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#!/usr/bin/perl -w
## Demonstration using a pipe to send input to a child process
use strict;
use IPC::Run qw( start pump finish );
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 $out;
my $h = start ['bc'], '<pipe', \*IN, '>', \$out;
my $tmp = select IN;
$| = 1;
select $tmp;
print IN "a = i = $i ; i\n";
while () {
$out = '';
pump $h until $out =~ s/.*?(\d+)\n/$1/g;
print "bc said: $out\n";
if ( $out > $i ) {
## i! is always >i for i > 0
print "result = ", $out, "\n";
close(IN);
last;
}
elsif ( $out == '1' ) {
## End of calculation loop, get bc to output the result
print IN "a\n";
}
else {
print IN "i = i - 1 ; a = a * i ; i\n";
}
}
finish $h ;
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