Page 587 - Beginning PHP 5.3

Chapter 18: String Matching with Regular Expressions
echo preg_match( “/^\d+\:/”, “12: The Sting” ); // Displays “1”
echo preg_match( “/^\d+\:/”, “Die Hard 2: Die Harder” ); // Displays “0”

The caret ( ^ ) symbol specifies that the rest of the pattern will only match at the start of the string.
Similarly, you can use the dollar ( $ ) symbol to anchor a pattern to the end of the string:

echo preg_match( “/\[(G|PG|PG-13|R|NC-17)\]$/”, “The Sting [PG]” ); //
Displays “1”
echo preg_match( “/\[(G|PG|PG-13|R|NC-17)\]$/”, “[PG] Amadeus” ); //
Displays “0”

By combining the two anchors, you can ensure that a string contains only the desired pattern,
nothing more:

echo preg_match( “/^Hello, \w+$/”, “Hello, world” ); // Displays “1”

echo preg_match( “/^Hello, \w+$/”, “Hello, world!” ); // Displays “0”
The second match fails because the target string contains a non - word character ( ! ) between the searched -
for pattern and the end of the string.

You can use other anchors for more control over your matching. Here ’ s a full list of the anchors you can
use within a regular expression:

Anchor Meaning
^ Matches at the start of the string
$ Matches at the end of the string

\b Matches at a word boundary (between a \w character and a \W character)
\B Matches except at a word boundary
\A Matches at the start of the string

\z Matches at the end of the string
\Z Matches at the end of the string or just before a newline at the end of the string
\G Matches at the starting offset character position, as passed to the preg_match()
function

It ’ s important to note that an anchor doesn ’ t itself match any characters; it merely ensures that the
pattern appears at a specified point in the target string.

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