You don't make clear if you *need* a log file or if that is just your strategy for accomplishing your analysis.

If you are open to other ways of grabbing the data, you might skip redirecting the results to a file. Consider using back-ticks or qx(...) and then just wait for each run before proceeding. Here's a brief example with a generous sprinkling of intermediate variables for clarity.

#!/usr/bin/perl5 -w
use strict;

my ($avg_time, $raw_data, @times,
    $time_count, $total_time);
my $repeats = 5;
my $addr = 'www.perlmonks.net';
for (my $i = 1; $i <= $repeats; $i++) {
   $raw_data = `ping $addr`;   # NOTE back-ticks
   
   # Now do something interesting. We'll just...
   @times = $raw_data =~ /time=(\d+)/g;
   $total_time = 0;
   $time_count = 0;
   for (@times) {
      $total_time += $_;
      $time_count++;
   }
   $avg_time = $total_time / $time_count;
   print "$i. Average time: ${avg_time}ms\n";
}
[download]

1. Average time: 61.25ms
2. Average time: 61.75ms
3. Average time: 60.75ms
4. Average time: 62ms
5. Average time: 62.25ms
[download]

It solves the ping problem, but doesn't solve "executing another program WITHOUT stoping mine".

This ping thing came into my mind, because where I'm living now I have a BAD ISDN connection that needs to be controlled, so I started opening a window and ping perlmonks -t and just look at it.

After, as a good programmer, I saw so many data passing in the screen and the only thing that I could think about was "ANALYSE!!!!!", so I changed the ping -t into a log file, and started to make a little program that got a little bit bigger, and bigger, and finally, I wanted to put all toghether, and then... the rest you know...

So my main question is not how to ping and log, or how to ping and analyse, is how to execute something else without worying about it after started...

I got a lot of answers that worked below like as for example system "open ping -t perlmonks.org >ping.log".

That one worked perfeclty for what I needed, like that I can open a text editor, I can open a Browser, and in windows, I can say the file that I want to open, or the site (in the case of the browser)...




-------
[]'s
FiReWaLL
The only thing you regret in life, is the risk you don't take.

• exec replaces the current process binary with a new executable binary. Hence, if you ran a perl script and called exec in the same process, you would lose anything that you wrote in that perl script (with some exceptions which are not relevant under Winduz).
• fork will create a new process and populate it with instructions or a new process, hence giving birth to
• system which is essentially a fork and exec. The process creates a child process and populates it with the shell command. It then proceeds to waitpid on that system call.

AgentM Systems nor Nasca Enterprises nor Bone::Easy nor Macperl is responsible for the comments made by AgentM. Remember, you can build any logical system with NOR.

Of course, it's still to note that the fork() implementation of ActiveState Perl, while amazing, does not yet work correctly, as the Win32 API dosen't support fork() in a native way. It's easy to break forking programs by passing sockets to your children.

If you don't need to pass information between your parent and child process, it might be easier to use system() calls to start new instances of the child script(s)...

But you may want to try and get rid of the external program altogether and use Net::Ping. Then you have control over the entire process.

An example from the docs:

    $p = Net::Ping->new();
    print "$host is alive.\n" if $p->ping($host);
    $p->close();
[download]

Net::Ping doesn't use ICMP, but UDP/TCP to connect to the echo port of a machine. I tried using it, but found out you couldn't use ICMP and most machines don't have their echo port enabled for obvious reasons... In my current version I use Open3. The options for ping probably don't apply to Windows ping. I use FreeBSD 4.2 here.

#!/usr/local/bin/perl5 -w

use IPC::Open3;
use Symbol;

# .ping contains hostnames, each on a seperate line.
open(HOSTS, "<.ping") || die("Can't open hostsfile! ($!)\n");
@hosts = <HOSTS>;
close(HOSTS);

%PING = ();
%STATUS = (
  -1 => "Host not found",
   0 => "Not done",
   1 => "Host is alive",
   2 => "No reply from host",
);

foreach $host (@hosts) {
  chomp $host;
  $WTR = gensym();
  $RDR = gensym();
  $ERR = gensym();
  $PING{$host}{'PID'} = open3($WTR, $RDR, $ERR, "/sbin/ping -n -q -c 1
+ $host");
  close($WTR);
  while (<$RDR>) { $PING{$host}{'OUT'} .= $_; }
  while (<$ERR>) { $PING{$host}{'ERR'} .= $_; }
  $PING{$host}{'STATUS'} = 0;
}

foreach $host (keys %PING) {
  if(defined($PING{$host}{'ERR'})) {
    if($PING{$host}{'ERR'} =~ /Unknown host/) {
      $PING{$host}{'STATUS'} = -1;
      next;
    }
  }
  if($PING{$host}{'OUT'} =~ /.*, (.*) packets received.*/) {
    $PING{$host}{'STATUS'} = ($1 == 1?1:2);
  }
}

foreach $host (keys %PING) {
  printf "%-30s %s\n", $host, $STATUS{$PING{$host}{'STATUS'}};
}
[download]

According to the docs it supports icmp:

    $p = Net::Ping->new("icmp");
    foreach $host (@host_array)
    {
        print "$host is ";
        print "NOT " unless $p->ping($host, 2);
        print "reachable.\n";
        sleep(1);
    }
    $p->close();
[download]

system ("start path\to\command");
[download]

For the record, qx/.../  is the same as back-ticks.

Update: Merlyn is correct, of course in his post following this one. I was just trying to make a friendly connection regarding function. But the effect of different delimiters has a bearing on function. Back-peddling as fast as possible... Umm... let's just call them close relatives...

Almost. qx`...` would be the same as backticks. qx/.../ would have a slash for a delimiter, and hence require a different backslashing strategy. And qx'...' would have single-quote for a delimiter and not support variable interpolation or backslash escaping.

-- Randal L. Schwartz, Perl hacker