Oracle XE and SQLPlus
Immediately after Oracle Express Edition installation, trying to run SQLPlus command line tool was giving TNS listener not found error. tnsping was working fine. After a restart it started working. If you need to run sqlplus.exe without restarting the machine set the environment variable ORACLE_HOME. SQLPlus should know oracle home directory to find tnsnames.ora file. Oracle installation didn't set this environment variable. This variable must point to the database installation directory. In my case it is F:\oraclexe\app\oracle\product\10.2.0\server. After a system restart SQLPlus is working without this variable. SQLPlus should be reading this from the registry.