Today I found my `.vimrc` didn't take effect, it is ok just hours ago.

When launch vim with `$vim --plugin`, `:scriptnames` echo nothing: `.vimrc` file is not sourced. (Note: `/etc/vimrc` was removed to debug this problem.) 

Then I tried to google and find `$VIMINIT` variable looks suspicious. 

Here is the value of `$VIMINIT`:

    $ echo $VIMINIT
    set number

Vim document about `VIMINIT`:

>      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.
>         -  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) (*)
>                     "s:.vimrc"          (for Amiga) (*)
>                     "home:.vimrc"       (for Amiga) (*)
>                     "$VIM/.vimrc"       (for OS/2 and Amiga) (*)
>                     "$HOME/_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 (*)!

I could not understand the vim document fully, It seems that `$VIMINIT` may mess the startup of vim. 

Clear `$VIMINIT`:

    $ VIMINIT=
    $ echo $VIMINIT
    

Launch vim and try `:scriptnames` again, `.vimrc` was still not sourced.