Scan and Change IP on Alpine Linux

ip.sh

#!/bin/sh

# Parsing command line arguments
while [ "$1" != "" ]; do
    case $1 in
        --ip )    shift
                  IP=$1
                  ;;
        * )       echo "Invalid argument"
                  exit 1
    esac
    shift
done

set_ip() {
    # Write IP to /etc/network/interfaces
    echo "auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
    address $1
    netmask 255.255.255.0
    gateway 158.132.32.1
    dns-nameservers 1.1.1.1" > /etc/network/interfaces

    # Restart networking
    /etc/init.d/networking restart
}

find_free_ip() {
    for i in $(seq 1 254)
    do
        IP="$1.$i"
        if ! ping -c 1 -W 1 "$IP" > /dev/null
        then
            set_ip "$IP"
            exit 0
        fi
    done
    echo "No free IP found"
    exit 1
}

# If IP address is not provided, scan the default subnet
if [ -z "$IP" ]; then
    echo "IP address not provided. Scanning default subnet."
    find_free_ip "158.132.58"
fi

# Count the number of dots in the IP
dots=$(echo $IP | tr -cd '.' | wc -c)

# If the IP address has two dots, it's a subnet
if [ "$dots" -eq 2 ]; then
    find_free_ip "$IP"
# If the IP address has three dots, it's a full IP address
elif [ "$dots" -eq 3 ]; then
    if ! ping -c 1 -W 1 "$IP" > /dev/null
    then
        set_ip "$IP"
    else
        echo "IP address $IP is not available. Please provide another one."
        exit 1
    fi
else
    echo "Invalid IP address or subnet provided."
    exit 1
fi

Run the script as follows:

ash ip.sh --ip 158.132.32

or

ash ip.sh --ip 158.132.32.70