the global dbname in there will be the service name:

[ora9ir2@localhost admin]$ cat listener.ora
# LISTENER.ORA Network Configuration File: /home/ora9ir2/network/admin/listener.ora
# Generated by Oracle configuration tools.

LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC))
)
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = localhost.localdomain)(PORT = 1521))
)
)
)

SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(SID_NAME = PLSExtProc)
(ORACLE_HOME = /home/ora9ir2)
(PROGRAM = extproc)
)
(SID_DESC =
(GLOBAL_DBNAME = WRONG)
(ORACLE_HOME = /home/ora9ir2)
(SID_NAME = ora9ir2)
)
)



when I ask that listener what services do you provide:

[ora9ir2@localhost admin]$ lsnrctl services

LSNRCTL for Linux: Version 9.2.0.4.0 - Production on 27-FEB-2005 09:08:05

Copyright (c) 1991, 2002, Oracle Corporation. All rights reserved.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC)))
Services Summary...
Service "PLSExtProc" has 1 instance(s).
Instance "PLSExtProc", status UNKNOWN, has 1 handler(s) for this service...
Handler(s):
"DEDICATED" established:0 refused:0
LOCAL SERVER
Service "WRONG" has 1 instance(s).
Instance "ora9ir2", status UNKNOWN, has 1 handler(s) for this service...
Handler(s):
"DEDICATED" established:0 refused:0
LOCAL SERVER
The command completed successfully
[ora9ir2@localhost admin]$





[ora9ir2@localhost admin]$ sh -vx t.sh
sqlplus 'scott/tiger@(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost.localdomain)(PORT=1521)))(CONNECT_DATA=(SERVICE_NAME=ora9ir2)))'
+ sqlplus 'scott/tiger@(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost.localdomain)(PORT=1521)))(CONNECT_DATA=(SERVICE_NAME=ora9ir2)))'
SQL*Plus: Release 9.2.0.4.0 - Production on Sun Feb 27 09:10:04 2005

Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.

ERROR:
ORA-12514: TNS:listener could not resolve SERVICE_NAME given in connect
descriptor


Enter user-name:
ERROR:
ORA-01017: invalid username/password; logon denied


Enter user-name:
ERROR:
ORA-01017: invalid username/password; logon denied


SP2-0157: unable to CONNECT to ORACLE after 3 attempts, exiting SQL*Plus
sqlplus 'scott/tiger@(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost.localdomain)(PORT=1521)))(CONNECT_DATA=(SERVICE_NAME=WRONG)))'
+ sqlplus 'scott/tiger@(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost.localdomain)(PORT=1521)))(CONNECT_DATA=(SERVICE_NAME=WRONG)))'

SQL*Plus: Release 9.2.0.4.0 - Production on Sun Feb 27 09:10:07 2005

Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.


Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.4.0 - Production

SQL>


so, the global dbname is the service name -- it is just a way to keep it "all straight", in a multi-database environment, you might think about using the global dbnames (and using the right ones, not the wrong ones) -- as service names so you know what the service names are implicitly (global database names) and have a reasonable expectation of what database you are connecting to.