Install Oracle Client 12c Official

# Switch to oracle user
sudo su - oracle
Add to /etc/profile.d/oracle.sh (system-wide) or your app user’s .bashrc:
export ORACLE_HOME=/opt/oracle/instantclient_12_2
export LD_LIBRARY_PATH=$ORACLE_HOME:$LD_LIBRARY_PATH
export PATH=$ORACLE_HOME:$PATH
export TNS_ADMIN=$ORACLE_HOME/network/admin   # For tnsnames.ora
export NLS_LANG=AMERICAN_AMERICA.AL32UTF8    # Prevents character set errors
export SQLPATH=$ORACLE_HOME

The TNS_ADMIN nuance: If you don’t set this, sqlplus expects tnsnames.ora in $ORACLE_HOME/network/admin. Without the directory, it fails silently. install oracle client 12c
Create the directory:
sudo mkdir -p $ORACLE_HOME/network/admin

If you downloaded the client from the Oracle website, it usually comes in a compressed format (e.g., .zip). # Switch to oracle user sudo su -