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+<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-env">
+
+<refmeta>
+ <refentrytitle>nix-env</refentrytitle>
+ <manvolnum>1</manvolnum>
+ <refmiscinfo class="source">Nix</refmiscinfo>
+ <refmiscinfo class="version"><xi:include href="version.txt" parse="text"/></refmiscinfo>
+</refmeta>
+
+<refnamediv>
+ <refname>nix-env</refname>
+ <refpurpose>manipulate or query Nix user environments</refpurpose>
+</refnamediv>
+
+<refsynopsisdiv>
+ <cmdsynopsis>
+ <command>nix-env</command>
+ <xi:include href="opt-common-syn.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(/db:nop/*)" />
+ <arg><option>--arg</option> <replaceable>name</replaceable> <replaceable>value</replaceable></arg>
+ <arg><option>--argstr</option> <replaceable>name</replaceable> <replaceable>value</replaceable></arg>
+ <arg>
+ <group choice='req'>
+ <arg choice='plain'><option>--file</option></arg>
+ <arg choice='plain'><option>-f</option></arg>
+ </group>
+ <replaceable>path</replaceable>
+ </arg>
+ <arg>
+ <group choice='req'>
+ <arg choice='plain'><option>--profile</option></arg>
+ <arg choice='plain'><option>-p</option></arg>
+ </group>
+ <replaceable>path</replaceable>
+ </arg>
+ <arg>
+ <arg choice='plain'><option>--system-filter</option></arg>
+ <replaceable>system</replaceable>
+ </arg>
+ <arg><option>--dry-run</option></arg>
+ <arg choice='plain'><replaceable>operation</replaceable></arg>
+ <arg rep='repeat'><replaceable>options</replaceable></arg>
+ <arg rep='repeat'><replaceable>arguments</replaceable></arg>
+ </cmdsynopsis>
+</refsynopsisdiv>
+
+
+<refsection><title>Description</title>
+
+<para>The command <command>nix-env</command> is used to manipulate Nix
+user environments. User environments are sets of software packages
+available to a user at some point in time. In other words, they are a
+synthesised view of the programs available in the Nix store. There
+may be many user environments: different users can have different
+environments, and individual users can switch between different
+environments.</para>
+
+<para><command>nix-env</command> takes exactly one
+<emphasis>operation</emphasis> flag which indicates the subcommand to
+be performed. These are documented below.</para>
+
+</refsection>
+
+
+
+<!--######################################################################-->
+
+<refsection><title>Common options</title>
+
+<para>This section lists the options that are common to all
+operations. These options are allowed for every subcommand, though
+they may not always have an effect. <phrase condition="manual">See
+also <xref linkend="sec-common-options" />.</phrase></para>
+
+<variablelist>
+
+ <varlistentry><term><option>--file</option></term>
+ <term><option>-f</option></term>
+
+ <listitem><para>Specifies the Nix expression (designated below as
+ the <emphasis>active Nix expression</emphasis>) used by the
+ <option>--install</option>, <option>--upgrade</option>, and
+ <option>--query --available</option> operations to obtain
+ derivations. The default is
+ <filename>~/.nix-defexpr</filename>.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--profile</option></term>
+ <term><option>-p</option></term>
+
+ <listitem><para>Specifies the profile to be used by those
+ operations that operate on a profile (designated below as the
+ <emphasis>active profile</emphasis>). A profile is a sequence of
+ user environments called <emphasis>generations</emphasis>, one of
+ which is the <emphasis>current
+ generation</emphasis>.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--dry-run</option></term>
+
+ <listitem><para>For the <option>--install</option>,
+ <option>--upgrade</option>, <option>--uninstall</option>,
+ <option>--switch-generation</option>,
+ <option>--delete-generations</option> and
+ <option>--rollback</option> operations, this flag will cause
+ <command>nix-env</command> to print what
+ <emphasis>would</emphasis> be done if this flag had not been
+ specified, without actually doing it.</para>
+
+ <para><option>--dry-run</option> also prints out which paths will
+ be <link linkend="gloss-substitute">substituted</link> (i.e.,
+ downloaded) and which paths will be built from source (because no
+ substitute is available).</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--system-filter</option> <replaceable>system</replaceable></term>
+
+ <listitem><para>By default, operations such as <option>--query
+ --available</option> show derivations matching any platform. This
+ option allows you to use derivations for the specified platform
+ <replaceable>system</replaceable>.</para></listitem>
+
+ </varlistentry>
+
+</variablelist>
+
+<variablelist condition="manpage">
+ <xi:include href="opt-common.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(//db:variablelist[@xml:id='opt-common']/*)" />
+</variablelist>
+
+</refsection>
+
+
+
+<!--######################################################################-->
+
+<refsection><title>Files</title>
+
+<variablelist>
+
+ <varlistentry><term><filename>~/.nix-defexpr</filename></term>
+
+ <listitem><para>A directory that contains the default Nix
+ expressions used by the <option>--install</option>,
+ <option>--upgrade</option>, and <option>--query
+ --available</option> operations to obtain derivations. The
+ <option>--file</option> option may be used to override this
+ default.</para>
+
+ <para>The Nix expressions in this directory are combined into a
+ single set, with each file as an attribute that has the name of
+ the file. Thus, if <filename>~/.nix-defexpr</filename> contains
+ two files, <filename>foo</filename> and <filename>bar</filename>,
+ then the default Nix expression will essentially be
+
+<programlisting>
+{
+ foo = import ~/.nix-defexpr/foo;
+ bar = import ~/.nix-defexpr/bar;
+}</programlisting>
+
+ </para>
+
+ <para>The command <command>nix-channel</command> places symlinks
+ to the downloaded Nix expressions from each subscribed channel in
+ this directory.</para>
+
+ </listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><filename>~/.nix-profile</filename></term>
+
+ <listitem><para>A symbolic link to the user's current profile. By
+ default, this symlink points to
+ <filename><replaceable>prefix</replaceable>/var/nix/profiles/default</filename>.
+ The <envar>PATH</envar> environment variable should include
+ <filename>~/.nix-profile/bin</filename> for the user environment
+ to be visible to the user.</para></listitem>
+
+ </varlistentry>
+
+</variablelist>
+
+</refsection>
+
+
+
+<!--######################################################################-->
+
+<refsection xml:id="rsec-nix-env-install"><title>Operation <option>--install</option></title>
+
+<refsection><title>Synopsis</title>
+
+<cmdsynopsis>
+ <command>nix-env</command>
+ <group choice='req'>
+ <arg choice='plain'><option>--install</option></arg>
+ <arg choice='plain'><option>-i</option></arg>
+ </group>
+ <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="opt-inst-syn.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(/db:nop/*)" />
+ <group choice='opt'>
+ <arg choice='plain'><option>--preserve-installed</option></arg>
+ <arg choice='plain'><option>-P</option></arg>
+ </group>
+ <group choice='opt'>
+ <arg choice='plain'><option>--remove-all</option></arg>
+ <arg choice='plain'><option>-r</option></arg>
+ </group>
+ <arg choice='plain' rep='repeat'><replaceable>args</replaceable></arg>
+</cmdsynopsis>
+
+</refsection>
+
+
+<refsection><title>Description</title>
+
+<para>The install operation creates a new user environment, based on
+the current generation of the active profile, to which a set of store
+paths described by <replaceable>args</replaceable> is added. The
+arguments <replaceable>args</replaceable> map to store paths in a
+number of possible ways:
+
+<itemizedlist>
+
+ <listitem><para>By default, <replaceable>args</replaceable> is a set
+ of derivation names denoting derivations in the active Nix
+ expression. These are realised, and the resulting output paths are
+ installed. Currently installed derivations with a name equal to the
+ name of a derivation being added are removed unless the option
+ <option>--preserve-installed</option> is
+ specified.</para>
+
+ <para>If there are multiple derivations matching a name in
+ <replaceable>args</replaceable> that have the same name (e.g.,
+ <literal>gcc-3.3.6</literal> and <literal>gcc-4.1.1</literal>), then
+ the derivation with the highest <emphasis>priority</emphasis> is
+ used. A derivation can define a priority by declaring the
+ <varname>meta.priority</varname> attribute. This attribute should
+ be a number, with a higher value denoting a lower priority. The
+ default priority is <literal>0</literal>.</para>
+
+ <para>If there are multiple matching derivations with the same
+ priority, then the derivation with the highest version will be
+ installed.</para>
+
+ <para>You can force the installation of multiple derivations with
+ the same name by being specific about the versions. For instance,
+ <literal>nix-env -i gcc-3.3.6 gcc-4.1.1</literal> will install both
+ version of GCC (and will probably cause a user environment
+ conflict!).</para></listitem>
+
+ <listitem><para>If <link
+ linkend='opt-attr'><option>--attr</option></link>
+ (<option>-A</option>) is specified, the arguments are
+ <emphasis>attribute paths</emphasis> that select attributes from the
+ top-level Nix expression. This is faster than using derivation
+ names and unambiguous. To find out the attribute paths of available
+ packages, use <literal>nix-env -qaP '*'</literal>.</para></listitem>
+
+ <listitem><para>If <option>--from-profile</option>
+ <replaceable>path</replaceable> is given,
+ <replaceable>args</replaceable> is a set of names denoting installed
+ store paths in the profile <replaceable>path</replaceable>. This is
+ an easy way to copy user environment elements from one profile to
+ another.</para></listitem>
+
+ <listitem><para>If <option>--from-expression</option> is given,
+ <replaceable>args</replaceable> are Nix <link
+ linkend="ss-functions">functions</link> that are called with the
+ active Nix expression as their single argument. The derivations
+ returned by those function calls are installed. This allows
+ derivations to be specified in an unambiguous way, which is necessary
+ if there are multiple derivations with the same
+ name.</para></listitem>
+
+ <listitem><para>If <replaceable>args</replaceable> are store
+ derivations, then these are <link
+ linkend="rsec-nix-store-realise">realised</link>, and the resulting
+ output paths are installed.</para></listitem>
+
+ <listitem><para>If <replaceable>args</replaceable> are store paths
+ that are not store derivations, then these are <link
+ linkend="rsec-nix-store-realise">realised</link> and
+ installed.</para></listitem>
+
+</itemizedlist>
+
+</para>
+
+</refsection>
+
+
+<refsection><title>Flags</title>
+
+<variablelist>
+
+ <varlistentry><term><option>--prebuild-only</option> / <option>-b</option></term>
+
+ <listitem><para>Use only derivations for which a substitute is
+ registered, i.e., there is a pre-built binary available that can
+ be downloaded in lieu of building the derivation. Thus, no
+ packages will be built from source.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--preserve-installed</option></term>
+ <term><option>-P</option></term>
+
+ <listitem><para>Do not remove derivations with a name matching one
+ of the derivations being installed. Usually, trying to have two
+ versions of the same package installed in the same generation of a
+ profile will lead to an error in building the generation, due to
+ file name clashes between the two versions. However, this is not
+ the case for all packages.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--remove-all</option></term>
+ <term><option>-r</option></term>
+
+ <listitem><para>Remove all previously installed packages first.
+ This is equivalent to running <literal>nix-env -e '*'</literal>
+ first, except that everything happens in a single
+ transaction.</para></listitem>
+
+ </varlistentry>
+
+</variablelist>
+
+</refsection>
+
+
+<refsection xml:id='refsec-nix-env-install-examples'><title>Examples</title>
+
+<para>To install a specific version of <command>gcc</command> from the
+active Nix expression:
+
+<screen>
+$ nix-env --install gcc-3.3.2
+installing `gcc-3.3.2'
+uninstalling `gcc-3.1'</screen>
+
+Note the the previously installed version is removed, since
+<option>--preserve-installed</option> was not specified.</para>
+
+<para>To install an arbitrary version:
+
+<screen>
+$ nix-env --install gcc
+installing `gcc-3.3.2'</screen>
+
+</para>
+
+<para>To install using a specific attribute:
+
+<screen>
+$ nix-env -i -A gcc40mips
+$ nix-env -i -A xorg.xorgserver</screen>
+
+</para>
+
+<para>To install all derivations in the Nix expression <filename>foo.nix</filename>:
+
+<screen>
+$ nix-env -f ~/foo.nix -i '*'</screen>
+
+</para>
+
+<para>To copy the store path with symbolic name <literal>gcc</literal>
+from another profile:
+
+<screen>
+$ nix-env -i --from-profile /nix/var/nix/profiles/foo -i gcc</screen>
+
+</para>
+
+<para>To install a specific store derivation (typically created by
+<command>nix-instantiate</command>):
+
+<screen>
+$ nix-env -i /nix/store/fibjb1bfbpm5mrsxc4mh2d8n37sxh91i-gcc-3.4.3.drv</screen>
+
+</para>
+
+<para>To install a specific output path:
+
+<screen>
+$ nix-env -i /nix/store/y3cgx0xj1p4iv9x0pnnmdhr8iyg741vk-gcc-3.4.3</screen>
+
+</para>
+
+<para>To install from a Nix expression specified on the command-line:
+
+<screen>
+$ nix-env -f ./foo.nix -i -E \
+ 'f: (f {system = "i686-linux";}).subversionWithJava'</screen>
+
+I.e., this evaluates to <literal>(f: (f {system =
+"i686-linux";}).subversionWithJava) (import ./foo.nix)</literal>, thus
+selecting the <literal>subversionWithJava</literal> attribute from the
+set returned by calling the function defined in
+<filename>./foo.nix</filename>.</para>
+
+<para>A dry-run tells you which paths will be downloaded or built from
+source:
+
+<screen>
+$ nix-env -f pkgs/top-level/all-packages.nix -i f-spot --dry-run
+(dry run; not doing anything)
+installing `f-spot-0.0.10'
+the following derivations will be built:
+ /nix/store/0g63jv9aagwbgci4nnzs2dkxqz84kdja-libgnomeprintui-2.12.1.tar.bz2.drv
+ /nix/store/0gfarvxq6sannsdw8a1ir40j1ys2mqb4-ORBit2-2.14.2.tar.bz2.drv
+ /nix/store/0i9gs5zc04668qiy60ga2rc16abkj7g8-sqlite-2.8.17.drv
+ <replaceable>...</replaceable>
+the following paths will be substituted:
+ /nix/store/8zbipvm4gp9jfqh9nnk1n3bary1a37gs-perl-XML-Parser-2.34
+ /nix/store/b8a2bg7gnyvvvjjibp4axg9x1hzkw36c-mono-1.1.4
+ <replaceable>...</replaceable></screen>
+
+</para>
+
+</refsection>
+
+</refsection>
+
+
+
+<!--######################################################################-->
+
+<refsection xml:id="rsec-nix-env-upgrade"><title>Operation <option>--upgrade</option></title>
+
+<refsection><title>Synopsis</title>
+
+<cmdsynopsis>
+ <command>nix-env</command>
+ <group choice='req'>
+ <arg choice='plain'><option>--upgrade</option></arg>
+ <arg choice='plain'><option>-u</option></arg>
+ </group>
+ <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="opt-inst-syn.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(/db:nop/*)" />
+ <group choice='opt'>
+ <arg choice='plain'><option>--lt</option></arg>
+ <arg choice='plain'><option>--leq</option></arg>
+ <arg choice='plain'><option>--eq</option></arg>
+ <arg choice='plain'><option>--always</option></arg>
+ </group>
+ <arg choice='plain' rep='repeat'><replaceable>args</replaceable></arg>
+</cmdsynopsis>
+
+</refsection>
+
+<refsection><title>Description</title>
+
+<para>The upgrade operation creates a new user environment, based on
+the current generation of the active profile, in which all store paths
+are replaced for which there are newer versions in the set of paths
+described by <replaceable>args</replaceable>. Paths for which there
+are no newer versions are left untouched; this is not an error. It is
+also not an error if an element of <replaceable>args</replaceable>
+matches no installed derivations.</para>
+
+<para>For a description of how <replaceable>args</replaceable> is
+mapped to a set of store paths, see <link
+linkend="rsec-nix-env-install"><option>--install</option></link>. If
+<replaceable>args</replaceable> describes multiple store paths with
+the same symbolic name, only the one with the highest version is
+installed.</para>
+
+</refsection>
+
+<refsection><title>Flags</title>
+
+<variablelist>
+
+ <varlistentry><term><option>--lt</option></term>
+
+ <listitem><para>Only upgrade a derivation to newer versions. This
+ is the default.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--leq</option></term>
+
+ <listitem><para>In addition to upgrading to newer versions, also
+ “upgrade” to derivations that have the same version. Version are
+ not a unique identification of a derivation, so there may be many
+ derivations that have the same version. This flag may be useful
+ to force “synchronisation” between the installed and available
+ derivations.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--eq</option></term>
+
+ <listitem><para><emphasis>Only</emphasis> “upgrade” to derivations
+ that have the same version. This may not seem very useful, but it
+ actually is, e.g., when there is a new release of Nixpkgs and you
+ want to replace installed applications with the same versions
+ built against newer dependencies (to reduce the number of
+ dependencies floating around on your system).</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--always</option></term>
+
+ <listitem><para>In addition to upgrading to newer versions, also
+ “upgrade” to derivations that have the same or a lower version.
+ I.e., derivations may actually be downgraded depending on what is
+ available in the active Nix expression.</para></listitem>
+
+ </varlistentry>
+
+</variablelist>
+
+<para>For the other flags, see <option
+linkend="rsec-nix-env-install">--install</option>.</para>
+
+</refsection>
+
+<refsection><title>Examples</title>
+
+<screen>
+$ nix-env --upgrade gcc
+upgrading `gcc-3.3.1' to `gcc-3.4'
+
+$ nix-env -u gcc-3.3.2 --always <lineannotation>(switch to a specific version)</lineannotation>
+upgrading `gcc-3.4' to `gcc-3.3.2'
+
+$ nix-env --upgrade pan
+<lineannotation>(no upgrades available, so nothing happens)</lineannotation>
+
+$ nix-env -u '*' <lineannotation>(try to upgrade everything)</lineannotation>
+upgrading `hello-2.1.2' to `hello-2.1.3'
+upgrading `mozilla-1.2' to `mozilla-1.4'</screen>
+
+</refsection>
+
+<refsection xml:id="ssec-version-comparisons"><title>Versions</title>
+
+<para>The upgrade operation determines whether a derivation
+<varname>y</varname> is an upgrade of a derivation
+<varname>x</varname> by looking at their respective
+<literal>name</literal> attributes. The names (e.g.,
+<literal>gcc-3.3.1</literal> are split into two parts: the package
+name (<literal>gcc</literal>), and the version
+(<literal>3.3.1</literal>). The version part starts after the first
+dash not following by a letter. <varname>x</varname> is considered an
+upgrade of <varname>y</varname> if their package names match, and the
+version of <varname>y</varname> is higher that that of
+<varname>x</varname>.</para>
+
+<para>The versions are compared by splitting them into contiguous
+components of numbers and letters. E.g., <literal>3.3.1pre5</literal>
+is split into <literal>[3, 3, 1, "pre", 5]</literal>. These lists are
+then compared lexicographically (from left to right). Corresponding
+components <varname>a</varname> and <varname>b</varname> are compared
+as follows. If they are both numbers, integer comparison is used. If
+<varname>a</varname> is an empty string and <varname>b</varname> is a
+number, <varname>a</varname> is considered less than
+<varname>b</varname>. The special string component
+<literal>pre</literal> (for <emphasis>pre-release</emphasis>) is
+considered to be less than other components. String components are
+considered less than number components. Otherwise, they are compared
+lexicographically (i.e., using case-sensitive string comparison).</para>
+
+<para>This is illustrated by the following examples:
+
+<screen>
+1.0 &lt; 2.3
+2.1 &lt; 2.3
+2.3 = 2.3
+2.5 > 2.3
+3.1 > 2.3
+2.3.1 > 2.3
+2.3.1 > 2.3a
+2.3pre1 &lt; 2.3
+2.3pre3 &lt; 2.3pre12
+2.3a &lt; 2.3c
+2.3pre1 &lt; 2.3c
+2.3pre1 &lt; 2.3q</screen>
+
+</para>
+
+</refsection>
+
+</refsection>
+
+
+
+<!--######################################################################-->
+
+<refsection><title>Operation <option>--uninstall</option></title>
+
+<refsection><title>Synopsis</title>
+
+<cmdsynopsis>
+ <command>nix-env</command>
+ <group choice='req'>
+ <arg choice='plain'><option>--uninstall</option></arg>
+ <arg choice='plain'><option>-e</option></arg>
+ </group>
+ <arg choice='plain' rep='repeat'><replaceable>drvnames</replaceable></arg>
+</cmdsynopsis>
+</refsection>
+
+<refsection><title>Description</title>
+
+<para>The uninstall operation creates a new user environment, based on
+the current generation of the active profile, from which the store
+paths designated by the symbolic names
+<replaceable>names</replaceable> are removed.</para>
+
+</refsection>
+
+<refsection><title>Examples</title>
+
+<screen>
+$ nix-env --uninstall gcc
+$ nix-env -e '*' <lineannotation>(remove everything)</lineannotation></screen>
+
+</refsection>
+
+</refsection>
+
+
+
+<!--######################################################################-->
+
+<refsection xml:id="rsec-nix-env-set-flag"><title>Operation <option>--set-flag</option></title>
+
+<refsection><title>Synopsis</title>
+
+<cmdsynopsis>
+ <command>nix-env</command>
+ <arg choice='plain'><option>--set-flag</option></arg>
+ <arg choice='plain'><replaceable>name</replaceable></arg>
+ <arg choice='plain'><replaceable>value</replaceable></arg>
+ <arg choice='plain' rep='repeat'><replaceable>drvnames</replaceable></arg>
+</cmdsynopsis>
+</refsection>
+
+<refsection><title>Description</title>
+
+<para>The <option>--set-flag</option> operation allows meta attributes
+of installed packages to be modified. There are several attributes
+that can be usefully modified, because they affect the behaviour of
+<command>nix-env</command> or the user environment build
+script:
+
+<itemizedlist>
+
+ <listitem><para><varname>priority</varname> can be changed to
+ resolve filename clashes. The user environment build script uses
+ the <varname>meta.priority</varname> attribute of derivations to
+ resolve filename collisions between packages. Lower priority values
+ denote a higher priority. For instance, the GCC wrapper package and
+ the Binutils package in Nixpkgs both have a file
+ <filename>bin/ld</filename>, so previously if you tried to install
+ both you would get a collision. Now, on the other hand, the GCC
+ wrapper declares a higher priority than Binutils, so the former’s
+ <filename>bin/ld</filename> is symlinked in the user
+ environment.</para></listitem>
+
+ <listitem><para><varname>keep</varname> can be set to
+ <literal>true</literal> to prevent the package from being upgraded
+ or replaced. This is useful if you want to hang on to an older
+ version of a package.</para></listitem>
+
+ <listitem><para><varname>active</varname> can be set to
+ <literal>false</literal> to “disable” the package. That is, no
+ symlinks will be generated to the files of the package, but it
+ remains part of the profile (so it won’t be garbage-collected). It
+ can be set back to <literal>true</literal> to re-enable the
+ package.</para></listitem>
+
+</itemizedlist>
+
+</para>
+
+</refsection>
+
+<refsection><title>Examples</title>
+
+<para>To prevent the currently installed Firefox from being upgraded:
+
+<screen>
+$ nix-env --set-flag keep true firefox</screen>
+
+After this, <command>nix-env -u</command> will ignore Firefox.</para>
+
+<para>To disable the currently installed Firefox, then install a new
+Firefox while the old remains part of the profile:
+
+<screen>
+$ nix-env -q \*
+firefox-2.0.0.9 <lineannotation>(the current one)</lineannotation>
+
+$ nix-env --preserve-installed -i firefox-2.0.0.11
+installing `firefox-2.0.0.11'
+building path(s) `/nix/store/myy0y59q3ig70dgq37jqwg1j0rsapzsl-user-environment'
+collision between `/nix/store/<replaceable>...</replaceable>-firefox-2.0.0.11/bin/firefox'
+ and `/nix/store/<replaceable>...</replaceable>-firefox-2.0.0.9/bin/firefox'.
+<lineannotation>(i.e., can’t have two active at the same time)</lineannotation>
+
+$ nix-env --set-flag active false firefox
+setting flag on `firefox-2.0.0.9'
+
+$ nix-env --preserve-installed -i firefox-2.0.0.11
+installing `firefox-2.0.0.11'
+
+$ nix-env -q \*
+firefox-2.0.0.11 <lineannotation>(the enabled one)</lineannotation>
+firefox-2.0.0.9 <lineannotation>(the disabled one)</lineannotation></screen>
+
+</para>
+
+<para>To make files from <literal>binutils</literal> take precedence
+over files from <literal>gcc</literal>:
+
+<screen>
+$ nix-env --set-flag priority 5 binutils
+$ nix-env --set-flag priority 10 gcc</screen>
+
+</para>
+
+</refsection>
+
+</refsection>
+
+
+
+<!--######################################################################-->
+
+<refsection><title>Operation <option>--query</option></title>
+
+<refsection><title>Synopsis</title>
+
+<cmdsynopsis>
+ <command>nix-env</command>
+ <group choice='req'>
+ <arg choice='plain'><option>--query</option></arg>
+ <arg choice='plain'><option>-q</option></arg>
+ </group>
+ <group choice='opt'>
+ <arg choice='plain'><option>--installed</option></arg>
+ <arg choice='plain'><option>--available</option></arg>
+ <arg choice='plain'><option>-a</option></arg>
+ </group>
+
+ <sbr />
+
+ <arg>
+ <group choice='req'>
+ <arg choice='plain'><option>--status</option></arg>
+ <arg choice='plain'><option>-s</option></arg>
+ </group>
+ </arg>
+ <arg>
+ <group choice='req'>
+ <arg choice='plain'><option>--attr-path</option></arg>
+ <arg choice='plain'><option>-P</option></arg>
+ </group>
+ </arg>
+ <arg><option>--no-name</option></arg>
+ <arg>
+ <group choice='req'>
+ <arg choice='plain'><option>--compare-versions</option></arg>
+ <arg choice='plain'><option>-c</option></arg>
+ </group>
+ </arg>
+ <arg><option>--system</option></arg>
+ <arg><option>--drv-path</option></arg>
+ <arg><option>--out-path</option></arg>
+ <arg><option>--description</option></arg>
+ <arg><option>--meta</option></arg>
+
+ <sbr />
+
+ <arg><option>--xml</option></arg>
+ <arg><option>--json</option></arg>
+ <arg>
+ <group choice='req'>
+ <arg choice='plain'><option>--prebuilt-only</option></arg>
+ <arg choice='plain'><option>-b</option></arg>
+ </group>
+ </arg>
+
+ <arg>
+ <group choice='req'>
+ <arg choice='plain'><option>--attr</option></arg>
+ <arg choice='plain'><option>-A</option></arg>
+ </group>
+ <replaceable>attribute-path</replaceable>
+ </arg>
+
+ <sbr />
+
+ <arg choice='plain' rep='repeat'><replaceable>names</replaceable></arg>
+</cmdsynopsis>
+
+</refsection>
+
+
+<refsection><title>Description</title>
+
+<para>The query operation displays information about either the store
+paths that are installed in the current generation of the active
+profile (<option>--installed</option>), or the derivations that are
+available for installation in the active Nix expression
+(<option>--available</option>). It only prints information about
+derivations whose symbolic name matches one of
+<replaceable>names</replaceable>. The wildcard <literal>*</literal>
+shows all derivations.</para>
+
+<para>The derivations are sorted by their <literal>name</literal>
+attributes.</para>
+
+</refsection>
+
+
+<refsection><title>Source selection</title>
+
+<para>The following flags specify the set of things on which the query
+operates.</para>
+
+<variablelist>
+
+ <varlistentry><term><option>--installed</option></term>
+
+ <listitem><para>The query operates on the store paths that are
+ installed in the current generation of the active profile. This
+ is the default.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--available</option></term>
+ <term><option>-a</option></term>
+
+ <listitem><para>The query operates on the derivations that are
+ available in the active Nix expression.</para></listitem>
+
+ </varlistentry>
+
+</variablelist>
+
+</refsection>
+
+
+<refsection><title>Queries</title>
+
+<para>The following flags specify what information to display about
+the selected derivations. Multiple flags may be specified, in which
+case the information is shown in the order given here. Note that the
+name of the derivation is shown unless <option>--no-name</option> is
+specified.</para>
+
+<!-- TODO: fix the terminology here; i.e., derivations, store paths,
+user environment elements, etc. -->
+
+<variablelist>
+
+ <varlistentry><term><option>--xml</option></term>
+
+ <listitem><para>Print the result in an XML representation suitable
+ for automatic processing by other tools. The root element is
+ called <literal>items</literal>, which contains a
+ <literal>item</literal> element for each available or installed
+ derivation. The fields discussed below are all stored in
+ attributes of the <literal>item</literal>
+ elements.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--json</option></term>
+
+ <listitem><para>Print the result in a JSON representation suitable
+ for automatic processing by other tools.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--prebuild-only</option> / <option>-b</option></term>
+
+ <listitem><para>Show only derivations for which a substitute is
+ registered, i.e., there is a pre-built binary available that can
+ be downloaded in lieu of building the derivation. Thus, this
+ shows all packages that probably can be installed
+ quickly.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--status</option></term>
+ <term><option>-s</option></term>
+
+ <listitem><para>Print the <emphasis>status</emphasis> of the
+ derivation. The status consists of three characters. The first
+ is <literal>I</literal> or <literal>-</literal>, indicating
+ whether the derivation is currently installed in the current
+ generation of the active profile. This is by definition the case
+ for <option>--installed</option>, but not for
+ <option>--available</option>. The second is <literal>P</literal>
+ or <literal>-</literal>, indicating whether the derivation is
+ present on the system. This indicates whether installation of an
+ available derivation will require the derivation to be built. The
+ third is <literal>S</literal> or <literal>-</literal>, indicating
+ whether a substitute is available for the
+ derivation.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--attr-path</option></term>
+ <term><option>-P</option></term>
+
+ <listitem><para>Print the <emphasis>attribute path</emphasis> of
+ the derivation, which can be used to unambiguously select it using
+ the <link linkend="opt-attr"><option>--attr</option> option</link>
+ available in commands that install derivations like
+ <literal>nix-env --install</literal>.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--no-name</option></term>
+
+ <listitem><para>Suppress printing of the <literal>name</literal>
+ attribute of each derivation.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--compare-versions</option> /
+ <option>-c</option></term>
+
+ <listitem><para>Compare installed versions to available versions,
+ or vice versa (if <option>--available</option> is given). This is
+ useful for quickly seeing whether upgrades for installed
+ packages are available in a Nix expression. A column is added
+ with the following meaning:
+
+ <variablelist>
+
+ <varlistentry><term><literal>&lt;</literal> <replaceable>version</replaceable></term>
+
+ <listitem><para>A newer version of the package is available
+ or installed.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><literal>=</literal> <replaceable>version</replaceable></term>
+
+ <listitem><para>At most the same version of the package is
+ available or installed.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><literal>></literal> <replaceable>version</replaceable></term>
+
+ <listitem><para>Only older versions of the package are
+ available or installed.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><literal>- ?</literal></term>
+
+ <listitem><para>No version of the package is available or
+ installed.</para></listitem>
+
+ </varlistentry>
+
+ </variablelist>
+
+ </para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--system</option></term>
+
+ <listitem><para>Print the <literal>system</literal> attribute of
+ the derivation.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--drv-path</option></term>
+
+ <listitem><para>Print the path of the store
+ derivation.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--out-path</option></term>
+
+ <listitem><para>Print the output path of the
+ derivation.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--description</option></term>
+
+ <listitem><para>Print a short (one-line) description of the
+ derivation, if available. The description is taken from the
+ <literal>meta.description</literal> attribute of the
+ derivation.</para></listitem>
+
+ </varlistentry>
+
+ <varlistentry><term><option>--meta</option></term>
+
+ <listitem><para>Print all of the meta-attributes of the
+ derivation. This option is only available with
+ <option>--xml</option>.</para></listitem>
+
+ </varlistentry>
+
+</variablelist>
+
+</refsection>
+
+
+<refsection><title>Examples</title>
+
+<screen>
+$ nix-env -q '*' <lineannotation>(show installed derivations)</lineannotation>
+bison-1.875c
+docbook-xml-4.2
+firefox-1.0.4
+MPlayer-1.0pre7
+ORBit2-2.8.3
+...
+
+$ nix-env -qa '*' <lineannotation>(show available derivations)</lineannotation>
+firefox-1.0.7
+GConf-2.4.0.1
+MPlayer-1.0pre7
+ORBit2-2.8.3
+...
+
+$ nix-env -qas '*' <lineannotation>(show status of available derivations)</lineannotation>
+-P- firefox-1.0.7 <lineannotation>(not installed but present)</lineannotation>
+--S GConf-2.4.0.1 <lineannotation>(not present, but there is a substitute for fast installation)</lineannotation>
+--S MPlayer-1.0pre3 <lineannotation>(i.e., this is not the installed MPlayer, even though the version is the same!)</lineannotation>
+IP- ORBit2-2.8.3 <lineannotation>(installed and by definition present)</lineannotation>
+...
+
+<lineannotation>(show available derivations in the Nix expression <!-- !!! <filename>-->foo.nix<!-- </filename> -->)</lineannotation>
+$ nix-env -f ./foo.nix -qa '*'
+foo-1.2.3
+
+$ nix-env -qc '*' <lineannotation>(compare installed versions to what’s available)</lineannotation>
+<replaceable>...</replaceable>
+acrobat-reader-7.0 - ? <lineannotation>(package is not available at all)</lineannotation>
+autoconf-2.59 = 2.59 <lineannotation>(same version)</lineannotation>
+firefox-1.0.4 &lt; 1.0.7 <lineannotation>(a more recent version is available)</lineannotation>
+<replaceable>...</replaceable>
+
+<lineannotation>(show info about a specific package, in XML)</lineannotation>
+$ nix-env -qa --xml --description firefox
+<![CDATA[<?xml version='1.0' encoding='utf-8'?>
+<items>
+ <item attrPath="0.0.firefoxWrapper"
+ description="Mozilla Firefox - the browser, reloaded (with various plugins)"
+ name="firefox-1.5.0.7" system="i686-linux" />
+</items>]]></screen>
+
+</refsection>
+
+</refsection>
+
+
+
+<!--######################################################################-->
+
+<refsection><title>Operation <option>--switch-profile</option></title>
+
+<refsection><title>Synopsis</title>
+
+<cmdsynopsis>
+ <command>nix-env</command>
+ <group choice='req'>
+ <arg choice='plain'><option>--switch-profile</option></arg>
+ <arg choice='plain'><option>-S</option></arg>
+ </group>
+ <arg choice='req'><replaceable>path</replaceable></arg>
+</cmdsynopsis>
+
+</refsection>
+
+
+<refsection><title>Description</title>
+
+<para>This operation makes <replaceable>path</replaceable> the current
+profile for the user. That is, the symlink
+<filename>~/.nix-profile</filename> is made to point to
+<replaceable>path</replaceable>.</para>
+
+</refsection>
+
+<refsection><title>Examples</title>
+
+<screen>
+$ nix-env -S ~/my-profile</screen>
+
+</refsection>
+
+</refsection>
+
+
+
+<!--######################################################################-->
+
+<refsection><title>Operation <option>--list-generations</option></title>
+
+<refsection><title>Synopsis</title>
+
+<cmdsynopsis>
+ <command>nix-env</command>
+ <arg choice='plain'><option>--list-generations</option></arg>
+</cmdsynopsis>
+
+</refsection>
+
+
+<refsection><title>Description</title>
+
+<para>This operation print a list of all the currently existing
+generations for the active profile. These may be switched to using
+the <option>--switch-generation</option> operation. It also prints
+the creation date of the generation, and indicates the current
+generation.</para>
+
+</refsection>
+
+
+<refsection><title>Examples</title>
+
+<screen>
+$ nix-env --list-generations
+ 95 2004-02-06 11:48:24
+ 96 2004-02-06 11:49:01
+ 97 2004-02-06 16:22:45
+ 98 2004-02-06 16:24:33 (current)</screen>
+
+</refsection>
+
+</refsection>
+
+
+
+<!--######################################################################-->
+
+<refsection><title>Operation <option>--delete-generations</option></title>
+
+<refsection><title>Synopsis</title>
+
+<cmdsynopsis>
+ <command>nix-env</command>
+ <arg choice='plain'><option>--delete-generations</option></arg>
+ <arg choice='plain' rep='repeat'><replaceable>generations</replaceable></arg>
+</cmdsynopsis>
+
+</refsection>
+
+
+<refsection><title>Description</title>
+
+<para>This operation deletes the specified generations of the current
+profile. The generations can be a list of generation numbers, the
+special value <literal>old</literal> to delete all non-current
+generations, or a value such as <literal>30d</literal> to delete all
+generations older than the specified number of days (except for the
+generation that was active at that point in time).
+Periodically deleting old generations is important to make garbage
+collection effective.</para>
+
+</refsection>
+
+<refsection><title>Examples</title>
+
+<screen>
+$ nix-env --delete-generations 3 4 8
+
+$ nix-env --delete-generations 30d
+
+$ nix-env -p other_profile --delete-generations old</screen>
+
+</refsection>
+
+</refsection>
+
+
+
+<!--######################################################################-->
+
+<refsection><title>Operation <option>--switch-generation</option></title>
+
+<refsection><title>Synopsis</title>
+
+<cmdsynopsis>
+ <command>nix-env</command>
+ <group choice='req'>
+ <arg choice='plain'><option>--switch-generation</option></arg>
+ <arg choice='plain'><option>-G</option></arg>
+ </group>
+ <arg choice='req'><replaceable>generation</replaceable></arg>
+</cmdsynopsis>
+
+</refsection>
+
+
+<refsection><title>Description</title>
+
+<para>This operation makes generation number
+<replaceable>generation</replaceable> the current generation of the
+active profile. That is, if the
+<filename><replaceable>profile</replaceable></filename> is the path to
+the active profile, then the symlink
+<filename><replaceable>profile</replaceable></filename> is made to
+point to
+<filename><replaceable>profile</replaceable>-<replaceable>generation</replaceable>-link</filename>,
+which is in turn a symlink to the actual user environment in the Nix
+store.</para>
+
+<para>Switching will fail if the specified generation does not exist.</para>
+
+</refsection>
+
+
+<refsection><title>Examples</title>
+
+<screen>
+$ nix-env -G 42
+switching from generation 50 to 42</screen>
+
+</refsection>
+
+</refsection>
+
+
+
+<!--######################################################################-->
+
+<refsection><title>Operation <option>--rollback</option></title>
+
+<refsection><title>Synopsis</title>
+
+<cmdsynopsis>
+ <command>nix-env</command>
+ <arg choice='plain'><option>--rollback</option></arg>
+</cmdsynopsis>
+
+</refsection>
+
+<refsection><title>Description</title>
+
+<para>This operation switches to the “previous” generation of the
+active profile, that is, the highest numbered generation lower than
+the current generation, if it exists. It is just a convenience
+wrapper around <option>--list-generations</option> and
+<option>--switch-generation</option>.</para>
+
+</refsection>
+
+
+<refsection><title>Examples</title>
+
+<screen>
+$ nix-env --rollback
+switching from generation 92 to 91
+
+$ nix-env --rollback
+error: no generation older than the current (91) exists</screen>
+
+</refsection>
+
+</refsection>
+
+
+<refsection condition="manpage"><title>Environment variables</title>
+
+<variablelist>
+
+ <varlistentry><term><envar>NIX_PROFILE</envar></term>
+
+ <listitem><para>Location of the Nix profile. Defaults to the
+ target of the symlink <filename>~/.nix-profile</filename>, if it
+ exists, or <filename>/nix/var/nix/profiles/default</filename>
+ otherwise.</para></listitem>
+
+ </varlistentry>
+
+ <xi:include href="env-common.xml#xmlns(db=http://docbook.org/ns/docbook)xpointer(//db:variablelist[@xml:id='env-common']/*)" />
+</variablelist>
+
+</refsection>
+
+
+</refentry>