Show IP address on prelogin message

show-ip-before-login.sh

#!/bin/bash
# based on http://offbytwo.com/2008/05/09/show-ip-address-of-vm-as-console-pre-login-message.html
# based on https://gist.github.com/rm/3780228
# A better IP address method https://www.linuxquestions.org/questions/blog/sag47-492023/using-a-script-to-get-your-ip-address-35251/

# need to be root to write out these files
if [ "$(id -u)" != "0" ]; then
    echo "Need to run as root.  Maybe use sudo..."
    exit
fi

GET_IP_ADDRESS='/usr/local/bin/get-ip-address'
if [ ! -f "${GET_IP_ADDRESS}" ]; then
    cat >"${GET_IP_ADDRESS}" <<EOF
#!/bin/sh
#get ip address based on default route
ip -o ro get \$(ip ro | awk '\$1 == "default" { print \$3 }') | awk '{print \$5}'
EOF
    chmod 0755 "${GET_IP_ADDRESS}"
fi


if [ ! -f '/etc/issue-standard' ]; then
    cp '/etc/issue' '/etc/issue-standard'
    cat >'/etc/network/if-up.d/show-ip-before-login' <<EOF
#/bin/sh
if [ "\${METHOD}" = "loopback" ]; then
    exit 0
fi

# Only run from ifup.
#if [ "\${MODE}" != "start" ]; then
#    exit 0
#fi

grep -v "^\$" /etc/issue-standard >/etc/issue
echo -n " " >>/etc/issue
$GET_IP_ADDRESS >>/etc/issue
echo "" >> /etc/issue
EOF
    chmod 0755 /etc/network/if-up.d/show-ip-before-login
fi