Regular Expression

[JonD]

Im trying to make sure a user can only enter a string which has characters [a-zA-Z_0-9] (This eqivalent to '\w'?), but it seems to not work.

If the string only contains these characters do this, otherwise do that.

if(!preg_match('\w', $string))
  postError;
else
  continue;

Can anyone see why is isnt working?

 

[growse]

You're saying "If this string is a single whitespace character". So " " will not match. You need to match either a whitespace character that's surrounded by 0 or many other characters:

(.*?)\w(.*?)

or just match a string of characters you want 1 or many times:

[a-zA-Z0-9]+

 

[JonD]

if (!preg_match('[a-zA-Z_0-9]+', $string))
{
// bla bla
}

Returns the following error:

Warning: preg_match() [function.preg-match]: Unknown modifier '+' in mypage.php on line 19

 

[Augmented]

You need to put the expression between delimiters:

if (!preg_match('|[a-zA-Z_0-9]+|', $string))
{
// bla bla
}

I used the pipe here, but you can use other characters like a # or a /.

 

[JonD]

No errors this time but this string was accepted:

23424\"\"%\"&\"\"

Any Ideas?

Im running the string through strip_tags first:

$string = strip_tags($_POST['variable']);

!preg_match(.....

 

[Dj_Jestar]

\w means single word, no whitespace.

<?php

if (preg_match('/^[a-z0-9_]+$/im', $string))
{
    // $string only contains a-z, 0-9 chars (upper and lower)
}

?>