How can I make fork in Perl in different scripts?

Answer 1

Perl has a fork function.

See perldoc perlfaq8 - How do I start a process in the background?

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(contributed by brian d foy)

There's not a single way to run code in the background so you don't have to wait for it to finish before your program moves on to other tasks. Process management depends on your particular operating system, and many of the techniques are in perlipc. Several CPAN modules may be able to help, including IPC::Open2 or IPC::Open3 , IPC::Run , Parallel::Jobs , Parallel::ForkManager , POE , Proc::Background , and Win32::Process .

There are many other modules you might use, so check those namespaces for other options too. If you are on a Unix-like system, you might be able to get away with a system call where you put an & on the end of the command:

    system("cmd &")

You can also try using fork, as described in perlfunc (although this is the same thing that many of the modules will do for you).

STDIN, STDOUT, and STDERR are shared

Both the main process and the backgrounded one (the "child" process) share the same STDIN, STDOUT and STDERR filehandles. If both try to access them at once, strange things can happen. You may want to close or reopen these for the child. You can get around this with opening a pipe (see open) but on some systems this means that the child process cannot outlive the parent.

Signals

You'll have to catch the SIGCHLD signal, and possibly SIGPIPE too. SIGCHLD is sent when the backgrounded process finishes. SIGPIPE is sent when you write to a filehandle whose child process has closed (an untrapped SIGPIPE can cause your program to silently die). This is not an issue with system("cmd&").

Zombies

You have to be prepared to "reap" the child process when it finishes. $SIG{CHLD} = sub { wait }; $SIG{CHLD} = 'IGNORE'; You can also use a double fork. You immediately wait() for your first child, and the init daemon will wait() for your grandchild once it exits.

unless ($pid = fork) {
        unless (fork) { 
            exec "what you really wanna do";
            die "exec failed!";
  }

        exit 0;
    }

    waitpid($pid, 0);

See Signals in perlipc for other examples of code to do this. Zombies are not an issue with system("prog &").system("prog &").

Answer 2

Use fork and exec.

Answer 3

If you need to get the PID of a perl script you can use the $$ variable. You can put it in your another_process.pl then have it output the pid to a file. Can you be more clear on like fork? You can always use the fork exec combination.

Answer 4

It's true that you can use fork/exec, but I think it will be much easier to simply use the pipe form of open. Not only is the return value the pid you are looking for, you can be connected to either the stdin or stdout of the process, depending on how you open. For instance:

open my $handle, "foo|";

will return the pid of foo and connect you to the stdout so that if you you get a line of output from foo. Using "|foo" instead will allow you to write to foo's stdin.

You can also use open2 and open3 to do both simultaneously, though that has some major caveats applied as you can run in to unexpected issues due to io buffering.