1Net::libnetFAQ(3pm) Perl Programmers Reference Guide Net::libnetFAQ(3pm)
2
6 libnetFAQ - libnet Frequently Asked Questions
7
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 http://search.cpan.org/~gbarr/libnet/
14 How to contribute to this document
16 You may mail corrections, additions, and suggestions to me
17 gbarr@pobox.com.
18
20 Copyright (c) 1997-1998 Graham Barr. All rights reserved. This
21 document is free; you can redistribute it and/or modify it under the
22 terms of the Artistic License.
23 Disclaimer
25 This information is offered in good faith and in the hope that it may
26 be of use, but is not guaranteed to be correct, up to date, or suitable
27 for any particular purpose whatsoever. The authors accept no liability
28 in respect of this information or its use.
29
31 What is libnet ?
32 libnet is a collection of perl5 modules which all related to network
33 programming. The majority of the modules available provided the client
34 side of popular server-client protocols that are used in the internet
35 community.
36 Which version of perl do I need ?
38 libnet has been know to work with versions of perl from 5.002 onwards.
39 However if your release of perl is prior to perl5.004 then you will
40 need to obtain and install the IO distribution from CPAN. If you have
41 perl5.004 or later then you will have the IO modules in your
42 installation already, but CPAN may contain updates.
43 What other modules do I need ?
45 The only modules you will need installed are the modules from the IO
46 distribution. If you have perl5.004 or later you will already have
47 these modules.
48 What machines support libnet ?
50 libnet itself is an entirely perl-code distribution so it should work
51 on any machine that perl runs on. However IO may not work with some
52 machines and earlier releases of perl. But this should not be the case
53 with perl version 5.004 or later.
54 Where can I get the latest libnet release
56 The latest libnet release is always on CPAN, you will find it in
57 http://www.cpan.org/modules/by-module/Net/
59 The latest release and information is also available on the libnet web
61 page at
62 http://search.cpan.org/~gbarr/libnet/
64
66 How do I download files from an FTP server ?
67 An example taken from an article posted to comp.lang.perl.misc
68 #!/your/path/to/perl
70 # a module making life easier
72 use Net::FTP;
74 # for debugging: $ftp = Net::FTP->new('site','Debug',10);
76 # open a connection and log in!
77 $ftp = Net::FTP->new('target_site.somewhere.xxx');
79 $ftp->login('username','password');
80 # set transfer mode to binary
82 $ftp->binary();
84 # change the directory on the ftp site
86 $ftp->cwd('/some/path/to/somewhere/');
88 foreach $name ('file1', 'file2', 'file3') {
90 # get's arguments are in the following order:
92 # ftp server's filename
93 # filename to save the transfer to on the local machine
94 # can be simply used as get($name) if you want the same name
95 $ftp->get($name,$name);
97 }
98 # ftp done!
100 $ftp->quit;
102 How do I transfer files in binary mode ?
104 To transfer files without <LF><CR> translation Net::FTP provides the
105 "binary" method
106 $ftp->binary;
108 How can I get the size of a file on a remote FTP server ?
110 How can I get the modification time of a file on a remote FTP server ?
111 How can I change the permissions of a file on a remote server ?
112 The FTP protocol does not have a command for changing the permissions
113 of a file on the remote server. But some ftp servers may allow a chmod
114 command to be issued via a SITE command, eg
115 $ftp->quot('site chmod 0777',$filename);
117 But this is not guaranteed to work.
119 Can I do a reget operation like the ftp command ?
121 How do I get a directory listing from an FTP server ?
122 Changing directory to "" does not fail ?
123 Passing an argument of "" to ->cwd() has the same affect of calling
124 ->cwd() without any arguments. Turn on Debug (See below) and you will
125 see what is happening
126 $ftp = Net::FTP->new($host, Debug => 1);
128 $ftp->login;
129 $ftp->cwd("");
130 gives
132 Net::FTP=GLOB(0x82196d8)>>> CWD /
134 Net::FTP=GLOB(0x82196d8)<<< 250 CWD command successful.
135 I am behind a SOCKS firewall, but the Firewall option does not work ?
137 The Firewall option is only for support of one type of firewall. The
138 type supported is an ftp proxy.
139 To use Net::FTP, or any other module in the libnet distribution,
141 through a SOCKS firewall you must create a socks-ified perl executable
142 by compiling perl with the socks library.
143 I am behind an FTP proxy firewall, but cannot access machines outside ?
145 Net::FTP implements the most popular ftp proxy firewall approach. The
146 scheme implemented is that where you log in to the firewall with
147 "user@hostname"
148 I have heard of one other type of firewall which requires a login to
150 the firewall with an account, then a second login with "user@hostname".
151 You can still use Net::FTP to traverse these firewalls, but a more
152 manual approach must be taken, eg
153 $ftp = Net::FTP->new($firewall) or die $@;
155 $ftp->login($firewall_user, $firewall_passwd) or die $ftp->message;
156 $ftp->login($ext_user . '@' . $ext_host, $ext_passwd) or die $ftp->message.
157 My ftp proxy firewall does not listen on port 21
159 FTP servers usually listen on the same port number, port 21, as any
160 other FTP server. But there is no reason why this has to be the case.
161 If you pass a port number to Net::FTP then it assumes this is the port
163 number of the final destination. By default Net::FTP will always try to
164 connect to the firewall on port 21.
165 Net::FTP uses IO::Socket to open the connection and IO::Socket allows
167 the port number to be specified as part of the hostname. So this
168 problem can be resolved by either passing a Firewall option like
169 "hostname:1234" or by setting the "ftp_firewall" option in Net::Config
170 to be a string in in the same form.
171 Is it possible to change the file permissions of a file on an FTP server ?
173 The answer to this is "maybe". The FTP protocol does not specify a
174 command to change file permissions on a remote host. However many
175 servers do allow you to run the chmod command via the "SITE" command.
176 This can be done with
177 $ftp->site('chmod','0775',$file);
179 I have seen scripts call a method message, but cannot find it documented ?
181 Net::FTP, like several other packages in libnet, inherits from
182 Net::Cmd, so all the methods described in Net::Cmd are also available
183 on Net::FTP objects.
184 Why does Net::FTP not implement mput and mget methods
186 The quick answer is because they are easy to implement yourself. The
187 long answer is that to write these in such a way that multiple
188 platforms are supported correctly would just require too much code.
189 Below are some examples how you can implement these yourself.
190 sub mput {
192 my($ftp,$pattern) = @_;
193 foreach my $file (glob($pattern)) {
194 $ftp->put($file) or warn $ftp->message;
195 } }
196 sub mget {
198 my($ftp,$pattern) = @_;
199 foreach my $file ($ftp->ls($pattern)) {
200 $ftp->get($file) or warn $ftp->message;
201 } }
202
204 Why can't the part of an Email address after the @ be used as the hostname
205 ?
206 The part of an Email address which follows the @ is not necessarily a
207 hostname, it is a mail domain. To find the name of a host to connect
208 for a mail domain you need to do a DNS MX lookup
209 Why does Net::SMTP not do DNS MX lookups ?
211 Net::SMTP implements the SMTP protocol. The DNS MX lookup is not part
212 of this protocol.
213 The verify method always returns true ?
215 Well it may seem that way, but it does not. The verify method returns
216 true if the command succeeded. If you pass verify an address which the
217 server would normally have to forward to another machine, the command
218 will succeed with something like
219 252 Couldn't verify <someone@there> but will attempt delivery anyway
221 This command will fail only if you pass it an address in a domain the
223 server directly delivers for, and that address does not exist.
224
226 How can I debug my scripts that use Net::* modules ?
227 Most of the libnet client classes allow options to be passed to the
228 constructor, in most cases one option is called "Debug". Passing this
229 option with a non-zero value will turn on a protocol trace, which will
230 be sent to STDERR. This trace can be useful to see what commands are
231 being sent to the remote server and what responses are being received
232 back.
233 #!/your/path/to/perl
235 use Net::FTP;
237 my $ftp = new Net::FTP($host, Debug => 1);
239 $ftp->login('gbarr','password');
240 $ftp->quit;
241 this script would output something like
243 Net::FTP: Net::FTP(2.22)
245 Net::FTP: Exporter
246 Net::FTP: Net::Cmd(2.0801)
247 Net::FTP: IO::Socket::INET
248 Net::FTP: IO::Socket(1.1603)
249 Net::FTP: IO::Handle(1.1504)
250 Net::FTP=GLOB(0x8152974)<<< 220 imagine FTP server (Version wu-2.4(5) Tue Jul 29 11:17:18 CDT 1997) ready.
252 Net::FTP=GLOB(0x8152974)>>> user gbarr
253 Net::FTP=GLOB(0x8152974)<<< 331 Password required for gbarr.
254 Net::FTP=GLOB(0x8152974)>>> PASS ....
255 Net::FTP=GLOB(0x8152974)<<< 230 User gbarr logged in. Access restrictions apply.
256 Net::FTP=GLOB(0x8152974)>>> QUIT
257 Net::FTP=GLOB(0x8152974)<<< 221 Goodbye.
258 The first few lines tell you the modules that Net::FTP uses and their
260 versions, this is useful data to me when a user reports a bug. The last
261 seven lines show the communication with the server. Each line has three
262 parts. The first part is the object itself, this is useful for
263 separating the output if you are using multiple objects. The second
264 part is either "<<<<" to show data coming from the server or
265 ">>>>" to show data going to the server. The remainder of the
266 line is the command being sent or response being received.
267
269 Copyright (c) 1997 Graham Barr. All rights reserved.
270perl v5.16.3 2013-02-26 Net::libnetFAQ(3pm)