How can I execute an external Windows command and instantly return in Perl?

Question

I've tried using system() with fork(), tried exec(), and am still not getting what I need.

I want to write a Perl script which executes, let's say, a different Perl script five times in a row (sending it different parameter values), but I have it run concurrently. I realize I could turn my script into a .pm file and reference it, but I'd prefer to keep the child script independent of the parent...

• system() works, but executes the commands consecutively (makes sense per documentation)
• exec() doesn’t work - it only executes the first method (makes sense per doc)
• I added a fork() to the child Perl script and then tried using system()
• this did not work either.
• backtick command ' documents says it works the same as system()...

Isn't there a simple way in Perl (I'm using Windows XP) to execute a process, and not care about the return values or anything and just continue on into the next line of the parent script?

Answer 1

You can do it like this (fork in the parent, exec in the child):

for my $cmd qw(command1 command2 command3) {
    exec $cmd unless fork
}

The way that exec $cmd unless fork works is that fork will return a true value in the parent (the process id) and will return a false value in the child, thus exec $cmd only gets run if fork returns false (aka, in the child).

Or if you want to keep tabs on the process as it runs concurrently:

my @procs;

for my $cmd qw(cmd1 cmd2 cmd3) {

    open my $handle, '-|', $cmd or die $!;

    push @procs, $handle;
}

Then you can read from an element of @procs if you need to.

Or take a look at one of the many CPAN modules, like Forks::Super that handle the details of fork management.

Answer 2

On Windows, you can give the super-secret 1 flag to the system, IIRC.

system 1, @cmd;

A Google search for this question on PerlMonks gives: Start an MS window in the background from a Perl script