freebsd and macos fixes

freebsd and macos share stat and sed history with some differences from
gnu

tested on freebsd and linux, mac just verified with man pages and stack
overflow

zfs-inplace-rebalancing.sh

@@ -60,9 +60,29 @@ function rebalance () {
     # this shouldn't be needed in the typical case of `find` only finding files with links == 1
     # but this can run for a long time, so it's good to double check if something changed
     if [[ "${skip_hardlinks_flag,,}" == "true"* ]]; then
-        hardlink_count=$(stat -c "%h" "${file_path}")
+	if [[ "${OSTYPE,,}" == "linux-gnu"* ]]; then
+	    # Linux
+	    #
+	    #  -c  --format=FORMAT
+	    #      use the specified FORMAT instead of the default; output a
+	    #      newline after each use of FORMAT
+	    #  %h     number of hard links
 
-        if [ "${hardlink_count}" -ge 2 ]; then
+	    hardlink_count=$(stat -c "%h" "${file_path}")
+	elif [[ "${OSTYPE,,}" == "darwin"* ]] || [[ "${OSTYPE,,}" == "freebsd"* ]]; then
+	    # Mac OS
+	    # FreeBSD
+	    #  -f format
+	    #  Display information using the specified format
+	    #   l       Number of hard links to file (st_nlink)
+
+	    hardlink_count=$(stat -f %l "${file_path}")
+	else
+		echo "Unsupported OS type: $OSTYPE"
+		exit 1
+	fi
+
+	if [ "${hardlink_count}" -ge 2 ]; then
             echo "Skipping hard-linked file: ${file_path}"
             return
         fi
@@ -180,7 +200,7 @@ function rebalance () {
         else
         rebalance_count_line_nr="$((line_nr + 1))"
         rebalance_count="$((rebalance_count + 1))"
-        sed -i "${rebalance_count_line_nr}s/.*/${rebalance_count}/" "./${rebalance_db_file_name}"
+        sed -i '' "${rebalance_count_line_nr}s/.*/${rebalance_count}/" "./${rebalance_db_file_name}"
         fi
     fi
 }