{
    # use a closure to make a private memory for sub. 
    my %escapes;
 
    sub uri_escape {
        my($text) = @_;
        # the first time the sub is called %escapes is undef  
        # so we build a char->hex map. because we use a closure
        # %escapes survives from one calling of this function 
        # to the next so we only map this once
        %escapes || do{ $escapes{chr $_} = sprintf("%%%02X", $_) for 0..255 };
      return undef unless defined $text;
    	$text =~ s/([^A-Za-z0-9\-_.!~*'()])/$escapes{$1}/g;
      return $text;
    }
}