How can I restrict some special characters only in PHP?

Question

I am using preg_match for restrict the special characters in form post. Now I need to restrict some special characters only like %,$,#,* and I need to post like bé. How to possible to restrict some special characters only.

My code:

<?php $firstname=''; if(isset($_POST['submit'])) { $firstname=$_POST['firstname']; if(preg_match("/[^a-zA-Z0-9]+/", $firstname)) { echo 'Invalid Name'; } else { echo $firstname; } } ?> <html> <body> <form method="post"> <input type="text" name="firstname"/> <input type="submit" name="submit" value="Submit"/> </form> </body> </html>

Maybe this will help you. stackoverflow.com/a/14114419/466082 — Arturs
– Arturs, Commented Aug 13, 2014 at 8:33
I suggest allowing - as a character in firstnames.... haven't you every heard of Jean-Claude Van Damme? Though I can't think of any first names that contain numbers off the top of my head — Mark Baker
– Mark Baker, Commented Aug 13, 2014 at 8:38

β.εηοιτ.βε · Accepted Answer · 2020-06-21 18:05:24Z

3

You should use:

([%\$#\*]+)

to match those characters.

So in preg_match you should use:

if(preg_match("/([%\$#\*]+)/", $firstname)) { echo 'Invalid Name'; } else { echo $firstname; }

edited Jun 21, 2020 at 18:05

β.εηοιτ.βε

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answered Aug 13, 2014 at 8:32

Marcin Nabiałek

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3 Comments

georg Over a year ago

So, (^_^;) is a valid name?

Marcin Nabiałek Over a year ago

@georg Of course not, but OP wanted only restrict selected characters

georg Over a year ago

Look, your code is quite different from what the OP has, because he (correctly) whitelists, and you blacklist. Blacklisting never works.

georg · Accepted Answer · 2014-08-13 08:40:06Z

Blacklisting (=enumerating invalid characters) is not an option in the unicode world. Consider for example, a "name" like this:

Ж☝ⓚƒ

You don't really want to blacklist all of these.

A whitelisting approach is, on the contrary, quite simple using the u mode and unicode properties:

var_dump(preg_match('/^[\p{L}\p{N}]+$/u', 'ßäßå')); // 1 var_dump(preg_match('/^[\p{L}\p{N}]+$/u', 'r2d2')); // 1 var_dump(preg_match('/^[\p{L}\p{N}]+$/u', 'w#t?')); // 0 var_dump(preg_match('/^[\p{L}\p{N}]+$/u', 'Ж☝ⓚƒ')); // 0

And since we're talking about validating real names, please read Falsehoods Programmers Believe About Names before you start complicating things.

You could add some punctuations like ' or - for O'Connors or Jean-François
@M42: the linked article is quite helpful and entertaining - read it!
Sure, I've already read it, I just said it may have punctuation in name.
@M42: I understand. The thing is, if we start adding punctation, we should do this correctly (to disallow things like O'O'Connor) and then our assumptions about the structure will turn out wrong (they will do), and this is a never-ending story. There's no algorithm to validate every possible human name.

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