@FILEWRITEB

@FILEWRITEB[n,length,string]:  Writes the specified number of bytes from 
string to the file whose handle is n.  Returns the number of bytes 
written, or "-1" if an error occurred. 

If you plan to write binary data with @FILEWRITEB, you should open the 
file in binary mode (see @FILEOPEN).  If you want to write text a line at 
a time you should use @FILEWRITE instead, and open the file in text mode. 

Be sure to read the cautionary note about file functions under Variable 
Functions.