Hey all!

I am trying to make a bidirectional communication to an external program using IPC::Open2. The problem is: I cannot "read" program's output unless I close the writer handle before attempting to read.

Such a problem is mentioned also here (I am not using Oracle but the essence of the problem is the same i guess): http://rootshell.be/~yong321/computer/OracleAndPerl.html (Pls see the first code block in Appendix section, also copied below).

use IPC::Open2;
local (*Reader, *Writer);
$pid = open2(\*Reader, \*Writer, "e:/oracle/ora81/bin/sqlplus -s scott
+/tiger");
print Writer "set pagesize 100\n";
print Writer "select * from emp;\n";
print Writer "exit\n";
close Writer;    #have to close Writer before read

#have to read and print one line at a time
while (<Reader>)
 { print "$_";
 }

close Reader;
waitpid($pid, 0);    #makes your program cleaner
[download]

It says: "the Writer has to be closed before you can read from the Reader". Why? Is there a way to overcome because I need to make read-write-read-write-read-... sequentially and I cannot open a new connection every time I want to read.

However such a code block would perfectly work (again there is a read followed by a write):

use IPC::Open2;
local (*Reader, *Writer);
$pid = open2(\*Reader, \*Writer, "bc -l");
$sum = 2;
for (1 .. 5) {
    print Writer "$sum * $sum\n";
    chomp($sum = <Reader>);
}
close Writer;
close Reader;
waitpid($pid, 0);
print "sum is $sum\n";
[download]

I desperately need your opinion.