Page 588 - Beginning PHP 5.3

Part III: Using PHP in Practice
\A and \z are similar to ^ and $ . The difference is that ^ and $ will also match at the beginning and end
of a line, respectively, if matching a multi - line string in multi - line mode (explained in the “ Altering
Matching Behavior with Pattern Modifiers ” section later in the chapter). \A and \z only match at the
beginning and end of the target string, respectively.

\Z is useful when reading lines from a file that may or may not have a newline character at the end.

\b and \B are handy when searching text for complete words:

echo preg_match( “/over/”, “My hovercraft is full of eels” ); //
Displays “1”
echo preg_match( “/\bover\b/”, “My hovercraft is full of eels” ); //
Displays “0”
echo preg_match( “/\bover\b/”, “One flew over the cuckoo’s nest” ); //

Displays “1”
When using \b , the beginning or end of the string is also considered a word boundary:

echo preg_match( “/\bover\b/”, “over and under” ); // Displays “1”

By using the \b anchor, along with alternatives within a subexpression, it ’ s possible to enhance the
earlier “ date detection ” example further, so that it matches only two - or four - digit years (and not three -
digit years):
echo preg_match( “/\b(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)” .
“\/\d{1,2}\/(\d{2}|\d{4})\b/”, “jul/15/2006” ); // Displays “1”

echo preg_match( “/\b(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)” .
“\/\d{1,2}\/(\d{2}|\d{4})\b/”, “jul/15/206” ); // Displays “0”

The last part of the expression reads, “ Match either two digits or four digits, followed by a word
boundary (or the end of the string) ” :

(\d{2}|\d{4})\b

You can also create your own types of anchor; for example, you can match text only when it comes before
an ampersand, or only when it follows a capital letter (without actually including the ampersand or
capital letter in the match). These kinds of custom anchors are known as lookahead and lookbehind
assertions, and they ’ re out of the scope of this chapter; however, you can read about them in the PHP
manual at http://www.php.net/manual/en/regexp.reference.assertions.php .

Finding Multiple Matches with

preg_match_all()

Though the preg_match() function is useful for many string matching scenarios, it only finds the first
pattern match in the target string. Sometimes you want to find all matches within a string. For example,
you might want to extract a list of all the phone numbers mentioned in an email message, or count the
number of links in an HTML Web page.

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