Gain insights into pattern matching with regular expressions in C#. Explore data validation, information extraction, and more using String and Regex APIs with practical examples.

Regular expressions provide an extremely powerful method for pattern matching with strings. They are very useful for parsing information like dates, phone numbers, or zip codes from important text files, such as code files, log files, spreadsheets, or documents. The course discusses everyday use cases of regular expressions, e.g., data validation, information extraction, pattern matching, and search and replace.

This course will teach you the core concepts of pattern matching, character classes, special and meta characters, and quantifiers. You will also learn conditional regular expressions including lookahead and lookbehind assertions. You will also learn the APIs used in C# for regular expressions with hands-on code widgets. 

This course will teach you how to perform pattern matching with a regular expression using String and Regex APIs for the above-mentioned practical use cases in C#.

Tarun Telang

Tarun Telang is a passionate software engineer, leader, architect, author, and active contributor in various online technical forums.

C# and Microsoft Expert

Working with Regular Expressions in C#

# Applications of regular expressions

Regular expressions are widely used in different disciplines. These include information technology, biology, linguistics, and the social sciences.

**Text processing** is an essential part of programming. At the bare minimum, every program must read input from some source, often a file or stream, and convert it into useful data. This conversion step often involves parsing text strings to identify their contents, so that we can use them for further computation.

We can use regular expressions to perform the following operations on textual data:

Use cases of regular expressions with examples

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In C#, we represent regular expressions with a unique **pattern language**. The format of these patterns is similar to how the Perl programming language represents regular expressions.

We learn more details about this pattern language later in this course.

# Word count tool

A simple example of using regular expressions is to count the number of words in a string. This has many practical applications, such as automation and logging. The regular expression we can use to resolve this task is `\b\w{1,}\b`.

This regular expression contains two parts: `\b` and `\w{1,}`. The first part, `\b`, is a boundary marker. For this example, we assume that the string of words to be counted starts with a #key# word boundary:A word boundary is any character that is not a letter, digit or underscore (`_`) #key#. A boundary can be either before or after (inclusive) a word.  The `\w{1,}` part of the regular expression means to match one or more occurrences of any letter, digit, or underscore.

## Example 1:

The following example shows how to use the regular expression to count the number of words in a string:

Find out the usage of regular expressions in some common applications.

Use Cases	Examples
String-based pattern matching	Extracting IP addresses from a server log file.
Parsing data	Parsing data from a variety of sources, such as log files, YAML, CSV, XML, JSON files.
Searching and replacing	Searching for sensitive information like credit-card numbers and masking it as XXXX-XXXX-XXXX-XXXX in the text documents.
String manipulation in a document	Converting all the strings representing the date in a text document from DD-MM-YYYY format to MM-DD-YYYY format.
Data validation	Validation of input data values like phone numbers, zip codes, email addresses, etc.
Extracting information	Extracting hashtags from a document containing tweets or blog posts.

Introduction

Building Blocks of .NET Regular Expressions

Advanced Concepts

Course Wrap Up

Applications of Regular Expressions

Applications of regular expressions

Use cases of regular expressions with examples

Word count tool