Ошибка в скрипте на Перле

use strict;
use CGI 'param';
 
my $sid = param("SID");
my $category = param("category");
 
# <UserData><SID>some_session_id</SID><CategoryID>49070</CategoryID></UserData></GetCategory2CSResponse>
my $addition = join '', "<UserData><SID>", $sid, "</SID><CategoryID>", $category, "</CategoryID></UserData></GetCategory2CSResponse>";
 
sysopen FILE_OLD, "source.xml", O_RDONLY;
sysopen FILE_NEW, "final.xml", O_WRONLY|O_TRUNC|O_CREATE;
 
my @buf = <FILE_OLD>;
 
print FILE_NEW @buf;
print FILE_NEW $addition;
 
close (FILE_OLD);
close (FILE_NEW);