When bash is called non-interactively, PS1 is unset. However, if it's a login shell, ~/.bash_profile is still sourced. Therefore, testing PS1 tells us if this is a login but non-interactive shell (such as: ssh host 'uptime'). Testing PS1 before setting it preserves that state for later tests if desired.

version 5.0
set nocompatible
set autoindent
set cindent
set mouse=a
set smartindent
set smarttab
set tabstop=3
syntax on
set sw=3
set bg=dark
set textwidth=78
set sm
hi Normal guibg=black guifg=white