Several of the perl IPC::Open2 examples seem incomplete, including perldoc (which waitpid's on a process with open file descriptors) and a gnuplot example (which assumes gnuplot exit'd). Below is a complete perl IPC::Open2 example that interfaces with mysql (yes, it's contrived; you should be using DBI ;).

sub mysql($) {
        my ($argv) = @_;
        my $cmd = sprintf "mysql --batch --raw -A -u %s --password=%s -h %s %s", 
                $argv->{'user'}, $argv->{'password'}, $argv->{'host'}, $argv->{'db'};
        my ($child_stdin, $child_stdout);
        my $pid = IPC::Open2::open2($child_stdout, $child_stdin, $cmd);
        return sub {
                my ($query) = @_;
                print $child_stdin $query;
                close $child_stdin;
                my $discard_header = <$child_stdout>;
                my @ret = map { s/\r?\n$//; $_ }  <$child_stdout>;
                close $child_stdout;
                kill 9, $pid;
                waitpid $pid, 0;
                return \@ret;

my $two = mysql( { user=> 'root', ... } )->('select 1+1')->[0];