ORA-00955

I have the following error when I run the sql script

CREATE  SYNONYM abc FOR ABC
                *
ERROR at line 1:
ORA-00955: name is already used by an existing object

In my .sql file
I have the following lines

CREATE  SYNONYM abc FOR ABC;
....
exit;


I think the error is because abc already existed

I want to know how I put a condition to say]

if object abc existed already, need to run

CREATE  SYNONYM abc FOR ABC;

the following statement is correct?

IF NOT EXISTS (abc)
CREATE  SYNONYM abc FOR ABC;