Recipe 13.4 Finding the nth Occurrence of a Match
13.4.1 Problem
You want to find the
nth word match instead of the first one.
13.4.2 Solution
Use preg_match_all(
) to pull all the matches into an array;
then pick out the specific matches you're interested
in:
preg_match_all ("/$pattern/$modifiers", $string, $matches)
foreach($matches[1] as $match) {
print "$match\n";
}
13.4.3 Discussion
Unlike in Perl, PHP's Perl-compatible regular
expressions don't support the /g
modifier that allows you to loop through the string one match at a
time. You need to use preg_match_all( ) instead of
preg_match( ).
The preg_match_all( ) function returns a
two-dimensional array. The first element holds an array of matches of
the complete pattern. The second element also holds an array of
matches, but of the parenthesized submatches within each complete
match. So, to get the third potato, you access the
third element of the second element of the
$matches array:
$potatoes = 'one potato two potato three potato four';
preg_match_all("/(\w+)\s+potato\b/", $potatoes, $matches);
print $matches[1][2];
three
Instead of returning an array divided into full matches and then
submatches, preg_match_all( ) returns an array
divided by matches, with each submatch inside. To trigger this, pass
PREG_SET_ORDER in as the fourth argument. Now,
three isn't in
$matches[1][2], as previously, but in
$matches[2][1].
Check the return value of preg_match_all( ) to
find the number of matches:
print preg_match_all("/(\w+)\s+potato\b/", $potatoes, $matches);
3
Note that there are only three matches, not four, because
there's no trailing potato after
the word four in the string.
13.4.4 See Also
Documentation on preg_match_all( ) at http://www.php.net/preg-match-all.
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