- •Advanced Bash-Scripting Guide
- •Dedication
- •Table of Contents
- •Part 1. Introduction
- •Advanced Bash-Scripting Guide
- •Chapter 2. Starting Off With a Sha-Bang
- •2.1. Invoking the script
- •2.2. Preliminary Exercises
- •Part 2. Basics
- •Chapter 3. Exit and Exit Status
- •Chapter 4. Special Characters
- •Chapter 5. Introduction to Variables and Parameters
- •5.1. Variable Substitution
- •5.2. Variable Assignment
- •5.3. Bash Variables Are Untyped
- •5.4. Special Variable Types
- •Chapter 6. Quoting
- •Chapter 7. Tests
- •7.1. Test Constructs
- •7.2. File test operators
- •7.3. Comparison operators (binary)
- •7.4. Nested if/then Condition Tests
- •7.5. Testing Your Knowledge of Tests
- •8.1. Operators
- •8.2. Numerical Constants
- •Part 3. Beyond the Basics
- •Chapter 9. Variables Revisited
- •9.1. Internal Variables
- •9.2. Manipulating Strings
- •9.3. Parameter Substitution
- •9.4. Typing variables: declare or typeset
- •9.5. Indirect References to Variables
- •9.6. $RANDOM: generate random integer
- •9.7. The Double Parentheses Construct
- •Chapter 10. Loops and Branches
- •10.1. Loops
- •10.2. Nested Loops
- •10.3. Loop Control
- •10.4. Testing and Branching
- •Chapter 11. Internal Commands and Builtins
- •12.1. Basic Commands
- •12.2. Complex Commands
- •12.3. Time / Date Commands
- •12.4. Text Processing Commands
- •12.5. File and Archiving Commands
- •12.6. Communications Commands
- •12.7. Terminal Control Commands
- •12.8. Math Commands
- •12.9. Miscellaneous Commands
- •Chapter 13. System and Administrative Commands
- •Chapter 14. Command Substitution
- •Chapter 15. Arithmetic Expansion
- •Chapter 16. I/O Redirection
- •16.1. Using exec
- •16.2. Redirecting Code Blocks
- •16.3. Applications
- •Chapter 17. Here Documents
- •Chapter 18. Recess Time
- •Part 4. Advanced Topics
- •Chapter 19. Regular Expressions
- •19.1. A Brief Introduction to Regular Expressions
- •19.2. Globbing
- •Chapter 20. Subshells
- •Chapter 21. Restricted Shells
- •Chapter 22. Process Substitution
- •Chapter 23. Functions
- •23.1. Complex Functions and Function Complexities
- •23.2. Local Variables
- •Chapter 24. Aliases
- •Chapter 25. List Constructs
- •Chapter 26. Arrays
- •Chapter 27. Files
- •Chapter 28. /dev and /proc
- •28.2. /proc
- •Chapter 29. Of Zeros and Nulls
- •Chapter 30. Debugging
- •Chapter 31. Options
- •Chapter 32. Gotchas
- •Chapter 33. Scripting With Style
- •Chapter 34. Miscellany
- •34.2. Shell Wrappers
- •34.3. Tests and Comparisons: Alternatives
- •34.4. Optimizations
- •34.5. Assorted Tips
- •34.6. Oddities
- •34.7. Security Issues
- •34.8. Portability Issues
- •34.9. Shell Scripting Under Windows
- •Chapter 35. Bash, version 2
- •36. Endnotes
- •36.1. Author's Note
- •36.2. About the Author
- •36.3. Tools Used to Produce This Book
- •36.4. Credits
- •List of Tables
- •List of Examples
- •Bibliography
Arithmetic Expansion
Advanced Bash-Scripting Guide:
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Chapter 15. Arithmetic Expansion
Arithmetic expansion provides a powerful tool for performing arithmetic operations in scripts. Translating a string into a numerical expression is relatively straightforward using backticks, double parentheses, or let.
Variations
Arithmetic expansion with backticks (often used in conjunction with expr)
z=`expr $z + 3` # 'expr' does the expansion.
Arithmetic expansion with double parentheses, and using let
The use of backticks in arithmetic expansion has been superseded by double parentheses $((...)) or the very convenient let construction.
z=$(($z+3))
#$((EXPRESSION)) is arithmetic expansion. # Not to be confused with
#command substitution.
let z=z+3
let "z += 3" #If quotes, then spaces and special operators allowed.
# 'let' is actually arithmetic evaluation, rather than expansion.
All the above are equivalent. You may use whichever one "rings your chimes".
Examples of arithmetic expansion in scripts:
1.Example 12-6
2.Example 10-14
3.Example 26-1
4.Example 26-4
5.Example A-17
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