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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 ;