procedure ins_or_upd ( s varchar2 ... ) is
begin
   update ... where column=s;
   if SQL%rowcount = 0 then 
       insert ...
   end if;
end;
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I have twenty five fields (scalars)that I am reading from the file per line . How do I pass the variables to the stored procedure in my perl script. Thanks

That depends on the DBMS you are using. I know Oracle so I can only
tell you how to go about this with PL/SQL.
In PL/SQL your could have a stored function that could tell your script if a record exist or not so that your script could choose either to do a insert or an update. You could also just use a stored procedure like the one I mentioned earlier and just add your fields to the parameter list. You could also do everything from your script. Your script could do the update and if the row count is zero that means your script needs to do an insert.

• if it's not very big (say, up to some thousands of rows), start by reading all the values of "$Control" that are currently present in the database, and storing these as keys of a hash -- e.g. if you "select" all values of that field into @Control, then  $hash{$_}++ for (@Control);
• if it's a very big database, figure out a quick/easy query to look for a given value of $Control in your DB, and just do that for every input record you process.

In either case, as you process your input file data, if the given value of $Control exists/is found, then execute an update, else execute an insert.

If you need more details about how to do that, you should give more details about what you're using and what you've tried so far.