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62 lines
2.1 KiB
Markdown
62 lines
2.1 KiB
Markdown
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# Generic Builder Syntax
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Recall from [???](#ex-hello-builder) that the builder looked something
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like this:
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PATH=$perl/bin:$PATH
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tar xvfz $src
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cd hello-*
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./configure --prefix=$out
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make
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make install
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The builders for almost all Unix packages look like this — set up some
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environment variables, unpack the sources, configure, build, and
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install. For this reason the standard environment provides some Bash
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functions that automate the build process. A builder using the generic
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build facilities in shown in [example\_title](#ex-hello-builder2).
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buildInputs="$perl"
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source $stdenv/setup
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genericBuild
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- The buildInputs variable tells `setup` to use the indicated packages
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as “inputs”. This means that if a package provides a `bin`
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subdirectory, it's added to PATH; if it has a `include`
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subdirectory, it's added to GCC's header search path; and so
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on.\[1\]
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- The function `genericBuild` is defined in the file `$stdenv/setup`.
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- The final step calls the shell function `genericBuild`, which
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performs the steps that were done explicitly in
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[???](#ex-hello-builder). The generic builder is smart enough to
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figure out whether to unpack the sources using `gzip`, `bzip2`, etc.
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It can be customised in many ways; see the Nixpkgs manual for
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details.
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Discerning readers will note that the buildInputs could just as well
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have been set in the Nix expression, like this:
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```
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buildInputs = [ perl ];
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```
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The `perl` attribute can then be removed, and the builder becomes even
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shorter:
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source $stdenv/setup
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genericBuild
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In fact, `mkDerivation` provides a default builder that looks exactly
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like that, so it is actually possible to omit the builder for Hello
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entirely.
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1. How does it work? `setup` tries to source the file
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`pkg/nix-support/setup-hook` of all dependencies. These “setup
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hooks” can then set up whatever environment variables they want;
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for instance, the setup hook for Perl sets the PERL5LIB environment
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variable to contain the `lib/site_perl` directories of all inputs.
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