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return unmatched characters with a regex funtion, php

Posted on 2009-03-30
Last Modified: 2013-12-12
Using PHP I need to validate a string in a function and eventually return something to the user like:

"Sorry, '<' is an invalid character"

I'm fine with just pulling the first unmatched character, but if it's easy enough we can show all of the invalid characters.

It's only for one small text field.

Allowed characters:


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Question by:kenitech
  • 4
  • 2
LVL 54

Expert Comment

ID: 24025155

Try the expression in the snippet below.

Let me know if you have any questions or need more information.

preg_match('/^[A-Za-z0-9 .!?':"()-]+$/',$value));

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LVL 54

Accepted Solution

b0lsc0tt earned 250 total points
ID: 24025162

Oops.  I misread this a bit.  You can get all characters that don't match with ...

preg_match_all('/[^A-Za-z0-9.!?\':"()-]/', $value, $result, PREG_PATTERN_ORDER);
$result = $result[0];

The variable $result is an array.  You can change it to a string or go through each item.

Let me know if you have a question.


Author Comment

ID: 24025323
this is great thanks! before I accept/close, can you just please clarify the php documentation for preg_match_all?


is it me or is it somewhat confusing that the $matches parameter is explained,
"Array of all matches in multi-dimensional array ordered according to flags ."

The output is the unmatched elements, though. This is what I want, but reading this leads me to believe otherwise.

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LVL 54

Expert Comment

ID: 24029432
Actually the output is the matched items.  If you notice I changed the expression so it will match the characters you don't want to allow.  Overlooking that change would make it seem to show non-matches.  Notice the ^ that is right after the open bracket ( [ ).
Let me know if you have any other questions on preg_match_all or what I provided.  I am glad it helped.

Author Closing Comment

ID: 31564648
LVL 54

Expert Comment

ID: 24029628
Your welcome!  I'm glad I could help.  Thanks for the grade, the points and the fun question.

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