Script to post Nagios notifications into a Slack channel

slack_nagios.sh

#!/bin/bash

# This script is used by Nagios to post alerts into a Slack channel
# using the Incoming WebHooks integration. Create the channel, botname
# and integration first and then add this notification script in your
# Nagios configuration.
#
# All variables that start with NAGIOS_ are provided by Nagios as 
# environment variables when an notification is generated.
# A list of the env variables is available here: 
#   http://nagios.sourceforge.net/docs/3_0/macrolist.html
#
# More info on Slack
# Website: https://slack.com/
# Twitter: @slackhq, @slackapi
#
# My info
# Website: http://matthewcmcmillan.blogspot.com/
# Twitter: @matthewmcmillan

#Modify these variables for your environment
MY_NAGIOS_HOSTNAME="nagios.yourdomain.com"
SLACK_HOSTNAME="yourslack.slack.com"
SLACK_TOKEN="xyxyxyourslackkey"
SLACK_CHANNEL="#alerts"
SLACK_BOTNAME="nagios"


#Set the message icon based on Nagios service state
if [ "$NAGIOS_SERVICESTATE" = "CRITICAL" ]
then
    ICON=":exclamation:"
elif [ "$NAGIOS_SERVICESTATE" = "WARNING" ]
then
    ICON=":warning:"
elif [ "$NAGIOS_SERVICESTATE" = "OK" ]
then
    ICON=":white_check_mark:"
elif [ "$NAGIOS_SERVICESTATE" = "UNKNOWN" ]
then
    ICON=":question:"
else
    ICON=":white_medium_square:"
fi

#Send message to Slack
curl -X POST --data "payload={\"channel\": \"${SLACK_CHANNEL}\", \"username\": \"${SLACK_USERNAME}\", \"text\": \"${ICON} HOST: ${NAGIOS_HOSTNAME}   SERVICE: ${NAGIOS_SERVICEDISPLAYNAME}     MESSAGE: ${NAGIOS_SERVICEOUTPUT} <https://${MY_NAGIOS_HOSTNAME}/cgi-bin/nagios3/status.cgi?host=${NAGIOS_HOSTNAME}|See Nagios>\"}" https://${SLACK_HOSTNAME}/services/hooks/incoming-webhook?token=${SLACK_TOKEN}

I apologize if this has been answered somewhere and I missed it. I have Slack notifications working, but some of my hosts send messages like this:
corp-dc01.WinAD/$ is $:
$

For some reason, the variables are not passing correctly. For other alerts, they are fine. And for these alerts, the email works fine. It is just for Slack on some Host Alerts.
Any ideas why this is happening?
Thanks

@tjderby same problem here