1Net::libnetFAQ(3)     User Contributed Perl Documentation    Net::libnetFAQ(3)
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NAME

6       libnetFAQ - libnet Frequently Asked Questions
7

DESCRIPTION

9   Where to get this document
10       This document is distributed with the libnet distribution, and is also
11       available on the libnet web page at
12
13       <https://metacpan.org/release/libnet>
14
15   How to contribute to this document
16       You may report corrections, additions, and suggestions on the CPAN
17       Request Tracker at
18
19       <https://rt.cpan.org/Public/Bug/Report.html?Queue=libnet>
20
22       Copyright (C) 1997-1998 Graham Barr.  All rights reserved.  This
23       document is free; you can redistribute it and/or modify it under the
24       same terms as Perl itself, i.e. under the terms of either the GNU
25       General Public License or the Artistic License, as specified in the
26       LICENCE file.
27
28       Steve Hay <shay@cpan.org <mailto:shay@cpan.org>> is now maintaining
29       libnet as of version 1.22_02.
30
31   Disclaimer
32       This information is offered in good faith and in the hope that it may
33       be of use, but is not guaranteed to be correct, up to date, or suitable
34       for any particular purpose whatsoever.  The authors accept no liability
35       in respect of this information or its use.
36

Obtaining and installing libnet

38   What is libnet ?
39       libnet is a collection of perl5 modules which all related to network
40       programming. The majority of the modules available provided the client
41       side of popular server-client protocols that are used in the internet
42       community.
43
44   Which version of perl do I need ?
45       This version of libnet requires Perl 5.8.1 or higher.
46
47   What other modules do I need ?
48       No non-core modules are required for normal use, except on os390, which
49       requires Convert::EBCDIC.
50
51       Authen::SASL is required for AUTH support.
52
53       IO::Socket::SSL version 2.007 or higher is required for SSL support.
54
55       IO::Socket::IP version 0.25 or IO::Socket::INET6 version 2.62 is
56       required for IPv6 support.
57
58   What machines support libnet ?
59       libnet itself is an entirely perl-code distribution so it should work
60       on any machine that perl runs on.
61
62   Where can I get the latest libnet release
63       The latest libnet release is always on CPAN, you will find it in
64
65       <https://metacpan.org/release/libnet>
66

Using Net::FTP

68   How do I download files from an FTP server ?
69       An example taken from an article posted to comp.lang.perl.misc
70
71           #!/your/path/to/perl
72
73           # a module making life easier
74
75           use Net::FTP;
76
77           # for debugging: $ftp = Net::FTP->new('site','Debug',10);
78           # open a connection and log in!
79
80           $ftp = Net::FTP->new('target_site.somewhere.xxx');
81           $ftp->login('username','password');
82
83           # set transfer mode to binary
84
85           $ftp->binary();
86
87           # change the directory on the ftp site
88
89           $ftp->cwd('/some/path/to/somewhere/');
90
91           foreach $name ('file1', 'file2', 'file3') {
92
93           # get's arguments are in the following order:
94           # ftp server's filename
95           # filename to save the transfer to on the local machine
96           # can be simply used as get($name) if you want the same name
97
98             $ftp->get($name,$name);
99           }
100
101           # ftp done!
102
103           $ftp->quit;
104
105   How do I transfer files in binary mode ?
106       To transfer files without <LF><CR> translation Net::FTP provides the
107       "binary" method
108
109           $ftp->binary;
110
111   How can I get the size of a file on a remote FTP server ?
112   How can I get the modification time of a file on a remote FTP server ?
113   How can I change the permissions of a file on a remote server ?
114       The FTP protocol does not have a command for changing the permissions
115       of a file on the remote server. But some ftp servers may allow a chmod
116       command to be issued via a SITE command, eg
117
118           $ftp->quot('site chmod 0777',$filename);
119
120       But this is not guaranteed to work.
121
122   Can I do a reget operation like the ftp command ?
123   How do I get a directory listing from an FTP server ?
124   Changing directory to "" does not fail ?
125       Passing an argument of "" to ->cwd() has the same affect of calling
126       ->cwd() without any arguments. Turn on Debug (See below) and you will
127       see what is happening
128
129           $ftp = Net::FTP->new($host, Debug => 1);
130           $ftp->login;
131           $ftp->cwd("");
132
133       gives
134
135           Net::FTP=GLOB(0x82196d8)>>> CWD /
136           Net::FTP=GLOB(0x82196d8)<<< 250 CWD command successful.
137
138   I am behind a SOCKS firewall, but the Firewall option does not work ?
139       The Firewall option is only for support of one type of firewall. The
140       type supported is an ftp proxy.
141
142       To use Net::FTP, or any other module in the libnet distribution,
143       through a SOCKS firewall you must create a socks-ified perl executable
144       by compiling perl with the socks library.
145
146   I am behind an FTP proxy firewall, but cannot access machines outside ?
147       Net::FTP implements the most popular ftp proxy firewall approach. The
148       scheme implemented is that where you log in to the firewall with
149       "user@hostname"
150
151       I have heard of one other type of firewall which requires a login to
152       the firewall with an account, then a second login with "user@hostname".
153       You can still use Net::FTP to traverse these firewalls, but a more
154       manual approach must be taken, eg
155
156           $ftp = Net::FTP->new($firewall) or die $@;
157           $ftp->login($firewall_user, $firewall_passwd) or die $ftp->message;
158           $ftp->login($ext_user . '@' . $ext_host, $ext_passwd) or die $ftp->message.
159
160   My ftp proxy firewall does not listen on port 21
161       FTP servers usually listen on the same port number, port 21, as any
162       other FTP server. But there is no reason why this has to be the case.
163
164       If you pass a port number to Net::FTP then it assumes this is the port
165       number of the final destination. By default Net::FTP will always try to
166       connect to the firewall on port 21.
167
168       Net::FTP uses IO::Socket to open the connection and IO::Socket allows
169       the port number to be specified as part of the hostname. So this
170       problem can be resolved by either passing a Firewall option like
171       "hostname:1234" or by setting the "ftp_firewall" option in Net::Config
172       to be a string in the same form.
173
174   Is it possible to change the file permissions of a file on an FTP server ?
175       The answer to this is "maybe". The FTP protocol does not specify a
176       command to change file permissions on a remote host. However many
177       servers do allow you to run the chmod command via the "SITE" command.
178       This can be done with
179
180         $ftp->site('chmod','0775',$file);
181
182   I have seen scripts call a method message, but cannot find it documented ?
183       Net::FTP, like several other packages in libnet, inherits from
184       Net::Cmd, so all the methods described in Net::Cmd are also available
185       on Net::FTP objects.
186
187   Why does Net::FTP not implement mput and mget methods
188       The quick answer is because they are easy to implement yourself. The
189       long answer is that to write these in such a way that multiple
190       platforms are supported correctly would just require too much code.
191       Below are some examples how you can implement these yourself.
192
193       sub mput {
194         my($ftp,$pattern) = @_;
195         foreach my $file (glob($pattern)) {
196           $ftp->put($file) or warn $ftp->message;
197         } }
198
199       sub mget {
200         my($ftp,$pattern) = @_;
201         foreach my $file ($ftp->ls($pattern)) {
202           $ftp->get($file) or warn $ftp->message;
203         } }
204

Using Net::SMTP

206   Why can't the part of an Email address after the @ be used as the hostname
207       ?
208       The part of an Email address which follows the @ is not necessarily a
209       hostname, it is a mail domain. To find the name of a host to connect
210       for a mail domain you need to do a DNS MX lookup
211
212   Why does Net::SMTP not do DNS MX lookups ?
213       Net::SMTP implements the SMTP protocol. The DNS MX lookup is not part
214       of this protocol.
215
216   The verify method always returns true ?
217       Well it may seem that way, but it does not. The verify method returns
218       true if the command succeeded. If you pass verify an address which the
219       server would normally have to forward to another machine, the command
220       will succeed with something like
221
222           252 Couldn't verify <someone@there> but will attempt delivery anyway
223
224       This command will fail only if you pass it an address in a domain the
225       server directly delivers for, and that address does not exist.
226

Debugging scripts

228   How can I debug my scripts that use Net::* modules ?
229       Most of the libnet client classes allow options to be passed to the
230       constructor, in most cases one option is called "Debug". Passing this
231       option with a non-zero value will turn on a protocol trace, which will
232       be sent to STDERR. This trace can be useful to see what commands are
233       being sent to the remote server and what responses are being received
234       back.
235
236           #!/your/path/to/perl
237
238           use Net::FTP;
239
240           my $ftp = new Net::FTP($host, Debug => 1);
241           $ftp->login('gbarr','password');
242           $ftp->quit;
243
244       this script would output something like
245
246        Net::FTP: Net::FTP(2.22)
247        Net::FTP:   Exporter
248        Net::FTP:   Net::Cmd(2.0801)
249        Net::FTP:   IO::Socket::INET
250        Net::FTP:     IO::Socket(1.1603)
251        Net::FTP:       IO::Handle(1.1504)
252
253        Net::FTP=GLOB(0x8152974)<<< 220 imagine FTP server (Version wu-2.4(5) Tue Jul 29 11:17:18 CDT 1997) ready.
254        Net::FTP=GLOB(0x8152974)>>> user gbarr
255        Net::FTP=GLOB(0x8152974)<<< 331 Password required for gbarr.
256        Net::FTP=GLOB(0x8152974)>>> PASS ....
257        Net::FTP=GLOB(0x8152974)<<< 230 User gbarr logged in.  Access restrictions apply.
258        Net::FTP=GLOB(0x8152974)>>> QUIT
259        Net::FTP=GLOB(0x8152974)<<< 221 Goodbye.
260
261       The first few lines tell you the modules that Net::FTP uses and their
262       versions, this is useful data to me when a user reports a bug. The last
263       seven lines show the communication with the server. Each line has three
264       parts. The first part is the object itself, this is useful for
265       separating the output if you are using multiple objects. The second
266       part is either "<<<<" to show data coming from the server or
267       "&gt&gt&gt&gt" to show data going to the server. The remainder of the
268       line is the command being sent or response being received.
269
271       Copyright (C) 1997-1998 Graham Barr.  All rights reserved.
272
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275perl v5.36.0                      2022-07-22                 Net::libnetFAQ(3)
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