Read unbuffered data from pipe in Perl - linux

Question

I am trying to read unbufferd data from a pipe in Perl. For example in the program below:
open FILE,"-|","iostat -dx 10 5";
$old=select FILE;
$|=1;
select $old;
$|=1;
foreach $i (<FILE>) {
print "GOT: $i\n";
}
iostat spits out data every 10 seconds (five times). You would expect this program to do the same. However, instead it appears to hang for 50 seconds (i.e. 10x5), after which it spits out all the data.
How can I get the to return whatever data is available (in an unbuffered manner), without waiting all the way for EOF?
P.S. I have seen numerous references to this under Windows - I am doing this under Linux.

Answer 1

#!/usr/bin/env perl
use strict;
use warnings;
open(PIPE, "iostat -dx 10 1 |") || die "couldn't start pipe: $!";
while (my $line = <PIPE>) {
print "Got line number $. from pipe: $line";
}
close(PIPE) || die "couldn't close pipe: $! $?";

Answer 2

If it is fine to wait in your Perl script instead on the linux command, this should work.
I don't think Linux will give control back to the Perl script before the command execution is completed.
#!/usr/bin/perl -w
my $j=0;
while($j!=5)
{
open FILE,"-|","iostat -dx 10 1";
$old=select FILE;
$|=1;
select $old;
$|=1;
foreach $i (<FILE>)
{
print "GOT: $i";
}
$j++;
sleep(5);
}

Answer 3

I have below code working for me
#!/usr/bin/perl
use strict;
use warnings;
open FILE,"-|","iostat -dx 10 5";
while (my $old=<FILE>)
{
print "GOT: $old\n";
}

Answer 4

The solutions so far did not work for me with regards to unbuffering (Windows ActiveState Perl 5.10).
According to http://perldoc.perl.org/PerlIO.html, "To get an unbuffered stream specify an unbuffered layer (e.g. :unix ) in the open call:".
So
open(PIPE, '-|:unix', 'iostat -dx 10 1') or die "couldn't start pipe: $!";
while (my $line = <PIPE>) {
print "Got $line";
}
close(PIPE);
which worked in my case.