How deeply does The Well-Grounded Rubyist, Fourth Edition cover non-greedy quantifier?

Defines `*?` and `+?`, contrasts greedy matching, and explains backtracking with a digit example.

Non-greedy quantifier

As explained in The Well-Grounded Rubyist, Fourth Edition

A non-greedy quantifier matches the fewest repetitions needed for the remainder of the regular expression to match.

A question mark after `*` or `+` makes the quantifier non-greedy: it matches the fewest repetitions that still let the rest of the pattern succeed. Unlike a greedy quantifier, it can stop at the first `!` rather than the last. section 11.5.2

Greedy matching is not absolute: the regexp engine can backtrack when needed to make the whole pattern match. For example, `\d+` in `/\d+5/` matches `234`, leaving `5` for the rest of the pattern. section 11.5.2

>> /.+?!/.match(string)[0]
=> "abc!"

Compare this with the greedy `/ .+! /` example: adding `?` makes the match stop at the first exclamation point. section 11.5.2

Matching across lines

In `/\(.*?\)/m`, `.*?` matches the fewest characters through a closing parenthesis; the `m` modifier lets the wildcard match newline characters. section 11.5.4

How The Well-Grounded Rubyist, Fourth Edition covers it

Cover of The Well-Grounded Rubyist, Fourth Edition

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Related concepts

greedy matchingcontrasts with · Greedy matching is regular-expression behavior in which a quantifier matches as much text as possible while still allowing the overall pattern to match.
quantifierkind of · A regular-expression quantifier is syntax that specifies how many times a preceding pattern element may or must match.
telomereaddresses · A telomere is a specialized repetitive DNA sequence at the end of a chromosome or other DNA sequence.
regular expressionused by · A formal pattern notation that describes sets of strings and enables text to be matched, searched, extracted, or transformed.
catastrophic backtrackingcontrasts with · Catastrophic backtracking is pathological regular-expression matching in which ambiguous alternatives cause exponentially many paths to be explored, potentially causing extreme execution time.
regex engineused by · A regular-expression engine is software that interprets regular-expression patterns and applies them to text for matching, searching, splitting, or transformation.

This explainer was generated by Manning's knowledge graph from the text of The Well-Grounded Rubyist, Fourth Edition. The section links point to the parts of the book it draws on.