#!/usr/bin/perl -w

## Demonstration of using a scalar to queue input to a child process

use strict ;

use IPC::Run qw( start timeout ) ;

die "usage: $0 <num>\n\nwhere <num> is a positive integer\n" unless @ARGV ;
my $i = shift ;
die "\$i must be > 0, not '$i'" unless $i =~ /^\d+$/ && $i > 0 ;

my ( $in, $out ) ;

my $h = start ['bc'], \$in, \$out, timeout( 5 ) ;

$in = "a = i = $i ; i\n" ;

while () {
   $out = '' ;
   $h->pump until $out =~ s/.*?(\d+)\n/$1/g ;
   print "bc said: $out\n" ;
   if ( $out  > $i ) {
      print "result = $out\n" ;
      $in = undef ;
      last ;
   }
   elsif ( $out == '1' ) {
      ## End of calculation loop, get bc to output the result
      $in = "a\n" ;
   }
   else {
      $in = "i = i - 1 ; a = a * i ; i\n" ;
   }
}

$h->finish ;