your program whould work, if you replace 1.3 with 1..3 and 1.10 with 1..10. .. is the range operator. And you may remove the first 3 lines from your example. Ahh and a typo on $ |= 1; it should read $| = 1; here the whole thing again.

#!/usr/bin/perl
use strict;
$SIG{PIPE} = 'IGNORE';
open( PIPE, "|net2.pl" ) or die "Cannot open pipe:$!";
select PIPE;
$| = 1;
select STDOUT;

my $count = 0;
for ( 1 .. 10 ) {
  warn "Writing line $_\n";
  if ( print PIPE "This is line number $_\n" ) {
    $count++;
  }
  else {
    warn " An error occured during writing :$!";
    last;
  }
  sleep 1;
}
close PIPE or die " Cannot close pipe : $!";
print "Wrote $count lines of text \n";
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And net2.pl

#!/usr/bin/perl
use strict;
for (1..3) {
  last unless defined (my $line = <>);
  warn " Read_three,got $line\n";
}
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