forked from lix-project/lix
* More doc updates.
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Eelco Dolstra
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<refentry>
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<refnamediv>
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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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</refnamediv>
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<refsynopsisdiv>
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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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<arg><replaceable>hash</replaceable></arg>
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</cmdsynopsis>
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</refsynopsisdiv>
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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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<refsection><title>Description</title>
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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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<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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</refsection>
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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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<refsection>
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<title>Examples</title>
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<para>The environment variable <envar>NIX_HASH_ALGO</envar> specifies
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which hash algorithm to use. It can be either <literal>md5</literal>,
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<literal>sha1</literal>, or <literal>sha256</literal>. The default is
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<literal>md5</literal>.</para>
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<screen>
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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 environment variable <envar>PRINT_PATH</envar> is set, the path
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of the downloaded file in the Nix store is also printed.</para>
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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.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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0bbd1df101bc0294d440471e50feca71
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$ PRINT_PATH=1 nix-prefetch-url ftp://ftp.nluug.nl/pub/gnu/make/make-3.80.tar.bz2
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0bbd1df101bc0294d440471e50feca71
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/nix/store/wvyz8ifdn7wyz1p3pqyn0ra45ka2l492-make-3.80.tar.bz2</screen>
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</refsection>
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</refsection>
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</refentry>
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@ -189,7 +189,7 @@ linkend="sec-nix-build"><command>nix-build</command></link> does.</para>
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<cmdsynopsis>
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<command>nix-store</command>
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<arg choice='plain'><option>--gc</option></arg>
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<group choice='req'>
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<group>
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<arg choice='plain'><option>--print-roots</option></arg>
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<arg choice='plain'><option>--print-live</option></arg>
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<arg choice='plain'><option>--print-dead</option></arg>
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@ -451,7 +451,7 @@ most one query can be specified. The default query is
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<cmdsynopsis>
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<command>nix-store</command>
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<arg choice='req'><option>--register-validity</option></arg>
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<arg choice='plain'><option>--register-validity</option></arg>
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</cmdsynopsis>
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</refsection>
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@ -473,7 +473,7 @@ most one query can be specified. The default query is
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<cmdsynopsis>
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<command>nix-store</command>
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<arg choice='req'><option>--substitute</option></arg>
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<arg choice='plain'><option>--substitute</option></arg>
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<arg choice='plain'
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rep='repeat'><replaceable>srcpath</replaceable> <replaceable>subpath</replaceable></arg>
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</cmdsynopsis>
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@ -501,7 +501,8 @@ deployment.</para>
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<title>Synopsis</title>
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<cmdsynopsis>
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<command>nix-store</command>
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<arg choice='req'><option>--verify</option></arg>
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<arg choice='plain'><option>--verify</option></arg>
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<arg><option>--check-contents</option></arg>
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</cmdsynopsis>
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</refsection>
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@ -514,6 +515,25 @@ automatically repaired. Inconsistencies are generally the result of
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the Nix store or database being modified by non-Nix tools, or of bugs
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in Nix itself.</para>
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<para>There is one option:
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<variablelist>
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<varlistentry><term><option>--check-contents</option></term>
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<listitem><para>Checks that the contents of every valid store path
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has not been altered by computing a SHA-256 hash of the contents
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and comparing it with the hash stored in the Nix database at build
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time. Paths that have been modified are printed out. For large
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stores, <option>--check-contents</option> is obviously quite
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slow.</para></listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsection>
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</refsection>
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