SP2-0158
SP2-0158 means that the issued command is not supported by this release of SQL*Plus utility. For example, we use SQL*Plus 11.2.0.4 to connect to a multitenant database like this.
C:\Users\scott>sqlplus sys/password@orclcdb as sysdba
SQL*Plus: Release 11.2.0.4.0 Production on Wed Feb 3 19:37:44 2019
...
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Connected to:
Oracle Database 18c Enterprise Edition Release 18.0.0.0.0 - Production
We'd like to know what PDB we have by issuing SHOW PDBS.
SQL> show pdbs;
SP2-0158: unknown SHOW option "pdbs"
Since Oracle multitenant databases starts from 12c, so there's no way to know the new feature for SQL*Plus 11.2.0.4.0.
For the same reason, all multitenant related commands like SHOW CON_NAME cannot be used, either.
Solution
Use higher releases of SQL*Plus or SQL Developer to issue the command. In my opinion, Oracle instant client is the fastest way to make it work.