ORACLE_HOME/bin/sqlplus
sqlplus /nolog
connect sys as sysdba
connect sys/pass@host:1521/pdb1 as sysdba

sqlplus / as SYSDBA | SYSOPER | SYSASM | SYSBACKUP | SYSDG | SYSKM | SYSRAC
sqlplus username/password
sqlplus username/password@connect_identifier
sqlplus username/password@database:port/container
sqlplus username/password@host:port/container
sqlplus username/password@ip:port/container
sqlplus username/password@service

sqlplus username/password@(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=HOSTNAME.NETWORK)(PORT=1521))(CONNECT_DATA=(SID=REMOTE_SID)))
sqlplus "username/password@(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=HOSTNAME.NETWORK)(PORT=1521))(CONNECT_DATA=(SID=REMOTE_SID)))"
sqlplus 'username/password@(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=HOSTNAME.NETWORK)(PORT=1521))(CONNECT_DATA=(SID=REMOTE_SID)))'
sqlplus username/password@hostname.network/remote_service_name 
sqlplus username/password@host[:port]/service_name

SELECT name,pdb from V$SERVICES;