How Remove Special Charecters from File Field in Drupal

function sukant_rout_init()
{
if (!empty($_FILES['files']))
{
foreach ($_FILES['files']['name'] as $field => $filename)
{
$_FILES['files']['name'][$field] = preg_replace('`[^\.a-z0-9]`i','_',$filename);
}
}
}
Replace sukant_rout by your module name