monitor

#!/bin/bash

case $# in
    0) # 0 args, no interface, no command
        IFACE="wifi0"
        CMD=""
    ;;
    1) # 1 arg: ambiguous
        # 1 arg: interface, no command
        if [[ $1 == wifi* ]] || [[ $1 == wlp* ]]; then
            IFACE="$1"
            CMD=""
        # 1 arg: no interface, command
        else
            IFACE="wifi0"
            CMD="$1"
        fi
    ;;
    2) # 2 args: interface, command
        IFACE="$1"
        CMD="$2"
    ;;
    *) # wtf, bail
        echo "Invalid arguments"
        exit 1
    ;;
esac

# Bail if interface doesn't exist
if ! ip link show "$IFACE" > /dev/null; then
    exit 1
fi

case $CMD in
    "on")
        sudo ip link set "$IFACE" down
        sudo iw dev "$IFACE" set type monitor
        sudo ip link set "$IFACE" up
        ;;
    "off")
        sudo ip link set "$IFACE" down
        sudo iw dev "$IFACE" set type managed
        sudo ip link set "$IFACE" up
    ;;
    "up")
        sudo ip link set "$IFACE" up
    ;;
    "down")
        sudo ip link set "$IFACE" down
    ;;
esac

echo -n "$IFACE: "
if ip link show "$IFACE" | grep 'UP' -q; then
    echo -n "interface is up, "
else
    echo -n "interface is down, "
fi

if ip link show "$IFACE" | grep 'radiotap' -q; then
    echo "in monitor mode."
else
    echo "not in monitor mode."
fi