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#!/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 ;
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