Thanks for pointing out those flaws, sgifford. I did modify my method, so it didn't need to use the delay with select. It waits in a loop until output is available. This will give multiline output from READ, but now I'm stumped by another problem. It seems the output buffer which bc writes to with IPC::Open3 is limited to 4060 bytes. I've tried alot of things, but no matter what I do, bc stops output at 4060 bytes, but will give full output if run by itself from the command line. Try 123^12345 ; which if run from the commandline will output about 16k, but when run from IPC::Open3 will clip at 4060 bytes. 
#!/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 ERRO
+R-> $error \e[0m \n"}
     if($rsize > 0){sysread(READ,$answer,$rsize); print "Output->$quer
+y = $answer\n"}
            } until(($esize > 0)or($rsize > 0));

}

[download]

In reply to Re: Re: Re: Re: IPC::Open3 and blocking filehandles by zentara
in thread IPC::Open3 and blocking filehandles by zentara

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.