#!/usr/bin/perl
use Net::Ping;
my @host_array = ( '1.2.3.4', ... );
my @up;
$" = "\n";
my $p = Net::Ping->new( "syn", 5 );
$p->{port_num} = 7;
$p->ping($_) for (@host_array);
while ( my ( $host, $rtt, $ip ) = $p->ack ) {
  push @up, $ip;
}
print @up;