22.2 Running Guix Before It Is Installed

In order to keep a sane working environment, you will find it useful to test the changes made in your local source tree checkout without actually installing them. So that you can distinguish between your “end-user” hat and your “motley” costume.

To that end, all the command-line tools can be used even if you have not run make install. To do that, you first need to have an environment with all the dependencies available (see Building from Git), and then simply prefix each command with ./pre-inst-env (the pre-inst-env script lives in the top build tree of Guix; it is generated by running ./bootstrap followed by ./configure). As an example, here is how you would build the hello package as defined in your working tree (this assumes guix-daemon is already running on your system; it’s OK if it’s a different version):

$ ./pre-inst-env guix build hello

Similarly, an example for a Guile session using the Guix modules:

$ ./pre-inst-env guile -c '(use-modules (guix utils)) (pk (%current-system))'

;;; ("x86_64-linux")

… and for a REPL (see Using Guix Interactively):

$ ./pre-inst-env guile
scheme@(guile-user)> ,use(guix)
scheme@(guile-user)> ,use(gnu)
scheme@(guile-user)> (define snakes
                       (fold-packages
                         (lambda (package lst)
                           (if (string-prefix? "python"
                                               (package-name package))
                               (cons package lst)
                               lst))
                         '()))
scheme@(guile-user)> (length snakes)
$1 = 361

If you are hacking on the daemon and its supporting code or if guix-daemon is not already running on your system, you can launch it straight from the build tree⁴⁰:

$ sudo -E ./pre-inst-env guix-daemon --build-users-group=guixbuild

The pre-inst-env script sets up all the environment variables necessary to support this, including PATH and GUILE_LOAD_PATH.

Note that ./pre-inst-env guix pull does not upgrade the local source tree; it simply updates the ~/.config/guix/current symlink (see Invoking guix pull). Run git pull instead if you want to upgrade your local source tree.

Sometimes, especially if you have recently updated your repository, running ./pre-inst-env will print a message similar to the following example:

;;; note: source file /home/user/projects/guix/guix/progress.scm
;;;       newer than compiled /home/user/projects/guix/guix/progress.go

This is only a note and you can safely ignore it. You can get rid of the message by running make -j4. Until you do, Guile will run slightly slower because it will interpret the code instead of using prepared Guile object (.go) files.

You can run make automatically as you work using watchexec from the watchexec package. For example, to build again each time you update a package file, run ‘watchexec -w gnu/packages -- make -j4’.