131 lines
4.7 KiB
XML
131 lines
4.7 KiB
XML
<refentry xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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version="5.0"
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xml:id="sec-nix-prefetch-url">
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<refmeta>
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<refentrytitle>nix-prefetch-url</refentrytitle>
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<manvolnum>1</manvolnum>
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<refmiscinfo class="source">Nix</refmiscinfo>
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<refmiscinfo class="version"><xi:include href="../version.txt" parse="text"/></refmiscinfo>
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</refmeta>
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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 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><option>--version</option></arg>
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<arg><option>--type</option> <replaceable>hashAlgo</replaceable></arg>
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<arg><option>--print-path</option></arg>
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<arg><option>--unpack</option></arg>
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<arg><option>--name</option> <replaceable>name</replaceable></arg>
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<arg choice='plain'><replaceable>url</replaceable></arg>
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<arg><replaceable>hash</replaceable></arg>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsection><title>Description</title>
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<para>The command <command>nix-prefetch-url</command> downloads the
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file referenced by the URL <replaceable>url</replaceable>, prints its
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cryptographic hash, and copies it into the Nix store. The file name
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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 following the
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final slash in <replaceable>url</replaceable>.</para>
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<para>This command is just a convenience for Nix expression writers.
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Often a Nix expression fetches some source distribution from the
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network using the <literal>fetchurl</literal> expression contained in
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Nixpkgs. However, <literal>fetchurl</literal> requires a
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cryptographic hash. If you don't know the hash, you would have to
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download the file first, and then <literal>fetchurl</literal> would
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download it again when you build your Nix expression. Since
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<literal>fetchurl</literal> uses the same name for the downloaded file
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as <command>nix-prefetch-url</command>, the redundant download can be
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avoided.</para>
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<para>If <replaceable>hash</replaceable> is specified, then a download
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is not performed if the Nix store already contains a file with the
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same hash and base name. Otherwise, the file is downloaded, and an
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error if signaled if the actual hash of the file does not match the
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specified hash.</para>
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<para>This command prints the hash on standard output. Additionally,
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if the option <option>--print-path</option> is used, the path of the
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downloaded file in the Nix store is also printed.</para>
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</refsection>
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<refsection><title>Options</title>
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<variablelist>
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<varlistentry><term><option>--type</option> <replaceable>hashAlgo</replaceable></term>
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<listitem><para>Use the specified cryptographic hash algorithm,
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which can be one of <literal>md5</literal>,
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<literal>sha1</literal>, and
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<literal>sha256</literal>.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--print-path</option></term>
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<listitem><para>Print the store path of the downloaded file on
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standard output.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--unpack</option></term>
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<listitem><para>Unpack the archive (which must be a tarball or zip
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file) and add the result to the Nix store. The resulting hash can
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be used with functions such as Nixpkgs’s
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<varname>fetchzip</varname> or
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<varname>fetchFromGitHub</varname>.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--name</option> <replaceable>name</replaceable></term>
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<listitem><para>Override the name of the file in the Nix store. By
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default, this is
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<literal><replaceable>hash</replaceable>-<replaceable>basename</replaceable></literal>,
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where <replaceable>basename</replaceable> is the last component of
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<replaceable>url</replaceable>. Overriding the name is necessary
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when <replaceable>basename</replaceable> contains characters that
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are not allowed in Nix store paths.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsection>
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<refsection><title>Examples</title>
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<screen>
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$ nix-prefetch-url ftp://ftp.gnu.org/pub/gnu/hello/hello-2.10.tar.gz
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0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i
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$ nix-prefetch-url --print-path mirror://gnu/hello/hello-2.10.tar.gz
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0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i
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/nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz
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$ nix-prefetch-url --unpack --print-path https://github.com/NixOS/patchelf/archive/0.8.tar.gz
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079agjlv0hrv7fxnx9ngipx14gyncbkllxrp9cccnh3a50fxcmy7
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/nix/store/19zrmhm3m40xxaw81c8cqm6aljgrnwj2-0.8.tar.gz
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</screen>
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</refsection>
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</refentry>
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