http://www.perlmonks.org?node_id=1106019

x12345 has asked for the wisdom of the Perl Monks concerning the following question:

Hello, the experts:
According to someone's code, I try to reproduce the following: open a filehandle to run a command in remote linux machine, set it to non-blocking filehand, then use a sysread loop to read the results from the filehandle. It does't work. Could you help me check what is wrong in my code :

my $cmd = '/opt/rssh/bin/ssh'; my $machine = "remote_machine"; open(my $fh, "-|", "$cmd $machine \"hostname;uptime\" 2>&1") or die "c +annot 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 $result = ""; while ($bytes_read) { my $buf; $bytes_read = sysread($out, $buf, $blocksize); if (defined($bytes_read)) { if ($bytes_read == 0) { close($out); last; } else { print "\nbuf content\n"; $result.= $buf; } }else { if ($! == EAGAIN()) { print "\nEAGAIN is set\n"; last; } else { last; } } } print "\nresult is: $result \n";
The result is:
EAGAIN is set result is:
But if I replace the "while ($bytes_read) " with the while (<$fl>) as the following, I can get the result.
my $cmd = '/opt/rssh/bin/ssh'; my $machine = "remote_machine"; open(my $fh, "-|", "$cmd $machine \"hostname;uptime\" 2>&1") or die "c +annot open fh"; #my $flags = fcntl($fh, F_GETFL, 0) or die "\ncan't get flags for the +pipe: $!\n"; #fcntl($fh, F_SETFL, $flags | O_NONBLOCK) or die "\ncan't set flags: $ +!\n"; my @result ; while (<$fh>) { # chomp; push @result,$_; } print "\nresult is: @result \n";

The result is
result is: ccwsge0553 13:40:10 up 4 days, 2 min, 0 users, load average: 0.08, 0.03, 0.01
What is wrong in my code with non-blocking/sysread? Thanks in advance!