I need to get rid of all non-alphanumeric characters from a string - how can I do it?

$var = "This string has some ' bogus ( characters. 922";
 $var =~ s/\W/_/g;
   print $var; 

The output of this would be:

This_string_has_some___bogus___characters__922  

This is useful if you are creating a file, and need the name to be friendly to the filesystem. Or if you are creating a string for a hash, or something where odd characters just present some extra headaches.