= Access a top level package from the Nixpkgs/NixOS repo

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$ mkdir tempwork
$ cd tempwork
$ cp ../flake.nix flake.nix
$ git add flake.nix
$ nix develop
$ git add flake.lock
$ git commit -a -m temp
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[source,nix,linenums,highlight=15]
.flake.nix
....
$# cat flake.nix
....

Here's a demonstration using the shell.

....
$ cowsay "Moo!"     # Fails; dependency not available
$# start-shell nix develop <<EOL
$ cowsay "Moo!"     # Works in development environment
$# EOL
....

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Good adoc0 scripts clean up after themselves.
$ cd .. ; rm -rf tempwork # clean up
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