need to poll/manage thousands of wireless devices which, being wireless, may be off line so I would like a quick test to determine on/off line status before attempting a login so I am trying to use "ping" but had problems with hangs (ping never completes) so I added timeout but still hangs some times immediately after line 11 (never reaches line18 or 21) code 
  1 #! /usr/bin/perl -w
  2 
  3 sub ping {
  4     my $ip = shift || die "ping: no ip provided\n";
  5     my $debug = shift || 0;
  6 
  7     my $TIMEOUT = 5;
  8     my $remaining = 0;
  9     my $result = 0 ;
 10 
 11     print LOG "ping v 1 entry IP $ip debug $debug\n" if $debug;
 12     my @lines;
 13     eval {
 14         local $SIG{ALRM} = sub {die "alarm\n"} ;
 15         alarm $TIMEOUT ;
 16         @lines  = split /^/m,`ping -n -W 2 -c 5 -i 0.2 -w 1 $ip`;
 17         $remaining = alarm 0;
 18         print LOG "ping($ip): remaining $remaining\n" if $debug;
 19     };
 20     if($@) {
 21         print LOG qq{ping("$ip"): timed out\n} if $debug;
 22         return 0;
 23     }
 24     for my $line (@lines) {
 25         if($line =~ /Host Unreachable/o) {
 26             print LOG qq{ping($ip): Host Unreachable\n};
 27             last;
 28         }
 29         print LOG "    ping: $line" if $debug;
 30         if($line =~ / from $ip/) {
 31             $result++;
 32         }
 33     }
 34     if($result > 2) {
 35         printf LOG "ping($ip): returning result $result\n" if $deb
+ug;
 36         return $result;
 37     } else {
 38         printf LOG "ping($ip): returning result 0\n" if $debug;
 39         return 0;
 40     }
 41 }
 42 
 43 1;
 44

[download]
The module originaly was embedded in a large program (~500 line). To simply testing, I wrote just a short loop to observe behavior and gor even stranger symptoms. 

 17 while(my $s = $S->fetchrow_hashref) {
 18     my $ip = $$s{d07};
 19     my $start = time();
 20     printf LOG "\nService $$s{number} $ip\n";
 21     my $ping = ping($ip,1) ;
 22     printf LOG "reply \"$ping\" \nelapsed time %d seconds.\n",
              time() - $start;
 23 }
 24

[download]

After running (under nohup) through a hundred or so IPs, the output of the printf at line 22 disappeared from the LOG file. There were no hangs for this simple loop, also no timeouts reported.

Even stranger, attidional jobs appeared out of nowhere.

[john@scan test]$ jobs
[1]   Running                 nohup ./ping.pl &
[2]   Running                 nohup ./ping.pl &
[3]-  Running                 nohup ./ping.pl &
[4]+  Running                 nohup ./ping.pl &
[john@scan test]$

[download]

and zomnies where left behind

john     25136  0.0  0.0   4336   648 pts/3    S    15:51   0:00 ping 
+-n -W 2 -c 5 -i 0.2 -w 1 10.105.44.202
john     25137  0.0  0.0   4336   636 pts/3    S    15:51   0:00 ping 
+-n -W 2 -c 5 -i 0.2 -w 1 10.104.10.22
john     25138  0.0  0.0   4336   636 pts/3    S    15:51   0:00 ping 
+-n -W 2 -c 5 -i 0.2 -w 1 10.104.41.200
john     25139  0.0  0.0   4336   640 pts/3    S    15:51   0:00 ping 
+-n -W 2 -c 5 -i 0.2 -w 1 10.107.8.245
john     25140  0.0  0.0   2044   572 ?        S    15:51   0:00 ping 
+-n -W 2 -c 5 -i 0.2 -w 1 10.104.13.115

[download]

I think I have done something horrible wrong in the ping module. Can you spot the mistake?

In reply to backticks strange behavior by kp2a

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