From c74248c56e6e5558603be6c6eda43eb439772f20 Mon Sep 17 00:00:00 2001
From: Michael Lohmann <michael.lohmann@bevuta.com>
Date: Thu, 12 Jan 2023 15:45:19 +0100
Subject: [PATCH] install-multi-user: ignore profile_target backups that have
 no change

If there was a prior nix installation that created this backup file and
then you tried to install it again, it would stop to tell you there is
this file. But if the file and its backup are identical in content,
there is no harm in continuing and in a later step overwriting the
existing backup file with the identical one. This is just a convenience
feature.
---
 scripts/install-multi-user.sh | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/scripts/install-multi-user.sh b/scripts/install-multi-user.sh
index f149ea0d7..b2f2a9e45 100644
--- a/scripts/install-multi-user.sh
+++ b/scripts/install-multi-user.sh
@@ -445,6 +445,14 @@ EOF
         #       a row for different files.
         if [ -e "$profile_target$PROFILE_BACKUP_SUFFIX" ]; then
             # this backup process first released in Nix 2.1
+
+            if diff -q "$profile_target$PROFILE_BACKUP_SUFFIX" "$profile_target" > /dev/null; then
+                # a backup file for the rc-file exist, but they are identical,
+                # so we can safely ignore it and overwrite it with the same
+                # content later
+                continue
+            fi
+
             failure <<EOF
 I back up shell profile/rc scripts before I add Nix to them.
 I need to back up $profile_target to $profile_target$PROFILE_BACKUP_SUFFIX,