[Perl] Network Programming with Perl - Part 4

Network Programming with Perl

From Issue #60
April 1999

Apr 01, 1999  By James Lee

 in

• Software

Using Perl to make network task is easy—here's how.

Net::Ping Module

Listing 12.

The Net::Ping module makes pinging hosts easy. Listing 12, ping.pl, is a program similar to a program on my server that pings my ISP to keep my connection alive. First, a newNet::Ping object is created. The protocol chosen is tcp (the choices are tcp, udp and icmp; the default is udp). The second argument is the timeout (two seconds). Then an infinite loop is executed, pinging the desired host. Theping() method returns true if the host responds, false otherwise, and an appropriate message is printed. Then the program sleeps ten seconds and pings again.

An example output of Listing 12, ping.pl, is:

Success: Wed Nov  4 14:47:58 1998
Success: Wed Nov  4 14:48:08 1998
Success: Wed Nov  4 14:48:18 1998
Success: Wed Nov  4 14:48:28 1998
Success: Wed Nov  4 14:48:38 1998
Success: Wed Nov  4 14:48:48 1998

Net::Telnet Module

Listing 13.

The Net::Telnet module makes automating TELNET sessions easy. Listing 13, telnet.pl, is an example of connecting to a machine, sending a few system commands and printing the result.

First, a server and a user name are used. The user name defaults to the user running the script by assigning to $user the value $ENV{USER}. (The hash %ENV contains all of the environment variables the script inherits from the shell.)

Next, the password is requested, then read in. Note that turning off the stty echoing is done through a system call. It can also be done using the Term::ReadKeymodule.

Then, a Net::Telnet object is created. To log in to the server using this object, thelogin method is called. Several system commands are executed using the cmdmethod which returns the STDOUT of the system command which is then printed. Note that part of that output is the system prompt, which is printed along with the output of the command.

Also note that the code $tn->cmd('/usr/bin/who') is evaluated in list context and stored in @who, which is an array that contains all the lines of ouptut of that command, one line of output per array element.

After all of the system commands are executed, the TELNET session is closed.

Here is an example output of Listing 13, telnet.pl:

Enter password:

Hostname: server.onsight.com
[james@server james]
Here's who:
james    tty1     Oct 24 21:07
james    ttyp1    Oct 27 20:59 (:0.0)
james    ttyp2    Oct 24 21:11 (:0.0)
james    ttyp6    Oct 28 07:16 (:0.0)
james    ttyp8    Oct 28 19:02 (:0.0)
[james@server james]
What is your command: date
Thu Oct 29 14:39:57 EST 1998
[james@server james]

Net::FTP Module

Listing 14.

The Net::FTP module makes automating FTP sessions easy. Listing 14, ftp.pl, is an example of connecting and getting a file.

A Net::FTP object is created, the login is called to log in to the machine, the cwdchanges the working directory and the get method gets the file. Then the session is terminated with quit.

There are methods to do many common FTP operations: put, binary, rename,delete, etc. To see a list of all the available methods, type:

perldoc Net::FTP

Here is an example output of Listing 14, ftp.pl:

[james@k2 networking]$ ftp.pl server.onsight.com
Enter your password:
Before
----------------------------------------
/bin/ls: *.gz: No such file or directory
----------------------------------------
After
----------------------------------------
perl5.005_51.tar.gz
----------------------------------------

Archive a Web Site

Using both Net::Telnet and Net::FTP, a very simple script can be created that can archive a directory structure on a remote machine.

Listing 15.

Listing 15, taritup.pl, is a Perl program that is similar to a program I use that logs in to my ISP and archives my web site.

The steps this program follows are:

• Start a session on the remote machine with TELNET.

• Go to the web page directory using cd.

• Archive the directory using tar.

• Start an FTP session to the remote machine.

• Change to the directory containing the tar file.

• Get the tar file.

• Quit the FTP session.

• Back in the TELNET session, delete the tar file on the remote machine.

• Close the TELNET session.

This program outputs text to let the user know how the script is progressing.