Net::SSH::Perl and handling dead hosts

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

I have a script that cycles through several systems and collects the data of various shell commands. I do not know which systems will be up or have a SSH server running. Thus I need the script to skip any bad connections.

#!/usr/bin/perl

use strict;
use warnings;

use Net::SSH::Perl;

my ($ssh, $cmd, $x, $stdout, $stderr, $exit);

# commands to be passed to remote server
my @commands = (
    'uptime',
    'tail /var/log/secure',
    'tail /var/log/messages',
    'exit');


my $user = 'root';
my $pass = 'root1';

open LOGFILE, "> hw-survey-log" || die "could not open file $!";

# connect to many hosts, on after another
for ($x=3; $x<255; $x+=2){

    # make new connection
    $ssh = Net::SSH::Perl->new("10.0.0.$x",
        protocol => 2) || next;
    $ssh->login($user, $pass) || next;

    print LOGFILE "\nHostname: 10.0.0.$x:\n";

    # execute all commands
    foreach $cmd (@commands){

        # pass command and record results
        ($stdout, $stderr, $exit) = ssh->cmd($cmd);
        print LOGFILE $stdout.$stderr.$exit;
    }
}
    
close LOGFILE;
[download]

I thought that the || next; would handle this. However, the script dies after the first attempt:

Can't connect to 10.0.0.3, port 22: No route to host at /usr/lib/perl5
+/vendor_perl/5.8.5/Net/SSH/Perl.pm line 206.
[download]

I can see in the pm code that there is a die:

    connect($sock, sockaddr_in($rport, $raddr))
        or die "Can't connect to $ssh->{host}, port $rport: $!";
[download]

It would be nice if there was a way around this without modifying the module.

Neil Watson
watson-wilson.ca

Comment on Net::SSH::Perl and handling dead hosts Select or Download Code

Replies are listed 'Best First'.
Re: Net::SSH::Perl and handling dead hosts by Random_Walk (Prior) on Feb 16, 2005 at 15:08 UTC
you could put your attempt to connect into an eval and catch the die `eval {$ssh->login($user, $pass)}; next if $@;` [download] Cheers, R. Pereant, qui ante nos nostra dixerunt!	[reply] [d/l]
Re^2: Net::SSH::Perl and handling dead hosts by neilwatson (Priest) on Feb 16, 2005 at 15:34 UTC
That did the trick. Thanks. Neil Watson watson-wilson.ca	[reply]
Re: Net::SSH::Perl and handling dead hosts by friedo (Prior) on Feb 16, 2005 at 15:10 UTC
How about wrapping it in an eval? `for ($x=3; $x<255; $x+=2){ # make new connection eval { $ssh = Net::SSH::Perl->new("10.0.0.$x", protocol =>2); $ssh->login($user, $pass); }; next if $@; }` [download] Update: Nicer formatting.	[reply] [d/l]
Re: Net::SSH::Perl and handling dead hosts by eXile (Priest) on Feb 16, 2005 at 16:04 UTC
You could also try to use the Expect module to cope with unreliable input. There's a good tutorial on how to use it in the tutorials section.	[reply]