Regex Lookahead and Lookbehind: Zero-Width Assertions
Master regex lookahead and lookbehind assertions. Learn positive and negative zero-width assertions with real-world pattern examples.
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Tags: developer-tools, regex, advanced
Regex Lookahead and Lookbehind: Zero-Width Assertions Explained Lookahead and lookbehind are zero-width assertions — they match a position in the string relative to surrounding text, without consuming any characters. This means you can match something only if it's followed by (or preceded by) something else, without including that context in the match. That distinction — matching without consuming — solves problems that regular character matching can't handle cleanly. Test the examples in this guide at theproductguy.in/tools/regex-tester. --- What "Zero-Width" Means A normal match consumes characters. After matching , the engine moves past those digits. A lookahead asserts something about what follows the current position without advancing. After a lookahead succeeds (or fails), the…
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