchas
Section 14.2. The bash shopt Command
Section 14.3. Common Extensions
Section 14.4. Download Information
Section 14.5. Other Extended Bourne-Style Shells
Section 14.6. Shell Versions
Section 14.7. Shell Initialization and Termination
Section 14.8. Summary
Chapter 15. Secure Shell Scripts: Getting Started
Section 15.1. Tips for Secure Shell Scripts
Section 15.2. Restricted Shell
Section 15.3. Trojan Horses
Section 15.4. Setuid Shell Scripts: A Bad Idea
Section 15.5. ksh93 and Privileged Mode
Section 15.6. Summary
Appendix A. Writing Manual Pages
Section A.1. Manual Pages for pathfind
Section A.2. Manual-Page Syntax Checking
Section A.3. Manual-Page Format Conversion
Section A.4. Manual-Page Installation
Appendix B. Files and Filesystems
Section B.1. What Is a File?
Section B.2. How Are Files Named?
Section B.3. What s in a Unix File?
Section B.4. The Unix Hierarchical Filesystem
Section B.5. How Big Can Unix Files Be?
Section B.6. Unix File Attributes
Section B.7. Unix File Ownership and Privacy Issues
Section B.8. Unix File Extension Conventions
Section B.9. Summary
Appendix C. Important Unix Commands
Section C.1. Shells and Built-in Commands
Section C.2. Text Manipulation
Section C.3. Files
Section C.4. Processes
Section C.5. Miscellaneous Programs
Chapter 16. Bibliography
Section 16.1. Unix Programmer s Manuals
Section 16.2. Programming with the Unix Mindset
Section 16.3. Awk and Shell
Section 16.4. Standards
Section 16.5. Security and Cryptography
Section 16.6. Unix Internals
Section 16.7. O Reilly Books
Section 16.8. Miscellaneous Books
Colophon
Index
The user or programmer new to Unix is suddenly faced with a bewildering variety of programs, each of which often has multiple options. Questions such as What purpose do they serve? and How do I use them? spring to mind.This book s job is to answer those questions. It teaches you how to combine the Unix tools, together with the standard shell, to get your job done. This is the art of shell scripting. Shell scripting requires not just a knowledge of the shell language, but also a knowledge of the individual Unix programs: why each one is there, and how to use them by themselves and in combination with the other programs.Why should you learn shell scripting? Because often, medium-size to large problems can be decomposed into smaller pieces, each of which is amenable to being solved with one of the Unix tools. A shell script, when done well, can often solve a problem in a mere fraction of the time it would take to solve the same problem using a conventional programming language such as C or C++. It is also possible to make shell scripts portable—i.e., usable across a range of Unix and POSIX-compliant systems, with little or no modification.
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