ping hosts in subnet

#!/bin/bash
# +-----------------------------------------------------------------------------------------+
# | nmap host check - scans subnet on ip's                                                  |
# |                                                                                         |
# |                                                                                         |
# |                                                                                         |
# | Augustus 2011 flip hess [email protected]                                             |
# +-----------------------------------------------------------------------------------------+

# Global variables:

PATH='/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin'
SCRIPT_PATH="${0}"
ARGS="${#}"

# Functions:

  # exit function
  function die()
  {
    echo "${1}"
    exit 1
  }

  # Shows usage function.
  function fShowUsage()
  {
    echo "Usage: ${SCRIPT_PATH}"
    return 0
  }

  # check for.......
  function fCheck()
  {
    # script depends on:
    [ -x $(which nmap) ] || die "This script depends on nmap"

    # user must be root:
    [ $(whoami) = root ] || die "User must be root!"

    # check for arguments:
    [ ${ARGS} = 0 ] || { fShowUsage; exit 1; }

    echo ""

    return 0
  }

  # The main function.
  function fMain()
  {
   # determine subnet
   NET="$( ifconfig | grep 'Bcast:' | cut -d ":" -f 2 | cut -d "." -f 1,2,3 )"

   # ping all subnet hosts /24
   HOSTS="$( nmap ${NET}.0/24 -sP | grep 'report' | sed -e "s/.*${NET}.//" -e 's/)//g' )"

   # for loopje met mooie resultaatjes:
   for HOST in ${HOSTS}
   do
     NAME="$( host ${NET}.${HOST} | grep 'domain' | awk '{ print $NF }' | cut -d '.' -f 1,2,3 )"
     echo "${NET}.${HOST}.:${NAME}"
     ONLINE[`expr ${#ONLINE[@]} + 1`]=${HOST}
   done
   echo
   echo "Computers online: ${#ONLINE[*]}"

   return 0

  }

 # check environment:
  fCheck

 # Start the program:
  fMain "${@}"

 # Exit with previous return code:
  exit "${?}"