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Why Doesn't this regex return a positive result?

Posted on 2014-03-07
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Last Modified: 2014-03-07
I'm not familiar with regex and a temp programmer used this code.
        $pattern = '^[AD]([HF][12]|[Z][1])([0][1234569]|[1][0-9]|[2][123]|[3][34]|[4][0]|[5][1346])([0][12345679]|[1][0])([0][12345]|[1][03]|[2][03679]|[3][2389]|[4][01]|[5][1]|[9][5])([0][0123458]|[1][8]|[2][68]|[3][8]|[4][8]|[H][B])*^';
        
        //check if the product code matches a valid code pattern
        if(!preg_match($pattern, $pc)){
            $error = 'Please enter a valid product code';
        }

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$pc is equal to "AF141020100"

I'm wondering if someone could explain how this code does not match the pattern specified.
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Question by:dmleves49
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Expert Comment

by:Dan Craciun
ID: 39913593
Because it expects to be AF140, not AF141

HTH,
Dan
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Accepted Solution

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Dan Craciun earned 500 total points
ID: 39913604
Try this pattern to match:
$pattern='^[AD]([HF][12]|[Z][1])([0][1234569]|[1][0-9]|[2][123]|[3][34]|[4][01]|[5][1346])([0][12345679]|[1][0])([0][12345]|[1][03]|[2][03679]|[3][2389]|[4][01]|[5][1]|[9][5])([0][0123458]|[1][8]|[2][68]|[3][8]|[4][8]|[H][B])*$'

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Expert Comment

by:Ray Paseur
ID: 39913722
http://xkcd.com/1171/

Try writing down the rules for the product code.  I'll bet the regular expression could be a LOT simpler.
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Author Comment

by:dmleves49
ID: 39913751
Thanks Dan. I was able to aquaint myself with regex enough to figure it out. The first two characters could only equal 33 or 34 if they started with a 3 or 40 if they started with a 4, etc.
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LVL 35

Expert Comment

by:Dan Craciun
ID: 39913758
OK. So what was deficient in my answer?
See here for the grading guide: http://support.experts-exchange.com/customer/portal/articles/481419-what-grade-should-i-award-

In case of any other grade than A you are required to explain what was deficient about the solution.

Thank you.
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Author Comment

by:dmleves49
ID: 39913944
I'm new here so I don't want to cause any problems as I appreciated everyone's help. I do however feel that getting the answer correct isn't actually what I requested.

I would have expected something like what I originally discovered. For Example:

The reason that your product code does not match the regex is because each set of parentheses is testing 2 digits. The first set of digits that do not match in your regex are "41" because [4][0] will only match "40". If you used [4][01] then it would match 40 or 41.

I'll upgrade your mark though. I just thought it required a bit of explanation since I said I wasn't familiar with regex.
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Author Closing Comment

by:dmleves49
ID: 39913950
Sorry Dan , I only saw your code comment, not your explanation. My bad.
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Expert Comment

by:Dan Craciun
ID: 39914167
No worries, mate. Thanks for the points and welcome to EE.

Dan
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