jbaribeault has asked for the wisdom of the Perl Monks concerning the following question:

Strange question, but when I run my little Solaris Ping -s output muncher, if I try to redirect stdout a la '> filename' the file doesn't get anything in it. The script runs fine to the screen. Here are the two command lines:

ping -s 192.168.1.1 | pinglog.pl

Works fine - output as expected...

ping -s 192.168.1.1 | pinglog.pl > pinglog.out

pinglog.out remains empty...what is going on??
Here is the script: 
#!/usr/bin/perl -w

use strict;

my $newnum = 0;

while (<>) {
    next if $_ =~ /data bytes/;
    my ($a, $b) = split (/:/, $_);
    chomp $b;
    my ($seq, $seqnum, $lat, $latsec) = split '=', $b;
    $seqnum =~ s/\s+//;
    $seqnum =~ s/.time//;
    # for debug...
    # print "seq: $seqnum\texpected: $newnum\n";
    unless ($seqnum == $newnum ) {
        print "Ping failed at " . localtime(time - ($seqnum - $newnum)
+) . "\t";
        print "restored at " . localtime() . "\t";
        print "Total Time (s) = " . ($seqnum - $newnum) . "\n";
    }

    $newnum = $seqnum + 1;
}

[download]
Any ideas?? Thanks ahead of time!

Replies are listed 'Best First'.
(z) Re: Redirect Question
by zigdon (Deacon) on Sep 15, 2003 at 16:44 UTC
    Like it was mentioned above, is it possible that your output is buffered? Try adding $| = 1 to the top of your script, see if that helps?

    -- zigdon

[reply]
[d/l]
      Aha! The solution!

      Now, what did that do??? Was I not getting enough input into the buffer for the file write to happen; if so, how much is the buffer usually? Did the $| change the size of the buffer?
      Thanks for the quick fix!!
[reply]
        AFAIK, the buffer size varies by platform, and by what's the destination. For STDOUT to the terminal, the buffer is usually around 256 bytes, I think. For files, it's probably several K, at least. All $| does it set the buffer to autoflush - see perlvar for details.

        -- zigdon

[reply]
[d/l]
Re: Redirect Question
by phydeauxarff (Priest) on Sep 15, 2003 at 18:04 UTC
    On another note, why not go ahead and just add Net::Ping to your script so it will have the functionality instead of requiring you to pipe in output from ping?

    use Net::Ping;
my $ping = new Net::Ping ("icmp");
my $PING_TIMEOUT = 2;
my $IP=$_;
     if ($ping->ping($IP, $PING_TIMEOUT))
        {
                print "Ping Succeeded \n";
        }
        else { print "Ping failed\n";}
$ping->close();

    [download]

    Then you can just run your script with your IP as an argument...this would even make it easy to automate automate the script to run a list of IP's on a regular basis.

[reply]
[d/l]
      Thanks all!
      The script is just a quick-and-dirty capture to quantify some outage times for a customer. Since I knew I could just grok the output from a ping -s on solaris, that is what I did - simple. Thanks for the ideas though, and I will use Net:Ping if I ever need to do this again.
      Cheers!
[reply]
Re: Redirect Question
by nimdokk (Vicar) on Sep 15, 2003 at 16:25 UTC
    One thing, I think you will need to read from ARGV instead of $_.

    "Ex libris un peut de tout"
[reply]
Re: Redirect Question
by kutsu (Priest) on Sep 15, 2003 at 16:32 UTC

    The  > pinglog.pl won't ever happen becuase it's waiting on ping to stop before it does, at least I think. You might try this, untested: 

    ping -c 5 -s 192.168.1.1 | pinglog.pl > pinglog.out

    [download]

    "Pain is weakness leaving the body, I find myself in pain everyday" -me

[reply]
[d/l]
[select]
      On solaris, the -s for the ping command makes it send 1 packet every second, indefinetly. The point of this script is to catch holes in the sequence number and calculate timestamps for the lost pings, and log the timestamps to a file.

      I have even tried writing to an output file handle with my print statements to no avail. Works to the screen if I just use print, print FH doesn't. Ack :(
[reply]

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