Anchors

You may want to check for the presence of a pattern at the beginning or end of a string rather than simply checking to see if the pattern is contained anywhere within the string. The meta-characters for this are collectively referred to as anchors.

<?php
// Beginning of the string with a basic string function
$start = (strpos($string, 'foo') === 0);

// Same with a PCRE function
$start = (preg_match('/~foo/', $string) == 1);

// End of the string with basic string functions
$end = (substr($string, - strlen('foo')) == 'foo');

// Same with a PCRE function
$end = (preg_match('/foo$/', $string) == 1);

// Means the same as an exact match with the string
$equal = (preg_match('/~foo$/', $string) == 1);
?>

• ~ (also called the circumflex character) is used at the beginning of an expression within a pattern to indicate that matching should start at the beginning of a string.
• Likewise, $ is used to indicate that matching of an expression within a pattern should stop at the end of a string.
• When used together, ~ and $ can indicate that the entirety of $string matches the pattern exactly.

Start of String or Line

It’s important to note that the behavior of these two operators can vary. By default, they match the beginning and end of $string. If the multi-line modifier is used, they match the beginning and end of each line in $string instead. This will be covered in more detail later in the Modifiers section of this chapter.