SP2-0667: Message file sp1.msb not found and SP2-0750: You may need to set ORACLE_HOME to your Oracle software directory

SP2-0667: Message file sp1<lang>.msb not found
SP2-0750: You may need to set ORACLE_HOME to your Oracle software directory

After Installing or Upgrading 12C or 11G you may get this error while connecting to sqlplus utility,  this error is because your sqlplus is not in your path.

Issue below commands and then retry.

export ORACLE_SID="Name of Database"
export ORACLE_HOME="Location of your home"
export PATH=$ORACLE_HOME/bin:$PATH.

Thanks.