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Net::libnetFAQ(3)      Perl Programmers	Reference Guide	     Net::libnetFAQ(3)

       libnetFAQ - libnet Frequently Asked Questions

   Where to get	this document
       This document is	distributed with the libnet distribution, and is also
       available on the	libnet web page	at

   How to contribute to	this document
       You may report corrections, additions, and suggestions on the CPAN
       Request Tracker at

Author and Copyright Information
       Copyright (C) 1997-1998 Graham Barr.  All rights	reserved.  This
       document	is free; you can redistribute it and/or	modify it under	the
       terms of	the Artistic License.

       Steve Hay <> is now	maintaining libnet as of version

       This information	is offered in good faith and in	the hope that it may
       be of use, but is not guaranteed	to be correct, up to date, or suitable
       for any particular purpose whatsoever.  The authors accept no liability
       in 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 network
       programming. The	majority of the	modules	available provided the client
       side of popular server-client protocols that are	used in	the internet

   Which version of perl do I need ?
       This version of libnet requires Perl 5.8.1 or higher.

   What	other modules do I need	?
       No non-core modules are required	for normal use,	except on os390, which
       requires	Convert::EBCDIC.

       Authen::SASL is required	for AUTH support.

       IO::Socket::SSL version 2.007 or	higher is required for SSL support.

       IO::Socket::IP version 0.25 or IO::Socket::INET6	version	2.62 is
       required	for IPv6 support.

   What	machines support libnet	?
       libnet itself is	an entirely perl-code distribution so it should	work
       on any machine that perl	runs on.

   Where can I get the latest libnet release
       The latest libnet release is always on CPAN, you	will find it in

Using Net::FTP
   How do I download files from	an FTP server ?
       An example taken	from an	article	posted to comp.lang.perl.misc


	   # a module making life easier

	   use Net::FTP;

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

	   $ftp	= Net::FTP->new('');

	   # set transfer mode to binary


	   # change the	directory on the ftp site


	   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 done!


   How do I transfer files in binary mode ?
       To transfer files without <LF><CR> translation Net::FTP provides	the
       "binary"	method


   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 permissions
       of a file on the	remote server. But some	ftp servers may	allow a	chmod
       command 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	is happening

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


	   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
       type supported 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 executable
       by 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
       scheme implemented is that where	you log	in to the firewall with

       I have heard of one other type of firewall which	requires a login to
       the firewall with an account, then a second login with "user@hostname".
       You can still use Net::FTP to traverse these firewalls, but a more
       manual approach must 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
       other FTP 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 port
       number of the final destination.	By default Net::FTP will always	try to
       connect to the firewall on port 21.

       Net::FTP	uses IO::Socket	to open	the connection and IO::Socket allows
       the port	number to be specified as part of the hostname.	So this
       problem can be resolved by either passing a Firewall option like
       "hostname:1234" or by setting the "ftp_firewall"	option in Net::Config
       to be a string 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 change file permissions on a remote host. However many
       servers do allow	you to run the chmod command via the "SITE" command.
       This can	be done	with


   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, so all	the methods described in Net::Cmd are also available
       on Net::FTP objects.

   Why does Net::FTP not implement mput	and mget methods
       The quick answer	is because they	are easy to implement yourself.	The
       long answer is that to write these in such a way	that multiple
       platforms are supported correctly would just require too	much code.
       Below are some 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 domain you 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	part
       of this protocol.

   The verify method always returns true ?
       Well it may seem	that way, but it does not. The verify method returns
       true if the command succeeded. If you pass verify an address which the
       server would normally have to forward to	another	machine, the command
       will succeed with something like

	   252 Couldn't	verify <someone@there> but will	attempt	delivery anyway

       This command will fail only if you pass it an address in	a domain the
       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 the
       constructor, in most cases one option is	called "Debug".	Passing	this
       option with a non-zero value will turn on a protocol trace, which will
       be sent to STDERR. This trace can be useful to see what commands	are
       being sent to the remote	server and what	responses are being received


	   use Net::FTP;

	   my $ftp = new Net::FTP($host, Debug => 1);

       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 lines show	the communication with the server. Each	line has three
       parts. The first	part is	the object itself, this	is useful for
       separating the output if	you are	using multiple objects.	The second
       part is either "<<<<" to	show data coming from the server or
       "&gt&gt&gt&gt" to show data going to the	server.	The remainder of the
       line is the command being sent or response being	received.

       Copyright (C) 1997-1998 Graham Barr.  All rights	reserved.

perl v5.28.3			  2020-05-14		     Net::libnetFAQ(3)

NAME | DESCRIPTION | Author and Copyright Information | Obtaining and installing libnet | Using Net::FTP | Using Net::SMTP | Debugging scripts | AUTHOR AND COPYRIGHT

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