bash Idioms: Write Powerful, Flexible, Readable Shell Scripts

Description

Shell scripts are everywhere, especially those written in bash compatible syntax, and it's extremely useful to be able to understand and write them, but they can be complex and obscure. Complexity is the enemy of security, but it's also the enemy of readability and understanding. With this practical book, you'll learn how to decipher old bash code and write new code that's as clear and readable as possible. Your future you will thank you. Authors Carl Albing and JP Vossen show you how to use the power and flexibility of the shell to your advantage. You'll learn how to read and write scripts like an expert, so that you can: • Write useful, flexible, and readable bash code...with style • Decode bash code such as ${MAKEMELC,,} and ${PATHNAME##*/} • Save time and ensure consistency when automating tasks • Amaze and impress colleagues with bash idioms • Discover how bash idioms can make your code clean and concise Cover Copyright Table of Contents Preface Running bash bash on Mac bash in Containers Revision Control Hello World Conventions Used in This Book Using Code Examples O’Reilly Online Learning How to Contact Us Acknowledgments bash Reviewers O’Reilly From Carl From JP Chapter 1. A Big “if” Idiom The Big “if” Or ELSE… More than One More than One Again Don’t Do This Style and Readability: Recap Chapter 2. Looping Lingo Looping Constructs Explicit Values Similar to Python Quotes and Spaces Developing and Testing for Loops while and until Style and Readability: Recap Chapter 3. Just in CASE Make Your Case A Realistic Use Case Motivation Our Script Wrapper Scripts One More Twist Style and Readability: Recap Chapter 4. Variable Vernacular Variable Reference Parameter Expansion Shorthand for basename Path or Prefix Removal Shorthand for dirname or Suffix Removal Other Modifiers Conditional Substitutions Default Values Comma-Separated Lists Modified Value $RANDOM Command Substitution Style and Readability: Recap Chapter 5. Expressions and Arithmetic Arithmetic No Parentheses Needed Compound Commands Style and Readability: Recap Chapter 6. Functional Framework Calling Functions Defining Functions Function Parameters Function Return Values Local Variables Function Special Cases Time for printf POSIX Output Getting or Using the Date and Time printf for Reuse or Debugging Style and Readability: Recap Chapter 7. List and Hash Handling Commonalities Lists Hashes A Simple Word Count Example Style and Readability: Recap Chapter 8. Arguing Your First Argument Having Options Parsing Options Long Arguments HELP! Debug and Verbose Version Style and Readability: Recap Chapter 9. Files and More Reading Files read mapfile Brute Force Fiddling with $IFS for Fun and Profit, to Read Files Pretend Files Drop-in Directories Using a Library Shebang! Unofficial bash Strict Mode Exit Codes It’s a Trap! Here-Documents and Here-Strings Are We Interactive? Summary Chapter 10. Beyond Idioms: Working with bash Prompts bash Time Zone Getting User Input read pause select Aliases Functions Local Variables Readline Hacks Using logger from bash Handling JSON with jq Grepping the Process List Rotating Old Files Embedded Documentation bash Debugging bash Unit Testing Summary Chapter 11. Developing Your Style Guide Readability Comments Names Functions Quoting Layout Syntax Other Script Template Other Style Guides bash Linter Summary Appendix A. The bash Idioms Style Guide Readability Comments Names Functions Quoting Layout Syntax Other Script Template Index About the Authors Colophon