Ethereum/geth synchronization check

bc_integrity.sh

#!/bin/bash
# Using crontab command:
# */10 * * * * $HOME/bc_integrity.sh ropsten 30311 200 'http://slackhook' >> $HOME/bc_integrity.log 2>&1
# You might want to cleanup log file, use crontab command:
# 0 8 * * * echo "$(tail -10000 $HOME/bc_integrity.log)" > $HOME/bc_integrity.log

network=$1           # ethereum network in letters (mainnet, ropsten, rinkeby etc.)
port=$2              # local geth port
threshold=$3         # number of blocks behind
slackHook=$4         # slack hook url

curBlock=$(geth --exec "eth.blockNumber" attach http://localhost:${port})
if [ $? -ne 0 ]; then
  curBlock=0
fi

# Get latest block number from etherscan

etherscanDomain="api.etherscan.io"
if [ "$network" != "mainnet" ]; then
  etherscanDomain="api-$network.etherscan.io"
fi

echo "> Checking blockchain state on ${network} at $(date)"

ethBlock=$(( $(curl -s -X GET "https://${etherscanDomain}/api?module=proxy&action=eth_blockNumber" | grep -Eo '"result":.*?[^\\]"' | cut -d \: -f 2 | cut -d \" -f 2) ));

echo "> Latest block number from Etherscan: $ethBlock"
echo "> Latest block number from localhost:${port} : $curBlock"

# Check if node is out of sync.
# Will send notification when current block number is <threshold> blocks behind latest block on etherscan.
if [[ ( $(( ${ethBlock} - ${curBlock} )) -ge $threshold ) ]]; then
  echo "> Blockchain out of sync or stoped working!"
  if [[ -n $slackHook ]]; then
    echo "> Notify via Slack..."
    curl -s -X POST -H 'Content-type: application/json' --data "{\"text\": \"Our blockchain is out of sync w/ $(( ${ethBlock} - ${curBlock} )) blocks on ${network} on ${HOSTNAME}.\"}" "$slackHook"
  fi
else
  echo "> Blockchain is fine..."
fi