From 3bb168b0997d2ba2ef15e8eef2890582c8a6df9c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Mon, 26 Oct 2015 22:17:25 +0100
Subject: utils: Add 'switch-symlinks', moved from (guix ui).

* guix/ui.scm (switch-symlinks): Move to...
* guix/utils.scm: ... here.  New procedure.
* guix/scripts/pull.scm: Use it.
---
 guix/utils.scm | 8 ++++++++
 1 file changed, 8 insertions(+)

(limited to 'guix/utils.scm')

diff --git a/guix/utils.scm b/guix/utils.scm
index f1317ac756..1542e86f7a 100644
--- a/guix/utils.scm
+++ b/guix/utils.scm
@@ -74,6 +74,7 @@
             arguments-from-environment-variable
             file-extension
             file-sans-extension
+            switch-symlinks
             call-with-temporary-output-file
             call-with-temporary-directory
             with-atomic-file-output
@@ -557,6 +558,13 @@ minor version numbers from version-string."
         (substring file 0 dot)
         file)))
 
+(define (switch-symlinks link target)
+  "Atomically switch LINK, a symbolic link, to point to TARGET.  Works
+both when LINK already exists and when it does not."
+  (let ((pivot (string-append link ".new")))
+    (symlink target pivot)
+    (rename-file pivot link)))
+
 (define* (string-replace-substring str substr replacement
                                    #:optional
                                    (start 0)
-- 
cgit v1.2.3