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8.6 Build Utilities

As soon as you start writing non-trivial package definitions (see Defining Packages) or other build actions (see G-Expressions), you will likely start looking for helpers for “shell-like” actions—creating directories, copying and deleting files recursively, manipulating build phases, and so on. The (guix build utils) module provides such utility procedures.

Most build systems load (guix build utils) (see Build Systems). Thus, when writing custom build phases for your package definitions, you can usually assume those procedures are in scope.

When writing G-expressions, you can import (guix build utils) on the “build side” using with-imported-modules and then put it in scope with the use-modules form (see Using Guile Modules in GNU Guile Reference Manual):

(with-imported-modules '((guix build utils))  ;import it
  (computed-file "empty-tree"
                 #~(begin
                     ;; Put it in scope.
                     (use-modules (guix build utils))

                     ;; Happily use its 'mkdir-p' procedure.
                     (mkdir-p (string-append #$output "/a/b/c")))))

The remainder of this section is the reference for most of the utility procedures provided by (guix build utils).

8.6.1 Dealing with Store File Names

This section documents procedures that deal with store file names.

Scheme Procedure: %store-directory

Return the directory name of the store.

Scheme Procedure: store-file-name? file

Return true if file is in the store.

Scheme Procedure: strip-store-file-name file

Strip the /gnu/store and hash from file, a store file name. The result is typically a "package-version" string.

Scheme Procedure: package-name->name+version name

Given name, a package name like "foo-0.9.1b", return two values: "foo" and "0.9.1b". When the version part is unavailable, name and #f are returned. The first hyphen followed by a digit is considered to introduce the version part.

8.6.2 File Types

The procedures below deal with files and file types.

Scheme Procedure: directory-exists? dir

Return #t if dir exists and is a directory.

Scheme Procedure: executable-file? file

Return #t if file exists and is executable.

Return #t if file is a symbolic link (aka. a “symlink”).

Scheme Procedure: elf-file? file
Scheme Procedure: ar-file? file
Scheme Procedure: gzip-file? file

Return #t if file is, respectively, an ELF file, an ar archive (such as a .a static library), or a gzip file.

Scheme Procedure: reset-gzip-timestamp file [#:keep-mtime? #t]

If file is a gzip file, reset its embedded timestamp (as with gzip --no-name) and return true. Otherwise return #f. When keep-mtime? is true, preserve file’s modification time.

8.6.3 File Manipulation

The following procedures and macros help create, modify, and delete files. They provide functionality comparable to common shell utilities such as mkdir -p, cp -r, rm -r, and sed. They complement Guile’s extensive, but low-level, file system interface (see POSIX in GNU Guile Reference Manual).

Scheme Syntax: with-directory-excursion directory body

Run body with directory as the process’s current directory.

Essentially, this macro changes the current directory to directory before evaluating body, using chdir (see Processes in GNU Guile Reference Manual). It changes back to the initial directory when the dynamic extent of body is left, be it via normal procedure return or via a non-local exit such as an exception.

Scheme Procedure: mkdir-p dir

Create directory dir and all its ancestors.

Scheme Procedure: install-file file directory

Create directory if it does not exist and copy file in there under the same name.

Scheme Procedure: make-file-writable file

Make file writable for its owner.

Scheme Procedure: copy-recursively source destination [#:log (current-output-port)] [#:follow-symlinks? #f] [#:keep-mtime? #f]

Copy source directory to destination. Follow symlinks if follow-symlinks? is true; otherwise, just preserve them. When keep-mtime? is true, keep the modification time of the files in source on those of destination. Write verbose output to the log port.

Scheme Procedure: delete-file-recursively dir [#:follow-mounts? #f]

Delete dir recursively, like rm -rf, without following symlinks. Don’t follow mount points either, unless follow-mounts? is true. Report but ignore errors.

Scheme Syntax: substitute* file ((regexp match-var…) body…) …

Substitute regexp in file by the string returned by body. body is evaluated with each match-var bound to the corresponding positional regexp sub-expression. For example:

(substitute* file
  (("hello")
   "good morning\n")
  (("foo([a-z]+)bar(.*)$" all letters end)
   (string-append "baz" letter end)))

Here, anytime a line of file contains hello, it is replaced by good morning. Anytime a line of file matches the second regexp, all is bound to the complete match, letters is bound to the first sub-expression, and end is bound to the last one.

When one of the match-var is _, no variable is bound to the corresponding match substring.

Alternatively, file may be a list of file names, in which case they are all subject to the substitutions.

Be careful about using $ to match the end of a line; by itself it won’t match the terminating newline of a line.

8.6.4 File Search

This section documents procedures to search and filter files.

Scheme Procedure: file-name-predicate regexp

Return a predicate that returns true when passed a file name whose base name matches regexp.

Scheme Procedure: find-files dir [pred] [#:stat lstat] [#:directories? #f] [#:fail-on-error? #f]

Return the lexicographically sorted list of files under dir for which pred returns true. pred is passed two arguments: the absolute file name, and its stat buffer; the default predicate always returns true. pred can also be a regular expression, in which case it is equivalent to (file-name-predicate pred). stat is used to obtain file information; using lstat means that symlinks are not followed. If directories? is true, then directories will also be included. If fail-on-error? is true, raise an exception upon error.

Here are a few examples where we assume that the current directory is the root of the Guix source tree:

;; List all the regular files in the current directory.
(find-files ".")
 ("./.dir-locals.el" "./.gitignore" )

;; List all the .scm files under gnu/services.
(find-files "gnu/services" "\\.scm$")
 ("gnu/services/admin.scm" "gnu/services/audio.scm" )

;; List ar files in the current directory.
(find-files "." (lambda (file stat) (ar-file? file)))
 ("./libformat.a" "./libstore.a" )
Scheme Procedure: which program

Return the complete file name for program as found in $PATH, or #f if program could not be found.

8.6.5 Build Phases

The (guix build utils) also contains tools to manipulate build phases as used by build systems (see Build Systems). Build phases are represented as association lists or “alists” (see Association Lists in GNU Guile Reference Manual) where each key is a symbol naming the phase and the associated value is a procedure (see Build Phases).

Guile core and the (srfi srfi-1) module both provide tools to manipulate alists. The (guix build utils) module complements those with tools written with build phases in mind.

Scheme Syntax: modify-phases phases clause

Modify phases sequentially as per each clause, which may have one of the following forms:

(delete old-phase-name)
(replace old-phase-name new-phase)
(add-before old-phase-name new-phase-name new-phase)
(add-after old-phase-name new-phase-name new-phase)

Where every phase-name above is an expression evaluating to a symbol, and new-phase an expression evaluating to a procedure.

The example below is taken from the definition of the grep package. It adds a phase to run after the install phase, called fix-egrep-and-fgrep. That phase is a procedure (lambda* is for anonymous procedures) that takes a #:outputs keyword argument and ignores extra keyword arguments (see Optional Arguments in GNU Guile Reference Manual, for more on lambda* and optional and keyword arguments.) The phase uses substitute* to modify the installed egrep and fgrep scripts so that they refer to grep by its absolute file name:

(modify-phases %standard-phases
  (add-after 'install 'fix-egrep-and-fgrep
    ;; Patch 'egrep' and 'fgrep' to execute 'grep' via its
    ;; absolute file name instead of searching for it in $PATH.
    (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")))
        #t))))

In the example below, phases are modified in two ways: the standard configure phase is deleted, presumably because the package does not have a configure script or anything similar, and the default install phase is replaced by one that manually copies the executable files to be installed:

(modify-phases %standard-phases
  (delete 'configure)      ;no 'configure' script
  (replace 'install
    (lambda* (#:key outputs #:allow-other-keys)
      ;; The package's Makefile doesn't provide an "install"
      ;; rule so do it by ourselves.
      (let ((bin (string-append (assoc-ref outputs "out")
                                "/bin")))
        (install-file "footswitch" bin)
        (install-file "scythe" bin)
        #t))))

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