Spawning self - are backticks forking with same name

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

Under solaris with a non-threads version of Perl 5.6.1, I am watching my process with ptree. I hope someone may be able to explain the behavior. The program uses backticks and makes several calls to system, but I frequently see my script's name repeated twice on the ptree, even though it doesn't call itself. Is this a side effect of fork?

6852  perl -w script.pl
  9768  perl -w script.pl        ? Doesn't call self ?
[download]

Despite the fact the script doesn't invoke itself, the ptree shows it being a child of itself. If this fork or system? Some other magic?

Comment on Spawning self - are backticks forking with same name Download Code

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Re: Spawning self - are backticks forking with same name by Joost (Canon) on Aug 31, 2007 at 22:06 UTC
If the script spawns a lot processes and those processes take a significant amount of time to exec() (or the parent process takes some time to fork()) it's possible that what you're seeing is just because of the time it takes between the fork() and exec() implicit in the qx operator. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply]
Re: Spawning self - are backticks forking with same name by perlofwisdom (Pilgrim) on Aug 31, 2007 at 21:32 UTC
When your perl script makes an external call (via system(), or backticks ``, and other methods) a sub-process is kicked off on the operating system. This sub-process is tied to your original script (parent/child). When the process completes, the child process goes away. So, you were on the right track all along.	[reply]
Re: Spawning self - are backticks forking with same name by bruceb3 (Pilgrim) on Aug 31, 2007 at 21:38 UTC
Using Solaris 10 and a trival Perl script, I can not reproduce the same symptoms. Here is the script; `sleep 120;` [download] Then to get it started I am running it using the perl command. `# perl -w p.pl` [download] The output of ptree is doesn't have two perl processes like you are seeing. `624 /sbin/sh 625 bash --login -o vi 651 perl -w p.pl` [download] I realise that we are using different versions of Solaris (you are most likely running Solaris 9) but I don't thin that this would make a difference. What is happening in your script? Are you using open with a "\|" somewhere?	[reply] [d/l] [select]