forked from lix-project/lix
Merge pull request #8990 from fricklerhandwerk/example-nix-env-install-outputs
add clarifying example to `nix-env` output selection
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commit
6b6cfec8a5
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@ -19,12 +19,15 @@ current generation of the active profile, to which a set of store paths
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described by *args* is added. The arguments *args* map to store paths in
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a number of possible ways:
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- By default, *args* is a set of derivation names denoting derivations
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- By default, *args* is a set of [derivation] names denoting derivations
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in the active Nix expression. These are realised, and the resulting
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output paths are installed. Currently installed derivations with a
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name equal to the name of a derivation being added are removed
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unless the option `--preserve-installed` is specified.
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[derivation]: @docroot@/language/derivations.md
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If there are multiple derivations matching a name in *args* that
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have the same name (e.g., `gcc-3.3.6` and `gcc-4.1.1`), then the
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derivation with the highest *priority* is used. A derivation can
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@ -66,8 +69,59 @@ a number of possible ways:
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- If *args* are store paths that are not store derivations, then these
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are [realised](@docroot@/command-ref/nix-store/realise.md) and installed.
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- By default all outputs are installed for each derivation. That can
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be reduced by setting `meta.outputsToInstall`.
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- By default all outputs are installed for each derivation.
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This can be overridden by adding a `meta.outputsToInstall` attribute on the derivation listing a subset of the output names.
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<!-- TODO: add anchor link to `outputs` when #7320 is merged -->
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Example:
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The file `example.nix` defines a [derivation] with two outputs `foo` and `bar`, each containing a file.
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```nix
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# example.nix
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let
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pkgs = import <nixpkgs> {};
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command = ''
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${pkgs.coreutils}/bin/mkdir -p $foo $bar
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echo foo > $foo/foo-file
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echo bar > $bar/bar-file
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'';
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in
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derivation {
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name = "example";
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builder = "${pkgs.bash}/bin/bash";
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args = [ "-c" command ];
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outputs = [ "foo" "bar" ];
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system = builtins.currentSystem;
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}
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```
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Installing from this Nix expression will make files from both outputs appear in the current profile.
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```console
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$ nix-env --install --file example.nix
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installing 'example'
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$ ls ~/.nix-profile
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foo-file
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bar-file
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manifest.nix
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```
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Adding `meta.outputsToInstall` to that derivation will make `nix-env` only install files from the specified outputs.
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```nix
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# example-outputs.nix
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import ./example.nix // { meta.outputsToInstall = [ "bar" ]; }
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```
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```console
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$ nix-env --install --file example-outputs.nix
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installing 'example'
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$ ls ~/.nix-profile
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bar-file
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manifest.nix
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```
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# Flags
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