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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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