How deeply does The Well-Grounded Rubyist, Fourth Edition cover word boundary?

Explains transitions, string edges, and the \b/\B contrast through a compact matching example.

Word boundary

As explained in The Well-Grounded Rubyist, Fourth Edition

A word boundary anchor constrains a match to a transition between word and non-word characters or to a string boundary.

A word boundary anchor, written \b, matches a position where a word character and a non-word character meet, or where the string begins or ends. It checks the position without consuming a character. For example, /\bword/ matches “word” in “!word!sword” because the exclamation mark begins a boundary, while /\Bword/ matches “word” inside “sword” because that position is not a boundary. section 11.5.3

Use the two related anchors to control whether a match may cross a word boundary:

\b requires a transition between a \w character and a non-\w character, or a string edge. section 11.5.3
Whitespace and other non-\w characters count as boundaries, so the anchor can distinguish a standalone word from the same letters inside a larger word. section 11.5.3

Match a word at its start

The pattern /\bword/ matches the first “word” in “!word!sword” but not the occurrence inside “sword”.

How The Well-Grounded Rubyist, Fourth Edition covers it

Cover of The Well-Grounded Rubyist, Fourth Edition

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Also explained in

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Data-Oriented Programming: Reduce software complexityA word boundary is a position in text recognized by a regular expression as the boundary between a word character and a non-word character.
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Regular Expression Puzzles and AI Coding AssistantsA word boundary is a regular-expression zero-width assertion that matches a position at the transition between word and non-word characters or at a string edge.

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Related concepts

regular expressionused by · A formal pattern notation that describes sets of strings and enables text to be matched, searched, extracted, or transformed.
regular-expression anchorkind of · A regular-expression anchor is a zero-width assertion that constrains matching to a specific position in text, such as its beginning or end.
negative lookahead assertionused by · A negative lookahead assertion is a regular-expression assertion that succeeds when its pattern does not match immediately after the current position without consuming characters.
raw string literalconfigured by · A raw string literal is a string-literal syntax that treats most backslashes and other contents literally, reducing ordinary escape processing.
assertionkind of · A regular-expression assertion tests a condition at a position in the input without consuming characters as part of the match.

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.