Here I tried to output some space key in the beginning of a line. However, SQL Plus seems to ignore those space keys. If I add something like '--' before the space keys, it works. Is there a way to print space key before other characters?

Test:

SQL> exec dbms_output.put_line(' there are space in the beginning of the line.') ;
there are space in the beginning of the line.

PL/SQL procedure successfully completed.

SQL> exec dbms_output.put_line('-- there are space in the beginning of the line.') ;
-- there are space in the beginning of the line.

PL/SQL procedure successfully completed.[FONT=courier new][FONT=courier new]