How can I check with a regex that a string contains only certain allowed characters?

Question

I need a special regular expression and have no experience in them whatsoever, so I am turning to you guys on this one.

I need to validate a classifieds title field so it doesn't have any special characters in it, almost.

Only letters and numbers should be allowed, and also the three Swedish letters å, ä, ö (upper- or lowercase).

Besides the above, these should also be allowed:

• The "&" sign.
• Parentheses "()"
• Mathematical signs "-", "+", "%", "/", "*"
• Dollar and Euro signs
• One accent signed letter: "é". // Only this one is required
• Double quote and single quote signs.
• The comma "," and point "." signs

Answer 1

Try this:

^[\s\da-zA-ZåäöÅÄÖ&()+%/*$€é,.'"-]*$

Breakdown:

^ = matches the start of the string

[...]* = matches any characters (or ranges) inside the brackets one or more times

$ = matches the end of the string

Updated with all the suggestions from the comments. Thanks guys!

Answer 2

Hey buddy, its really very very simple. Just do a regex replace of anything you don't want...

In this example - I simple say "this stuff is not allowed"

More specifically it says "if its not in this regex match, replace that character with an empty string.

PHP:

$result = preg_replace('#([^a-zA-Z0-9£()+=%/*$,.])#imx', '', $subject);

if the section where you have a-zA-Z0-9£()+=%/*$ simply add the character your want to pass your regex and be allowed in the post.

---

Edit:

More expansive

This vbersion of the regex contains all upper case and lower case accented characters. Their in ASCII format as I don't know the key to write them!

$result = preg_replace('#([^a-zA-Z0-9£()+=%/*$,.\x99\xBC\xBD\xBE\xC0\xC1\xC2\xC3\xC4\xC5\xC7\xC8\xC9\xCA\xCB\xCC\xCD\xCE\xCF\xD1\xD2\xD3\xD4\xD5\xD6\xE0\xE1\xE2\xE3\xE4\xE5\xE7\xE8\xE9\xEA\xEB\xEC\xED\xEE\xEF\xF1\xF2\xF3\xF4\xF5\xF6\xF7\xF9\xFA\xFB\xFC\xFD])#imx', '', $subject);

Answer 3

^[\sa-zA-Z0-9åäö&()+%/*$€é,.'"-]*$

will match all the required characters.

In PHP:

if (preg_match('#^[\sa-zA-Z0-9åäö&()+%/*$€é,.\'"-]*$#i', $subject)) {
 # Successful match
} else {
 # Match attempt failed
}

Answer 4

PHP has a variety of functions that can help with text validation. You may find them more appropriate than a straight regex. Consider strip_tags(), htmlspecialchars(), htmlentities()

As well, if you are running >PHP5.2, you can use the excellent Filter functions, which were designed for exactly your situation.