Shell Skript: Online Ping Check

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##                                                                       ##
##                           Online Ping Check                           ##
##                                                                       ##
## Creation:    03.08.2011                                               ##
## Last Update: 29.08.2016                                               ##
##                                                                       ##
## Copyright (c) 2011-2016 by Georg Kainzbauer <http://www.gtkdb.de>     ##
##                                                                       ##
## This program is free software; you can redistribute it and/or modify  ##
## it under the terms of the GNU General Public License as published by  ##
## the Free Software Foundation; either version 2 of the License, or     ##
## (at your option) any later version.                                   ##
##                                                                       ##
###########################################################################
#!/bin/bash

# IP address or hostname ("$1" if informations are set by the command call)
HOST=$1

# Start value for error counter
ERROR=0

# End value for error counter
MAXERROR=1

# Log file
LOGFILE=/var/log/online_check.log

# Who will be informed in case if anything goes wrong (if you do not want to be informed via mail, set this option to "")
MAILNOTIFY=""

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# NORMALLY THERE IS NO NEED TO CHANGE ANYTHING BELOW THIS COMMENT #
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# Check if host is reachable
function check()
{
  ping -c 1 $HOST >/dev/null 2>&1
  status $?
}

# Check delayed (30 seconds) if host is reachable
function delayedcheck()
{
  sleep 30
  check
}

# Check status of ping check
function status()
{
  # Host not reachable
  if [ $? -gt 0 ] ; then

    # Increment error counter and report error if maxerror value is reached
    if [ $((++ERROR)) -ge ${MAXERROR} ] ; then
      error "Host ($HOST) not reachable!"

    # Run delayed ping check if maxerror value is not reached
    else
      delayedcheck
    fi

  # Host is reachable
  else
    log "Host ($HOST) is reachable!"
  fi
}

# Print log message to log file
function log()
{
  echo `date +%d.%m.%Y%t%H:%M:%S` "    LOG:" $1 >>${LOGFILE}
}

# Report error message
function error()
{
  # Print error message to log file
  echo `date +%d.%m.%Y%t%H:%M:%S` "    ERROR:" $1 >>${LOGFILE}

  # Report error message by mail
  if [ -n "$MAILNOTIFY" ] ; then
    echo `date +%d.%m.%Y%t%H:%M:%S` "    ERROR:" $1 | mail -s "ERROR while running online check" $MAILNOTIFY
  fi

  # Exit script with error
  exit 1
}

# Check if IP address or hostname is available
if [ ! -n "$HOST" ] ; then
  error "No IP address or hostname available!"
fi

# Run ping check
check

# Exit script successfully
exit 0