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The guix repl command gives you access to a warm and friendly
read-eval-print loop (REPL) (see Invoking guix repl). If
you’re getting into Guix programming—defining your own packages,
writing manifests, defining services for Guix System or Guix Home,
etc.—you will surely find it convenient to toy with ideas at the REPL.
If you use Emacs, the most convenient way to do that is with Geiser
(see The Perfect Setup), but you do not have to use Emacs to enjoy
the REPL. When using guix repl or guile in the
terminal, we recommend using Readline for completion and Colorized to
get colorful output. To do that, you can run:
guix install guile guile-readline guile-colorized
... and then create a .guile file in your home directory containing this:
(use-modules (ice-9 readline) (ice-9 colorized)) (activate-readline) (activate-colorized)
The REPL lets you evaluate Scheme code; you type a Scheme expression at the prompt, and the REPL prints what it evaluates to:
$ guix repl scheme@(guix-user)> (+ 2 3) $1 = 5 scheme@(guix-user)> (string-append "a" "b") $2 = "ab"
It becomes interesting when you start fiddling with Guix at the REPL.
The first thing you’ll want to do is to “import” the (guix)
module, which gives access to the main part of the programming
interface, and perhaps a bunch of useful Guix modules. You could type
(use-modules (guix)), which is valid Scheme code to import a
module (see Using Guile Modules in GNU Guile Reference
Manual), but the REPL provides the use command as a
shorthand notation (see REPL Commands in GNU Guile Reference
Manual):
scheme@(guix-user)> ,use (guix) scheme@(guix-user)> ,use (gnu packages base)
Notice that REPL commands are introduced by a leading comma. A REPL
command like use is not valid Scheme code; it’s interpreted
specially by the REPL.
Guix extends the Guile REPL with additional commands for convenience.
Among those, the build command comes in handy: it ensures that
the given file-like object is built, building it if needed, and returns
its output file name(s). In the example below, we build the
coreutils and grep packages, as well as a “computed
file” (see computed-file), and we use the
scandir procedure to list the files in Grep’s /bin
directory:
scheme@(guix-user)> ,build coreutils
$1 = "/gnu/store/…-coreutils-8.32-debug"
$2 = "/gnu/store/…-coreutils-8.32"
scheme@(guix-user)> ,build grep
$3 = "/gnu/store/…-grep-3.6"
scheme@(guix-user)> ,build (computed-file "x" #~(mkdir #$output))
building /gnu/store/…-x.drv...
$4 = "/gnu/store/…-x"
scheme@(guix-user)> ,use(ice-9 ftw)
scheme@(guix-user)> (scandir (string-append $3 "/bin"))
$5 = ("." ".." "egrep" "fgrep" "grep")
As a packager, you may be willing to inspect the build phases or flags of a given package; this is particularly useful when relying a lot on inheritance to define package variants (see Defining Package Variants) or when package arguments are a result of some computation, both of which can make it harder to foresee what ends up in the package arguments. Additional commands let you inspect those package arguments:
scheme@(guix-user)> ,phases grep
$1 = (modify-phases %standard-phases
(add-after 'install 'fix-egrep-and-fgrep
(lambda* (#:key outputs #:allow-other-keys)
(let* ((out (assoc-ref outputs "out"))
(bin (string-append out "/bin")))
(substitute* (list (string-append bin "/egrep")
(string-append bin "/fgrep"))
(("^exec grep")
(string-append "exec " bin "/grep")))))))
scheme@(guix-user)> ,configure-flags findutils
$2 = (list "--localstatedir=/var")
scheme@(guix-user)> ,make-flags binutils
$3 = '("MAKEINFO=true")
At a lower-level, a useful command is lower: it takes a file-like
object and “lowers” it into a derivation (see Derivations) or a
store file:
scheme@(guix-user)> ,lower grep $6 = #<derivation /gnu/store/…-grep-3.6.drv => /gnu/store/…-grep-3.6 7f0e639115f0> scheme@(guix-user)> ,lower (plain-file "x" "Hello!") $7 = "/gnu/store/…-x"
The full list of REPL commands can be seen by typing ,help guix
and is given below for reference.
Lower object and build it if it’s not already built, returning its output file name(s).
Lower object into a derivation or store file name and return it.
Change build verbosity to level.
This is similar to the --verbosity command-line option (see Common Build Options): level 0 means total silence, level 1 shows build events only, and higher levels print build logs.
These REPL commands return the value of one element of the
arguments field of package (see package Reference): the
first one show the staged code associated with #:phases
(see Build Phases), the second shows the code for
#:configure-flags, and ,make-flags returns the code for
#:make-flags.
Run exp, a monadic expression, through the store monad. See The Store Monad, for more information.
Enter a new REPL to evaluate monadic expressions (see The Store Monad). You can quit this “inner” REPL by typing ,q.
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