Section 15.4. Words and Whitespace Regexps

15.4. Words and Whitespace Regexps

While there are many other patterns for use in regular expressions , they generally aren't very common. So far we've looked at all but five of the most common ones, which leaves us with . (a period), \s, \S, \b, and \B.

The pattern . will match any single character except \n (new line). Therefore, c.twill match "cat," but not "cart."

The next two, \s and \S, equate to "Match any whitespace " and "Match any non-whitespace," respectively. That is, if you specify [\s\S], your regular expression will match any single character, regardless of what it is; if you use [\s\S]*, your regular expression will match anything. For example:

     $string = "Foolish child!";     preg_match("/[\S]{7}[\s]{1}[\S]{6}/", $string); 

That matches precisely seven non-whitespace characters, followed by one whitespace character, followed by six non-whitespace charactersthe exact string.

The last two patterns, \b and \B, equate to "On a word boundary" and "Not on a word boundary," respectively. That is, if you use the regexp /oo\b/, it will match "foo," "moo," "boo," and "zoo," because the "oo" is at the end of the word, but not "fool," "wool," or "pool," because the "oo" is inside the word. The \B pattern is the opposite, which means it would match only patterns that aren't on the edges of a wordusing the previous example, "fool," "wool," and "pool" would be matched, whereas "foo," "moo," "boo," and "zoo" would not.

For example:

     $string = "Foolish child!";     if (preg_match("/oo\b/i", $string)) {             // we will not get here     }     preg_match("/oo\B/i", $string);     // opposite of previous search; returns true     preg_match("/no\b/", "he said 'no!'");     // returns true; \b is smart enough to know that !, ', ?, and other symbols     aren't part of words     preg_match("/royalty\b/", "royalty-free photograph");     // returns true; \b considers hyphenated words to be separate