open FH, "whois x.x.x.x 2>&1 |";
my $ofh = select FH;
$|=1;
while (<FH>) {
    print;
}
close FH;
[download]

Turn on warnings and you'll see exactly what the problem is with this piece of code.

Check out IO::Select, which does what you want.

IO::Select seems like a good choice, but unfortunately it does not work. i.e. if the whois server is unavailable, I get no output.

open my $WHOIS, "jwhois x.x.x.x 2>&1 |";
my $s = IO::Select->new($WHOIS);

while (my @ready = $s->can_read) {
    for my $fh (@ready) {
        if ($fh == $WHOIS) {
            my $buf = <$fh>;
            if ($buf) {
                print $buf;
            }
            else {
               close($fh);
            }
        }
    }
}
[download]

Note that this works great, if the server sends some output and then closes the connection, but not for servers which send some output and then hang.


--
Rohan

Since his standard output is connected to your standard input, and not to a terminal, it is heavily buffered.

Mucking around with $| will never help, since it's the other program's buffering, not your own, that's causing the problem.

The solution is to trick it into thinking it's talking to a terminal by using Expect.pm or Expect::Simple.

Yes. Expect did solve this problem for me. Especially the raw_pty method.


--
Rohan

Or if you don't want to use Expect when you're not planning on using all of its complexity, you could do something like: http://www.perlmonks.org/?node_id=393312 to put a pesudo-tty inbetween you and the command.

open FH, "whois x.x.x.x 2>&1 |";
my $ofh =select(FH);
$|=1;
select($ofh); #changed
while (<FH>) {
    print;
}
close FH;
[download]

Doesn't seem to work on mine. IO::Handle too does not help.

use strict; use warnings;
use IO::Handle;

open my $WHOIS, "jwhois x.x.x.x 2>&1 |";
my $io = IO::Handle->new;
$io->fdopen($WHOIS, "r");
$io->blocking(0);
print $io->getline;
$io->close;
[download]

I don't get any output, if the server is unavailable.


--
Rohan

Do you mean to use $io->autoflush(1) ? Try this code:

use strict; use warnings;
use IO::Handle;

open my $WHOIS, "whois x.x.x.x 2>&1 |";
my $io = IO::Handle->new;
$io->fdopen($WHOIS, "r");
$io->autoflush(1);
while(my $line = $io->getline){
    print $line;
}
$io->close;
[download]

This is working fine on my environment.

Both sysread and <FH> will return immediately if some data (for <FH>, a whole line) were collected from the pipe. There is no need to turn on autoflush ($|) for the FH filehandle. If you are not getting the data it is because whois is probably not sending it. Probably it is using stdio, and since its output is a pipe, it is buffered. If that's the case, then there's not much you can do about it. None of the versions of whois that I have produce this status message so I cannot test whether this is so, but you can verify whether yours is outputting any data with truss or strace:

truss -t write whois x.x.x.x 2>&1 | cat
[download]

Its not particularly about the whois command, but on how to obtain program output which blocks. The whois command is a perfect example for this.


--
Rohan

perhaps the backticks will give you a way. Then you can use something like this $myvar = `whois x.x.x.x` ; Then you can manipulate/search/test the output from the command, through $myvar. G

Or maybe you want to regex the output, and if it is empty, leave the loop.