MAN page from Mandriva 2007 perl-5.8.8-7.1mdv2007.0.i586.rpm

Net::libnetFAQ

Section: Perl Programmers Reference Guide (3pm)
Updated: 2001-09-21
Index

NAME

libnetFAQ - libnet Frequently Asked Questions

DESCRIPTION

Where to get this document

This document is distributed with the libnet distribution, and is alsoavailable on the libnet web page at

    http://search.cpan.org/~gbarr/libnet/

How to contribute to this document

You may mail corrections, additions, and suggestions to megbarrAATTpobox.com.

Author and Copyright Information

Disclaimer

This information is offered in good faith and in the hope that it maybe of use, but is not guaranteed to be correct, up to date, or suitablefor any particular purpose whatsoever. The authors accept no liabilityin respect of this information or its use.

Obtaining and installing libnet

What is libnet ?

libnet is a collection of perl5 modules which all related to networkprogramming. The majority of the modules available provided theclient side of popular server-client protocols that are used inthe internet community.

Which version of perl do I need ?

libnet has been know to work with versions of perl from 5.002 onwards. Howeverif your release of perl is prior to perl5.004 then you will need toobtain and install the IO distribution from CPAN. If you have perl5.004or later then you will have the IO modules in your installation already,but CPAN may contain updates.

What other modules do I need ?

The only modules you will need installed are the modules from the IOdistribution. If you have perl5.004 or later you will already havethese modules.

What machines support libnet ?

libnet itself is an entirely perl-code distribution so it should workon any machine that perl runs on. However IO may not workwith some machines and earlier releases of perl. But thisshould not be the case with perl version 5.004 or later.

Where can I get the latest libnet release

The latest libnet release is always on CPAN, you will find itin

 http://www.cpan.org/modules/by-module/Net/

The latest release and information is also available on the libnet web pageat

 http://search.cpan.org/~gbarr/libnet/

Using Net::FTP

How do I download files from an FTP server ?

An example taken from an article posted to comp.lang.perl.misc

    #!/your/path/to/perl

    # a module making life easier

    use Net::FTP;

    # for debuging: $ftp = Net::FTP->new('site','Debug',10);    # open a connection and log in!

    $ftp = Net::FTP->new('target_site.somewhere.xxx');    $ftp->login('username','password');

    # set transfer mode to binary

    $ftp->binary();

    # change the directory on the ftp site

    $ftp->cwd('/some/path/to/somewhere/');

    foreach $name ('file1', 'file2', 'file3') {

    # get's arguments are in the following order:    # ftp server's filename    # filename to save the transfer to on the local machine    # can be simply used as get($name) if you want the same name

      $ftp->get($name,$name);    }

    # ftp done!

    $ftp->quit;

How do I transfer files in binary mode ?

To transfer files without <LF><CR> translation Net::FTP providesthe "binary" method

    $ftp->binary;

How can I get the size of a file on a remote FTP server ?

How can I get the modification time of a file on a remote FTP server ?

How can I change the permissions of a file on a remote server ?

The FTP protocol does not have a command for changing the permissionsof a file on the remote server. But some ftp servers may allow a chmodcommand to be issued via a SITE command, eg

    $ftp->quot('site chmod 0777',$filename);

But this is not guaranteed to work.

Can I do a reget operation like the ftp command ?

How do I get a directory listing from an FTP server ?

Changing directory to does not fail ?

Passing an argument of "" to ->cwd() has the same affect of calling ->cwd()without any arguments. Turn on Debug (See below) and you will see what ishappening

    $ftp = Net::FTP->new($host, Debug => 1);    $ftp->login;    $ftp->cwd("");

gives

    Net::FTP=GLOB(0x82196d8)>>> CWD /    Net::FTP=GLOB(0x82196d8)<<< 250 CWD command successful.

I am behind a SOCKS firewall, but the Firewall option does not work ?

The Firewall option is only for support of one type of firewall. The typesupported is an ftp proxy.

To use Net::FTP, or any other module in the libnet distribution,through a SOCKS firewall you must create a socks-ified perl executableby compiling perl with the socks library.

I am behind an FTP proxy firewall, but cannot access machines outside ?

Net::FTP implements the most popular ftp proxy firewall approach. The schemeimplemented is that where you log in to the firewall with "userAATThostname"

I have heard of one other type of firewall which requires a login to thefirewall with an account, then a second login with "userAATThostname". You canstill use Net::FTP to traverse these firewalls, but a more manual approachmust be taken, eg

    $ftp = Net::FTP->new($firewall) or die $@;    $ftp->login($firewall_user, $firewall_passwd) or die $ftp->message;    $ftp->login($ext_user . '@' . $ext_host, $ext_passwd) or die $ftp->message.

My ftp proxy firewall does not listen on port 21

FTP servers usually listen on the same port number, port 21, as any otherFTP server. But there is no reason why this has to be the case.

If you pass a port number to Net::FTP then it assumes this is the portnumber of the final destination. By default Net::FTP will always tryto connect to the firewall on port 21.

Net::FTP uses IO::Socket to open the connection and IO::Socket allowsthe port number to be specified as part of the hostname. So this problemcan be resolved by either passing a Firewall option like "hostname:1234"or by setting the "ftp_firewall" option in Net::Config to be a stringin in the same form.

Is it possible to change the file permissions of a file on an FTP server ?

The answer to this is ``maybe''. The FTP protocol does not specify a command to changefile permissions on a remote host. However many servers do allow you to run thechmod command via the "SITE" command. This can be done with

  $ftp->site('chmod','0775',$file);

I have seen scripts call a method message, but cannot find it documented ?

Net::FTP, like several other packages in libnet, inherits from Net::Cmd, soall the methods described in Net::Cmd are also available on Net::FTPobjects.

Why does Net::FTP not implement mput and mget methods

The quick answer is because they are easy to implement yourself. The longanswer is that to write these in such a way that multiple platforms aresupported correctly would just require too much code. Below aresome examples how you can implement these yourself.

sub mput {
  my($ftp,$pattern) = @_;
  foreach my $file (glob($pattern)) {
    $ftp->put($file) or warn $ftp->message;
  }}

sub mget {
  my($ftp,$pattern) = @_;
  foreach my $file ($ftp->ls($pattern)) {
    $ftp->get($file) or warn $ftp->message;
  }}

Using Net::SMTP

Why can't the part of an Email address after the @ be used as the hostname ?

The part of an Email address which follows the @ is not necessarily a hostname,it is a mail domain. To find the name of a host to connect for a mail domainyou need to do a DNS MX lookup

Why does Net::SMTP not do DNS MX lookups ?

Net::SMTP implements the SMTP protocol. The DNS MX lookup is not partof this protocol.

The verify method always returns true ?

Well it may seem that way, but it does not. The verify method returns trueif the command succeeded. If you pass verify an address which theserver would normally have to forward to another machine, the commandwill succeed with something like

    252 Couldn't verify <someoneAATTthere> but will attempt delivery anyway

This command will fail only if you pass it an address in a domainthe server directly delivers for, and that address does not exist.

Debugging scripts

How can I debug my scripts that use Net::* modules ?

Most of the libnet client classes allow options to be passed to theconstructor, in most cases one option is called "Debug". Passingthis option with a non-zero value will turn on a protocol trace, whichwill be sent to STDERR. This trace can be useful to see what commandsare being sent to the remote server and what responses are beingreceived back.

    #!/your/path/to/perl

    use Net::FTP;

    my $ftp = new Net::FTP($host, Debug => 1);    $ftp->login('gbarr','password');    $ftp->quit;

this script would output something like

 Net::FTP: Net::FTP(2.22) Net::FTP:   Exporter Net::FTP:   Net::Cmd(2.0801) Net::FTP:   IO::Socket::INET Net::FTP:     IO::Socket(1.1603) Net::FTP:       IO::Handle(1.1504)

 Net::FTP=GLOB(0x8152974)<<< 220 imagine FTP server (Version wu-2.4(5) Tue Jul 29 11:17:18 CDT 1997) ready. Net::FTP=GLOB(0x8152974)>>> user gbarr Net::FTP=GLOB(0x8152974)<<< 331 Password required for gbarr. Net::FTP=GLOB(0x8152974)>>> PASS .... Net::FTP=GLOB(0x8152974)<<< 230 User gbarr logged in.  Access restrictions apply. Net::FTP=GLOB(0x8152974)>>> QUIT Net::FTP=GLOB(0x8152974)<<< 221 Goodbye.

The first few lines tell you the modules that Net::FTP uses and their versions,this is useful data to me when a user reports a bug. The last seven linesshow the communication with the server. Each line has three parts. The firstpart is the object itself, this is useful for separating the outputif you are using multiple objects. The second part is either "<<<<" toshow data coming from the server or "&gt&gt&gt&gt" to show datagoing to the server. The remainder of the line is the commandbeing sent or response being received.

AUTHOR AND COPYRIGHT

$Id: //depot/libnet/Net/libnetFAQ.pod#6 $

Index

NAME
DESCRIPTION
Where to get this document
How to contribute to this document
Author and Copyright Information
Disclaimer
Obtaining and installing libnet
What is libnet ?
Which version of perl do I need ?
What other modules do I need ?
What machines support libnet ?
Where can I get the latest libnet release
Using Net::FTP
How do I download files from an FTP server ?
How do I transfer files in binary mode ?
How can I get the size of a file on a remote FTP server ?
How can I get the modification time of a file on a remote FTP server ?
How can I change the permissions of a file on a remote server ?
Can I do a reget operation like the ftp command ?
How do I get a directory listing from an FTP server ?
Changing directory to does not fail ?
I am behind a SOCKS firewall, but the Firewall option does not work ?
I am behind an FTP proxy firewall, but cannot access machines outside ?
My ftp proxy firewall does not listen on port 21
Is it possible to change the file permissions of a file on an FTP server ?
I have seen scripts call a method message, but cannot find it documented ?
Why does Net::FTP not implement mput and mget methods
Using Net::SMTP
Why can't the part of an Email address after the @ be used as the hostname ?
Why does Net::SMTP not do DNS MX lookups ?
The verify method always returns true ?
Debugging scripts
How can I debug my scripts that use Net::* modules ?
AUTHOR AND COPYRIGHT

This document was created byman2html,using the manual pages.