SP2-0750: You may need to set ORACLE_HOME to your Oracle software directory

-bash-3.00$ sqlplus /nolog
Error 6 initializing SQL*Plus
Message file sp1<lang>.msb not found
SP2-0750: You may need to set ORACLE_HOME to your Oracle software directory
-bash-3.00$

This can occur when the .bash_profile is not configured properly:

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EXAMPLE .bashrc:
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-bash-3.00$ cat .basrhc
#!/usr/local/bin/bash
export PATH=/usr/local/bin:/usr/local/mysql:/usr/local/mysql/bin:/usr/local/sparc-sun-solaris2.10/bin:/usr/local/ssl:/usr/local/ssl/lib:/usr/local/sbin:/usr/local/include:/usr/local/include/libxml2:/usr/bin:/usr/sbin:/usr/lib:/export/home/oracle/bin:/export/home/oracle:/export/home/oracle/instantclient:/export/home/oracle/sqlplus/mesg
export ORACLE_BASE=/export/home/oracle
export ORACLE_HOME=/usr/local/oracle
export ORACLE_OWNER=oracle
export ORACLE_SID=cprod1
export SQLPATH=/export/home/oracle/instantclient/
export NLS_LANG=AMERICAN_AMERICA.UTF8
export LD_LIBRARY_PATH=/usr/local/lib:/usr/local/include:/usr/lib
export BLIB=/usr/local/bin
export JAVA_HOME=/usr/bin
alias ll='ls -al'
alias lld='ls -al |grep drw'

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CHANGE TO
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-bash-3.00$ cat .bashrc
# .bash_profile
CC=gcc ; export CC
CPPFLAGS="-I/usr/local/ssl/include" ; export CPPFLAGS
DISPLAY=ussan-triage01.corp.hds.com:0.0 ; export DISPLAY
PATH=/usr/local/bin:/usr/local/mysql:/usr/local/mysql/bin:/usr/local/sparc-sun-solaris2.10/bin:/usr/local/ssl:/usr/local/ssl/lib:/usr/local/sbin:/usr/local/include:/usr/local/include/libxml2:/usr/bin:/usr/sbin:/usr/lib:/export/home/oracle/bin:/export/home/oracle:/export/home/oracle/instantclient:/export/home/oracle/sqlplus/mesg:/usr/local/scripts
export PATH
ORACLE_BASE=/export/home/oracle ;export ORACLE_BASE
ORACLE_HOME=/export/home/oracle; export ORACLE_HOM
ORACLE_OWNER=oracle ; export ORACLE_OWNER
ORACLE_SID=cprod1 ; export ORACLE_SID
SQLPATH=/export/home/oracle/instantclient/ ;export SQLPATH
NLS_LANG=AMERICAN_AMERICA.UTF8 ; export NLS_LANG
LD_LIBRARY_PATH=/usr/local/lib:/usr/local/include:/usr/lib ; export LD_LIBRARY_PATH
BLIB=/usr/local/bin ;export BLIB
JAVA_HOME=/usr/bin ; export JAVA_HOME
TERM=xtermc  ;export TERM
alias ll='ls -al'
alias lld='ls -al |grep drw'
alias vi='vim'

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