To use, clone to ~/.config/fish and run make to download any plugin submodules.

I have /bin/sh set as my user login shell. My ~/.profile is used upon login and a ~/.config/sh/env is sourced for interative shells, which does exec fish. This avoids any issues with your login shell or SHELL being non-POSIX.

# ~/.profile
# If the shell is interactive, this file will be sourced, too.
# Make sure this file is private: `chmod 600 $ENV`
ENV="${HOME}/.conifg/sh/env"

# Cache the result of `uname` (it never changes) instead of
# needing to repeatedly invoke it in scripts.
UNAME="$(uname)"

export ENV UNAME

# ~/.config/sh/env
if [ "x$(printf %.1s "$0")" = x- ]; then
  exec fish -l
else
  exec fish
fi