test and demonstrate the use of Net::SSH::Expect Perl module to connect via SSH using key authentication, to known and unknown hosts, running commands and processing captured standard output from those commands

test_net_ssh_expect.pl

#!/usr/bin/env perl

use warnings;
use strict;

use Date::Parse;
use Net::SSH::Expect;
use POSIX qw(strftime);

# set to a known host on your network
# that has not been ssh shell connected
# to by this user before
my $known_host = "some_server_we_know";

# invoke a Net::SSH::Expect object
my $ssh = Net::SSH::Expect->new (
            host => "localhost",
            user => 'marshyon', 
            raw_pty => 1
);

# as we have already set up an SSH key pair and 
# loaded it with 'ssh-add' and tested the connection
# manually, we need no password to connect to the 
# target server ....
$ssh->run_ssh() or die "SSH process couldn't start: $!";

# we over-ride the current console prompt, likely set by 
# .bashrc or system wide bash or profile with one that we 
# know has no 'escape characters' ( e.g. colors ) and that
# we can use later to pattern match returned output
my $set_promt_cmd = q(PS1='console:\h \$ ');
$ssh->exec($set_promt_cmd);

# get the hosname of the host we are connected to
my $hostname = $ssh->exec("hostname");
$hostname=~ m{(.+?)\nconsole:}msx;

# using the custom prompt we set earlier, the hostname
# can be accurately extracted from captured stdout
print "hostname is [$1]\n";

# now we can ssh to a server that exists but we 
# have not visited before

my $ssh_session = $ssh->exec("ssh $known_host");

# testing the returned output we can see that this is the 
# case and respond to not accept and record the key from
# this connection
if( $ssh_session =~ m{Are you sure you want to continue}i ) {
    print "we have not seen this one before,....\n";
    $ssh->exec("no");
}

# next we try to connect to a server that does not
# exist or is otherwise off line
$ssh_session = $ssh->exec("ssh no_server_anywhere");
if( $ssh_session =~ m{Could not}i ) {
    print ">>>\n$ssh_session\n";
    print "this one seems like its a gonner...\n";
}

# on the current server connection we now run a command to
# list the current directory
# nb: ls will 'colourise' it's output unless we use the switch
#     '--color=never' - colours will contain escape characters
#     that will goose some pattern matching from working
#     properly 
my $listing_cmd = 'ls --color=never -al';
my $listing = $ssh->exec($listing_cmd);
$listing =~ m{(.+)\nconsole:}msx;
print ">>\n$1\n.................\n";

# lastly, lets do something useful with the listing we just
# got back, namely extract file name, file date when last modified 
# and the size of each file
# file
my @file_listing = split(/\n/, $listing);

foreach my $file_list (@file_listing) {
    # here is an example of what we are trying to match ....
    # -rw------- 1 marshyon marshyon 2089 Jul 29 13:57 .bash_history
    # here is the regex in an 'if' with comments ( the x switch in ... match {} msx .. 
    # lets us add comments to the regular expression ) ....
    if( $file_list =~ m{ 
                         \S+ \s+ \d+ \s+   # non space(s), space(s), digit(s), space(s)
                         marshyon \s+  # literal string, space(s)
                         marshyon \s+  # literal string, space(s), 
                         ( \d+ ) \s+ # capture digit(s) into $1 followed by space(s)
                         (.+?) \s+   # one or more characters non greedy captured to $2, space(s)
                         (\S+) $     # non space(s) captured to $3 to end of line
                       }msx ) {
        my ($size, $date_str, $file) = ($1, $2, $3);

        # using Date::Parse modules function, parse date string        
        my $epoch = str2time($date_str);
        my $date_formatted = strftime "%Y-%m-%d %H:%M", localtime;
        print "size[$size] epoch[$epoch] date_formatted[$date_formatted] file[$file]\n";
    }
}