Regular Expressions

A regular expression, often abbreviated as regex or regexp, is a powerful sequence of characters that defines a search pattern, primarily used for string searching and manipulation. By using a specialized syntax of metacharacters (e.g., `*`, `+`, `?`) and literal characters, a regex can describe a set of strings with common properties. Theoretically grounded in formal language theory, each regular expression corresponds to a finite automaton, an abstract machine that can recognize the specified patterns, making them an indispensable tool in tasks ranging from input validation in web forms to parsing text with command-line utilities and within programming languages.

1. Introduction to Regular Expressions
   1. Definition and Core Concepts
      1. What Are Regular Expressions
      2. Pattern Matching Fundamentals
      3. Text Processing Context
   2. Purpose and Applications
      1. String Searching
      2. String Replacement
      3. Input Validation
      4. Data Extraction
      5. Text Processing Automation
   3. Historical Development
      1. Mathematical Origins
      2. Stephen Kleene's Work
      3. Computer Science Adoption
      4. Evolution in Programming Languages
   4. Regular Expressions vs Other Pattern Matching
      1. Wildcards and Globbing
      2. String Methods
      3. Parser Generators
      4. When to Use Regular Expressions