Go to your Oracle binaries folder and export environment variables, if they are not set already. Then, run SQL*Plus command line utility with option /nolog .

[root@localhost /]# cd /usr/lib/oracle/xe/app/oracle/product/10.2.0/server/bin/

[root@localhost bin]#. ./oracle_env.sh

[root@localhost bin]# sqlplus /nolog

SQL> connect myuser/mypassword@localhost/xe

Connected.

SQL> select count(*) as c from mytablespace.mytable
  2    /
         C
----------
       123

I hope this helps some beginners.