perlquestion
VinsWorldcom
<p>I have yet another [cpan://Net::SSH2] question that I haven't found a definitive solution to yet. So here goes.</p>
<p><b>BACKGROUND</b></p>
<p>Windows 7 x64 / Strawberry Perl 5.16.1 / Net::SSH2 0.45 - note that Net::SSH2 comes bundled with Strawberry, I did not compile myself.</p>
<p>I've created a simple SSH client using Net::SSH2 and I can connect fine, I've gotten past the freezing issue on Windows ($chan->blocking(0)) and even the issue where the command output lagged one command behind (binmode($chan)), but only sometimes.</p>
<p>I'm testing my client to both CentOS and Cisco router with SSH enabled.</p>
<p><b>ISSUE</b></p>
<p>The issue I see is that if I execute a long command (e.g., 'ls -alR /' on linux, 'show run' on Cisco router) I start to see some output and then just get the prompt back. When I issue the next command, I get the remainder of output from the first long command - or maybe just some of it if it's a really long output.</p>
<p>To my novice mind, it seems to be a buffering problem and I've tried the flush() method of Net::SSH2 to no avail. My other thought is that I need to set $| on the $chan filehandle, which also didn't solve it. My final desperation was to actually read the POD line-by-line and found the poll() method and some Google-ing turned up an example of it's usage.</p>
<p>I tried:</p>
<c>
my @poll = ({handle => $chan, events => 'in'});
if($ssh2->poll(250, \@poll) && $poll[0]->{revents}->{in}) {
print $buf while defined ($len = $chan->read($buf,512))
}
</c>
<p>and in a last ditch attempt:</p>
<c>
my ($rin, $rout, $ein, $eout) = ('', '', '', '');
vec($rin, $chan, 1) = 1; # tried $ssh2 and $chan,
# but should be: fileno($var) which errors
if (select($rout=$rin, undef, $eout=$ein, 5000)) {
print $buf while defined ($len = $chan->read($buf,512))
}
</c>
<p>Neither above command set fixed the issue.</p>
<p><b>QUESTION</b></p>
<p>I'm now thinking it may be due to blocking(0); however, if that isnt' used, Windows just hangs after the connect. How can I get Net::SSH2 to "wait" until all output from a command is printed without just adding an artificially long sleep? Note that I use Net::Telnet to connect to linux and Cisco routers and this isn't an issue - it patiently waits until all output is printed and never seems to chop command output (which I think is the buffering issue).</p>
<p><b>SCRIPT</b></p>
<c>
#!/usr/bin/perl
use strict;
use warnings;
use Net::SSH2;
use Term::ReadLine;
my $host = '10.254.254.1';
my $user = 'cisco';
my $pass = 'cisco';
my ($len, $buf);
my $ssh2 = Net::SSH2->new();
if ($ssh2->connect($host)) {
print "[Connected]\n";
if ($ssh2->auth_password($user, $pass)) {
print "[Authenticated]\n";
# Set up shell for interactive
my $chan = $ssh2->channel();
$chan->blocking(0); # Needed on Windows
$chan->shell();
#binmode($chan); # Seems to take care of both Unix SSH and Cisco servers
# Sometimes needed to "clear", flush() doesn't seem to work
# Otherwise, first command does not work
select(undef,undef,undef,0.2); # or sleep 1
print $buf while defined ($len = $chan->read($buf,512));
# START: Interactive Mode
my $prompt = "ssh> ";
my $ssh = Term::ReadLine->new("SSH");
$ssh->ornaments(0);
while (defined (my $cmd = $ssh->readline($prompt))) {
chomp $cmd;
if ($cmd =~ /^\s*$/) { next } # nothing
if ($cmd =~ /^\s*exit\s*$/) { last } # exit
$chan->write("$cmd\n");
select(undef,undef,undef,0.2); # or sleep 1
print $buf while defined ($len = $chan->read($buf,512))
}
# END: Interactive Mode
$chan->close
} else {
warn "Authentication failed\n"
}
} else {
warn "Unable to connect to host $host: $!\n"
}
</c>