#!/usr/bin/perl
use warnings;
use strict;
use IPC::Open3;
require 'sys/ioctl.ph';

#interface to "bc" calculator 
my $pid = open3(\*WRITE, \*READ,\*ERROR,"bc");
            #if \*ERROR is false, STDERR is sent to STDOUT  

my($error,$answer)=('','');

while(1){

print "Enter expression for bc, i.e. 2 + 2\n";
chomp(my $query = <STDIN>);

#send query to bc 
print WRITE "$query\n";

#timing delay needed tp let bc output 
select(undef,undef,undef,.01);

#see which filehandles have output from perldoc -q filehandle 
my $esize = pack("L", 0);
ioctl(\*ERROR, FIONREAD(), $esize) or die "Couldn't call ioctl: $!\n";
$esize = unpack("L", $esize);
print "esize-> $esize\n";

my $rsize = pack("L", 0);
ioctl(\*READ, FIONREAD(), $rsize) or die "Couldn't call ioctl: $!\n";
$rsize = unpack("L", $rsize);
print "rsize-> $rsize\n";


#get the output from bc 
if($esize > 0){sysread(ERROR,$error,$esize); print "Error-> $error\n"}
if($rsize > 0){sysread(READ,$answer,$rsize); print "Output->$query = $answer\n"}

($error,$answer,$rsize,$esize)=('','',0,0);
}