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View File Name : factorial_scalar

#!/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;