How to open sqlplus in linux.

Set environment variables: 
export ORACLE_HOME=/home/oracle/app/oracle/product/11.2.0/dbhome_1/
export PATH=/home/oracle/app/oracle/product/11.2.0/dbhome_1/bin:$PATH

Go to following location :
/home/oracle/app/oracle/product/11.2.0/dbhome_1/bin

Execute below command :
./sqlplus / as sysdba


Output :
SQL*Plus: Release 11.2.0.1.0 Production on Wed Oct 28 14:31:37 2015

Copyright (c) 1982, 2009, Oracle.  All rights reserved.

SQL>