If how to create these giant matchstick regexes interest you,
there is a wonderful(famous?) perl script generating a regex 6,598 chars long, more optimized and faster than earlier attempt at 4,724 bytes,
in Jeffrey Friedl's book, Mastering Regular Expressions, 1st edition, Oreilly, pp 312-316, Appedix B: Email Regex Program.
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If how to create these giant matchstick regexes interest you, there is a wonderful(famous?) perl script generating a regex 6,598 chars long, more optimized and faster than earlier attempt at 4,724 bytes, in Jeffrey Friedl's book, Mastering Regular Expressions, 1st edition, Oreilly, pp 312-316, Appedix B: Email Regex Program.