emacs.default.nix

with import <nixpkgs> {};

runCommand "dot-emacs" {
  # buildInputs could be here, but it doesn't do what you thought it would
} ''
  mkdir -p $out
  echo "Hello World" > $out/emacs.cfg
''

output.sh

#> nix-build ~/src/dotfiles
these derivations will be built:
  /nix/store/24l8p5md7jn8x7sgx5g2xgk6qflm0vkj-dot-weechat.drv
  /nix/store/9kig1f2jkjkvb5dxpp46zw8p691k3k5l-dot-emacs.drv
building path(s) ‘/nix/store/19i5gygdx9pa2xzzak4blg6iwjl1p8kv-dot-emacs’
building path(s) ‘/nix/store/m065zv7x2cfpr2jr1lwzakkv19dip3jw-dot-weechat’
/nix/store/19i5gygdx9pa2xzzak4blg6iwjl1p8kv-dot-emacs
/nix/store/m065zv7x2cfpr2jr1lwzakkv19dip3jw-dot-weechat
#> ls -la
total 16
drwxr-xr-x   4 dustinlacewell  wheel   136 Oct 13 12:32 .
drwxrwxrwt  32 root            wheel  1088 Oct 13 12:32 ..
lrwxr-xr-x   1 dustinlacewell  wheel    53 Oct 13 12:32 result -> /nix/store/19i5gygdx9pa2xzzak4blg6iwjl1p8kv-dot-emacs
lrwxr-xr-x   1 dustinlacewell  wheel    55 Oct 13 12:32 result-2 -> /nix/store/m065zv7x2cfpr2jr1lwzakkv19dip3jw-dot-weechat
#> ls result/
emacs.cfg
#> ls result-2/
weechat.cfg

weechat.default.nix

with import <nixpkgs> {};

runCommand "dot-weechat" {

} ''
  mkdir -p $out
  echo "Hello World" > $out/weechat.cfg
''