forked from lix-project/lix
176 lines
5.3 KiB
XML
176 lines
5.3 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-hash">
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<refmeta>
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<refentrytitle>nix-hash</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-hash</refname>
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<refpurpose>compute the cryptographic hash of a path</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<cmdsynopsis>
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<command>nix-hash</command>
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<arg><option>--flat</option></arg>
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<arg><option>--base32</option></arg>
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<arg><option>--truncate</option></arg>
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<arg><option>--type</option> <emphasis>hashAlgo</emphasis></arg>
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<arg choice='plain' rep='repeat'><emphasis>path</emphasis></arg>
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</cmdsynopsis>
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<cmdsynopsis>
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<command>nix-hash</command>
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<arg choice='plain'><option>--to-base16</option></arg>
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<arg choice='plain' rep='repeat'><emphasis>hash</emphasis></arg>
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</cmdsynopsis>
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<cmdsynopsis>
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<command>nix-hash</command>
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<arg choice='plain'><option>--to-base32</option></arg>
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<arg choice='plain' rep='repeat'><emphasis>hash</emphasis></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-hash</command> computes the
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cryptographic hash of the contents of each
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<emphasis>path</emphasis> and prints it on standard output. By
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default, it computes an MD5 hash, but other hash algorithms are
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available as well. The hash is printed in hexadecimal. To generate
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the same hash as <command>nix-prefetch-url</command> you have to
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specify multiple arguments, see below for an example.</para>
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<para>The hash is computed over a <emphasis>serialisation</emphasis>
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of each path: a dump of the file system tree rooted at the path. This
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allows directories and symlinks to be hashed as well as regular files.
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The dump is in the <emphasis>NAR format</emphasis> produced by <link
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linkend="refsec-nix-store-dump"><command>nix-store</command>
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<option>--dump</option></link>. Thus, <literal>nix-hash
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<emphasis>path</emphasis></literal> yields the same
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cryptographic hash as <literal>nix-store --dump
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<emphasis>path</emphasis> | md5sum</literal>.</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>--flat</option></term>
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<listitem><para>Print the cryptographic hash of the contents of
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each regular file <emphasis>path</emphasis>. That is, do
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not compute the hash over the dump of
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<emphasis>path</emphasis>. The result is identical to that
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produced by the GNU commands <command>md5sum</command> and
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<command>sha1sum</command>.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--base32</option></term>
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<listitem><para>Print the hash in a base-32 representation rather
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than hexadecimal. This base-32 representation is more compact and
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can be used in Nix expressions (such as in calls to
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<function>fetchurl</function>).</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--truncate</option></term>
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<listitem><para>Truncate hashes longer than 160 bits (such as
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SHA-256) to 160 bits.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--type</option> <emphasis>hashAlgo</emphasis></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>--to-base16</option></term>
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<listitem><para>Don’t hash anything, but convert the base-32 hash
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representation <emphasis>hash</emphasis> to
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hexadecimal.</para></listitem>
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</varlistentry>
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<varlistentry><term><option>--to-base32</option></term>
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<listitem><para>Don’t hash anything, but convert the hexadecimal
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hash representation <emphasis>hash</emphasis> to
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base-32.</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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<para>Computing the same hash as <command>nix-prefetch-url</command>:
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<screen>
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$ nix-prefetch-url file://<(echo test)
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1lkgqb6fclns49861dwk9rzb6xnfkxbpws74mxnx01z9qyv1pjpj
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$ nix-hash --type sha256 --flat --base32 <(echo test)
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1lkgqb6fclns49861dwk9rzb6xnfkxbpws74mxnx01z9qyv1pjpj
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</screen>
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</para>
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<para>Computing hashes:
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<screen>
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$ mkdir test
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$ echo "hello" > test/world
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$ nix-hash test/ <lineannotation>(MD5 hash; default)</lineannotation>
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8179d3caeff1869b5ba1744e5a245c04
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$ nix-store --dump test/ | md5sum <lineannotation>(for comparison)</lineannotation>
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8179d3caeff1869b5ba1744e5a245c04 -
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$ nix-hash --type sha1 test/
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e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6
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$ nix-hash --type sha1 --base32 test/
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nvd61k9nalji1zl9rrdfmsmvyyjqpzg4
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$ nix-hash --type sha256 --flat test/
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error: reading file `test/': Is a directory
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$ nix-hash --type sha256 --flat test/world
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5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03</screen>
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</para>
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<para>Converting between hexadecimal and base-32:
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<screen>
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$ nix-hash --type sha1 --to-base32 e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6
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nvd61k9nalji1zl9rrdfmsmvyyjqpzg4
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$ nix-hash --type sha1 --to-base16 nvd61k9nalji1zl9rrdfmsmvyyjqpzg4
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e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6</screen>
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</para>
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</refsection>
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</refentry>
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