Word Boundaries in Regular Expressions
1. Understanding Word Boundaries
Word boundaries in regular expressions are used to match positions where a word character is adjacent to a non-word character, or vice versa. They are represented by the metacharacters \b and \B.
2. The \b Boundary
The \b boundary matches a position that is either before the first character in a word, after the last character in a word, or between a word character and a non-word character. Word characters include letters, digits, and underscores.
Example:
Pattern: \bcat\b
Text: "The cat sat on the mat."
Matches: "cat"
Explanation: The \b ensures that "cat" is matched as a whole word, not as part of another word like "concatenate".
3. The \B Boundary
The \B boundary matches a position that is not a word boundary. It is used to match positions within words, where both the preceding and following characters are either word characters or non-word characters.
Example:
Pattern: \Bcat\B
Text: "The concatenation was successful."
Matches: "cat" in "concatenation"
Explanation: The \B ensures that "cat" is matched within a word, not at the start or end of a word.
4. Practical Examples
Understanding word boundaries is crucial for precise pattern matching. Here are some practical examples:
Example:
Pattern: \b\d+\b
Text: "There are 123 apples and 456 oranges."
Matches: "123", "456"
Explanation: The \b ensures that only whole numbers are matched, not digits within words like "apples".
Example:
Pattern: \Bing\B
Text: "The string was interesting."
Matches: "ing" in "string" and "interesting"
Explanation: The \B ensures that "ing" is matched within words, not at the boundaries.