Further Reading

Note that some of these resources are not specific to Ruby, so use them with caution and check if they apply to Ruby's syntax and features.

• rubular — Ruby regular expression editor, handy way to test your regexp
• RubyVerbalExpressions — construct regular expressions with natural language terms
• CommonRegexRuby — collection of common regular expressions
• regexp-examples — Generate strings that match a given Ruby regular expression
• Awesome Regex — curated collection of libraries, tools, frameworks and software
• stackoverflow: ruby regexp
• stackoverflow: regex FAQ
  • stackoverflow: regex tag is a good source of exercise questions
• rexegg — tutorials, tricks and more
• regular-expressions — tutorials and tools
• regexcrossword — tutorials and puzzles, only supports JavaScript flavor
• debuggex — railroad diagrams for regular expressions, doesn't support Ruby flavor
• swtch — stuff about regular expression implementation engines

Here's some links for specific topics:

• rexegg: best regex trick
• regular-expressions: matching numeric ranges
• regular-expressions: Continuing at The End of The Previous Match, especially the second section that discusses about implementation detail
• regular-expressions: Zero-Length Matches
• stackoverflow: Greedy vs Reluctant vs Possessive Quantifiers
• cloudflare: Details of the Cloudflare outage on July 2, 2019 — see appendix for details about CPU exhaustion caused due to regular expression backtracking