The following scripts displays  the primary key and foreign key constraints for a given table.

COLUMN CONSTRAINT_NAME FORMAT A25
COLUMN COLUMNS FORMAT A40
COLUMN TABLE_NAME FORMAT A40
SET LINESIZE 500
DEFINE TAB = &TABLENAME

select constraint_name, DECODE(constraint_type,'P','PRIMARY KEY','R','FOREIGN KEY',CONSTRAINT_TYPE) CONSTRAINT_TYPE,
        rtrim(
         max(decode(position,1,column_name,null)) || ','||
         max(decode(position,2,column_name,null)) || ','||
         max(decode(position,3,column_name,null)), ','  ) columns, table_name
    from (
  select a.constraint_name,
        a.constraint_type,
         b.column_name,
         b.position,
         b.table_name
    from ALL_constraints a, ALL_cons_columns b
  where
     (( a.constraint_type = 'P' and a.table_name = UPPER('&&TAB' ))
     or
      ( a.constraint_type = 'R' and a.r_constraint_name  =
                     ( select constraint_name
                          from ALL_constraints
                        where constraint_type = 'P'
                           and table_name = UPPER('&&TAB' ))
      ) )
     and a.constraint_name = b.constraint_name
     )
  group by constraint_name, constraint_type, TABLE_NAME
  order by 2,1
 
undefine tablename
/
SET LINESIZE 100