passing preg_replace regex into a function

Question

I'm using a function to read specific query string variables and strip them of non-desired characters,

The problem is that, when I try to use the passed-in regex class of '[^ -a-zA-Z0-9]' , the function does not strip anything out... However if I hard-code that same regex into the function, it works just fine.

Any ideas? Is there something inherently 'bad' about passing the desired regex class into a function?

Here is the function:

function CleanURLVariable($variablename,$defaultvalue,$allowedcharclass,$lowercase) {

    if (isset($_GET[$variablename])) {
            $temp = preg_replace('/'.$allowedcharclass.'/i','',urldecode(trim($_GET[$variablename])));

            if ($lowercase) {
                $value = strtolower($temp); 
            } else {
                $value = $temp;
            }
            return $value ;
        } else {
            return $defaultvalue;
        }
} // end of function CleanURLVariable

Called like this:

$myCleanedVariable = CleanURLVariable('kw',false,'[^ -a-zA-Z0-9]',false);

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

Your regex is false, you need to place the hyphen at the beginning:

[^- a-zA-Z0-9]

Otherwise php is trying to create a range (space) to a.

$str = "sads#$!^!#adsd#gf\$dsgf";

echo preg_replace('/[^ -a-zA-Z0-9]/i','', $str) . PHP_EOL;
echo preg_replace('/[^- a-zA-Z0-9]/i','', $str) . PHP_EOL;

prints:

sads#$!^!#adsd#gf$dsgf

sadsadsdgfdsgf

edited Jun 20, 2020 at 9:12

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answered Mar 9, 2011 at 20:51

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1 Comment

Brian Adkins Over a year ago

I think you nailed it... I think I added the space and the dash as 'acceptable' characters at different times and didn't pay attention to the order... When I was testing the hard-coded version, I typed in the REGEX correctly instead of copy-paste... thanks

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