Here's how you can do it using threads, assuming that your Perl has threading built in. (run perl -V to check if you can use threads (look for usethreads=define)).

#!/usr/bin/perl

use strict;
use warnings;
use threads;

foreach (0..100)
{
    # create a thread to call the "run_system" subroutine
    # to run "ls -la" on the OS
    my $thread = threads->create("run_system", "ls -la");
    $thread->detach;
}

sub run_system
{
    my $cmd = shift;

    system($cmd);
}

__END__
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