This is from a script I wrote. It works both in Windows and Linux.
This is not exactly a "fork", but it is portable:

    if ($^O =~ /win32/i) {
        # win32 uses "start"
        my $cmd = "start \"Glynx-$children\" /MIN /LOW \"$^X\" \"$0\" 
+--slave";
        print "$cmd\n" if $VERBOSE;
        print "  [ FORKING: $children ]\n" if $VERBOSE;
        `$cmd`;
    }
    else {
        undef $pid;
        if (!defined($pid = fork)) {
            print "  [ cannot fork: $! ]\n" unless $QUIET;
            # exit 0;
        } 
        elsif ($pid) {
            print "  [ FORKING: $children ]\n" if $VERBOSE;
            # print "begat $pid";
            # print "I'm the parent";
        }
        else {
            # print "I'm the child";
        }
    }
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