<refentry xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xi="http://www.w3.org/2001/XInclude" version="5.0" xml:id="sec-nix-hash"> <refmeta> <refentrytitle>nix-hash</refentrytitle> <manvolnum>1</manvolnum> <refmiscinfo class="source">Nix</refmiscinfo> <refmiscinfo class="version"><xi:include href="../version.txt" parse="text"/></refmiscinfo> </refmeta> <refnamediv> <refname>nix-hash</refname> <refpurpose>compute the cryptographic hash of a path</refpurpose> </refnamediv> <refsynopsisdiv> <cmdsynopsis> <command>nix-hash</command> <arg><option>--flat</option></arg> <arg><option>--base32</option></arg> <arg><option>--truncate</option></arg> <arg><option>--type</option> <replaceable>hashAlgo</replaceable></arg> <arg choice='plain' rep='repeat'><replaceable>path</replaceable></arg> </cmdsynopsis> <cmdsynopsis> <command>nix-hash</command> <arg choice='plain'><option>--to-base16</option></arg> <arg choice='plain' rep='repeat'><replaceable>hash</replaceable></arg> </cmdsynopsis> <cmdsynopsis> <command>nix-hash</command> <arg choice='plain'><option>--to-base32</option></arg> <arg choice='plain' rep='repeat'><replaceable>hash</replaceable></arg> </cmdsynopsis> </refsynopsisdiv> <refsection><title>Description</title> <para>The command <command>nix-hash</command> computes the cryptographic hash of the contents of each <replaceable>path</replaceable> and prints it on standard output. By default, it computes an MD5 hash, but other hash algorithms are available as well. The hash is printed in hexadecimal.</para> <para>The hash is computed over a <emphasis>serialisation</emphasis> of each path: a dump of the file system tree rooted at the path. This allows directories and symlinks to be hashed as well as regular files. The dump is in the <emphasis>NAR format</emphasis> produced by <link linkend="refsec-nix-store-dump"><command>nix-store</command> <option>--dump</option></link>. Thus, <literal>nix-hash <replaceable>path</replaceable></literal> yields the same cryptographic hash as <literal>nix-store --dump <replaceable>path</replaceable> | md5sum</literal>.</para> </refsection> <refsection><title>Options</title> <variablelist> <varlistentry><term><option>--flat</option></term> <listitem><para>Print the cryptographic hash of the contents of each regular file <replaceable>path</replaceable>. That is, do not compute the hash over the dump of <replaceable>path</replaceable>. The result is identical to that produced by the GNU commands <command>md5sum</command> and <command>sha1sum</command>.</para></listitem> </varlistentry> <varlistentry><term><option>--base32</option></term> <listitem><para>Print the hash in a base-32 representation rather than hexadecimal. This base-32 representation is more compact and can be used in Nix expressions (such as in calls to <function>fetchurl</function>).</para></listitem> </varlistentry> <varlistentry><term><option>--truncate</option></term> <listitem><para>Truncate hashes longer than 160 bits (such as SHA-256) to 160 bits.</para></listitem> </varlistentry> <varlistentry><term><option>--type</option> <replaceable>hashAlgo</replaceable></term> <listitem><para>Use the specified cryptographic hash algorithm, which can be one of <literal>md5</literal>, <literal>sha1</literal>, and <literal>sha256</literal>.</para></listitem> </varlistentry> <varlistentry><term><option>--to-base16</option></term> <listitem><para>Don’t hash anything, but convert the base-32 hash representation <replaceable>hash</replaceable> to hexadecimal.</para></listitem> </varlistentry> <varlistentry><term><option>--to-base32</option></term> <listitem><para>Don’t hash anything, but convert the hexadecimal hash representation <replaceable>hash</replaceable> to base-32.</para></listitem> </varlistentry> </variablelist> </refsection> <refsection><title>Examples</title> <para>Computing hashes: <screen> $ mkdir test $ echo "hello" > test/world $ nix-hash test/ <lineannotation>(MD5 hash; default)</lineannotation> 8179d3caeff1869b5ba1744e5a245c04 $ nix-store --dump test/ | md5sum <lineannotation>(for comparison)</lineannotation> 8179d3caeff1869b5ba1744e5a245c04 - $ nix-hash --type sha1 test/ e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6 $ nix-hash --type sha1 --base32 test/ nvd61k9nalji1zl9rrdfmsmvyyjqpzg4 $ nix-hash --type sha256 --flat test/ error: reading file `test/': Is a directory $ nix-hash --type sha256 --flat test/world 5891b5b522d5df086d0ff0b110fbd9d21bb4fc7163af34d08286a2e846f6be03</screen> </para> <para>Converting between hexadecimal and base-32: <screen> $ nix-hash --type sha1 --to-base32 e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6 nvd61k9nalji1zl9rrdfmsmvyyjqpzg4 $ nix-hash --type sha1 --to-base16 nvd61k9nalji1zl9rrdfmsmvyyjqpzg4 e4fd8ba5f7bbeaea5ace89fe10255536cd60dab6</screen> </para> </refsection> </refentry>