OpenWrt persistent serial port symlinks

10-persistent-serial.sh

# Creates persistent serial port symlinks for USB devices,
# like mobile broadband modems, USB-UART bridges, etc,
# with layout very similar to udev symlinks
# Put under /etc/hotplug.d/tty

[ "${ACTION}" = "add" -o "${ACTION}" = "remove" ] || exit 0
[ "${SUBSYSTEM}" = "tty" ] || exit 0
[ -n "${DEVNAME}" -a -n "${DEVPATH}" ] || exit 1

if [ "${ACTION}" = "add" ]; then
        subsystem="$(basename $(readlink /sys${DEVPATH}/../../../subsystem))"

        [ "$subsystem" = "usb" ] || exit 0

        manufacturer="$(cat /sys${DEVPATH}/../../../../manufacturer)"
        product="$(cat /sys${DEVPATH}/../../../../product)"
        serial="$(cat /sys${DEVPATH}/../../../../serial)"
        interface="$(cat /sys${DEVPATH}/../../../bInterfaceNumber)"
        port="$(cat /sys${DEVPATH}/device/port_number)"

        id_link=$(echo "${subsystem}"-"${manufacturer}"_"${product}"-if"${interface}"-port"${port}" | sed s/[^0-9A-Za-z-]/_/g)
        path_link=$(echo "${DEVPATH}" | sed s%/devices/%% | sed s%/${DEVNAME}/tty/${DEVNAME}%%g | sed s/[^0-9A-Za-z-]/_/g)

        mkdir -p /dev/serial/by-id /dev/serial/by-path
        ln -sf "/dev/${DEVNAME}" "/dev/serial/by-id/${id_link}"
        ln -sf "/dev/${DEVNAME}" "/dev/serial/by-path/${path_link}"
elif [ "${ACTION}" = "remove" ]; then
        for link in $(find /dev/serial -type l); do
                [ -L ${link} -a "$(readlink ${link})" = "/dev/$DEVNAME" ] && rm ${link}
        done
fi

Could you please add information about license of this repository — is it allowed to copy, change and use the code in any purpose?
It would be great to see any popular open source license.

Since I posted it on pastebin-like site, just assume it's public domain.