Anchors in Regular Expressions
Anchors in Regular Expressions are special characters that allow you to specify the position of the pattern within the text. They do not match any characters but rather assert a position. The four primary anchors are ^, $, \b, and \B.
1. The ^ Anchor
The ^ anchor asserts the position at the start of a line. When used at the beginning of a pattern, it ensures that the pattern matches only if it appears at the start of the line.
Example:
Pattern: ^Hello
Matches: "Hello, world!"
Does not match: "Hi, Hello!"
2. The $ Anchor
The $ anchor asserts the position at the end of a line. When used at the end of a pattern, it ensures that the pattern matches only if it appears at the end of the line.
Example:
Pattern: world$
Matches: "Hello, world"
Does not match: "Hello, world!"
3. The \b Anchor
The \b anchor asserts a word boundary. It matches the position between a word character (like a letter) and a non-word character (like a space or punctuation). This is useful for matching whole words.
Example:
Pattern: \bcat\b
Matches: "The cat sat on the mat."
Does not match: "The caterpillar is cute."
4. The \B Anchor
The \B anchor asserts a non-word boundary. It matches the position where a word boundary does not occur. This is useful for matching patterns that are part of larger words.
Example:
Pattern: \Bcat\B
Matches: "The caterpillar is cute."
Does not match: "The cat sat on the mat."
By mastering these anchors, you can precisely control where your patterns match within text, making your Regular Expressions more powerful and flexible.