Fix: Adds a warning to the user if their secret file includes a trailing newline (#9601)

docker/rootfs/etc/s6-overlay/s6-rc.d/init-env-file/run

@@ -17,6 +17,9 @@ if find /run/s6/container_environment/*"_FILE" -maxdepth 1 > /dev/null 2>&1; the
 			if [[ -f ${SECRETFILE} ]]; then
 				# Trim off trailing _FILE
 				FILESTRIP=${FILENAME//_FILE/}
+				if [[ $(tail -n1 "${SECRETFILE}" | wc -l) != 0 ]]; then
+					echo "${log_prefix} Your secret: ${FILENAME##*/} contains a trailing newline and may not work as expected"
+				fi
 				# Set environment variable
 				cat "${SECRETFILE}" > "${FILESTRIP}"
 				echo "${log_prefix} ${FILESTRIP##*/} set from ${FILENAME##*/}"