Solr replication monitoring

I am using Solr replication on some projects for load balancing (not that Solr really needs that ;) ) and high-availability. Recently, due to a network problem, replication was stalled on one of the slave without me noticing it, so I wrote a small script to check the index version difference between master and slave and which admins can integrate with current monitoring system (nagios, zenoss, munin, whatever).

#!/bin/bash
if [ $# -lt 2 ]; then
 echo Usage: `basename $0` SolrMasterIP[:port] SolrSlaveIP[:port] [AlertThreshold]
 exit 1
fi
# read command params
MASTER=$1
SLAVE=$2
THRESHOLD=${3:-1}

# read index version from master and slave
MASTER_INDEX=`wget -qO - http://$1/solr/admin/replication/index.jsp | awk '/Index Version/ {print substr($3,0,length($3)-1)}'` 
[ -z "$MASTER_INDEX" ] && echo Error reading Master index && exit 2
SLAVE_INDEX=`wget -qO - http://$2/solr/admin/replication/index.jsp | awk '/Index Version/ {print substr($3,0,length($3)-1)}'`
[ -z "$SLAVE_INDEX" ] && echo Error reading Master index && exit 3

# check if master-slave index difference is within acceptable threshold
let "$MASTER_INDEX - $SLAVE_INDEX < $THRESHOLD" && echo Slave index version \($SLAVE_INDEX\) is behind master \($MASTER_INDEX\) && exit 4
echo Slave index version \($SLAVE_INDEX\) is in sync with master \($MASTER_INDEX\)