For Unix users and system administrators, this book contains shell scripts that help the reader easily crunch data and automate repetitive tasks, offering a way to quickly harness the full power of any Unix system. It provides tips, tricks, and organized knowledge needed to create scripts, as well as warnings of the traps in shell scripts.

The ability to program and customize the shell quickly, reliably, and portably to get the best out of any individual system is an important skill for anyone operating and maintaining Unix or Linux systems. "Classic Shell Scripting" gives you everything you need to master these essential skills.

Foreword

Preface

1. Background


1.1 Unix History


1.2 Software Tools Principles


1.3 Summary

2. Getting Started
2.1 Scripting Languages Versus Compiled Languages


2.2 Why Use a Shell Script?


2.3 A Simple Script


2.4 Self-Contained Scripts: The #! First Line


2.5 Basic Shell Constructs


2.6 Accessing Shell Script Arguments


2.7 Simple Execution Tracing
2.8 Internationalization and Localization


2.9 Summary

3. Searching and Substitutions


3.1 Searching for Text


3.2 Regular Expressions


3.3 Working with Fields


3.4 Summary
4. Text Processing Tools


4.1 Sorting Text


4.2 Removing Duplicates


4.3 Reformatting Paragraphs


4.4 Counting Lines, Words, and Characters


4.5 Printing


4.6 Extracting the First and Last Lines


4.7 Summary

5. Pipelines Can Do Amazing Things
5.1 Extracting Data from Structured Text Files


5.2 Structured Data for the Web


5.3 Cheating at Word Puzzles


5.4 Word Lists
5.5 Tag Lists


5.6 Summary

6. Variables, Making Decisions, and Repeating Actions


6.1 Variables and Arithmetic


6.2 Exit Statuses


6.3 The case Statement


6.4 Looping


6.5 Functions


6.6 Summary

7. Input and Output, Files, and Command Evaluation


7.1 Standard Input, Output, and Error


7.2 Reading Lines with read


7.3 More About Redirections


7.4 The Full Story on printf


7.5 Tilde Expansion and Wildcards


7.6 Command Substitution


7.7 Quoting


7.8 Evaluation Order and eval


7.9 Built-in Commands


7.10 Summary

8. Production Scripts


8.1 Path Searching


8.2 Automating Software Builds
8.3 Summary

9. Enough awk to Be Dangerous


9.1 The awk Command Line


9.2 The awk Programming Model


9.3 Program Elements
9.4 Records and Fields


9.5 Patterns and Actions


9.6 One-Line Programs in awk


9.7 Statements


9.8 User-Defined Functions
9.9 String Functions


9.10 Numeric Functions


9.11 Summary
10. Working with Files


10.1 Listing Files


10.2 Updating Modification Times with touch


10.3 Creating and Using Temporary Files


10.4 Finding Files


10.5 Running Commands: xargs
10.6 Filesystem Space Information


10.7 Comparing Files
10.8 Summary


11. Extended Example: Merging User Databases
11.1 The Problem


11.2 The Password Files


11.3 Merging Password Files


11.4 Changing File Ownership


11.5 Other Real-World Issues


11.6 Summary

12. Spellchecking


12.1 The spell Program


12.2 The Original Unix Spellchecking Prototype
12.3 Improving ispell and aspell


12.4 A Spellchecker in awk
12.5 Summary

13. Processes


13.1 Process Creation


13.2 Process Listing


13.3 Process Control and Deletion


13.4 Process System-Call Tracing


13.5 Process Accounting


13.6 Delayed Scheduling of Processes


13.7 The /proc Filesystem
13.8 Summary

14. Shell Portability Issues and Extensions


14.1 Gotchas


14.2 The bash shopt Command


14.3 Common Extensions
14.4 Download Information


14.5 Other Extended Bourne-Style Shells
14.6 Shell Versions


14.7 Shell Initialization and Termination
14.8 Summary


15. Secure Shell Scripts: Getting Started
15.1 Tips for Secure Shell Scripts


15.2 Restricted Shell
15.3 Trojan Horses


15.4 Setuid Shell Scripts: A Bad Idea
15.5 ksh93 and Privileged Mode


15.6 Summary

A. Writing Manual Pages

B. Files and Filesystems

C. Important Unix Commands
Bibliography

Glossary

Index