Regular expressions (regex) are powerful tools for pattern matching and text manipulation. In PowerShell, regex can be used to search, match, and replace text within strings. This section will cover the basics of regex, how to use them in PowerShell, and provide practical examples and exercises.

Regular expressions are sequences of characters that define a search pattern. They are commonly used for string matching and manipulation tasks such as:

• Validating input (e.g., email addresses, phone numbers)
• Searching for specific patterns within text
• Replacing or extracting parts of a string

Here are some basic components of regex syntax:

• Literal Characters: Match the exact characters (e.g., abc matches "abc").
• Metacharacters: Special characters with specific meanings (e.g., . matches any character except newline).
• Character Classes: Define a set of characters to match (e.g., [a-z] matches any lowercase letter).
• Quantifiers: Specify the number of occurrences (e.g., * matches 0 or more times, + matches 1 or more times).
• Anchors: Define positions within the string (e.g., ^ matches the start of a string, $ matches the end).

PowerShell provides several cmdlets and operators for working with regex:

• -match: Matches a string against a regex pattern.
• -replace: Replaces text matching a regex pattern.
• Select-String: Searches for text patterns in files or strings.

Explanation:

• The regex pattern \b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b matches a typical email address format.
• $matches[0] contains the matched email address.

Explanation:

• The regex pattern \$\d+ matches a dollar sign followed by one or more digits.
• The -replace operator replaces the matched text with "$200".

Explanation:

• The regex pattern \b\d{3}-\d{2}-\d{4}\b matches a Social Security number format.
• Select-String searches for the pattern in the file "sample.txt".

Task: Write a PowerShell script to validate phone numbers in the format (123) 456-7890.

Solution:

Task: Write a PowerShell script to extract domain names from a list of URLs.

Solution:

Task: Write a PowerShell script to replace dates in the format MM/DD/YYYY with YYYY-MM-DD.

Solution:

• Escaping Metacharacters: Remember to escape metacharacters (e.g., .) when you want to match them literally.
• Using Anchors: Use ^ and $ to ensure the pattern matches the entire string, not just a part of it.
• Testing Patterns: Use online regex testers to validate and test your patterns before using them in scripts.

Regular expressions are a powerful tool for text processing in PowerShell. By understanding the basic syntax and how to use regex with PowerShell cmdlets and operators, you can perform complex text manipulations efficiently. Practice with the provided exercises to reinforce your understanding and become proficient in using regex in your PowerShell scripts.