reading CLOB from file and UPDATE

I'm trying to read a CLOB from an ascii-file and then do an UPDATE on a column WHERE that column matches a constraint.

here is the code:

declare
    l_bfile   bfile := bfilename('MY_DIR','null1.txt');
    l_data    clob;
    l_soffset NUMBER := 1;
    l_doffset NUMBER := 1;
    l_lang    NUMBER := 0;
    l_warn    NUMBER;
begin
    DBMS_LOB.createtemporary (lob_loc => l_data,cache => TRUE,
                                 dur => DBMS_LOB.call);
    dbms_lob.fileopen( l_bfile, DBMS_LOB.file_readonly );
    DBMS_LOB.loadclobfromfile(l_data, l_bfile, DBMS_LOB.LOBMAXSIZE,
           l_soffset, l_doffset, 0, l_lang, l_warn  );
    dbms_lob.fileclose(l_bfile);
    update PROC