forked from lix-project/lix
2af9fd20c6
the term was hard to discover, as its definition and explanation were in a very long document lacking an overview section. search did not help because it occurs so often. - clarify wording in the definition - add an overview of installable types - add "installable" to glossary - link to definition from occurrences of the term - be more precise about where store derivation outputs are processed - installable Nix expressions must evaluate to a derivation Co-authored-by: Adam Joseph <54836058+amjoseph-nixpkgs@users.noreply.github.com>
74 lines
1.6 KiB
Markdown
74 lines
1.6 KiB
Markdown
R""(
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# Examples
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* Evaluate a Nix expression given on the command line:
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```console
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# nix eval --expr '1 + 2'
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```
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* Evaluate a Nix expression to JSON:
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```console
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# nix eval --json --expr '{ x = 1; }'
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{"x":1}
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```
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* Evaluate a Nix expression from a file:
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```console
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# nix eval -f ./my-nixpkgs hello.name
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```
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* Get the current version of the `nixpkgs` flake:
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```console
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# nix eval --raw nixpkgs#lib.version
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```
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* Print the store path of the Hello package:
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```console
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# nix eval --raw nixpkgs#hello
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```
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* Get a list of checks in the `nix` flake:
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```console
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# nix eval nix#checks.x86_64-linux --apply builtins.attrNames
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```
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* Generate a directory with the specified contents:
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```console
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# nix eval --write-to ./out --expr '{ foo = "bar"; subdir.bla = "123"; }'
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# cat ./out/foo
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bar
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# cat ./out/subdir/bla
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123
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# Description
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This command evaluates the given Nix expression and prints the
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result on standard output.
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# Output format
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`nix eval` can produce output in several formats:
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* By default, the evaluation result is printed as a Nix expression.
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* With `--json`, the evaluation result is printed in JSON format. Note
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that this fails if the result contains values that are not
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representable as JSON, such as functions.
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* With `--raw`, the evaluation result must be a string, which is
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printed verbatim, without any quoting.
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* With `--write-to` *path*, the evaluation result must be a string or
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a nested attribute set whose leaf values are strings. These strings
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are written to files named *path*/*attrpath*. *path* must not
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already exist.
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)""
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