Why it matters

Regex is powerful but easily misused. Understanding traps prevents production bugs.

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The architecture

Basic: literals, character classes, quantifiers (*, +, ?, {n,m}).

Anchors: ^ $ \b.

Groups: () with backreferences.

Regex mechanicsPatternregex syntaxNFA / DFAengineMatchagainst inputBackreferences make regex non-regular; enable catastrophic backtracking
Regex engine model.
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How it works end to end

Compilation: pattern → NFA → optionally DFA. DFA is O(n) match but O(2^m) construction.

Backtracking engines (PCRE, JS, Python): NFA-based. Fast normally; catastrophic on some patterns.

Linear-time engines (RE2, Go): DFA-based. Slower for many patterns but no catastrophic backtracking.