net-15-hostname

#!/usr/bin/env bash

_kernel="$(uname -s)"
if [ "${_kernel}" = 'FreeBSD' ]; then
    SED_I="sed -i ''"
else
    SED_I="sed -i''"
fi

function set_hostname() {
    local hostname=$1

    if [ -d /run/systemd/system/ ]; then
        hostnamectl set-hostname --static "${hostname}"
    else
        if [ -f /etc/sysconfig/network ]; then
            ${SED_I} '/^HOSTNAME=.*$/d' /etc/sysconfig/network
            echo "HOSTNAME=${hostname}" >>/etc/sysconfig/network
        elif [ "${_kernel}" = 'FreeBSD' ]; then
            sysrc hostname="${hostname}"
        else
            echo "${hostname}" >/etc/hostname
        fi

        hostname "${hostname}"
    fi
}

function set_domainname() {
    domain=$1
    ${SED_I} -e '/^domain .*/d' /etc/resolv.conf
    echo "domain ${domain}" >>/etc/resolv.conf
}

function get_first_ip() {
    local ip

    ip=${ip:-$(ip route get 1 2>/dev/null | grep 'src [0-9\.]\+' | head -1 | sed -e 's/^.*src \([0-9\.]*\).*$/\1/')}
    ip=${ip:-$(ip -4 address show scope global up 2>/dev/null | awk '/inet / { gsub(/\/[^\/]+$/, "", $2); print $2; exit}')}
    ip=${ip:-$(ifconfig 2>/dev/null | awk '/inet / { gsub(/\/[^\/]+$/, "", $2); print $2; exit}')}
    ip=${ip:-$(hostname -I 2>/dev/null | cut -d' ' -f1)}
    ip=${ip:-$(hostname -i 2>/dev/null)}

    echo "${ip}"
}

function get_dns_name() {
    text=$(LC_ALL=C host "$1" 2>/dev/null)
    [ $? = 0 ] || exit 0
    [[ $text == *"has no PTR record" ]] && exit 0
    name=$(echo "$text" | awk '/(has address|name pointer)/ {print $(NF)}' | sed 's/\.$//')
    echo $name
}

function update_hosts() {
    ip=$1
    name=$2
    hostname=$3

    if [ "x${hostname}" = "x${name}" ]; then
        hosts="${name}"
    else
        hosts="${name} ${hostname}"
    fi

    note='# one-contextd'
    entry="${ip} ${hosts}  ${note}"

    # update our old entry
    if grep -qi "${note}" /etc/hosts; then
        ${SED_I} -e "s/^.*${note}\$/${entry}/" /etc/hosts
    # update entry with same IP (but not localhost)
    elif grep -E "^${ip}[[:space:]]" /etc/hosts | grep -qv localhost; then
        ${SED_I} -e "/localhost/! s/^${ip}[[:space:]].*\$/${entry}/" /etc/hosts
    # update entry with same name
    elif grep -qE "[[:space:]]${name}([[:space:]]|#|\$)" /etc/hosts; then
        ${SED_I} -re "s/^.*[[:space:]]${name}([[:space:]#].*|$)/${entry}/" /etc/hosts
    # create new entry
    elif [ -f /etc/hosts ]; then
        ${SED_I} -e "1s/^/${entry}"$'\\\n/' /etc/hosts
    else
        echo "${entry}" >>/etc/hosts
    fi
}

#####

first_ip=$(get_first_ip)

if [ -n "$SET_HOSTNAME" ]; then
    name=$(echo "$SET_HOSTNAME" | \
        sed -e 's/[^-a-zA-Z0-9\.]/-/g' -e 's/^-*//g' -e 's/-*$//g')

elif [ -n "$DNS_HOSTNAME" ]; then
    name=$(get_dns_name "${first_ip}")

elif [ "${EC2_HOSTNAME}" = 'YES' ]; then
    # try to quickly get hostname from the EC2 metadata server or
    # create hostname based on the first IPv4 (format: "ip-1-2-3-4")
    name=$(curl -sf -m 5 'http://169.254.169.254/latest/meta-data/local-hostname' 2>/dev/null)
    if [ -z "${name}" ]; then
        name="$(echo "${first_ip}" | grep -x '[0-9\.]\+' | tr . -)"
        if [ -n "${name}" ]; then
            name="ip-${name}"
        fi
    fi
fi

if [ -n "${name}" ]; then
    # split host and domain names
    hostname=${name%%.*}
    domain=${name#*.}
    if [ "x${domain}" = "x${hostname}" ]; then
        domain=''
    fi

    # FreeBSD
    if [ "${_kernel}" = 'FreeBSD' ]; then
        set_hostname "${name}"
    else
        set_hostname "${hostname}"
    fi

    if [ -n "${domain}" ]; then
        set_domainname "${domain}"
    fi

    if [ -n "${DNS_HOSTNAME}" ]; then
        host_ip=$first_ip
    else
        # If selected hostname resolves on first IP,
        # use first IP for local hostname in /etc/hosts.
        # Otherwise use loopback IP.
        name_ip=$(get_dns_name "${name}")
        if [ "x${first_ip}" = "x${name_ip}" ]; then
            host_ip=$first_ip
        elif [ -f /etc/debian_version ]; then
            host_ip='127.0.1.1'
        else
            host_ip='127.0.0.1'
        fi
    fi

    if [ -n "${host_ip}" ]; then
        update_hosts "${host_ip}" "${name}" "${hostname}"
    fi
fi