http://qs321.pair.com?node_id=1106024


in reply to use sysread to read non-blocking filehandle

Two calls to last doesn't look right. Maybe one of these should be a next?

        if ($! == EAGAIN()) {
            print "\nEAGAIN is set\n";
            last;
        } else {
            last;
        }

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Re^2: use sysread to read non-blocking filehandle
by x12345 (Novice) on Nov 04, 2014 at 13:45 UTC
    If there are severals filehandles parallel at the same time, I can do a loop and next to read the filehandels. Here I just use a simple example to try non-blocking and sysread. So just one filehandle, set to non blocking, then read.
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      If I just use once sysread to try, it is still empty. Here is the code, what is wrong in the code? 
      my $cmd = '/opt/rssh/bin/ssh';
my $machine = "remote_machine";

open(my $fh, "-|", "$cmd $machine \"hostname;sleep 5;uptime\" 2>&1") o
+r die "cannot open fh";

my $flags = fcntl($fh, F_GETFL, 0) or die "\ncan't get flags for the p
+ipe: $!\n";
fcntl($fh, F_SETFL, $flags | O_NONBLOCK) or die "\ncan't set flags: $!
+\n";

my $out = $fh;
my $bytes_read = -1;
my $blocksize = 1024;
my $result = "";
my $buf;

$bytes_read = sysread($out, $buf, $blocksize);

print "\nl buf content is:\n $buf \n";
close $out;

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[reply]
[d/l]

        Maybe you want to learn what "nonblocking" really means?

        In short, "nonblocking" means that the sysread call will return immediately and tell you how many bytes were read at this time. If your filehandle has nothing to read, it will not block. Blocking means "wait until data is avilable".

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[d/l]

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