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.
Author: https://github.com/BenWiederhake Commit: https://github.com/SerenityOS/serenity/commit/aaa13e57396 Pull-request: https://github.com/SerenityOS/serenity/pull/2970 Reviewed-by: https://github.com/awesomekling
2020-08-02 22:05:45 +02:00 · 2020-08-02 22:05:45 +02:00 · aaa13e5739 · 2024-07-19 04:20:12 +09:00
commit aaa13e5739
parent 98e18d7339
1 changed files with 28 additions and 0 deletions
--- a/Meta/write-only-on-difference.sh
+++ 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