ZEND PHP 5 Certification STUDY GUIDE

90 ” Strings And Patterns
lier in this chapter. Therefore, you should use them only when appropriate—that is,
when using the simpler functions is either impossible or so complicated that it’s not
worth the effort.
A regular expression is a string that describes a set of matching rules. The simplest
possible regular expression is one that matches only one string; for example, Davey
matches only the string “Davey”. In fact, such a simple regular expression would be
pointless, as you could just as easily perform the match using strpos(), which is a
much faster alternative.
The real power of regular expressions comes into play when you don’t know the
exact string that you want to match. In this case, you can specify one or more metacharacters
and quantifiers, which do not have a literal meaning, but instead stand to
be interpreted in a special way.
In this chapter, we will discuss the basics of regular expressions that are required
by the exam. More thorough coverage is provided by the PHP manual, or by one of
the many regular expression books available (most notably, Mastering Regular Expressions,
by Jeffrey Friedl, published by O’Reilly Media).
Delimiters
A regular expression is always delimited by a starting and ending character. Any character
can be used for this purpose (as long as the beginning and ending delimiter
match); since any occurrence of this character inside the expression itself must be
escaped, it’s usually a good idea to pick a delimiter that isn’t likely to appear inside
the expression. By convention, the forward slash is used for this purpose—although,
for example, another character like the octothorpe is sometimes used when dealing
with pathnames or URLs.
Metacharacters
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The term “metacharacter” is a bit of a misnomer—as a metacharacter can actually
be composed of more than one character. However, every metacharacter represents
a single character in the matched expression. Here are the most common ones: