Regular Expressions(Theory of programming languages))

Regular expressions (regex) are powerful tools used for pattern matching and text manipulation. They are essential in many programming and data processing tasks for searching, editing, and validating strings.

1. Regular Expressions Presented by: Khuda Bux Magsi (CSC-23F-259)

2. Context Introduction to Regular Expression Basic Syntax and Metacharacters Practical Applications Regex Tools Conclusion

3. Introduction About Regular Expressions

4. What’s a Regular Expression? Regular expressions originated in 1951 , when mathematician  Stephen Cole Kleene  described regular languages using his mathematical notation called regular events. A regular expression, or regex, is a sequence of characters used to define a search pattern. It's a powerful tool for finding, matching, and manipulating text within a larger body of data. Regular Expressions are supported by many programming languages and tools, making them a widely used tool in software development.

5. What’s a Regular Expressions? Example

6. Basic Syntax Basic Syntax and Metacharacters

7. Basic Syntax of Regular Expression Regular expressions (regex) consist of a combination of literals and metacharacters that create search patterns for matching text. Understanding the basic syntax is crucial for crafting effective regex patterns. Regular expressions (regex) have a specific syntax that defines how patterns are constructed. Here's a breakdown of some fundamental elements: Literal Characters Special Characters Quantifiers Grouping Alternation

8. Basic Syntax of Regular Expression Literal Characters A literal character is any character that represents itself and is not interpreted as a special symbol or metacharacter in regex. For instance, the letter a in a regex pattern will match the character 'a' in the input text. Examples of Literal Characters Here are a few simple regex patterns using literal characters: ‘cat’: Matches the substring 'cat' in the text. Example: The cat is sleeping. (Matches 'cat' )

9. Basic Syntax of Regular Expression Special Characters These are the workhorses of regex, adding power and flexibility to your patterns. Some common ones include: . (Dot): Matches any single character except for newline characters. [] (Brackets): Define a set of characters that can match at a specific position. For example, "[abc]" will match any of the letters a, b, or c. *(Asterisk): Matches the preceding character zero or more times. So, "a*b" will match "b", "ab", "aab", "aaab", and so on. + (Plus): Matches the preceding character one or more times. "a+b" will match "ab", "aab", "aaab", and so on, but not just "b". ? (Question Mark ): Matches the preceding character zero or one time. "ca?t" will match "cat" or "ct".

10. Basic Syntax of Regular Expression Quantifiers: These are special characters like "*", "+", and "?" that specify how many times the preceding character or group can be repeated.

11. Basic Syntax of Regular Expression Grouping: Parentheses are used to group parts of the pattern. This allows you to apply quantifiers or other operations to the entire group. For instance, "(ab)*c" will match "c", "abc", "abbc", "abbbc", and so on.

12. Basic Syntax of Regular Expression Alternation: The pipe symbol ("|") is used for alternation. For example, "apple|banana" will match either "apple" or "banana".

13. Practical Application In Regular Expression

14. Validating Input Validating user input is crucial for ensuring data integrity and security in applications. Here are common validation techniques for specific types of user input.

15. Searching and Replacing Searching and replacing text based on patterns is a common task in text processing. Here are examples of how to search for patterns and replace them with desired text.

16. Regex Tools & Libraries Regular Expression

17. Regex Tools Online Regex Testers Regex101 : An interactive web-based tool that supports multiple regex flavors, including PCRE, JavaScript, and Python. It provides real-time regex matching, a detailed explanation of the regex, and a breakdown of each component. RegExr : Another online tool that offers a user-friendly interface for creating and testing regular expressions. It includes a library of regex snippets and a cheat sheet for common patterns. RegexPlanet : Supports various programming languages, providing a versatile platform for testing regex patterns against sample text.

18. Regex Tools Integrated Development Environment (IDE) Plugins Regex Plugin for Visual Studio Code: Enhances the regex capabilities within the VSCode environment, allowing for testing and debugging regex patterns directly in the editor . IntelliJ IDEA Regex Plugin: Provides similar functionality for IntelliJ-based IDEs, offering syntax highlighting, pattern matching, and error detection.

19. Conclusion Indispensable Tool : Regular expressions are essential for modern programming and text processing. They provide a flexible and powerful method for searching, matching, and manipulating strings. Versatile Applications : Useful for a wide range of tasks, from simple text searches to complex parsing and data extraction. Applicable in various domains, including data validation, web scraping, and log file analysis.

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