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A collection of in-depth information for using regular expressions safely and quickly in real work. It covers common mistakes, performance pitfalls, and syntax differences across languages.

Common Regex Mistakes and Pitfalls

Five regex mistakes beginners often run into, and how to fix them.

Regex Performance and ReDoS Awareness

Avoiding slow regexes and the catastrophic backtracking (ReDoS) that can paralyze a service.

Regex Differences Across Languages (JavaScript · Python · PCRE)

Even the same regex differs slightly in syntax and support from language to language.

Validating Input with Regex (Form Validation)

Practical tips and pitfalls for validating input like email, phone, and postal code with regex.

Regex Replacement Recipes

A collection of practical examples for reformatting text with capture groups and replacement strings.

Regex vs. String Methods: When to Use Which

Not every problem needs regex. For simple tasks, string methods are faster and easier to read.