ip_addr_reporter.sh

#!/usr/bin/env bash
# set -euxo pipefail

# ----
# 
# report ip address changes to slack channel 
#
# this script detects and reports ip address changes
# to me via personal slack message.
#
# this is useful for those times when i want to connect 
# via VPN and then SSH to my work pc.
#
# ----


ipfile="/tmp/ip_address_reporter.txt"
tmpfile=$(mktemp /tmp/ip_address_reporter.XXXXX)

# if ipfile doesnt exist, create it
test -f "${ipfile}" || touch "${ipfile}"

# add the hostname to tmpfile
hostname_s="$(hostname -s)"
printf "hostname: %s\n" "${hostname_s}" | tee -a ${tmpfile} >/dev/null

# get a list of interfaces
interfaces="$(ipconfig getiflist | xargs)"

# add interface addresses to tmpfile
for interface in ${interfaces}; do
    interface_addr="$(ipconfig getifaddr ${interface} || echo 'null')"
    printf "%s: %s\n" "${interface}" "${interface_addr}" | tee -a ${tmpfile} >/dev/null
done

# diff ipfile/tmpfile
diff_output=$(diff -u ${ipfile} ${tmpfile})
diff_result=$?

# if files are different
if [ $diff_result -ne 0 ]; then
    # log message
    printf "%s | ip change detected \n" "$(date +'%Y/%m/%d %H:%M:%S')"

    # ping slack
    printf "%s | sending message to slack \n"  "$(date +'%Y/%m/%d %H:%M:%S')"

    slack_payload=$(jq \
    --null-input \
    --arg x "\`\`\`${diff_output##*@}\`\`\`" \
    '{blocks: [{type: "header", text: {type: "plain_text", text: "ip change detected", emoji: false}},{type: "section", text: {type: "mrkdwn", text: $x }}]}')

    slack_response=$(curl -sS \
        -H "Content-Type: application/json" \
        -X POST https://hooks.slack.com/services/XXXXXXXXX/XXXXXXXXXXX/XXXXXXXXXXXXXXXXXXXXXXXX \
        -d "${slack_payload}")
    
    printf "%s | slack response: %s \n"  "$(date +'%Y/%m/%d %H:%M:%S')" "${slack_response}"

    # update ipfile
    printf "%s | %s\n" "$(date +'%Y/%m/%d %H:%M:%S')" "$(cp -v ${tmpfile} ${ipfile})"
    
else
    printf "%s | no ip change detected \n" "$(date +'%Y/%m/%d %H:%M:%S')"
fi

# clean up tmpfile
printf "%s | %s\n" "$(date +'%Y/%m/%d %H:%M:%S')" "$(rm -rfv ${tmpfile})"