can you please paste result : sqlplus /nolog
Upadate: please check below link:
This says that the OS cannot find the program named sqlplus in its PATH.
Start by a cd to the $ORACLE_HOME/bin and see if it works or not
$ cd /apps/oracle/oracle/product/11.2.0/db_1/bin
$ sqlplus username/userpasswd
If this works, you need to set your PATH to include your $ORACLE_HOME/bin directory.
$ export ORACLE_HOME=/apps/oracle/product/11.2.0
$ export PATH=$PATH:$/apps/oracle/oracle/product/11.2.0/db_1/bin
Next, we start SQL*Plus with the sql command
When starting SQL*Plus include the user name that you wish to connect to
Here is an example of use of this command
If Step1 doesn’t work you need to check in your $ORACLE_HOME/bin directory whether sqlplus program is present or not in the $ORACLE_HOME/bin directory, because there may be a chance of corrupting sqlplus program in the $ORACLE_HOME/bin directory sometimes.