serenity/Meta/write-only-on-difference.sh
Ben Wiederhake aaa13e5739 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.
2020-08-04 11:27:14 +02:00

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#!/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