If you want to test whether the SSH service on the remote host is ready to accept logins you can try connecting to TCP port 22 on the remote host and see if you can read the SSH banner from it. I adapted this example from the perlipc documentation:

use warnings;
use strict;
use Socket;
my ($remote,$port, $iaddr, $paddr, $proto, $line);

$remote  = $ARGV[0] || die "usage: $0 hostname";
$port    = 22 ;  # the SSH port
$iaddr   = inet_aton($remote) || die "no such host: $remote";
$paddr   = sockaddr_in($port, $iaddr);
$proto   = getprotobyname('tcp');

socket(SOCK, PF_INET, SOCK_STREAM, $proto) || die "socket() failed: $!
+";
print "Connecting to port 22...\n";
connect(SOCK, $paddr) || die "connect() failed: $!";
print "Connected.\n";
$line = <SOCK>;
print $line;
exit 0 if $line =~ /SSH/;
exit 1;
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With the SSH server on my box running:

$ perl sshping.pl localhost; echo $?
Connecting to port 22...
Connected.
SSH-1.99-OpenSSH_x.xx Debian-xxx
0
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If I stop the SSH server on my box:

$ perl sshping.pl localhost; echo $?
Connecting to port 22...
connect() failed: Connection refused at sshping.pl line 14.
111
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You might want to have the perl script loop (with a sleep for a few seconds) and retry the connect, or you could do that in an external bash script by checking the exit code...

$ if perl sshping.pl localhost; then echo up; else echo down; fi
Connecting to port 22...
connect() failed: Connection refused at sshping.pl line 14.
down
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