Regex: Replace any non-alphanumeric string except space

Question

My Apologies, I have never gotten to grips with regex expressions.

I need to remove anything (from a product name, some of them have ampersands in them) that isnt alphanumeric from a string, excluding the spaces.

So far I have this (found from another stackoverflow post):

$productname = preg_replace("~[\W]~","",$product['name']);

Now this replaces everything that is alphanumeric with "". Which is fine, except I want to exclude spaces as It is currently removing all spaces. Also, i cannot find anywhere what the tilde (~) does in regex.

With regards to the spaces, I have seen that there is a negative lookahead, achieved by ?!, but how to incorporate that in the above I don't know.

the ~ is a delimiter for PCRE regex, http://www.php.net/manual/pt_BR/regexp.reference.delimiters.php — rray, Nov 04 '13 at 14:40
`I have never gotten to grips with regex expressions.` Regex means "regular expressions", so you don't need to say regex expressions, because it's like saying: regular expressions expressions. Just a hint. :) — Rafael Barros, Nov 04 '13 at 14:53

Ibrahim Najjar · Accepted Answer · 2013-11-04T15:12:16.683

6

Also, i cannot find anywhere what the tilde (~) does in regex.

Regular expressions in PHP are enclosed in set of delimiters, usually ~ but you can use any non-alphanumeric character except for a few which are mentioned in the documentation.

Now if you want to replace any non-alphanumeric excluding spaces then you can do:

~[^a-zA-Z0-9\s]+~

^ inside the character class [] makes the character class match anything not mentioned inside of it like [^a] matches anything but a.
a-z match small letters.
A-Z match uppercase letters.
0-9 match digits.
\s match space characters.
^ makes the previous class match everything but what was mentioned.
+ after the characters class, makes the character class match one or more characters which are not mentioned in the character class.

\W alone matches non-word characters, so what are word characters ?

Word characters are usually any letters (small, uppercase), digits or underscore _.

Word characters \w (with small w) are usually equal to this character class [a-zA-Z0-9_].

\W (big W) matches non-word characters so it matches anything but what \w matches including spaces, so it will remove the spaces also.

edited Nov 04 '13 at 15:12

answered Nov 04 '13 at 14:41

Ibrahim Najjar

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This doesnt seem to work, it wipes my whole string clean. I want to remove **all** alaphanumeric characters *except* spaces? – Chud37 Nov 04 '13 at 14:52
@Chud37 You want to remove all alphanumeric or **non** alphanumeric ? – Ibrahim Najjar Nov 04 '13 at 14:53
Sorry: I want to remove **all** non-alaphanumeric characters **except** spaces – Chud37 Nov 04 '13 at 14:55
@Chud37 You are correct, sorry for this. I am gonna fix it or remove the answer. – Ibrahim Najjar Nov 04 '13 at 14:57
I didn't try it, I don't understand the logic in replacing \W with the extended version? – Chud37 Nov 04 '13 at 15:03
Brilliant, well explained, and works perfectly. Thank you so much @Sniffer. – Chud37 Nov 04 '13 at 15:16

Robert · Answer 2 · 2013-11-04T14:42:31.710

0

You can do simple negation in class block

$productname = preg_replace("#[^A-Za-z0-9]+#","",$product['name']);

it will replace with "" everything what is not alphanumeric

edited Nov 04 '13 at 14:42

answered Nov 04 '13 at 14:37

Robert

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Thank you, could you explain the above please? Also, why did you lose the `\W` in favor for `A-Za-z0-9`, and why is your start `^` inside the `[]`? – Chud37 Nov 04 '13 at 14:39
`^` is used for negation it means that the characters inside class cannot be in word. – Robert Nov 04 '13 at 14:42
This also removes the spaces. – Chud37 Nov 04 '13 at 15:05

Regex: Replace any non-alphanumeric string except space

2 Answers2