Easy but valuable enhancements to sqlplus adding a prompt and defining your editor on UNIX

add this to $ORACLE_HOME/sqlplus/admin/glogin.sql
— setup a prompt with user name and connect

set sqlprompt "_user'@'_connect_identifier > "

— set the default editor to vi

define _editor=vi

— from that point forward – all users will get the user that they are connected as and the SID / Connect Identifier embedded in their sqlprompt making connecting to many databases safer.
— and if you wanted you could add stuff like:

[oracle@o68-cdb admin]$ sqlplus / as sysdba
SQL*Plus: Release 12.2.0.1.0 Production on Fri Jul 7 10:41:18 2017
SQL> !cat glogin.sql
set sqlprompt "_user'@'_connect_identifier > "
SET PAGESIZE 999
SET LINESIZE 200
SET SERVEROUTPUT ON SIZE UNLIMITED FORMAT WRAPPED
DEFINE _EDITOR=vi
COLUMN segment_name FORMAT A36 WORD_WRAP
COLUMN object_name FORMAT A60 WORD_WRAP
COLUMN name FORMAT A36 WORD_WRAP
COLUMN value FORMAT A60 WORD_WRAP
define _editor=vi

For additional LonzoDB recent Oracle related posts.