Perl调用系统命令并保持脚本同时运行

Question

I am running a perl script that does a logical check and if certain conditions been met. Example: If it's been over a certain length of time I want to run a system() command on a linux server that runs another script that updates that data. script that updates the file takes 10-15 seconds, with the current amount of files it has to go through, but can be up to 30 seconds during peak times of the month.

I want the perl script to run and if it has to run the system() command, I don't want it to wait for the system() to finish before finishing the rest of the script. What is the best way to go about this?

Thank you

Answer 1

System runs a command in the shell, so you can use all of your shell features, including job control. So just stick & at the end of your command thus:

system "sleep 30 &";

Answer 2

Use fork to create a child process, and then in the child, call your other script using exec instead of system. exec will execute your other script in a separate process and return immediately, which will allow the child to finish. Meanwhile, your parent script can finish what it needs to do and exit as well.

Check this out. It may help you.

There's another good example of how to use fork on this page.

Answer 3

Not intended to be a pun due to publication date, but beware of zombies! It is a bit tricky, see perlipc for details. However, as far as I understood your problem, you don't need to maintain any relation between the updater and the caller processes. In this case, it is easier to just "fire and forget":

use strict;
use warnings qw(all);
use POSIX;

# fork child
unless (fork) {
    # create a new session
    POSIX::setsid();

    # fork grandchild
    unless (fork) {

        # close standard descriptors
        open STDIN, '<', '/dev/null';
        open STDOUT, '>', '/dev/null';
        open STDERR, '>', '/dev/null';

        # run another process
        exec qw(sleep 10);
    }

    # terminate child
    exit;
}

In this example, sleep 10 don't belong to the process' group anymore, so even killing the parent process won't affect the child.

Answer 4

在http://aaroncrane.co.uk/talks/pipes_and_processes/paper.html上有一个很好的教程，介绍如何从Perl运行外部程序（包括运行后台进程）。