The proper way to execute echo aabbcc >> file in backround

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

Hi ,

I am trying to execute :

system("while true; do echo aabbcc >> $temp_file; sleep 2; done &");
system("tail -f $temp_file >> $file &");
[download]

And then catch the events with the AnyEvent framework. It works but my system calls creates 2 zombie process when I kill my main program. The while and tail -f commands are still executing because the system calls are executing in an other group than my main script. How can I fix this ?

Thank you for your help. Regards

I finally got it working by using :

$childPid = open SON, "-|";

sub sigtrap() {
    print "\n";
    print("------      Killing all childrens then exeting ...      ---
+---\n");
    if(defined($childPid) && ! ($childPid == 0)){
        killfam 'KILL', ($childPid);
    }
    print "\n";
    print "Exiting ... \n";
    exit(1);
}

if ($childPid) {
    #parent
    system("while true; do echo aabbcc >> $temp_file; sleep 2; done");
}else {
    print "[$$]: Child...\n"; 
    system("tail -f $temp_file >> $file &");
    exit(0);
}
[download]

I finally understood that i needed to use a different process for each infinite running task and that if I wanted to do this in a non blocking mode I should do it on a fork.

Thank you all for your help

Comment on The proper way to execute echo aabbcc >> file in backround Select or Download Code

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Re: The proper way to execute echo aabbcc >> file in backround by karlgoethebier (Abbot) on Dec 06, 2013 at 12:55 UTC
"How can I fix this?" You can't, it does what you typed. Works as designed ;-) Try something like `perl -e 'system("tail -f foo &"); END{qx(killall tail)};'` I will be punished for this. BTW, why do you do this? Regards, Karl ŤThe Crux of the Biscuit is the Apostropheť	[reply] [d/l]
Re^2: The proper way to execute echo aabbcc >> file in backround by young_monk_love_perl (Novice) on Dec 06, 2013 at 13:18 UTC
Hi, thank you for your answer, can't I kill the system call process by pid and call it using fork ? By doing additional research I understood that my first code was poorly designed and that I should use a separate thread, could you provide me an example doing a separate thread and then killing it by using a clean way like Signals or PID please ?	[reply]
Re^3: The proper way to execute echo aabbcc >> file in backround by karlgoethebier (Abbot) on Dec 06, 2013 at 14:18 UTC
Some useful links for further reading: fork exec threads Parallel::ForkManager Best regards, Karl ŤThe Crux of the Biscuit is the Apostropheť	[reply]
Re^4: The proper way to execute echo aabbcc >> file in backround by young_monk_love_perl (Novice) on Dec 06, 2013 at 15:23 UTC
Re^5: The proper way to execute echo aabbcc >> file in backround by zentara (Archbishop) on Dec 06, 2013 at 17:53 UTC
Some notes below your chosen depth have not been shown here
Re^5: The proper way to execute echo aabbcc >> file in backround by taint (Chaplain) on Dec 06, 2013 at 17:31 UTC
Re^5: The proper way to execute echo aabbcc >> file in backround by karlgoethebier (Abbot) on Dec 06, 2013 at 17:41 UTC
Re: The proper way to execute echo aabbcc >> file in backround by Preceptor (Deacon) on Dec 07, 2013 at 13:12 UTC
What are you actually trying to accomplish here though? Writing out files in the background whilst the script is running? Because it looks like the result of what you're trying to do, is to write 'aabbcc' to $tempfile and $file every 2s. Without wanting to second guess too much, have you considered using threading? E.g.: `my $finished = 0 : shared; sub write_to_file { until ( $finished ) { open ( my $temp_fh, ">>", $temp_file ); print $temp_fh "aabbcc\n"; close ( $temp_fh ); } } #main bit of code here... $finished = 1; foreach my $thread ( threads -> list() ) { $thread -> join(); }` [download]	[reply] [d/l]


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