Understanding PHP preg_match_all: Syntax, Parameters, and Examples

PHP's preg_match_all() function performs a global regular expression match, searching a subject string for all occurrences of a pattern and storing the results in an array.

Parameters

pattern : the regular expression pattern as a string.

subject : the input string to search.

matches : an output array that receives the matches, ordered according to the flags.

flags : optional flags such as PREG_PATTERN_ORDER or PREG_SET_ORDER (cannot be combined).

offset : optional byte offset to start the search.

Return value

The function returns the number of full pattern matches (or FALSE on error).

Examples

Example 1 – extracting phone numbers:

<?php
preg_match_all("/\(?  (\d{3})?  \)?  (?(1)  [\-\s] ) \d{3}-\d{4}/x",
    "Call 555-1212 or 1-800-555-1212",
    $phones);
?>

Example 2 – capturing HTML tags with PREG_SET_ORDER:

<?php
$html = "<b>bold text</b><a href=howdy.html>click me</a>";
preg_match_all("/(<([\w]+)[^>]*>)(.*?)(<\/\\2>)/", $html, $matches, PREG_SET_ORDER);
foreach ($matches as $val) {
    echo "matched: " . $val[0] . "
";
    echo "part 1: " . $val[1] . "
";
    echo "part 2: " . $val[2] . "
";
    echo "part 3: " . $val[3] . "
";
    echo "part 4: " . $val[4] . "

";
}
?>

Example 3 – named subpatterns:

<?php
$str = <<<FOO
a: 1
b: 2
c: 3
FOO;
preg_match_all('/(?P<name>\w+): (?P<digit>\d+)/', $str, $matches);
print_r($matches);
?>