Flash a router running OpenWrt via SSH

flash_router.sh

#!/bin/sh

set -eu

if [ "$#" != 2 ]; then
    echo "Usage: $(basename "$0") <iface> <file>"
    exit 1
fi

IFACE="$1"
FILE="$2"

if ! ip link show dev "$IFACE" | grep -q "LOWER_UP"; then
    echo " + Waiting for Ethernet link..."
    ip -o monitor dev "$IFACE" | grep -q -m 1 "LOWER_UP"
fi

echo " + Establishing Network Manager connection..."
nmcli connection up Fixed ifname "$IFACE" > /dev/null

while sleep 2; do
    echo " + Determining remote address..."
    ADDR="$(ping -r -n -L -i 1 -w 60 -c 1 -I "$IFACE" ff02::1 | awk '/^[0-9]+ bytes from / {print $4}')"
    ADDR="${ADDR%:}"
    if [ -z "$ADDR" ]; then
        continue
    fi

    echo "   + Found it: ${ADDR}"

    echo "   + Testing SSH connection..."
    if ssh "$ADDR" true 2> /dev/null; then
        echo "     + OK!"
        break
    else
        echo "     + Failed!"
    fi
done

echo " + Copying image file..."
scp -q "$FILE" "[${ADDR}]:/tmp/firmware.bin"

echo " + Starting sysupgrade..."
set +e
ssh "$ADDR" sysupgrade -n /tmp/firmware.bin
set -e

echo " + Upgrade running. Please disconnect cable!"
ip -o monitor dev "$IFACE" | grep -q -m 1 "NO-CARRIER"

echo " + Exiting."