How to connect to pluggable database using ipc in Oracle XE 18c? Here is my listener configuration:
LSNRCTL for Linux: Version 18.0.0.0.0 - Production on 20-NOV-2020 20:01:25

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Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=NoteBook)(PORT=1521)))
STATUS of the LISTENER
------------------------
Alias                     LISTENER
Version                   TNSLSNR for Linux: Version 18.0.0.0.0 - Production
Start Date                20-NOV-2020 20:00:55
Uptime                    0 days 0 hr. 0 min. 29 sec
Trace Level               off
Security                  ON: Local OS Authentication
SNMP                      OFF
Default Service           XE
Listener Parameter File   /opt/oracle/product/18c/dbhomeXE/network/admin/listener.ora
Listener Log File         /opt/oracle/diag/tnslsnr/NoteBook/listener/alert/log.xml
Listening Endpoints Summary...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=NoteBook)(PORT=1521)))
  (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521)))
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcps)(HOST=127.0.0.1)(PORT=5500))(Security=(my_wallet_directory=/opt/oracle/product/18c/dbhomeXE/admin/XE/xdb_wallet))(Presentation=HTTP)(Session=RAW))
Services Summary...
Service &quot;XE&quot; has 1 instance(s).
  Instance &quot;XE&quot;, status READY, has 1 handler(s) for this service...
Service &quot;XEXDB&quot; has 1 instance(s).
  Instance &quot;XE&quot;, status READY, has 1 handler(s) for this service...
Service &quot;b470a0c2708d9acee0530401a8c035ac&quot; has 1 instance(s).
  Instance &quot;XE&quot;, status READY, has 1 handler(s) for this service...
Service &quot;xepdb1&quot; has 1 instance(s).
  Instance &quot;XE&quot;, status READY, has 1 handler(s) for this service...
The command completed successfully

I can connect to xepdb1 through tcp using sqlplus user/password@NoteBook/xepdb1, however, if I use use ipc (sqlplus user/password@xepdb1) to connect, it fails with an error ORA-12154: TNS:could not resolve the connect identifier specified.
How can I connect to a pluggable database using ipc?
&quot;if I use use ipc (sqlplus user/password@xepdb1) &quot;

That's not IPC, that's tcp.  It tries to find the entry for 'xepdb1' in the client's tnsnames.ora file. Then it tries to construct a tcp packet from the information found there, and send that packet to the specified host and port, where - hopefully - there is a listener.  Your error means that it could not find the specified entry in the client's tnsnames.ora.