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lookaround_assertions

🔍 Use Lookaround Assertions​

Use positive/negative lookahead (?=...), negative lookahead (?!...), and lookbehind (?<=...)/(?<!...) to match context without consuming characters. This is invaluable for validations and context-aware replacements without extra capturing groups.

text = 'foo123bar'
# Match digits only when preceded by letters and followed by letters
digits = text.scan(/(?<=[A-Za-z])\d+(?=[A-Za-z])/)
#=> ["123"]