The Ruby Way: Solutions and Techniques in Ruby Programming, Second Edition

3.4. Using Anchors

An anchor is a special expression that matches a position in a string rather than a character or sequence of characters. As we’ll see later, this is a simple case of a zero-width assertion, a match that doesn’t consume any of the string when it matches.

The most common anchors were already listed at the beginning of this chapter. The simplest are ^ and $, which match the beginning and end of the string.

string  = "abcXdefXghi"
/def/  =~ string     # 4
/abc/  =~ string     # 0
/ghi/  =~ string     # 8
/^def/ =~ string     # nil
/def$/ =~ string     # nil
/^abc/ =~ string     # 0
/ghi$/ =~ string     # 8

However, I’ve told a small lie. These anchors don’t actually match the beginning and end of the string but of the line. Consider the same patterns applied ...