Ok, here is a clumsy solution.
I have this entry in my /home/victoria/.psqlrc file,
\setenv EDITOR "/usr/bin/nvim"
As you see below, I symlink to that file, from postgres.
[victoria@victoria ~]$ sudo -u postgres -i
[postgres@victoria ~]$ pwd
/var/lib/postgres
[postgres@victoria ~]$ ls -la
total 108
drwxrwxr-x 6 postgres victoria 4096 Mar 16 12:48 .
drwxr-xr-x 33 root root 4096 Mar 16 00:00 ..
-rw------- 1 postgres postgres 385 Mar 16 12:49 .bash_history
-rwxr-xr-x 1 root root 806 Mar 16 12:41 .bashrc
drwx------ 2 postgres postgres 4096 Mar 16 12:23 .cache
drwxrwxr-x 2 postgres victoria 4096 Feb 23 13:26 data
drwx------ 3 postgres postgres 4096 Mar 16 12:12 .local
lrwxrwxrwx 1 postgres victoria 62 Feb 23 15:10 .psql_history-postgres -> /mnt/Vancouver/Programming/RDB/postgres/postgres/.psql_history
lrwxrwxrwx 1 postgres victoria 22 Feb 23 14:59 .psqlrc -> /home/victoria/.psqlrc
drwxr-xr-x 2 postgres postgres 4096 Mar 16 12:38 .vim
-rw------- 1 postgres postgres 895 Mar 16 12:48 .viminfo
-rw-r--r-- 1 postgres postgres 68234 Mar 16 12:47 .vimrc
## NOTE: .bashrc and .vimrc are edited COPIES (not symlinks) of /home/victoria/{.bashrc | .vimrc}
[postgres@victoria ~]$ cat /var/lib/postgres/.bashrc
export PSQL_EDITOR="/usr/bin/nvim -u /var/lib/postgres/.vimrc"
## "/var/lib/postgres/.vimrc" is the same as "/home/victoria/.vimrc" EXCEPT
## that I commented out line 77, "execute pathogen#infect(), as that was
## throwing an error when starting nvim (Neovim) as the psql \e external editor.
## Important (slight annoyance: need to load that "postgres" .bashrc file:
[postgres@victoria ~]$ exec bash
[postgres@victoria ~]$ psql
psql (10.2)
Type "help" for help.
[postgres]# \e ## can edit in Neovim, with ~/.vimrc settings, preferences, customizations ...
[postgres]# \q
[postgres@victoria ~]$ exit
exit
[victoria@victoria ~]$
I wasn't able to automatically run the "exec bash" command after starting postgres, hence the need to manually run it in the postgres shell, prior to launching psql.
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