Orchestrating Logic
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Comprehensive reference guide for regular expression syntax. Practical examples for all levels of expertise.
.Any character except newline\wWord character (letter, number, underscore)\dDigit (0-9)\sWhitespace (space, tab, newline)\WNon-word character\DNon-digit character\SNon-whitespace character[abc]Any character in the set (a, b, or c)[^abc]Any character NOT in the set[a-z]Any character in range a through z*0 or more+1 or more?0 or 1 (optional){3}Exactly 3 times{3,}3 or more times{3,5}3 to 5 times*?Lazy (smallest possible match)^Beginning of string / line$End of string / line\bWord boundary\BNon-word boundary(abc)Capture group (matches abc)(?:abc)Non-capturing groupa|bOR (matches a or b)\1Backreference to group #1(?=abc)Positive lookahead (followed by abc)(?!abc)Negative lookahead (not followed by abc)(?<=abc)Positive lookbehind (preceded by abc)(?<!abc)Negative lookbehind (not preceded by abc)By default, quantifiers like * and + are "greedy"—they match as much as possible. Append ? to make them "lazy" and match the smallest amount.
Use \\b to match complete words only. \\bcat\\b matches "cat" but not "category" or "bobcat".
/g (Global)Don't stop after first match
/i (Case Insens.)Ignore capitalization
^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$Explanation
This complex expression validates a standard email address format using beginning anchors, word groups, and length-limited top-level domains.
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Regular expressions operate on a series of tokens. Characters like brackets and carats have structural meaning that changes how the engine interprets the rest of the string. Our guide breaks down these tokens into logical groups for rapid learning and reference.
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