55 lines
1.8 KiB
XML
55 lines
1.8 KiB
XML
<refentry>
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<refnamediv>
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<refname>nix-prefetch-url</refname>
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<refpurpose>copy a file from a URL into the store and print its MD5 hash</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command>nix-prefetch-url</command>
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<arg choice='plain'><replaceable>url</replaceable></arg>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsection>
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<title>Description</title>
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<para>
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The command <command>nix-prefetch-url</command> downloads the
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file referenced by the URL <replaceable>url</replaceable>,
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prints its MD5 cryptographic hash code, and copies it into the
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Nix store. The file name in the store is
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<filename><replaceable>hash</replaceable>-<replaceable>basename</replaceable></filename>,
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where <replaceable>basename</replaceable> is everything
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following the final slash in <replaceable>url</replaceable>.
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</para>
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<para>
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This command is just a convenience to Nix expression writers.
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Often a Nix expressions fetch some source distribution from the
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network using the <literal>fetchurl</literal> expression
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contained in <literal>nixpkgs</literal>. However,
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<literal>fetchurl</literal> requires an MD5 hash. If you don't
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know the hash, you would have to download the file first, and
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then <literal>fetchurl</literal> would download it again when
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you build your Nix expression. Since
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<literal>fetchurl</literal> uses the same name for the
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downloaded file as <command>nix-prefetch-url</command>, the
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redundant download can be avoided.
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</para>
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</refsection>
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<refsection>
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<title>Examples</title>
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<screen>
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$ nix-prefetch-url ftp://ftp.nluug.nl/pub/gnu/make/make-3.80.tar.bz2
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...
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file has hash 0bbd1df101bc0294d440471e50feca71
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...</screen>
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</refsection>
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</refentry>
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