I'm having a difficulty with understanding how G anchor works in PHP flavor of regular expressions.
I'm inclined to think (even though I may be wrong) that G is used instead of ^ in situations when multiple matches of the same string are taking place.
Could someone please show an example of how Gshould be used, and explain how and why it works?
UPDATE
G forces the pattern to only return matches that are part of a continuous chain of matches. From the first match each subsequent match must be preceded by a match. If you break the chain the matches end.
<?php
$pattern = '#(match),#';
$subject = "match,match,match,match,not-match,match";
preg_match_all( $pattern, $subject, $matches );
//Will output match 5 times because it skips over not-match
foreach ( $matches[1] as $match ) {
echo $match . '<br />';
}
echo '<br />';
$pattern = '#(Gmatch),#';
$subject = "match,match,match,match,not-match,match";
preg_match_all( $pattern, $subject, $matches );
//Will only output match 4 times because at not-match the chain is broken
foreach ( $matches[1] as $match ) {
echo $match . '<br />';
}
?>
This is straight from the docs
The fourth use of backslash is for certain simple assertions. An assertion specifies a condition that has to be met at a particular point in a match, without consuming any characters from the subject string. The use of subpatterns for more complicated assertions is described below. The backslashed assertions are
G
first matching position in subject
The G assertion is true only when the current matching position is at the start point of the match, as specified by the offset argument of preg_match(). It differs from A when the value of offset is non-zero.
http://www.php.net/manual/en/regexp.reference.escape.php
You will have to scroll down that page a bit but there it is.
There is a really good example in ruby but it is the same in php.
