set define '&'
set verify off
set serveroutput on
declare
invalid_column_name exception;
pragma exception_init(invalid_column_name, -904);
l_update_text varchar2(100) :=
'update &&table_name set &&updated_column_name = '':a'' where &&key_column_name = :a';
begin
execute immediate l_update_text
using '&update_column_value', &key_column_value;
exception
when INVALID_COLUMN_NAME then
dbms_output.put('ERROR! You entered an invalid column name ');
dbms_output.put('(&updated_column_name or &key_column_name). Please ');
dbms_output.put_line('check your table definition and try again');
end;
/