guix.texi

When ``run'' through @var{%state-monad}, we obtain that additional state
value, which is the number of @code{square} calls.
@end defvr

@deffn {Monadic Procedure} current-state
Return the current state as a monadic value.
@end deffn

@deffn {Monadic Procedure} set-current-state @var{value}
Set the current state to @var{value} and return the previous state as a
monadic value.
@end deffn

@deffn {Monadic Procedure} state-push @var{value}
Push @var{value} to the current state, which is assumed to be a list,
and return the previous state as a monadic value.
@end deffn

@deffn {Monadic Procedure} state-pop
Pop a value from the current state and return it as a monadic value.
The state is assumed to be a list.
@end deffn

@deffn {Scheme Procedure} run-with-state @var{mval} [@var{state}]
Run monadic value @var{mval} starting with @var{state} as the initial
state.  Return two values: the resulting value, and the resulting state.
@end deffn

The main interface to the store monad, provided by the @code{(guix
store)} module, is as follows.

@defvr {Scheme Variable} %store-monad
The store monad---an alias for @var{%state-monad}.

Values in the store monad encapsulate accesses to the store.  When its
effect is needed, a value of the store monad must be ``evaluated'' by
passing it to the @code{run-with-store} procedure (see below.)
@end defvr

@deffn {Scheme Procedure} run-with-store @var{store} @var{mval} [#:guile-for-build] [#:system (%current-system)]
Run @var{mval}, a monadic value in the store monad, in @var{store}, an
open store connection.
@end deffn

@deffn {Monadic Procedure} text-file @var{name} @var{text} [@var{references}]
Return as a monadic value the absolute file name in the store of the file
containing @var{text}, a string.  @var{references} is a list of store items that the
resulting text file refers to; it defaults to the empty list.
@end deffn

@deffn {Monadic Procedure} interned-file @var{file} [@var{name}] @
         [#:recursive? #t]
Return the name of @var{file} once interned in the store.  Use
@var{name} as its store name, or the basename of @var{file} if
@var{name} is omitted.

When @var{recursive?} is true, the contents of @var{file} are added
recursively; if @var{file} designates a flat file and @var{recursive?}
is true, its contents are added, and its permission bits are kept.

The example below adds a file to the store, under two different names:

@example
(run-with-store (open-connection)
  (mlet %store-monad ((a (interned-file "README"))
                      (b (interned-file "README" "LEGU-MIN")))
    (return (list a b))))

@result{} ("/gnu/store/rwm@dots{}-README" "/gnu/store/44i@dots{}-LEGU-MIN")
@end example

@end deffn

The @code{(guix packages)} module exports the following package-related
monadic procedures:

@deffn {Monadic Procedure} package-file @var{package} [@var{file}] @
       [#:system (%current-system)] [#:target #f] @
       [#:output "out"] Return as a monadic
value in the absolute file name of @var{file} within the @var{output}
directory of @var{package}.  When @var{file} is omitted, return the name
of the @var{output} directory of @var{package}.  When @var{target} is
true, use it as a cross-compilation target triplet.
@end deffn

@deffn {Monadic Procedure} package->derivation @var{package} [@var{system}]
@deffnx {Monadic Procedure} package->cross-derivation @var{package} @
          @var{target} [@var{system}]
Monadic version of @code{package-derivation} and
@code{package-cross-derivation} (@pxref{Defining Packages}).
@end deffn


@node G-Expressions
@section G-Expressions

@cindex G-expression
@cindex build code quoting
So we have ``derivations'', which represent a sequence of build actions
to be performed to produce an item in the store (@pxref{Derivations}).
Those build actions are performed when asking the daemon to actually
build the derivations; they are run by the daemon in a container
(@pxref{Invoking guix-daemon}).

@cindex strata of code
It should come as no surprise that we like to write those build actions
in Scheme.  When we do that, we end up with two @dfn{strata} of Scheme
code@footnote{The term @dfn{stratum} in this context was coined by
Manuel Serrano et al.@: in the context of their work on Hop.  Oleg
Kiselyov, who has written insightful
@url{http://okmij.org/ftp/meta-programming/#meta-scheme, essays and code
on this topic}, refers to this kind of code generation as
@dfn{staging}.}: the ``host code''---code that defines packages, talks
to the daemon, etc.---and the ``build code''---code that actually
performs build actions, such as making directories, invoking
@command{make}, etc.

To describe a derivation and its build actions, one typically needs to
embed build code inside host code.  It boils down to manipulating build
code as data, and Scheme's homoiconicity---code has a direct
representation as data---comes in handy for that.  But we need more than
Scheme's normal @code{quasiquote} mechanism to construct build
expressions.

The @code{(guix gexp)} module implements @dfn{G-expressions}, a form of
S-expressions adapted to build expressions.  G-expressions, or
@dfn{gexps}, consist essentially in three syntactic forms: @code{gexp},
@code{ungexp}, and @code{ungexp-splicing} (or simply: @code{#~},
@code{#$}, and @code{#$@@}), which are comparable respectively to
@code{quasiquote}, @code{unquote}, and @code{unquote-splicing}
(@pxref{Expression Syntax, @code{quasiquote},, guile, GNU Guile
Reference Manual}).  However, there are major differences:

@itemize
@item
Gexps are meant to be written to a file and run or manipulated by other
processes.

@item
When a high-level object such as a package or derivation is unquoted
inside a gexp, the result is as if its output file name had been
introduced.

@item
Gexps carry information about the packages or derivations they refer to,
and these dependencies are automatically added as inputs to the build
processes that use them.
@end itemize

@cindex lowering, of high-level objects in gexps
This mechanism is not limited to package and derivation
objects: @dfn{compilers} able to ``lower'' other high-level objects to
derivations or files in the store can be defined,
such that these objects can also be inserted
into gexps.  For example, a useful type of high-level object that can be
inserted in a gexp is ``file-like objects'', which make it easy to
add files to the store and refer to them in
derivations and such (see @code{local-file} and @code{plain-file}
below.)

To illustrate the idea, here is an example of a gexp:

@example
(define build-exp
  #~(begin
      (mkdir #$output)
      (chdir #$output)
      (symlink (string-append #$coreutils "/bin/ls")
               "list-files")))
@end example

This gexp can be passed to @code{gexp->derivation}; we obtain a
derivation that builds a directory containing exactly one symlink to
@file{/gnu/store/@dots{}-coreutils-8.22/bin/ls}:

@example
(gexp->derivation "the-thing" build-exp)
@end example

As one would expect, the @code{"/gnu/store/@dots{}-coreutils-8.22"} string is
substituted to the reference to the @var{coreutils} package in the
actual build code, and @var{coreutils} is automatically made an input to
the derivation.  Likewise, @code{#$output} (equivalent to @code{(ungexp
output)}) is replaced by a string containing the derivation's output
directory name.

@cindex cross compilation
In a cross-compilation context, it is useful to distinguish between
references to the @emph{native} build of a package---that can run on the
host---versus references to cross builds of a package.  To that end, the
@code{#+} plays the same role as @code{#$}, but is a reference to a
native package build:

@example
(gexp->derivation "vi"
   #~(begin
       (mkdir #$output)
       (system* (string-append #+coreutils "/bin/ln")
                "-s"
                (string-append #$emacs "/bin/emacs")
                (string-append #$output "/bin/vi")))
   #:target "mips64el-linux")
@end example

@noindent
In the example above, the native build of @var{coreutils} is used, so
that @command{ln} can actually run on the host; but then the
cross-compiled build of @var{emacs} is referenced.

The syntactic form to construct gexps is summarized below.

@deffn {Scheme Syntax} #~@var{exp}
@deffnx {Scheme Syntax} (gexp @var{exp})
Return a G-expression containing @var{exp}.  @var{exp} may contain one
or more of the following forms:

@table @code
@item #$@var{obj}
@itemx (ungexp @var{obj})
Introduce a reference to @var{obj}.  @var{obj} may have one of the
supported types, for example a package or a
derivation, in which case the @code{ungexp} form is replaced by its
output file name---e.g., @code{"/gnu/store/@dots{}-coreutils-8.22}.

If @var{obj} is a list, it is traversed and references to supported
objects are substituted similarly.

If @var{obj} is another gexp, its contents are inserted and its
dependencies are added to those of the containing gexp.

If @var{obj} is another kind of object, it is inserted as is.

@item #$@var{obj}:@var{output}
@itemx (ungexp @var{obj} @var{output})
This is like the form above, but referring explicitly to the
@var{output} of @var{obj}---this is useful when @var{obj} produces
multiple outputs (@pxref{Packages with Multiple Outputs}).

@item #+@var{obj}
@itemx #+@var{obj}:output
@itemx (ungexp-native @var{obj})
@itemx (ungexp-native @var{obj} @var{output})
Same as @code{ungexp}, but produces a reference to the @emph{native}
build of @var{obj} when used in a cross compilation context.

@item #$output[:@var{output}]
@itemx (ungexp output [@var{output}])
Insert a reference to derivation output @var{output}, or to the main
output when @var{output} is omitted.

This only makes sense for gexps passed to @code{gexp->derivation}.

@item #$@@@var{lst}
@itemx (ungexp-splicing @var{lst})
Like the above, but splices the contents of @var{lst} inside the
containing list.

@item #+@@@var{lst}
@itemx (ungexp-native-splicing @var{lst})
Like the above, but refers to native builds of the objects listed in
@var{lst}.

@end table

G-expressions created by @code{gexp} or @code{#~} are run-time objects
of the @code{gexp?} type (see below.)
@end deffn

@deffn {Scheme Procedure} gexp? @var{obj}
Return @code{#t} if @var{obj} is a G-expression.
@end deffn

G-expressions are meant to be written to disk, either as code building
some derivation, or as plain files in the store.  The monadic procedures
below allow you to do that (@pxref{The Store Monad}, for more
information about monads.)

@deffn {Monadic Procedure} gexp->derivation @var{name} @var{exp} @
       [#:system (%current-system)] [#:target #f] [#:graft? #t] @
       [#:hash #f] [#:hash-algo #f] @
       [#:recursive? #f] [#:env-vars '()] [#:modules '()] @
       [#:module-path @var{%load-path}] @
       [#:references-graphs #f] [#:allowed-references #f] @
       [#:leaked-env-vars #f] @
       [#:script-name (string-append @var{name} "-builder")] @
       [#:local-build? #f] [#:substitutable? #t] [#:guile-for-build #f]
Return a derivation @var{name} that runs @var{exp} (a gexp) with
@var{guile-for-build} (a derivation) on @var{system}; @var{exp} is
stored in a file called @var{script-name}.  When @var{target} is true,
it is used as the cross-compilation target triplet for packages referred
to by @var{exp}.

Make @var{modules} available in the evaluation context of @var{exp};
@var{modules} is a list of names of Guile modules searched in
@var{module-path} to be copied in the store, compiled, and made available in
the load path during the execution of @var{exp}---e.g., @code{((guix
build utils) (guix build gnu-build-system))}.

@var{graft?} determines whether packages referred to by @var{exp} should be grafted when
applicable.

When @var{references-graphs} is true, it must be a list of tuples of one of the
following forms:

@example
(@var{file-name} @var{package})
(@var{file-name} @var{package} @var{output})
(@var{file-name} @var{derivation})
(@var{file-name} @var{derivation} @var{output})
(@var{file-name} @var{store-item})
@end example

The right-hand-side of each element of @var{references-graphs} is automatically made
an input of the build process of @var{exp}.  In the build environment, each
@var{file-name} contains the reference graph of the corresponding item, in a simple
text format.

@var{allowed-references} must be either @code{#f} or a list of output names and packages.
In the latter case, the list denotes store items that the result is allowed to
refer to.  Any reference to another store item will lead to a build error.

The other arguments are as for @code{derivation} (@pxref{Derivations}).
@end deffn

@cindex file-like objects
The @code{local-file} and @code{plain-file} procedures below return
@dfn{file-like objects}.  That is, when unquoted in a G-expression,
these objects lead to a file in the store.  Consider this G-expression:

@example
#~(system* (string-append #$glibc "/sbin/nscd") "-f"
           #$(local-file "/tmp/my-nscd.conf"))
@end example

The effect here is to ``intern'' @file{/tmp/my-nscd.conf} by copying it
to the store.  Once expanded, for instance @i{via}
@code{gexp->derivation}, the G-expression refers to that copy under
@file{/gnu/store}; thus, modifying or removing the file in @file{/tmp}
does not have any effect on what the G-expression does.
@code{plain-file} can be used similarly; it differs in that the file
content is directly passed as a string.

@deffn {Scheme Procedure} local-file @var{file} [@var{name}] @
   [#:recursive? #t]
Return an object representing local file @var{file} to add to the store; this
object can be used in a gexp.  @var{file} will be added to the store under @var{name}--by
default the base name of @var{file}.

When @var{recursive?} is true, the contents of @var{file} are added recursively; if @var{file}
designates a flat file and @var{recursive?} is true, its contents are added, and its
permission bits are kept.

This is the declarative counterpart of the @code{interned-file} monadic
procedure (@pxref{The Store Monad, @code{interned-file}}).
@end deffn

@deffn {Scheme Procedure} plain-file @var{name} @var{content}
Return an object representing a text file called @var{name} with the given
@var{content} (a string) to be added to the store.

This is the declarative counterpart of @code{text-file}.
@end deffn

@deffn {Monadic Procedure} gexp->script @var{name} @var{exp}
Return an executable script @var{name} that runs @var{exp} using
@var{guile} with @var{modules} in its search path.

The example below builds a script that simply invokes the @command{ls}
command:

@example
(use-modules (guix gexp) (gnu packages base))

(gexp->script "list-files"
              #~(execl (string-append #$coreutils "/bin/ls")
                       "ls"))
@end example

When ``running'' it through the store (@pxref{The Store Monad,
@code{run-with-store}}), we obtain a derivation that produces an
executable file @file{/gnu/store/@dots{}-list-files} along these lines:

@example
#!/gnu/store/@dots{}-guile-2.0.11/bin/guile -ds
!#
(execl (string-append "/gnu/store/@dots{}-coreutils-8.22"/bin/ls")
       "ls")
@end example
@end deffn

@deffn {Monadic Procedure} gexp->file @var{name} @var{exp}
Return a derivation that builds a file @var{name} containing @var{exp}.

The resulting file holds references to all the dependencies of @var{exp}
or a subset thereof.
@end deffn

@deffn {Monadic Procedure} text-file* @var{name} @var{text} @dots{}
Return as a monadic value a derivation that builds a text file
containing all of @var{text}.  @var{text} may list, in addition to
strings, objects of any type that can be used in a gexp: packages,
derivations, local file objects, etc.  The resulting store file holds
references to all these.

This variant should be preferred over @code{text-file} anytime the file
to create will reference items from the store.  This is typically the
case when building a configuration file that embeds store file names,
like this:

@example
(define (profile.sh)
  ;; Return the name of a shell script in the store that
  ;; initializes the 'PATH' environment variable.
  (text-file* "profile.sh"
              "export PATH=" coreutils "/bin:"
              grep "/bin:" sed "/bin\n"))
@end example

In this example, the resulting @file{/gnu/store/@dots{}-profile.sh} file
will references @var{coreutils}, @var{grep}, and @var{sed}, thereby
preventing them from being garbage-collected during its lifetime.
@end deffn

Of course, in addition to gexps embedded in ``host'' code, there are
also modules containing build tools.  To make it clear that they are
meant to be used in the build stratum, these modules are kept in the
@code{(guix build @dots{})} name space.

@cindex lowering, of high-level objects in gexps
Internally, high-level objects are @dfn{lowered}, using their compiler,
to either derivations or store items.  For instance, lowering a package
yields a derivation, and lowering a @code{plain-file} yields a store
item.  This is achieved using the @code{lower-object} monadic procedure.

@deffn {Monadic Procedure} lower-object @var{obj} [@var{system}] @
           [#:target #f]
Return as a value in @var{%store-monad} the derivation or store item
corresponding to @var{obj} for @var{system}, cross-compiling for
@var{target} if @var{target} is true.  @var{obj} must be an object that
has an associated gexp compiler, such as a @code{<package>}.
@end deffn


@c *********************************************************************
@node Utilities
@chapter Utilities

This section describes tools primarily targeted at developers and users
who write new package definitions.  They complement the Scheme
programming interface of Guix in a convenient way.

@menu
* Invoking guix build::         Building packages from the command line.
* Invoking guix edit::          Editing package definitions.
* Invoking guix download::      Downloading a file and printing its hash.
* Invoking guix hash::          Computing the cryptographic hash of a file.
* Invoking guix import::        Importing package definitions.
* Invoking guix refresh::       Updating package definitions.
* Invoking guix lint::          Finding errors in package definitions.
* Invoking guix size::          Profiling disk usage.
* Invoking guix graph::         Visualizing the graph of packages.
* Invoking guix environment::   Setting up development environments.
* Invoking guix publish::       Sharing substitutes.
@end menu

@node Invoking guix build
@section Invoking @command{guix build}

The @command{guix build} command builds packages or derivations and
their dependencies, and prints the resulting store paths.  Note that it
does not modify the user's profile---this is the job of the
@command{guix package} command (@pxref{Invoking guix package}).  Thus,
it is mainly useful for distribution developers.

The general syntax is:

@example
guix build @var{options} @var{package-or-derivation}@dots{}
@end example

@var{package-or-derivation} may be either the name of a package found in
the software distribution such as @code{coreutils} or
@code{coreutils-8.20}, or a derivation such as
@file{/gnu/store/@dots{}-coreutils-8.19.drv}.  In the former case, a
package with the corresponding name (and optionally version) is searched
for among the GNU distribution modules (@pxref{Package Modules}).

Alternatively, the @code{--expression} option may be used to specify a
Scheme expression that evaluates to a package; this is useful when
disambiguation among several same-named packages or package variants is
needed.

The @var{options} may be zero or more of the following:

@table @code

@item --expression=@var{expr}
@itemx -e @var{expr}
Build the package or derivation @var{expr} evaluates to.

For example, @var{expr} may be @code{(@@ (gnu packages guile)
guile-1.8)}, which unambiguously designates this specific variant of
version 1.8 of Guile.

Alternately, @var{expr} may be a G-expression, in which case it is used
as a build program passed to @code{gexp->derivation}
(@pxref{G-Expressions}).

Lastly, @var{expr} may refer to a zero-argument monadic procedure
(@pxref{The Store Monad}).  The procedure must return a derivation as a
monadic value, which is then passed through @code{run-with-store}.

@item --source
@itemx -S
Build the packages' source derivations, rather than the packages
themselves.

For instance, @code{guix build -S gcc} returns something like
@file{/gnu/store/@dots{}-gcc-4.7.2.tar.bz2}, which is GCC's source tarball.

The returned source tarball is the result of applying any patches and
code snippets specified in the package's @code{origin} (@pxref{Defining
Packages}).

@item --sources
Fetch and return the source of @var{package-or-derivation} and all their
dependencies, recursively.  This is a handy way to obtain a local copy
of all the source code needed to build @var{packages}, allowing you to
eventually build them even without network access.  It is an extension
of the @code{--source} option and can accept one of the following
optional argument values:

@table @code
@item package
This value causes the @code{--sources} option to behave in the same way
as the @code{--source} option.

@item all
Build all packages' source derivations, including any source that might
be listed as @code{inputs}.  This is the default value.

@example
$ guix build --sources tzdata
The following derivations will be built:
   /gnu/store/@dots{}-tzdata2015b.tar.gz.drv
   /gnu/store/@dots{}-tzcode2015b.tar.gz.drv
@end example

@item transitive
Build all packages' source derivations, as well as all source
derivations for packages' transitive inputs.  This can be used e.g. to
prefetch package source for later offline building.

@example
$ guix build --sources=transitive tzdata
The following derivations will be built:
   /gnu/store/@dots{}-tzcode2015b.tar.gz.drv
   /gnu/store/@dots{}-findutils-4.4.2.tar.xz.drv
   /gnu/store/@dots{}-grep-2.21.tar.xz.drv
   /gnu/store/@dots{}-coreutils-8.23.tar.xz.drv
   /gnu/store/@dots{}-make-4.1.tar.xz.drv
   /gnu/store/@dots{}-bash-4.3.tar.xz.drv
@dots{}
@end example

@end table

@item --system=@var{system}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}---instead of
the host's system type.

An example use of this is on Linux-based systems, which can emulate
different personalities.  For instance, passing
@code{--system=i686-linux} on an @code{x86_64-linux} system allows users
to build packages in a complete 32-bit environment.

@item --target=@var{triplet}
@cindex cross-compilation
Cross-build for @var{triplet}, which must be a valid GNU triplet, such
as @code{"mips64el-linux-gnu"} (@pxref{Configuration Names, GNU
configuration triplets,, configure, GNU Configure and Build System}).

@item --with-source=@var{source}
Use @var{source} as the source of the corresponding package.
@var{source} must be a file name or a URL, as for @command{guix
download} (@pxref{Invoking guix download}).

The ``corresponding package'' is taken to be one specified on the
command line whose name matches the base of @var{source}---e.g., if
@var{source} is @code{/src/guile-2.0.10.tar.gz}, the corresponding
package is @code{guile}.  Likewise, the version string is inferred from
@var{source}; in the previous example, it's @code{2.0.10}.

This option allows users to try out versions of packages other than the
one provided by the distribution.  The example below downloads
@file{ed-1.7.tar.gz} from a GNU mirror and uses that as the source for
the @code{ed} package:

@example
guix build ed --with-source=mirror://gnu/ed/ed-1.7.tar.gz
@end example

As a developer, @code{--with-source} makes it easy to test release
candidates:

@example
guix build guile --with-source=../guile-2.0.9.219-e1bb7.tar.xz
@end example

@dots{} or to build from a checkout in a pristine environment:

@example
$ git clone git://git.sv.gnu.org/guix.git
$ guix build guix --with-source=./guix
@end example

@item --no-grafts
Do not ``graft'' packages.  In practice, this means that package updates
available as grafts are not applied.  @xref{Security Updates}, for more
information on grafts.

@item --derivations
@itemx -d
Return the derivation paths, not the output paths, of the given
packages.

@item --root=@var{file}
@itemx -r @var{file}
Make @var{file} a symlink to the result, and register it as a garbage
collector root.

@item --log-file
Return the build log file names or URLs for the given
@var{package-or-derivation}s, or raise an error if build logs are
missing.

This works regardless of how packages or derivations are specified.  For
instance, the following invocations are equivalent:

@example
guix build --log-file `guix build -d guile`
guix build --log-file `guix build guile`
guix build --log-file guile
guix build --log-file -e '(@@ (gnu packages guile) guile-2.0)'
@end example

If a log is unavailable locally, and unless @code{--no-substitutes} is
passed, the command looks for a corresponding log on one of the
substitute servers (as specified with @code{--substitute-urls}.)

So for instance, let's say you want to see the build log of GDB on MIPS
but you're actually on an @code{x86_64} machine:

@example
$ guix build --log-file gdb -s mips64el-linux 
http://hydra.gnu.org/log/@dots{}-gdb-7.10
@end example

You can freely access a huge library of build logs!
@end table

@cindex common build options
In addition, a number of options that control the build process are
common to @command{guix build} and other commands that can spawn builds,
such as @command{guix package} or @command{guix archive}.  These are the
following:

@table @code

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{Package Modules}).

This allows users to define their own packages and make them visible to
the command-line tools.

@item --keep-failed
@itemx -K
Keep the build tree of failed builds.  Thus, if a build fail, its build
tree is kept under @file{/tmp}, in a directory whose name is shown at
the end of the build log.  This is useful when debugging build issues.

@item --dry-run
@itemx -n
Do not build the derivations.

@item --fallback
When substituting a pre-built binary fails, fall back to building
packages locally.

@item --substitute-urls=@var{urls}
@anchor{client-substitute-urls}
Consider @var{urls} the whitespace-separated list of substitute source
URLs, overriding the default list of URLs of @command{guix-daemon}
(@pxref{daemon-substitute-urls,, @command{guix-daemon} URLs}).

This means that substitutes may be downloaded from @var{urls}, provided
they are signed by a key authorized by the system administrator
(@pxref{Substitutes}).

@item --no-substitutes
Do not use substitutes for build products.  That is, always build things
locally instead of allowing downloads of pre-built binaries
(@pxref{Substitutes}).

@item --no-build-hook
Do not attempt to offload builds @i{via} the daemon's ``build hook''
(@pxref{Daemon Offload Setup}).  That is, always build things locally
instead of offloading builds to remote machines.

@item --max-silent-time=@var{seconds}
When the build or substitution process remains silent for more than
@var{seconds}, terminate it and report a build failure.

@item --timeout=@var{seconds}
Likewise, when the build or substitution process lasts for more than
@var{seconds}, terminate it and report a build failure.

By default there is no timeout.  This behavior can be restored with
@code{--timeout=0}.

@item --verbosity=@var{level}
Use the given verbosity level.  @var{level} must be an integer between 0
and 5; higher means more verbose output.  Setting a level of 4 or more
may be helpful when debugging setup issues with the build daemon.

@item --cores=@var{n}
@itemx -c @var{n}
Allow the use of up to @var{n} CPU cores for the build.  The special
value @code{0} means to use as many CPU cores as available.

@item --max-jobs=@var{n}
@itemx -M @var{n}
Allow at most @var{n} build jobs in parallel.  @xref{Invoking
guix-daemon, @code{--max-jobs}}, for details about this option and the
equivalent @command{guix-daemon} option.

@end table

Behind the scenes, @command{guix build} is essentially an interface to
the @code{package-derivation} procedure of the @code{(guix packages)}
module, and to the @code{build-derivations} procedure of the @code{(guix
derivations)} module.

In addition to options explicitly passed on the command line,
@command{guix build} and other @command{guix} commands that support
building honor the @code{GUIX_BUILD_OPTIONS} environment variable.

@defvr {Environment Variable} GUIX_BUILD_OPTIONS
Users can define this variable to a list of command line options that
will automatically be used by @command{guix build} and other
@command{guix} commands that can perform builds, as in the example
below:

@example
$ export GUIX_BUILD_OPTIONS="--no-substitutes -c 2 -L /foo/bar"
@end example

These options are parsed independently, and the result is appended to
the parsed command-line options.
@end defvr


@node Invoking guix edit
@section Invoking @command{guix edit}

@cindex package definition, editing
So many packages, so many source files!  The @command{guix edit} command
facilitates the life of packagers by pointing their editor at the source
file containing the definition of the specified packages.  For instance:

@example
guix edit gcc-4.8 vim
@end example

@noindent
launches the program specified in the @code{EDITOR} environment variable
to edit the recipe of GCC@tie{}4.8.4 and that of Vim.

If you are using Emacs, note that the Emacs user interface provides
similar functionality in the ``package info'' and ``package list''
buffers created by @kbd{M-x guix-search-by-name} and similar commands
(@pxref{Emacs Commands}).


@node Invoking guix download
@section Invoking @command{guix download}

When writing a package definition, developers typically need to download
the package's source tarball, compute its SHA256 hash, and write that
hash in the package definition (@pxref{Defining Packages}).  The
@command{guix download} tool helps with this task: it downloads a file
from the given URI, adds it to the store, and prints both its file name
in the store and its SHA256 hash.

The fact that the downloaded file is added to the store saves bandwidth:
when the developer eventually tries to build the newly defined package
with @command{guix build}, the source tarball will not have to be
downloaded again because it is already in the store.  It is also a
convenient way to temporarily stash files, which may be deleted
eventually (@pxref{Invoking guix gc}).

The @command{guix download} command supports the same URIs as used in
package definitions.  In particular, it supports @code{mirror://} URIs.
@code{https} URIs (HTTP over TLS) are supported @emph{provided} the
Guile bindings for GnuTLS are available in the user's environment; when
they are not available, an error is raised.  @xref{Guile Preparations,
how to install the GnuTLS bindings for Guile,, gnutls-guile,
GnuTLS-Guile}, for more information.

The following option is available:

@table @code
@item --format=@var{fmt}
@itemx -f @var{fmt}
Write the hash in the format specified by @var{fmt}.  For more
information on the valid values for @var{fmt}, @pxref{Invoking guix hash}.
@end table

@node Invoking guix hash
@section Invoking @command{guix hash}

The @command{guix hash} command computes the SHA256 hash of a file.
It is primarily a convenience tool for anyone contributing to the
distribution: it computes the cryptographic hash of a file, which can be
used in the definition of a package (@pxref{Defining Packages}).

The general syntax is:

@example
guix hash @var{option} @var{file}
@end example

@command{guix hash} has the following option:

@table @code

@item --format=@var{fmt}
@itemx -f @var{fmt}
Write the hash in the format specified by @var{fmt}.

Supported formats: @code{nix-base32}, @code{base32}, @code{base16}
(@code{hex} and @code{hexadecimal} can be used as well).

If the @option{--format} option is not specified, @command{guix hash}
will output the hash in @code{nix-base32}.  This representation is used
in the definitions of packages.

@item --recursive
@itemx -r
Compute the hash on @var{file} recursively.

In this case, the hash is computed on an archive containing @var{file},
including its children if it is a directory.  Some of @var{file}'s
meta-data is part of the archive; for instance, when @var{file} is a
regular file, the hash is different depending on whether @var{file} is
executable or not.  Meta-data such as time stamps has no impact on the
hash (@pxref{Invoking guix archive}).
@c FIXME: Replace xref above with xref to an ``Archive'' section when
@c it exists.

@end table

@node Invoking guix import
@section Invoking @command{guix import}

@cindex importing packages
@cindex package import
@cindex package conversion
The @command{guix import} command is useful for people willing to add a
package to the distribution but who'd rather do as little work as
possible to get there---a legitimate demand.  The command knows of a few
repositories from which it can ``import'' package meta-data.  The result
is a package definition, or a template thereof, in the format we know
(@pxref{Defining Packages}).

The general syntax is:

@example
guix import @var{importer} @var{options}@dots{}
@end example

@var{importer} specifies the source from which to import package
meta-data, and @var{options} specifies a package identifier and other
options specific to @var{importer}.  Currently, the available
``importers'' are:

@table @code
@item gnu
Import meta-data for the given GNU package.  This provides a template
for the latest version of that GNU package, including the hash of its
source tarball, and its canonical synopsis and description.

Additional information such as the package's dependencies and its
license needs to be figured out manually.

For example, the following command returns a package definition for
GNU@tie{}Hello:

@example
guix import gnu hello
@end example

Specific command-line options are:

@table @code
@item --key-download=@var{policy}
As for @code{guix refresh}, specify the policy to handle missing OpenPGP
keys when verifying the package's signature.  @xref{Invoking guix
refresh, @code{--key-download}}.
@end table

@item pypi
@cindex pypi
Import meta-data from the @uref{https://pypi.python.org/, Python Package
Index}@footnote{This functionality requires Guile-JSON to be installed.
@xref{Requirements}.}.  Information is taken from the JSON-formatted
description available at @code{pypi.python.org} and usually includes all
the relevant information, including package dependencies.

The command below imports meta-data for the @code{itsdangerous} Python
package:

@example
guix import pypi itsdangerous
@end example

@item gem
@cindex gem
Import meta-data from @uref{https://rubygems.org/,
RubyGems}@footnote{This functionality requires Guile-JSON to be
installed.  @xref{Requirements}.}.  Information is taken from the
JSON-formatted description available at @code{rubygems.org} and includes
most relevant information, including runtime dependencies.  There are
some caveats, however.  The meta-data doesn't distinguish between
synopses and descriptions, so the same string is used for both fields.
Additionally, the details of non-Ruby dependencies required to build
native extensions is unavailable and left as an exercise to the
packager.

The command below imports meta-data for the @code{rails} Ruby package:

@example
guix import gem rails
@end example

@item cpan
@cindex CPAN
Import meta-data from @uref{https://www.metacpan.org/, MetaCPAN}.
Information is taken from the JSON-formatted meta-data provided through
@uref{https://api.metacpan.org/, MetaCPAN's API} and includes most
relevant information, such as module dependencies.  License information
should be checked closely.  If Perl is available in the store, then the
@code{corelist} utility will be used to filter core modules out of the
list of dependencies.

The command command below imports meta-data for the @code{Acme::Boolean}
Perl module:

@example
guix import cpan Acme::Boolean
@end example

@item cran
@cindex CRAN
Import meta-data from @uref{http://cran.r-project.org/, CRAN}, the
central repository for the @uref{http://r-project.org, GNU@tie{}R
statistical and graphical environment}.

Information is extracted from the HTML package description.

The command command below imports meta-data for the @code{Cairo}
R package:

@example
guix import cran Cairo
@end example

@item nix
Import meta-data from a local copy of the source of the
@uref{http://nixos.org/nixpkgs/, Nixpkgs distribution}@footnote{This
relies on the @command{nix-instantiate} command of
@uref{http://nixos.org/nix/, Nix}.}.  Package definitions in Nixpkgs are
typically written in a mixture of Nix-language and Bash code.  This
command only imports the high-level package structure that is written in
the Nix language.  It normally includes all the basic fields of a
package definition.

When importing a GNU package, the synopsis and descriptions are replaced
by their canonical upstream variant.

As an example, the command below imports the package definition of
LibreOffice (more precisely, it imports the definition of the package
bound to the @code{libreoffice} top-level attribute):

@example
guix import nix ~/path/to/nixpkgs libreoffice