[RESOLVED] Preg_Match - search for special chracters

[si69j2]

Hi guys,

I'm relatively new to PHP and I want to create a preg_match statement that searches for numbers and special characters.

Currently I have.

preg_match("/([0-9])|(\"|}|{|!|@|£|\$|%|^|\&|()|\?||||[|]|-|\=|+|\§|\±)/", $string))

I want to use this as part of my form checking to ensure that no special characters are entered as a user name. I only want to accept characters that are either a-z or - or – or '. I want to detect any thing outside of this. I was told preg_match was the way to do it.

If someone could either suggest a better way of doing this that would be great.

[bradgrafelman]

In many cases (yours included), it is a lot easier to define a whitelist rather than a blacklist.

In other words, use preg_match() to match strings that are valid. If it doesn't match, then reject the input as invalid.

[si69j2]

bradgrafelman;10972430 wrote:

In many cases (yours included), it is a lot easier to define a whitelist rather than a blacklist.

In other words, use preg_match() to match strings that are valid. If it doesn't match, then reject the input as invalid.

Would this be the solution preg_match_all and compare the number of matches to the string length and if it doesn't match invalidate.

something like...

preg_match_all("/([a-zA-z])|(\'|-|\–)/", $string, $matches);
$int = count($matches);
$strint = strlen($string);

if ($int == $strint){
$valid = TRUE;
}else{
$valid = FALSE;
}

As this is how I would interpret your suggestion. Is this the best way. Its definitely simpler.

[bradgrafelman]

It'd be a lot simpler to just check the return value of [man]preg_match/man. Common usage in this situation might be:

if(!preg_match("/^[a-z'–-]+$/i", $string)) {
  // invalid
}

[si69j2]

I think I see what you mean, although I thought that preg_match would stop when it found the first character that matched the search. Nevertheless I will give it ago

besides my solution wouldn't work unless I included count($matches[0]) - incase anyone else reads this thread.

si69j2;10972432 wrote:

something like...

preg_match_all("/([a-zA-z])|(\'|-|\–)/", $string, $matches);
$int = count($matches);
.

Thanks for your assistance, I guess I still don't 100% understand preg_match.

[bradgrafelman]

si69j2 wrote:

I thought that preg_match would stop when it found the first character that matched the search

Not completely correct, but close - it will stop when it finds the first match to the pattern given. My pattern above includes a greedy '+' which means "one or more". Since it's not ungreedy, it tries to collect as many entities as possible.

[si69j2]

Just wanted to say thanks, your suggestion and example were invaluable. As my guestimates on how to achieve the same were more than a little code intensive lol.

Appreciate the speediness of your responses as well. Thanks