I was toying with using IPC3 to run bc as an educational example. See this nodeIPC3 buffer problemAnyways, I came up with some code to beat the 4k buffer limit, to give unlimited bc output. It's a hard to solve problem, do a groups.google search for "IPC perl buffer size limit". Anyways, here is what I came up with. All comments and criticisms welcome. It's how I learn :-) The basic trick I use is to use a do loop to keep reading the buffer until the buffer is less than full. Then I display the concantenated output string. The 4k buffer is 4060 bytes on my linux machine.
#!/usr/bin/perl
use warnings;
use strict;
use IPC::Open3;
require 'sys/ioctl.ph';

# I tested this with  
#  "q @ 2" to generate errors 
# "123^12345" to generate big output 
# "123^23456" to generate huge output 

#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,$errortot,$answertot)=('','',0,0,'',''
+);

print "Enter expression for bc, i.e. 2 + 2\n";
chomp(my $query = <STDIN>);
if(length($query) == 0){next} #removes empty input 

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

# this do loop waits and eliminates need for a delay 
# to wait for bc to  output 
# It is NOT limited to 4060 bytes from bc, it keeps reading 
# until a semi-full buffer is sent, which signals end of output 

  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); $errortot = $errorto
+t.$error}
     if($rsize > 0){sysread(READ,$answer,$rsize); $answertot = $answer
+tot.$answer}
    } until(($esize > 0)or(($rsize > 0)and($rsize < 4060)));


if(length($errortot) > 0){ print "\e[1;31m ERROR-> $errortot \e[0m \n"
+}
if(length($answertot) > 0){print "Output->$query = $answertot\n"}

}

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In reply to IPC3 buffer limit problem by zentara

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