From aaa13e57396ba5eecf31ef5f925a73f4cf31518a Mon Sep 17 00:00:00 2001
From: Ben Wiederhake <BenWiederhake.GitHub@gmx.de>
Date: Sun, 2 Aug 2020 22:05:45 +0200
Subject: [PATCH] Meta: Provide a way to only update a file if the output
 changes

This is only useful for build commands that update their destination in all cases
and thus sometimes confuse cmake into rebuilding everything needlessly.
---
 Meta/write-only-on-difference.sh | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100755 Meta/write-only-on-difference.sh

diff --git a/Meta/write-only-on-difference.sh b/Meta/write-only-on-difference.sh
new file mode 100755
index 0000000000..a6485e79a9
--- /dev/null
+++ b/Meta/write-only-on-difference.sh
@@ -0,0 +1,28 @@
+#!/bin/sh
+
+set -e
+
+if [ "$#" -lt "2" ]; then
+    echo "USAGE: $0 <file> <cmd...>"
+    exit 1
+fi
+
+DST_FILE="$1"
+shift
+
+# Just in case:
+mkdir -p -- "$(dirname -- "${DST_FILE}")"
+
+cleanup()
+{
+  rm -f -- "${DST_FILE}.tmp"
+}
+trap cleanup 0 1 2 3 6
+
+"$@" > "${DST_FILE}.tmp"
+# If we get here, the command was successful, and we can overwrite the destination.
+
+if ! cmp --quiet -- "${DST_FILE}.tmp" "${DST_FILE}"; then
+    # File changed, need to overwrite:
+    mv -f -- "${DST_FILE}.tmp" "${DST_FILE}"
+fi