See perlipc for details, and the perlfunc section on fork for a brief description. A simple example:

my $child_pid = fork();
if ( ! defined( $child_pid )) {
    warn "fork failed\n";
}
elsif ( $child_pid == 0 ) { # true for the child process
    exec( $cmd, @args );
}
# the parent gets here when the fork succeeds...
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That's great for UNIX-y systems.

fork() uses threads.pm on Windows, so (in some situations) you may wish to use Win32::Process::Create() instead.

-David

Even easier on Win32 is system( 1, $cmd ). It is unfortunate that this easy way to "spawn" (which the Perl C code knows how to do portably) was never exposed for Perl scripts to do portably.

- tye        

I have had good success with fork on Windows (perl release 5.6+). However, you can also use a piped open command which will not wait for the output. If the trailing character is a pipe symbol, "open" launches a new process with a read-only filehandle connected to it. For example:

open(NET, "netstat -i -n |") or die "can't fork: $!";
# You could go off and do other things here for a bit,
# and then come back to check on your results.
while (<NET>) { 
   # your code here...
}
close(NET) or die "can't close netstat: $!/$?";
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Please note that when you explictly close the piped filehandle, it will cause the parent process to wait for the child to finish (and I recommend closing it).

How do I start a process in the background?

Several modules can start other processes that do not lock your Perl program. You can use IPC::Open3, Parallel::Jobs, IPC::Run, and some of the POE modules. See CPAN for more details.

You could also use

system("cmd &")
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or you could use fork as documented in "fork" in perlfunc, with further examples in perlipc.