.exrc is the configuration file for
vi, whereas .vimrc is the config file for
No. Vim will use the .vimrc file if present, otherwise the .exrc file if present
Yes, unless you only put vi-compatible commands in there
From the Vim help on exrc:
c. Four places are searched for initializations. The first that exists
is used, the others are ignored. The $MYVIMRC environment variable is
set to the file that was first found, unless $MYVIMRC was already set
and when using VIMINIT.
- The environment variable VIMINIT (see also |compatible-default|) (*)
The value of $VIMINIT is used as an Ex command line.
- The user vimrc file(s):
"$HOME/.vimrc" (for Unix and OS/2) (*)
"$HOME/.vim/vimrc" (for Unix and OS/2) (*)
"s:.vimrc" (for Amiga) (*)
"home:.vimrc" (for Amiga) (*)
"home:vimfiles:vimrc" (for Amiga) (*)
"$VIM/.vimrc" (for OS/2 and Amiga) (*)
"$HOME/_vimrc" (for MS-DOS and Win32) (*)
"$HOME/vimfiles/vimrc" (for MS-DOS and Win32) (*)
"$VIM/_vimrc" (for MS-DOS and Win32) (*)
Note: For Unix, OS/2 and Amiga, when ".vimrc" does not exist,
"_vimrc" is also tried, in case an MS-DOS compatible file
system is used. For MS-DOS and Win32 ".vimrc" is checked
after "_vimrc", in case long file names are used.
Note: For MS-DOS and Win32, "$HOME" is checked first. If no
"_vimrc" or ".vimrc" is found there, "$VIM" is tried.
See |$VIM| for when $VIM is not set.
- The environment variable EXINIT.
The value of $EXINIT is used as an Ex command line.
- The user exrc file(s). Same as for the user vimrc file, but with
"vimrc" replaced by "exrc". But only one of ".exrc" and "_exrc" is
used, depending on the system. And without the (*)!