Oracle Database Discussions

Hi,
(the paths I mention below are just for this question, in real life they would be different)
Using Oracle on Linux (Debian)
Imagine I've 2 Oracle Homes on this machine: /u01/ora817 and /u01/ora920

PATH is set to : /usr/local/bin:/usr/bin:/bin:/usr/games:/u01/ora817/bin
ORACLE_HOME is set to: /u01/ora920
(PLEASE note: the Oracle part in PATH differs from ORACLE_HOME/bin)

Next I start sqlplus, which will run (from /u01/ora817/bin) because of a valid PATH to it and and valid ORACLE_HOME set (so sqlplus can find the message files and others, but from a different oracle_home)

My questions:
- I wonder what happens when I issue a 'startup nomount' --> what Oracle version (binaries) are used in the situation outlined above?
- In general: what role plays sqlplus in controlling an instance?
- Is it a good practice to incorparate an ORACLE_HOME/bin in the PATH environment variable? Or should I always issue commands like $ORACLE_HOME/bin/sqlplus to be sure of the version (oracle_home) used?

Thanks
Regards
Stephan

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