Sir im a beginer to oracle database my query is,How we can connect to a database if we do not know the ORACLE_HOME.
eg: if we have 5 databases running in a server and there are 5 different ORACLE_HOME ( ie, ORACLE_HOME is
different for each database ) how we can connect to the database without using an explicit export command.

sqlplus user/pwd@//<server>:<port>/<service>

-- in tnsnames.ora
<alias> =
 (DESCRIPTION =
   (ADDRESS_LIST =
     (ADDRESS = (PROTOCOL = TCP)(Host = <hostname>)(Port = <port>))
   )
 (CONNECT_DATA =
   (SERVICE_NAME = <service_name>)
 )
)

-- connect
sqlplus user/pwd@alias