EBS 12.2 for OHS where is ${ORACLE_INSTANCE} defined /sourced from ?

I am unable to find where from 12.2 OHS is sourcing the $ORACLE_INSTANCE ?

i checked under : /u02/app/oracle/product/122/fs1/FMW_Home/webtier/instances/EBS_web_TESTASCP_OHS1/config/OHS/EBS_web_TESTASCP

all conf files, i see it says $ORACLE_INSTANCE/config..

But i did not found where it gets defination of $ORACLE_INSTANCE.

i also checked in :

/u02/app/oracle/product/122/fs1/FMW_Home/webtier/ohs/conf

All confi files, i see same it says all relative path $ORACLE_INSTANCE/.....

But could not find the exact locaiton / defination where $ORACLE_INSTANCE is defined.

So is for opmn.xml files too i could not fine.