What Is Regex? A Practical Guide with Examples
Learn what regular expressions are, what they are used for, and how to read basic patterns with practical examples.
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Learn Regex by doing
Practical guides, testable examples, and exercises connected to the game. Start with the basics or jump into a real-world problem.
Regex for Beginners: Learn the Basics Without Memorizing
A beginner-friendly regex path covering literals, character classes, quantifiers, anchors, and practice.
Read guide →Regex in JavaScript: RegExp, test, match, replace and Flags
Practical JavaScript regex guide using literals, RegExp, test(), match(), replace(), and common flags.
Read guide →Regex in Python with re: search, fullmatch, findall and sub
Practical Python regex guide using the re module, raw strings, groups, extraction, and replacement.
Read guide →Email Regex: A Practical Pattern and Its Validation Limits
Learn a practical email Regex, understand each part, and see why complete email validation is more complicated.
Read guide →Brazilian CPF Regex: Validate the 000.000.000-00 Format
Regex for the common Brazilian CPF format, plus the important difference between formatting and check-digit validation.
Read guide →Brazilian CNPJ Regex: Validate the 00.000.000/0000-00 Format
Regex for the common Brazilian CNPJ format with an explanation of formatting versus check-digit validity.
Read guide →Phone Number Regex: Practical Patterns and Formatting Choices
Learn phone Regex patterns, optional formatting, international caveats, and why requirements should come first.
Read guide →URL Regex: Practical HTTP and HTTPS Examples
Learn a practical URL Regex for HTTP/HTTPS and understand protocols, domains, paths, and parsing limits.
Read guide →IP Address Regex: IPv4 Structure and Correct Validation
Learn a basic IPv4 Regex and why four numeric groups are not enough to guarantee a valid address.
Read guide →Date Regex: DD/MM/YYYY and Calendar Validation Limits
Regex examples for date formats, plus why matching DD/MM/YYYY does not guarantee a real calendar date.
Read guide →Number Regex: Integers, Signed Values, and Decimals
Practical Regex examples for digits, signed integers, decimals, and why numeric conversion still matters.
Read guide →Letters-Only Regex: ASCII, Accents, and Unicode
Regex patterns for letters only, including accented characters and Unicode considerations.
Read guide →Regex for Logs: Filter INFO, WARN, ERROR, Dates, and IDs
Use Regex to filter log levels and extract dates, IDs, and useful fields from application logs.
Read guide →20 Regex Examples to Copy, Test, and Adapt
Practical Regex examples for digits, words, email, phone, dates, URLs, files, and logs.
Read guide →Regex Exercises: A Practice Path from Beginner to Advanced
Practice Regex with progressive exercises and learn to use false positives and false negatives as feedback.
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