You've got the program at the wrong end of the pipe. You opened a pipe for inputting to from.pl. It's also not clear whether from.pl has the proper #! line and execute permissions.

Try this instead:

open(P, "perl from.pl |") or die "Can't pipe from from.pl: $?\n";
while (<P>) {
    print $_;
    $count++;
}
close(P) or die "Can't pipe from from.pl: $?\n";
print "$count\n";
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