I have a PHP regEx, how do add a condition for the number of characters?

Question

I have a regular expression that Im using in php:

$word_array = preg_split(
    '/(\/|\.|-|_|=|\?|\&|html|shtml|www|php|cgi|htm|aspx|asp|index|com|net|org|%|\+)/',
    urldecode($path), NULL, PREG_SPLIT_NO_EMPTY
);

It works great. It takes a chunk of url paramaters like:

/2009/06/pagerank-update.html

and returns an array like:

array(4) {
  [0]=>
  string(4) "2009"
  [1]=>
  string(2) "06"
  [2]=>
  string(8) "pagerank"
  [3]=>
  string(6) "update"
}

The only thing I need is for it to also not return strings that are less than 3 characters. So the "06" string is garbage and I'm currently using an if statement to weed them out.

score 4 · Accepted Answer · edited May 23 '17 at 10:24

The magic of the split. My original assumption was technically not correct (albeit a solution easier to come to). So let's check your split pattern:

(\/|\.|-|_|=|\?|\&|html|shtml|www|php|cgi|htm|aspx|asp|index|com|net|org|%|\+)

I re-arranged it a bit. The outer parenthesis is not necessary and I moved the single characters into a character class at the end:

 html|shtml|www|php|cgi|htm|aspx|asp|index|com|net|org|[\/._=?&%+-]

That for some sorting upfront. Let's call this pattern the split pattern, s in short and define it.

You want to match all parts that are not of those characters from the split-at pattern and at minimum three characters.

I could achieve this with the following pattern, including support of the correct split sequences and unicode support.

$pattern    = '/
    (?(DEFINE)
        (?<s> # define subpattern which is the split pattern
            html|shtml|www|php|cgi|htm|aspx|asp|index|com|net|org|
            [\\/._=?&%+-] # a little bit optimized with a character class
        )
    )
    (?:(?&s))          # consume the subpattern (URL starts with \/)
    \K                 # capture starts here
    (?:(?!(?&s)).){3,} # ensure this is not the skip pattern, take 3 characters minimum
/ux';

Or in smaller:

$path       = '/2009/06/pagerank-update.htmltesthtmltest%C3%A4shtml';
$subject    = urldecode($path);
$pattern    = '/(?(DEFINE)(?<s>html|shtml|www|php|cgi|htm|aspx|asp|index|com|net|org|[\\/._=?&%+-]))(?:(?&s))\K(?:(?!(?&s)).){3,}/u';
$word_array = preg_match_all($pattern, $subject, $m) ? $m[0] : [];
print_r($word_array);

Result:

Array
(
    [0] => 2009
    [1] => pagerank
    [2] => update
    [3] => test
    [4] => testä
)

The same principle can be used with preg_split as well. It's a little bit different:

$pattern = '/
    (?(DEFINE)       # define subpattern which is the split pattern
        (?<s>
    html|shtml|www|php|cgi|htm|aspx|asp|index|com|net|org|
    [\/._=?&%+-]
        )
    )
    (?:(?!(?&s)).){3,}(*SKIP)(*FAIL)       # three or more is okay
    |(?:(?!(?&s)).){1,2}(*SKIP)(*ACCEPT)   # two or one is none
    |(?&s)                                 # split @ split, at least
/ux';

Usage:

$word_array = preg_split($pattern, $subject, 0, PREG_SPLIT_NO_EMPTY);

Result:

Array
(
    [0] => 2009
    [1] => pagerank
    [2] => update
    [3] => test
    [4] => testä
)

These routines work as asked for. But this does have its price with performance. The cost is similar to the old answer.

Related questions:

Old answer, doing a two-step processing (first splitting, then filtering)

Because you are using a split routine, it will split - regardless of the length.

So what you can do is to filter the result. You can do that again with a regular expression (preg_filter), for example one that is dropping everything smaller three characters:

$word_array = preg_filter(
    '/^.{3,}$/', '$0', 
    preg_split(
        '/(\/|\.|-|_|=|\?|\&|html|shtml|www|php|cgi|htm|aspx|asp|index|com|net|org|%|\+)/',
        urldecode($path), 
        NULL, 
        PREG_SPLIT_NO_EMPTY
    )
);

Result:

Array
(
    [0] => 2009
    [2] => pagerank
    [3] => update
)

This does EXACTLY what I was asking for thank you. I hadn't used preg_filter before so thanks for adding to my code base. Also YES a function inside of a function. Its a great way to cut down on code and if you do any work with JavaScript its a standard practice. — RachelD, Dec 21 '12 at 18:21
you can also asssign to variables what I normally do. I will make the answer more readable. — hakre, Dec 21 '12 at 18:49
Ive been working with these scripts for a little while and I believe that yours gives more results. — RachelD, Dec 21 '12 at 20:22

score 1 · Answer 2 · answered Dec 21 '12 at 17:31

1

I'm guessing you're building a URL router of some kind.

Detecting which parameters are useful and which are not should not be part of this code. It may vary per page whether a short parameter is relevant.

In this case, couldn't you just ignore the 1'th element? Your page should (or 'handler') should have knowledge over which parameters it wants to be called with, it should do the triage.

answered Dec 21 '12 at 17:31

Halcyon

57,230
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I am not creating a router at all. I am searching batches of urls for useful information. But thank you for your answer. – RachelD Dec 21 '12 at 18:10

score 1 · Answer 3 · answered Dec 21 '12 at 17:38

I would think that if you were trying to derive meaning from the URL's that you would actually want to write clean URL's in such a way that you don't need a complex regex to derive the value.

In many cases this involves using server redirect rules and a front controller or request router.

So what you build are clean URL's like

/value1/value2/value3

Without any .html,.php, etc. in the URL at all.

It seems to me that you are not addressing the problem at the point of entry into the system (i.e the web server) adequately so as to make your URL parsing as simple as it should be.

I am not the one writing the urls I am searching batches of urls for useful information. But thank you for your answer. — RachelD, Dec 21 '12 at 18:11

score 1 · Answer 4 · answered Dec 21 '12 at 17:56

1

How about trying preg_match() instead of preg_split()?

The pattern (using the Assertions):

/([a-z0-9]{3,})(?<!htm|html|shtml|www|php|cgi|htm|aspx|asp|index|com|net|org)/iu

The function call:

$pattern = '/([a-z0-9]{3,})(?<!htm|html|shtml|www|php|cgi|htm|aspx|asp|index|com|net|org)/iu';
$subject = '/2009/06/pagerank-update.html';
preg_match_all($pattern, $subject, $matches);
print_r($matches);

You can try the function here: functions-online.com/preg_match_all.html

Hope this helps

answered Dec 21 '12 at 17:56

ᴍᴇʜᴏᴠ

4,804
4
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Thank you this is much faster than what I had in the beginning. – RachelD Dec 21 '12 at 18:22
After testing this method vs the below answer using the preg_filter this is faster. Im going call this the correct answer because of speed superiority. Thanks again! – RachelD Dec 21 '12 at 18:31
According to what was originally asked for, this does only a fraction of the job. That's why it is faster, too. – hakre Dec 21 '12 at 18:54
This solution fails to split at the diverse "html" in `$path = '/2009/06/pagerank-update.htmltesthtmltesthtml';` and with unicode characters inside the URL (mind the urldecode). – hakre Dec 21 '12 at 19:16
I updated my answer. It shows two patterns, one for `preg_match_all` and one for `preg_split`. – hakre Dec 21 '12 at 20:16

Andy Lester · Answer 5 · 2012-12-21T17:55:45.127

-3

Don't use a regex to break apart that path. Just use explode.

$dirs = explode( '/', urldecode($path) );

Then, if you need to break apart an individual element of the array, do that, like on your "pagerank-update" element at the end.

EDIT:

The key is that you have two different problems. First you want to break apart the path elements on slashes. Then, you want to break up the filename into smaller parts. Don't try to cram everything into one regex that tries to do everything.

Three discrete steps:

$dirs = explode...
Weed out arguments < 3 chars
Break up file argument at the end

It is far clearer if you break up your logic into discrete logical chunks rather than trying to make the regex do everything.

edited Dec 21 '12 at 17:55

answered Dec 21 '12 at 17:28

Andy Lester

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That won't break up the file name nor the file type which the OP requires. – Ryan Brodie Dec 21 '12 at 17:33
How does that solve the problem of removing short elements from the result? – Barmar Dec 21 '12 at 17:34
I dont think this is the fastest method which is why I was going with the preg_split method. If I could not return the chunks that are less than three chars long then I wouldn't have to do any further processing of the data. – RachelD Dec 21 '12 at 18:17
Two suggestions: First, without testing which one is faster, you don't know which one is faster, or by how much. You are guessing. Second, programmer time spent trying to debug and maintain a huge regex is much longer and much more expensive than a difference in milliseconds of machine time when this thing runs. – Andy Lester Dec 21 '12 at 18:24

I have a PHP regEx, how do add a condition for the number of characters?

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