Net::Telnet

Net::Telnet

Provides telnet client functionality.

This class also has, through delegation, all the methods of a socket object (by default, a TCPSocket, but can be set by the Proxy option to new()). This provides methods such as close() to end the session and sysread() to read data directly from the host, instead of via the waitfor() mechanism. Note that if you do use sysread() directly when in telnet mode, you should probably pass the output through preprocess() to extract telnet command sequences.

Overview

The telnet protocol allows a client to login remotely to a user account on a server and execute commands via a shell. The equivalent is done by creating a Net::Telnet class with the Host option set to your host, calling #login() with your user and password, issuing one or more #cmd() calls, and then calling #close() to end the session. The #waitfor(), #print(), #puts(), and #write() methods, which #cmd() is implemented on top of, are only needed if you are doing something more complicated.

A Net::Telnet object can also be used to connect to non-telnet services, such as SMTP or HTTP. In this case, you normally want to provide the Port option to specify the port to connect to, and set the Telnetmode option to false to prevent the client from attempting to interpret telnet command sequences. Generally, #login() will not work with other protocols, and you have to handle authentication yourself.

For some protocols, it will be possible to specify the Prompt option once when you create the Telnet object and use #cmd() calls; for others, you will have to specify the response sequence to look for as the Match option to every #cmd() call, or call #puts() and #waitfor() directly; for yet others, you will have to use #sysread() instead of #waitfor() and parse server responses yourself.

It is worth noting that when you create a new Net::Telnet object, you can supply a proxy IO channel via the Proxy option. This can be used to attach the Telnet object to other Telnet objects, to already open sockets, or to any read-write IO object. This can be useful, for instance, for setting up a test fixture for unit testing.

Examples

Log in and send a command, echoing all output to stdout

  localhost = Net::Telnet::new("Host" => "localhost",
                               "Timeout" => 10,
                               "Prompt" => /[$%#>] \z/n)
  localhost.login("username", "password") { |c| print c }
  localhost.cmd("command") { |c| print c }
  localhost.close

Check a POP server to see if you have mail

  pop = Net::Telnet::new("Host" => "your_destination_host_here",
                         "Port" => 110,
                         "Telnetmode" => false,
                         "Prompt" => /^\+OK/n)
  pop.cmd("user " + "your_username_here") { |c| print c }
  pop.cmd("pass " + "your_password_here") { |c| print c }
  pop.cmd("list") { |c| print c }

References

There are a large number of RFCs relevant to the Telnet protocol. RFCs 854-861 define the base protocol. For a complete listing of relevant RFCs, see http://www.omnifarious.org/~hopper/technical/telnet-rfc.html