Testing Socket Connections Programmatically

Often we have to use “telnet remotehost.somewhere.com 80” to test if a remote socket connection can be established.  This is fine for one time tests but can be a problem when it comes time to test a number of connections – especially if we want to test them programmatically from a script.  Perl to the rescue:

#!/usr/bin/perl
use IO::Socket;

my $sock = new IO::Socket::INET (
                   PeerAddr => $ARGV[0],
                   PeerPort => $ARGV[1],
                   Proto => tcp,
);

if ($sock) { print "Success!\n" } else { print "Failure!\n" };
close($sock);

Just copy this code into a file called “sockettest.pl” and “chmod 755 sockettest.pl” so that it is executable and you are ready to go.  (This presumes that you are using UNIX.  As the script is Perl, it should work anywhere.)
To use the code to test, for example, a website on port 80 or an SSH connection on port 22 just try these:

./sockettest.pl www.yahoo.com 80
./sockettest.pl myserver 22

You aren’t limited to known services.  You can test any socket that you want.  Very handy.  Now, if you have a bunch of servers, you could test them from a simple, one line BASH command like so (broken so as not to be one line here for ease of reading…)

for i in myserver1 myserver2 yourserver1 yourserver2 someoneelsesserver1
do
  echo $i $(./sockettest.pl "$i" 80)
done