PHP: Can preg_match include unmatched groups? - php

Question

Can the preg_match() function include groups it did not find in the matches array?
Here is the pattern I'm using:
/^([0-9]+)(.[0-9]+)?\s?([^iIbB])?([iI])?([bB])?$/
What I'm trying to is parse an human readable size into bytes. This pattern fits my requirement, but only if I can retrieve matches in the absolute group order.
This can produce upto 5 match groups, which would result in a matches array with indices 0-5. However if the string does not match all groups, then the matches array may have, for example, group 5 actually at index 3.
What I'd like is the final match in that pattern (5) to always be at the same index of the matches array. Because multiple groups are optional it's very important that when reading the matches array we know which group in the expression got matched.
Example situation: The regex tester at regexr.com will show all 5 groups including those not matched always in the correct order. By enabling the "global" and "multi-line" flags and using the following text, you can hover over the blue matches for a good visual.
500.2 KiB
256M
700 Mb
1.2GiB
You'll notice that not all groups are always matched, however the group indexes are always in the correct order.
Edit: Yes I did already try this in PHP with the following:
$matches = [];
$matchesC = 0;
$matchesN = 6;
if (!preg_match("/^([0-9]+)(\.[0-9]+)?\s?([^iIbB])?([iI])?([bB])?$/", $size, $matches) || ($matchesC = count($matches)) < $matchesN) {
print_r($matches);
throw new \Exception(sprintf("Could not parse size string. (%d/%d)", $matchesC, $matchesN));
}
When $size is "256M" that print_r($matches); returns:
Array
(
[0] => 256M
[1] => 256
[2] =>
[3] => M
)
Groups 4 and 5 are missing.

Answer 1

The non-participating groups are just not initialized with an empty string value in PHP, so, Group 4 and 5 are null in case of '256M' string. It seems that preg_match discards those non-initialized values from the end of the array.
In your case, you can make your capturing groups non-optional, but the patterns inside optional.
$arr = array('500.2 KiB', '256M', '700 Mb', '1.2GiB');
foreach ($arr as $s) {
if (preg_match('~^([0-9]+)(\.[0-9]+)?\s?([^ib]?)(i?)(b?)$~i', $s, $m)) {
print_r($m) . "\n";
}
}
Output:
Array
(
[0] => 500.2 KiB
[1] => 500
[2] => .2
[3] => K
[4] => i
[5] => B
)
Array
(
[0] => 256M
[1] => 256
[2] =>
[3] => M
[4] =>
[5] =>
)
Array
(
[0] => 700 Mb
[1] => 700
[2] =>
[3] => M
[4] =>
[5] => b
)
Array
(
[0] => 1.2GiB
[1] => 1
[2] => .2
[3] => G
[4] => i
[5] => B
)
See the PHP demo.

Answer 2

You can use T-Regx which can handle such cases with ease! It always checks whether a group is matched, even if it's last and unmatched. It also can differentiate between "" (matched empty) or null (unmatched):
pattern('^([0-9]+)(.[0-9]+)?\s?([^iIbB])?([iI])?([bB])?$')
->match($size)
->first(function (Match $match) {
// whether the group was used in a pattern
$match->hasGroup(14);
// whether the group was matched, even if last or empty string
$match->matched(5);
// group, or default value if not matched
$match->group(5)->orReturn('unmatched');
});