PATH settings for Oracle database
This is the minimum:

export ORACLE_HOME=/u01/app/oracle/product/12.1.0/db_1
export PATH=$ORACLE_HOME/bin:$PATH
export ORACLE_SID=orcl


Or use oraenv. Add the below in /etc/oratab if it is not already there:

orcl:/u01/app/oracle/product/12.1.0/db_1:N


Then interactively:

. oraenv
ORACLE_SID = [oracle] ? orcl
The Oracle base has been set to /u01/app/oracle


Or from a script:

export PATH=/usr/local/bin:$PATH # default path for oraenv, in case your PATH does not include it
export ORAENV_ASK=NO
export ORACLE_SID=orcl
. oraenv


It is not mandatory to set these in the profile, users can set themselves it when needed.