ishostavail (Source) 

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#!/bin/bash
##---------------------------------------------------------------------------##
#
#   Script: ishostavail
#   Author: Brian <genius@groupbcl.ca> :)
#   Date:   August 2001
#
#   usage: ishostavail [-v] [-t] host [port]
#
#   ishostavail is used to determine quickly if a given host is online by
#   attempting to open a socket to it (using TCL). If the open is
#   successful, the script assumes the host was reachable and returns 0,
#   else it returns 1.
#
#   By default the script attempts to open port 80 (http) on the assumption
#   you're trying to determine if a WWW host is available. You can over-
#   the default port by specifying its name or number after the host.
#
#   The -v switch enables verbose mode; otherwise this script produces
#   no output.
#
#   The -t (test) switch causes 0 to be returned on POSIX ECONNREFUSED,
#   on the assumption you are testing to see if the host even exists,
#   regardless of whether or not you can connect to a specified port.
#
##---------------------------------------------------------------------------##
# BUUS: This script is part of Brian's Useful Utilities Set
VERBOSE=false
TEST=false
PORT="http"

##---------------------------------------------------------------------------##
#   ErrorMsg - prints $1 on stderr; exits if $2 is "exit"
##---------------------------------------------------------------------------##
function ErrorMsg {
  echo "$1" >&2
  [ "$2" = "exit" ] && exit 1
}

##---------------------------------------------------------------------------##
#           M A I N   P R O C E S S I N G
##---------------------------------------------------------------------------##
[ -z "$1" ] && ErrorMsg "usage: ishostavail [-v] [-t] host [port]" exit

#--- Check the command line ---
for PARM in $*
do
  case $PARM in
   -t) TEST=true;;
   -v) VERBOSE=true;;
   *)
    if [ -z "$HOST" ]
     then HOST=$PARM
     else PORT=$PARM
    fi
   ;;
  esac
done

#----- If the host contains a ":", assume the user meant host:port -----
COLON_POS=$(expr index "$HOST" ":")
if [ $COLON_POS -gt 0 ]
then
  PORT=$(expr substr "$HOST" $((COLON_POS + 1)) 99)
  HOST=$(expr substr "$HOST" 1 $((COLON_POS - 1)) )
fi

#----- Try to contact the host -----
$VERBOSE && echo -n "ishostavail $HOST/$PORT: "
echo '
  set Host [lindex $argv 1]
  set Port [lindex $argv 2]
  set Test [lindex $argv 3]
  set Verbose [lindex $argv 4]
  set ExitCode 0
  if {[catch {set SOCKET [socket "$Host" "$Port"]} SockErr]} {
    if {[string range $errorCode 0 3] == "NONE" } { set ExitCode 1 }
    if {[string range $errorCode 0 16] == "POSIX ENETUNREACH" } { set ExitCode 1 }
    if {[string range $errorCode 0 17] == "POSIX EHOSTUNREACH" } { set ExitCode 1 }
    if {[string range $errorCode 0 17] == "POSIX ECONNREFUSED" } {
      if {$Test == "false"} { set ExitCode 1 }
    }
    if {$Verbose == "true"} {puts -nonewline stdout "$errorCode "}
  }
  exit $ExitCode
' | /usr/bin/tclsh - $HOST $PORT $TEST $VERBOSE
RC=$?
$VERBOSE && echo -n "(RC $RC) "

#----- Set the return code and exit -----
X="OK"; [ $RC != 0 ] && X="FAIL"
$VERBOSE && echo $X
exit $RC

# vim: tabstop=4