Dynamically Spool data within PL/SQL Block

I have a requirement as follows.

I have a master table A that has 10+ columns along with data and a configuration table B that has only 2 columns i.e table name and column name. For ex:-

Table A:-

C1 C2 C3 C4 C5 C6
-- -- -- -- -- -----
1 2 3 4 3 6
4 5 6 5 5 5

Table B:-

Table_Name Column_Name
--------- ----------
A C1
A C2
A C3

Now I need to write a sql script that should take the table A Columns defined in Table B and then based on the columns it should spool the columns output from Table A.

For above ex:- I need to spool the C1,C2,C3 columns data from Table A in to some Unix path using SQL SCRIPT.

Request someone to provide suggestions or script if you have some idea