Nagios plugin for monitoring last modified time stamps of website content

Inspired by this plugin and this discussion,  I have written a nagios plugin for monitoring the "Last-Modified" time of content on a website. The script uses curl to retrieve the header information and then warns if the content has not been updated within a specified period of time.   

I developed this plugin for checking that data & satellite plots on our aurora alert site were being refreshed at the expected intervals.

[james@orchid tmp]$ curl -s -I  http://auroraalert.otago.ac.nz/aurora/Suomi_NPP_DNBNCC_night_highresimage.png
HTTP/1.1 200 OK
Date: Tue, 14 Aug 2018 23:36:08 GMT
Server: Apache/2.4.6 (CentOS)
Last-Modified: Tue, 14 Aug 2018 05:56:06 GMT
ETag: "15cfb4-5735edda8345f"
Accept-Ranges: bytes
Content-Length: 1429428
Content-Type: image/png

 Nagios plugin shell script:

#!/usr/bin/env bash

DEFAULT_WARN_SECONDS=600
DEFAULT_CRIT_SECONDS=1200

while getopts  'hp:c:w:' option; do
    case $option in
        h) help=1;;
        p) path=$OPTARG;;
        c) crit=$OPTARG;;
        w) warn=$OPTARG;;
    esac
done
if [ -n "$help" ] || [ -z "$path" ]; then
    echo "usage: $0 -p [path (required)] -w [warning threshhold seconds] -c [critical threshold seconds]" 1>&2
    exit 3

fi
if [ -z "$warn" ]; then
    warn=$DEFAULT_WARN_SECONDS
fi
if [ -z "$crit" ]; then
    crit=$DEFAULT_CRIT_SECONDS
fi
modificationTimeStamp() {
    curl -s -I HEAD $path |
        awk '/Last-Modified/{ date=""; for(i=2;i<=NF;++i) date=(date " " $i); print date;}' |
        xargs -I{} date -d {} +"%s"
}
#seconds=$(($(date +'%s') - $(stat --format='%Y' $path)))
seconds=$(($(date +'%s') - $(modificationTimeStamp) ))
if [ $seconds -gt $crit ]; then
    echo "CRITICAL: $path was last modified $seconds seconds ago"
    exit 2
elif [ $seconds -gt $warn ]; then
    echo "WARNING: $path was last modified $seconds seconds ago"
    exit 1
else
    echo "OK: $path was last modified $seconds seconds ago"
    exit 0
fi

Add it to the command.cfg

#check last modified time on remote URL
define command{
        command_name    check_urlmtime
        command_line    $USER1$/check_urlmtime -p $ARG1$ -w $ARG2$ -c $ARG3$
        }

Example service entry

define service{
        use             generic-service         ; Inherit default values from a template
        host_name               auroraalert
        service_description     Soumi NPP satellite image
        check_command   check_urlmtime!"http://auroraalert.otago.ac.nz/aurora/Suomi_NPP_DNBNCC_night_highresimage.png"!86400!172800
        }