php|architect's Guide to Web Scraping with PHP - Wind Business ...

144 ” PCRE Extension
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POSIX Extended Regular Expressions
Many PHP developers will cut their teeth on regular expressions using the POSIX regular
expression extension, also called the ereg extension. The functions from this extension
are being deprecated in PHP 5.3 in favor of those in the PCRE extension, which
are faster and provide a more powerful feature set. Aside from differences in syntax
for some special character ranges, most ereg expressions require only the addition of
expression delimiters to work with preg functions.
P a t t e r nBasics
Let’s start with something simple: detection of a substring anywhere within a string.
N o t i c e that the pattern in the preg_match() call is fairly similar to the string used in
the strpos() call. In the former, / is used on either side of the pattern to indicate its
beginning and end. The first character in the pattern string is considered to be the
pattern delimiter and can be any character you specify. When choosing what you
want to use for this character (/ is the most common choice), bear in mind that you
will have to escape it (covered in the Escaping section later) if you use it within the
pattern. This will make more sense a little later in the chapter.
A difference between the two functions used in this example is that strpos() returns
the location of the substring within the string beginning at 0 or false if the
substring is not contained within the string. This requires the use of the === operator
to tell the difference between the substring being matched at the beginning of
the string or not at all. By contrast, preg_match() returns the number of matches it
found. This will be either 0 or 1 since preg_match() stops searching once it finds a
match.