A bit manual searching but its an alternative way...
Find the Oracle home or where the installation files for Oracle is installed on your linux server.
cd / <-- Goto root directory
find . -print| grep -i dbm*.sql
Result varies on how you installed Oracle but mine displays this
/db/oracle
Goto the folder
less /db/oracle/db1/sqlplus/doc/README.htm
scroll down and you should see something like this
SQL*Plus Release Notes - Release 11.2.0.2