#!/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  

while(1){

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

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);  

#this while loop waits and eliminates need for above delay 
#but is limited to 4060 bytes from bc 
  do {
      #see which filehandles have output from perldoc -q filehandle 
      $esize = pack("L", 0);
      ioctl(\*ERROR, FIONREAD(), $esize) or die "Couldn't call ioctl: $!\n";
      $esize = unpack("L", $esize);
      print "esize-> $esize\n" unless ($esize < 1);

      $rsize = pack("L", 0);
      ioctl(\*READ, FIONREAD(), $rsize) or die "Couldn't call ioctl: $!\n";
      $rsize = unpack("L", $rsize);
      print "rsize-> $rsize\n" unless ($rsize <1);

     #get the output from bc 
     if($esize > 0){sysread(ERROR,$error,$esize); print "\e[1;31m ERROR-> $error \e[0m \n"}
     if($rsize > 0){sysread(READ,$answer,$rsize); print "Output->$query = $answer\n"}
            } until(($esize > 0)or($rsize > 0));

}