2020-07-22 21:17:48 +00:00
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# A Simple Nix Expression
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This section shows how to add and test the [GNU Hello
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package](http://www.gnu.org/software/hello/hello.html) to the Nix
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Packages collection. Hello is a program that prints out the text “Hello,
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world\!”.
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To add a package to the Nix Packages collection, you generally need to
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do three things:
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1. Write a Nix expression for the package. This is a file that
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describes all the inputs involved in building the package, such as
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dependencies, sources, and so on.
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2020-07-24 09:43:44 +00:00
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2. Write a *builder*. This is a shell script that builds the package
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from the inputs. (In fact, it can be written in any language, but
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typically it's a `bash` shell script.)
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2020-07-22 21:17:48 +00:00
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3. Add the package to the file `pkgs/top-level/all-packages.nix`. The
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Nix expression written in the first step is a *function*; it
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requires other packages in order to build it. In this step you put
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it all together, i.e., you call the function with the right
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arguments to build the actual package.
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