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

Is it possible to capture the output of stderr in Net::OpenSSH to a variable instead of to a file? In this particular case I want the stderr of the following "new" function not the stderr of commands once I have the connection established. 

my $ssh = Net::OpenSSH->new($host);
  $ssh->error and
    die "Couldn't establish SSH connection: ". $ssh->error;

[download]

ssh->error does not provide all the information I need during a connection failure.
I get different reasons for failure to connect. Some are "administratively denied" other are just "disconnect" and all these messages go to stderr. It looks like I can capture the stderr to a file but I would like to avoid that if possible.

Replies are listed 'Best First'.
Re: Handling STDERR when using Net::OpenSSH
by jandrew (Chaplain) on Aug 20, 2013 at 17:23 UTC
    Are you familiar with $SIG{__WARN__} handlers?

    Update: moved the link to point directly at %SIG

[reply]
Re: Handling STDERR when using Net::OpenSSH
by kevbot (Vicar) on Aug 21, 2013 at 04:45 UTC
    The Capture::Tiny module can be used to capture STDERR. For example, 
    #!/usr/bin/env perl

use strict;
use warnings;
use Net::OpenSSH;
use Capture::Tiny ':all';

my $host = 'broken';
my $ssh;
my ($stdout, $stderr, @result) = capture {
    $ssh = Net::OpenSSH->new($host);
};

print "Captured STDERR: $stderr\n";

$ssh->error and die "Couldn't establish SSH connection: ". $ssh->error
+;

exit;

    [download]
    gives the output: 
    Captured STDERR: ssh: Could not resolve hostname broken: nodename nor 
+servname provided, or not known

Couldn't establish SSH connection: unable to establish master SSH conn
+ection: master process exited unexpectedly at ns.pl line 15.

    [download]
[reply]
[d/l]
[select]
      Thank you kevbot and jandrew. I could not get $SIG{__WARN__} to provide any satisfaction in captureing STDERR. Capture::Tiny worked very well. Just to be sure and to keep it from being confused with the openssh capture function I used Capture::Tiny::capture 
       my $ssh;
 my $LOGIN_TIMEOUT = 60;
 my ( $ssh_stdout, $ssh_stderr, @ssh_result ) = Capture::Tiny::capture
    {
      $ssh = Net::OpenSSH->new(
         $ip_address,
         batch_mode => 1,
         timeout => $LOGIN_TIMEOUT,
         kill_ssh_on_timeout => 1,
         master_opts => [ -o => "StrictHostKeyChecking=no", 
                          -o => "ConnectTimeout=60", 
                          -o => "ForwardX11=no" ],
                );
    };

      [download]
      Thank you very much.
[reply]
[d/l]
Re: Handling STDERR when using Net::OpenSSH
by salva (Canon) on Aug 26, 2013 at 09:00 UTC
    Is it possible to capture the output of stderr in Net::OpenSSH to a variable instead of to a file

    Not safely.

    The master SSH process is run on the background asynchronously. Any module redirecting its ouput to anything but a file may interfere with the module inner workings.

[reply]

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