if( my $pid = fork ) {
    print "I am the parent pid ($$), and I'm going to wait for $pid to exit.\n";
    my $kid;
    do {

	 $kid = waitpid $pid, 0;

    } while $kid > 0;
    exit 0;

} else {
    exec(qw(ls -al /tmp)); die "hrm, exec() failed: $!";
}

##</code><code>##

    # exec(qw(ls -al /tmp)); die ... blah
    open my $out, ">", "filename" or die $!;
    open my $in, "-|", qw(ls -al /tmp) or die $!;
    print $out $_ while <$in>;
    close $out;
    close $in;