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
12 available on the libnet web page at
13 http://search.cpan.org/~gbarr/libnet/
15 How to contribute to this document
17 You may mail corrections, additions, and suggestions to me
19 gbarr@pobox.com.
20
22 Copyright (c) 1997-1998 Graham Barr. All rights reserved. This docu‐
23 ment is free; you can redistribute it and/or modify it under the terms
24 of the Artistic License.
25 Disclaimer
27 This information is offered in good faith and in the hope that it may
29 be of use, but is not guaranteed to be correct, up to date, or suitable
30 for any particular purpose whatsoever. The authors accept no liability
31 in respect of this information or its use.
32
34 What is libnet ?
35 libnet is a collection of perl5 modules which all related to network
37 programming. The majority of the modules available provided the client
38 side of popular server-client protocols that are used in the internet
39 community.
40 Which version of perl do I need ?
42 libnet has been know to work with versions of perl from 5.002 onwards.
44 However if your release of perl is prior to perl5.004 then you will
45 need to obtain and install the IO distribution from CPAN. If you have
46 perl5.004 or later then you will have the IO modules in your installa‐
47 tion already, but CPAN may contain updates.
48 What other modules do I need ?
50 The only modules you will need installed are the modules from the IO
52 distribution. If you have perl5.004 or later you will already have
53 these modules.
54 What machines support libnet ?
56 libnet itself is an entirely perl-code distribution so it should work
58 on any machine that perl runs on. However IO may not work with some
59 machines and earlier releases of perl. But this should not be the case
60 with perl version 5.004 or later.
61 Where can I get the latest libnet release
63 The latest libnet release is always on CPAN, you will find it in
65 http://www.cpan.org/modules/by-module/Net/
67 The latest release and information is also available on the libnet web
69 page at
70 http://search.cpan.org/~gbarr/libnet/
72
74 How do I download files from an FTP server ?
75 An example taken from an article posted to comp.lang.perl.misc
77 #!/your/path/to/perl
79 # a module making life easier
81 use Net::FTP;
83 # for debuging: $ftp = Net::FTP->new('site','Debug',10);
85 # open a connection and log in!
86 $ftp = Net::FTP->new('target_site.somewhere.xxx');
88 $ftp->login('username','password');
89 # set transfer mode to binary
91 $ftp->binary();
93 # change the directory on the ftp site
95 $ftp->cwd('/some/path/to/somewhere/');
97 foreach $name ('file1', 'file2', 'file3') {
99 # get's arguments are in the following order:
101 # ftp server's filename
102 # filename to save the transfer to on the local machine
103 # can be simply used as get($name) if you want the same name
104 $ftp->get($name,$name);
106 }
107 # ftp done!
109 $ftp->quit;
111 How do I transfer files in binary mode ?
113 To transfer files without <LF><CR> translation Net::FTP provides the
115 "binary" method
116 $ftp->binary;
118 How can I get the size of a file on a remote FTP server ?
120 How can I get the modification time of a file on a remote FTP server ?
122 How can I change the permissions of a file on a remote server ?
124 The FTP protocol does not have a command for changing the permissions
126 of a file on the remote server. But some ftp servers may allow a chmod
127 command to be issued via a SITE command, eg
128 $ftp->quot('site chmod 0777',$filename);
130 But this is not guaranteed to work.
132 Can I do a reget operation like the ftp command ?
134 How do I get a directory listing from an FTP server ?
136 Changing directory to "" does not fail ?
138 Passing an argument of "" to ->cwd() has the same affect of calling
140 ->cwd() without any arguments. Turn on Debug (See below) and you will
141 see what is happening
142 $ftp = Net::FTP->new($host, Debug => 1);
144 $ftp->login;
145 $ftp->cwd("");
146 gives
148 Net::FTP=GLOB(0x82196d8)>>> CWD /
150 Net::FTP=GLOB(0x82196d8)<<< 250 CWD command successful.
151 I am behind a SOCKS firewall, but the Firewall option does not work ?
153 The Firewall option is only for support of one type of firewall. The
155 type supported is an ftp proxy.
156 To use Net::FTP, or any other module in the libnet distribution,
158 through a SOCKS firewall you must create a socks-ified perl executable
159 by compiling perl with the socks library.
160 I am behind an FTP proxy firewall, but cannot access machines outside ?
162 Net::FTP implements the most popular ftp proxy firewall approach. The
164 scheme implemented is that where you log in to the firewall with
165 "user@hostname"
166 I have heard of one other type of firewall which requires a login to
168 the firewall with an account, then a second login with "user@hostname".
169 You can still use Net::FTP to traverse these firewalls, but a more man‐
170 ual approach must be taken, eg
171 $ftp = Net::FTP->new($firewall) or die $@;
173 $ftp->login($firewall_user, $firewall_passwd) or die $ftp->message;
174 $ftp->login($ext_user . '@' . $ext_host, $ext_passwd) or die $ftp->message.
175 My ftp proxy firewall does not listen on port 21
177 FTP servers usually listen on the same port number, port 21, as any
179 other FTP server. But there is no reason why this has to be the case.
180 If you pass a port number to Net::FTP then it assumes this is the port
182 number of the final destination. By default Net::FTP will always try to
183 connect to the firewall on port 21.
184 Net::FTP uses IO::Socket to open the connection and IO::Socket allows
186 the port number to be specified as part of the hostname. So this prob‐
187 lem can be resolved by either passing a Firewall option like "host‐
188 name:1234" or by setting the "ftp_firewall" option in Net::Config to be
189 a string in in the same form.
190 Is it possible to change the file permissions of a file on an FTP
192 server ?
193 The answer to this is "maybe". The FTP protocol does not specify a com‐
195 mand to change file permissions on a remote host. However many servers
196 do allow you to run the chmod command via the "SITE" command. This can
197 be done with
198 $ftp->site('chmod','0775',$file);
200 I have seen scripts call a method message, but cannot find it docu‐
202 mented ?
203 Net::FTP, like several other packages in libnet, inherits from
205 Net::Cmd, so all the methods described in Net::Cmd are also available
206 on Net::FTP objects.
207 Why does Net::FTP not implement mput and mget methods
209 The quick answer is because they are easy to implement yourself. The
211 long answer is that to write these in such a way that multiple plat‐
212 forms are supported correctly would just require too much code. Below
213 are some examples how you can implement these yourself.
214 sub mput {
216 my($ftp,$pattern) = @_;
217 foreach my $file (glob($pattern)) {
218 $ftp->put($file) or warn $ftp->message;
219 } }
220 sub mget {
222 my($ftp,$pattern) = @_;
223 foreach my $file ($ftp->ls($pattern)) {
224 $ftp->get($file) or warn $ftp->message;
225 } }
226
228 Why can't the part of an Email address after the @ be used as the host‐
229 name ?
230 The part of an Email address which follows the @ is not necessarily a
232 hostname, it is a mail domain. To find the name of a host to connect
233 for a mail domain you need to do a DNS MX lookup
234 Why does Net::SMTP not do DNS MX lookups ?
236 Net::SMTP implements the SMTP protocol. The DNS MX lookup is not part
238 of this protocol.
239 The verify method always returns true ?
241 Well it may seem that way, but it does not. The verify method returns
243 true if the command succeeded. If you pass verify an address which the
244 server would normally have to forward to another machine, the command
245 will succeed with something like
246 252 Couldn't verify <someone@there> but will attempt delivery anyway
248 This command will fail only if you pass it an address in a domain the
250 server directly delivers for, and that address does not exist.
251
253 How can I debug my scripts that use Net::* modules ?
254 Most of the libnet client classes allow options to be passed to the
256 constructor, in most cases one option is called "Debug". Passing this
257 option with a non-zero value will turn on a protocol trace, which will
258 be sent to STDERR. This trace can be useful to see what commands are
259 being sent to the remote server and what responses are being received
260 back.
261 #!/your/path/to/perl
263 use Net::FTP;
265 my $ftp = new Net::FTP($host, Debug => 1);
267 $ftp->login('gbarr','password');
268 $ftp->quit;
269 this script would output something like
271 Net::FTP: Net::FTP(2.22)
273 Net::FTP: Exporter
274 Net::FTP: Net::Cmd(2.0801)
275 Net::FTP: IO::Socket::INET
276 Net::FTP: IO::Socket(1.1603)
277 Net::FTP: IO::Handle(1.1504)
278 Net::FTP=GLOB(0x8152974)<<< 220 imagine FTP server (Version wu-2.4(5) Tue Jul 29 11:17:18 CDT 1997) ready.
280 Net::FTP=GLOB(0x8152974)>>> user gbarr
281 Net::FTP=GLOB(0x8152974)<<< 331 Password required for gbarr.
282 Net::FTP=GLOB(0x8152974)>>> PASS ....
283 Net::FTP=GLOB(0x8152974)<<< 230 User gbarr logged in. Access restrictions apply.
284 Net::FTP=GLOB(0x8152974)>>> QUIT
285 Net::FTP=GLOB(0x8152974)<<< 221 Goodbye.
286 The first few lines tell you the modules that Net::FTP uses and their
288 versions, this is useful data to me when a user reports a bug. The last
289 seven lines show the communication with the server. Each line has three
290 parts. The first part is the object itself, this is useful for separat‐
291 ing the output if you are using multiple objects. The second part is
292 either "<<<<" to show data coming from the server or ">>>>" to
293 show data going to the server. The remainder of the line is the command
294 being sent or response being received.
295
297 Copyright (c) 1997 Graham Barr. All rights reserved.
298 $Id: //depot/libnet/Net/libnetFAQ.pod#6 $
300perl v5.8.8 2001-09-21 Net::libnetFAQ(3pm)