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68dc0745 | 1 | =head1 NAME |
2 | ||
d92eb7b0 | 3 | perlfaq9 - Networking ($Revision: 1.26 $, $Date: 1999/05/23 16:08:30 $) |
68dc0745 | 4 | |
5 | =head1 DESCRIPTION | |
6 | ||
7 | This section deals with questions related to networking, the internet, | |
8 | and a few on the web. | |
9 | ||
bd3a7847 | 10 | =head2 My CGI script runs from the command line but not the browser. (500 Server Error) |
68dc0745 | 11 | |
c8db1d39 TC |
12 | If you can demonstrate that you've read the following FAQs and that |
13 | your problem isn't something simple that can be easily answered, you'll | |
14 | probably receive a courteous and useful reply to your question if you | |
15 | post it on comp.infosystems.www.authoring.cgi (if it's something to do | |
16 | with HTTP, HTML, or the CGI protocols). Questions that appear to be Perl | |
17 | questions but are really CGI ones that are posted to comp.lang.perl.misc | |
18 | may not be so well received. | |
68dc0745 | 19 | |
c8db1d39 | 20 | The useful FAQs and related documents are: |
68dc0745 | 21 | |
c8db1d39 | 22 | CGI FAQ |
6cecdcac | 23 | http://www.webthing.com/tutorials/cgifaq.html |
68dc0745 | 24 | |
c8db1d39 | 25 | Web FAQ |
92c2ed05 | 26 | http://www.boutell.com/faq/ |
68dc0745 | 27 | |
c8db1d39 TC |
28 | WWW Security FAQ |
29 | http://www.w3.org/Security/Faq/ | |
30 | ||
31 | HTTP Spec | |
32 | http://www.w3.org/pub/WWW/Protocols/HTTP/ | |
33 | ||
34 | HTML Spec | |
35 | http://www.w3.org/TR/REC-html40/ | |
36 | http://www.w3.org/pub/WWW/MarkUp/ | |
37 | ||
38 | CGI Spec | |
39 | http://www.w3.org/CGI/ | |
40 | ||
41 | CGI Security FAQ | |
42 | http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt | |
43 | ||
44 | =head2 How can I get better error messages from a CGI program? | |
45 | ||
46 | Use the CGI::Carp module. It replaces C<warn> and C<die>, plus the | |
47 | normal Carp modules C<carp>, C<croak>, and C<confess> functions with | |
48 | more verbose and safer versions. It still sends them to the normal | |
49 | server error log. | |
50 | ||
51 | use CGI::Carp; | |
52 | warn "This is a complaint"; | |
53 | die "But this one is serious"; | |
54 | ||
55 | The following use of CGI::Carp also redirects errors to a file of your choice, | |
56 | placed in a BEGIN block to catch compile-time warnings as well: | |
57 | ||
58 | BEGIN { | |
59 | use CGI::Carp qw(carpout); | |
60 | open(LOG, ">>/var/local/cgi-logs/mycgi-log") | |
61 | or die "Unable to append to mycgi-log: $!\n"; | |
62 | carpout(*LOG); | |
63 | } | |
64 | ||
65 | You can even arrange for fatal errors to go back to the client browser, | |
66 | which is nice for your own debugging, but might confuse the end user. | |
67 | ||
68 | use CGI::Carp qw(fatalsToBrowser); | |
69 | die "Bad error here"; | |
70 | ||
71 | Even if the error happens before you get the HTTP header out, the module | |
72 | will try to take care of this to avoid the dreaded server 500 errors. | |
73 | Normal warnings still go out to the server error log (or wherever | |
74 | you've sent them with C<carpout>) with the application name and date | |
75 | stamp prepended. | |
76 | ||
68dc0745 | 77 | =head2 How do I remove HTML from a string? |
78 | ||
f29c64d6 | 79 | The most correct way (albeit not the fastest) is to use HTML::Parser |
bed171df | 80 | from CPAN. Another mostly correct |
7d7e76cf MS |
81 | way is to use HTML::FormatText which not only removes HTML but also |
82 | attempts to do a little simple formatting of the resulting plain text. | |
68dc0745 | 83 | |
84 | Many folks attempt a simple-minded regular expression approach, like | |
c47ff5f1 | 85 | C<< s/<.*?>//g >>, but that fails in many cases because the tags |
68dc0745 | 86 | may continue over line breaks, they may contain quoted angle-brackets, |
bd3a7847 GS |
87 | or HTML comment may be present. Plus, folks forget to convert |
88 | entities--like C<<> for example. | |
68dc0745 | 89 | |
90 | Here's one "simple-minded" approach, that works for most files: | |
91 | ||
92 | #!/usr/bin/perl -p0777 | |
93 | s/<(?:[^>'"]*|(['"]).*?\1)*>//gs | |
94 | ||
95 | If you want a more complete solution, see the 3-stage striphtml | |
96 | program in | |
97 | http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/striphtml.gz | |
98 | . | |
99 | ||
c8db1d39 TC |
100 | Here are some tricky cases that you should think about when picking |
101 | a solution: | |
102 | ||
103 | <IMG SRC = "foo.gif" ALT = "A > B"> | |
104 | ||
d92eb7b0 | 105 | <IMG SRC = "foo.gif" |
c8db1d39 TC |
106 | ALT = "A > B"> |
107 | ||
108 | <!-- <A comment> --> | |
109 | ||
110 | <script>if (a<b && a>c)</script> | |
111 | ||
112 | <# Just data #> | |
113 | ||
114 | <![INCLUDE CDATA [ >>>>>>>>>>>> ]]> | |
115 | ||
116 | If HTML comments include other tags, those solutions would also break | |
117 | on text like this: | |
118 | ||
119 | <!-- This section commented out. | |
120 | <B>You can't see me!</B> | |
121 | --> | |
122 | ||
68dc0745 | 123 | =head2 How do I extract URLs? |
124 | ||
54310121 | 125 | A quick but imperfect approach is |
68dc0745 | 126 | |
127 | #!/usr/bin/perl -n00 | |
128 | # qxurl - tchrist@perl.com | |
129 | print "$2\n" while m{ | |
130 | < \s* | |
131 | A \s+ HREF \s* = \s* (["']) (.*?) \1 | |
132 | \s* > | |
133 | }gsix; | |
134 | ||
135 | This version does not adjust relative URLs, understand alternate | |
d92eb7b0 GS |
136 | bases, deal with HTML comments, deal with HREF and NAME attributes |
137 | in the same tag, understand extra qualifiers like TARGET, or accept | |
138 | URLs themselves as arguments. It also runs about 100x faster than a | |
139 | more "complete" solution using the LWP suite of modules, such as the | |
140 | http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/xurl.gz program. | |
68dc0745 | 141 | |
142 | =head2 How do I download a file from the user's machine? How do I open a file on another machine? | |
143 | ||
144 | In the context of an HTML form, you can use what's known as | |
145 | B<multipart/form-data> encoding. The CGI.pm module (available from | |
146 | CPAN) supports this in the start_multipart_form() method, which isn't | |
147 | the same as the startform() method. | |
148 | ||
149 | =head2 How do I make a pop-up menu in HTML? | |
150 | ||
c47ff5f1 | 151 | Use the B<< <SELECT> >> and B<< <OPTION> >> tags. The CGI.pm |
68dc0745 | 152 | module (available from CPAN) supports this widget, as well as many |
153 | others, including some that it cleverly synthesizes on its own. | |
154 | ||
155 | =head2 How do I fetch an HTML file? | |
156 | ||
46fc3d4c | 157 | One approach, if you have the lynx text-based HTML browser installed |
158 | on your system, is this: | |
68dc0745 | 159 | |
160 | $html_code = `lynx -source $url`; | |
161 | $text_data = `lynx -dump $url`; | |
162 | ||
d92eb7b0 GS |
163 | The libwww-perl (LWP) modules from CPAN provide a more powerful way |
164 | to do this. They don't require lynx, but like lynx, can still work | |
165 | through proxies: | |
46fc3d4c | 166 | |
c8db1d39 TC |
167 | # simplest version |
168 | use LWP::Simple; | |
169 | $content = get($URL); | |
170 | ||
171 | # or print HTML from a URL | |
46fc3d4c | 172 | use LWP::Simple; |
6cecdcac | 173 | getprint "http://www.linpro.no/lwp/"; |
46fc3d4c | 174 | |
c8db1d39 | 175 | # or print ASCII from HTML from a URL |
65acb1b1 | 176 | # also need HTML-Tree package from CPAN |
46fc3d4c | 177 | use LWP::Simple; |
f29c64d6 | 178 | use HTML::Parser; |
46fc3d4c | 179 | use HTML::FormatText; |
180 | my ($html, $ascii); | |
181 | $html = get("http://www.perl.com/"); | |
182 | defined $html | |
183 | or die "Can't fetch HTML from http://www.perl.com/"; | |
184 | $ascii = HTML::FormatText->new->format(parse_html($html)); | |
185 | print $ascii; | |
186 | ||
c8db1d39 TC |
187 | =head2 How do I automate an HTML form submission? |
188 | ||
189 | If you're submitting values using the GET method, create a URL and encode | |
190 | the form using the C<query_form> method: | |
191 | ||
192 | use LWP::Simple; | |
193 | use URI::URL; | |
194 | ||
195 | my $url = url('http://www.perl.com/cgi-bin/cpan_mod'); | |
196 | $url->query_form(module => 'DB_File', readme => 1); | |
197 | $content = get($url); | |
198 | ||
199 | If you're using the POST method, create your own user agent and encode | |
200 | the content appropriately. | |
201 | ||
202 | use HTTP::Request::Common qw(POST); | |
203 | use LWP::UserAgent; | |
204 | ||
205 | $ua = LWP::UserAgent->new(); | |
206 | my $req = POST 'http://www.perl.com/cgi-bin/cpan_mod', | |
207 | [ module => 'DB_File', readme => 1 ]; | |
208 | $content = $ua->request($req)->as_string; | |
209 | ||
210 | =head2 How do I decode or create those %-encodings on the web? | |
68dc0745 | 211 | |
212 | Here's an example of decoding: | |
213 | ||
214 | $string = "http://altavista.digital.com/cgi-bin/query?pg=q&what=news&fmt=.&q=%2Bcgi-bin+%2Bperl.exe"; | |
215 | $string =~ s/%([a-fA-F0-9]{2})/chr(hex($1))/ge; | |
216 | ||
217 | Encoding is a bit harder, because you can't just blindly change | |
f1cbbd6e GS |
218 | all characters that are not letters, digits or underscores (C<\W>) |
219 | into their hex escapes. | |
68dc0745 | 220 | It's important that characters with special meaning like C</> and C<?> |
221 | I<not> be translated. Probably the easiest way to get this right is | |
222 | to avoid reinventing the wheel and just use the URI::Escape module, | |
bed171df | 223 | available from CPAN. |
68dc0745 | 224 | |
225 | =head2 How do I redirect to another page? | |
226 | ||
bb2c2f1d GS |
227 | According to RFC 2616, "Hypertext Transfer Protocol -- HTTP/1.1", the |
228 | preferred method is to send a C<Location:> header instead of a | |
229 | C<Content-Type:> header: | |
68dc0745 | 230 | |
231 | Location: http://www.domain.com/newpage | |
68dc0745 | 232 | |
233 | Note that relative URLs in these headers can cause strange effects | |
234 | because of "optimizations" that servers do. | |
235 | ||
c8db1d39 TC |
236 | $url = "http://www.perl.com/CPAN/"; |
237 | print "Location: $url\n\n"; | |
238 | exit; | |
239 | ||
d92eb7b0 GS |
240 | To target a particular frame in a frameset, include the "Window-target:" |
241 | in the header. | |
242 | ||
243 | print <<EOF; | |
244 | Location: http://www.domain.com/newpage | |
245 | Window-target: <FrameName> | |
246 | ||
247 | EOF | |
248 | ||
bd3a7847 GS |
249 | To be correct to the spec, each of those virtual newlines should |
250 | really be physical C<"\015\012"> sequences by the time your message is | |
251 | received by the client browser. Except for NPH scripts, though, that | |
252 | local newline should get translated by your server into standard form, | |
253 | so you shouldn't have a problem here, even if you are stuck on MacOS. | |
254 | Everybody else probably won't even notice. | |
c8db1d39 | 255 | |
68dc0745 | 256 | =head2 How do I put a password on my web pages? |
257 | ||
258 | That depends. You'll need to read the documentation for your web | |
259 | server, or perhaps check some of the other FAQs referenced above. | |
260 | ||
261 | =head2 How do I edit my .htpasswd and .htgroup files with Perl? | |
262 | ||
263 | The HTTPD::UserAdmin and HTTPD::GroupAdmin modules provide a | |
264 | consistent OO interface to these files, regardless of how they're | |
46fc3d4c | 265 | stored. Databases may be text, dbm, Berkley DB or any database with a |
68dc0745 | 266 | DBI compatible driver. HTTPD::UserAdmin supports files used by the |
267 | `Basic' and `Digest' authentication schemes. Here's an example: | |
268 | ||
269 | use HTTPD::UserAdmin (); | |
270 | HTTPD::UserAdmin | |
271 | ->new(DB => "/foo/.htpasswd") | |
272 | ->add($username => $password); | |
273 | ||
46fc3d4c | 274 | =head2 How do I make sure users can't enter values into a form that cause my CGI script to do bad things? |
275 | ||
276 | Read the CGI security FAQ, at | |
bd3a7847 | 277 | http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html , and the |
46fc3d4c | 278 | Perl/CGI FAQ at |
bd3a7847 | 279 | http://www.perl.com/CPAN/doc/FAQs/cgi/perl-cgi-faq.html . |
46fc3d4c | 280 | |
281 | In brief: use tainting (see L<perlsec>), which makes sure that data | |
282 | from outside your script (eg, CGI parameters) are never used in | |
283 | C<eval> or C<system> calls. In addition to tainting, never use the | |
284 | single-argument form of system() or exec(). Instead, supply the | |
285 | command and arguments as a list, which prevents shell globbing. | |
286 | ||
5a964f20 | 287 | =head2 How do I parse a mail header? |
68dc0745 | 288 | |
289 | For a quick-and-dirty solution, try this solution derived | |
bd3a7847 | 290 | from L<perlfunc/split>: |
68dc0745 | 291 | |
292 | $/ = ''; | |
293 | $header = <MSG>; | |
294 | $header =~ s/\n\s+/ /g; # merge continuation lines | |
295 | %head = ( UNIX_FROM_LINE, split /^([-\w]+):\s*/m, $header ); | |
296 | ||
297 | That solution doesn't do well if, for example, you're trying to | |
298 | maintain all the Received lines. A more complete approach is to use | |
299 | the Mail::Header module from CPAN (part of the MailTools package). | |
300 | ||
301 | =head2 How do I decode a CGI form? | |
302 | ||
c8db1d39 TC |
303 | You use a standard module, probably CGI.pm. Under no circumstances |
304 | should you attempt to do so by hand! | |
305 | ||
306 | You'll see a lot of CGI programs that blindly read from STDIN the number | |
307 | of bytes equal to CONTENT_LENGTH for POSTs, or grab QUERY_STRING for | |
308 | decoding GETs. These programs are very poorly written. They only work | |
309 | sometimes. They typically forget to check the return value of the read() | |
310 | system call, which is a cardinal sin. They don't handle HEAD requests. | |
311 | They don't handle multipart forms used for file uploads. They don't deal | |
312 | with GET/POST combinations where query fields are in more than one place. | |
313 | They don't deal with keywords in the query string. | |
314 | ||
315 | In short, they're bad hacks. Resist them at all costs. Please do not be | |
316 | tempted to reinvent the wheel. Instead, use the CGI.pm or CGI_Lite.pm | |
317 | (available from CPAN), or if you're trapped in the module-free land | |
318 | of perl1 .. perl4, you might look into cgi-lib.pl (available from | |
65acb1b1 | 319 | http://cgi-lib.stanford.edu/cgi-lib/ ). |
c8db1d39 TC |
320 | |
321 | Make sure you know whether to use a GET or a POST in your form. | |
322 | GETs should only be used for something that doesn't update the server. | |
323 | Otherwise you can get mangled databases and repeated feedback mail | |
324 | messages. The fancy word for this is ``idempotency''. This simply | |
325 | means that there should be no difference between making a GET request | |
326 | for a particular URL once or multiple times. This is because the | |
327 | HTTP protocol definition says that a GET request may be cached by the | |
328 | browser, or server, or an intervening proxy. POST requests cannot be | |
329 | cached, because each request is independent and matters. Typically, | |
330 | POST requests change or depend on state on the server (query or update | |
331 | a database, send mail, or purchase a computer). | |
68dc0745 | 332 | |
5a964f20 | 333 | =head2 How do I check a valid mail address? |
68dc0745 | 334 | |
c8db1d39 | 335 | You can't, at least, not in real time. Bummer, eh? |
68dc0745 | 336 | |
c8db1d39 TC |
337 | Without sending mail to the address and seeing whether there's a human |
338 | on the other hand to answer you, you cannot determine whether a mail | |
339 | address is valid. Even if you apply the mail header standard, you | |
340 | can have problems, because there are deliverable addresses that aren't | |
341 | RFC-822 (the mail header standard) compliant, and addresses that aren't | |
342 | deliverable which are compliant. | |
68dc0745 | 343 | |
c8db1d39 | 344 | Many are tempted to try to eliminate many frequently-invalid |
d92eb7b0 | 345 | mail addresses with a simple regex, such as |
783a39ac | 346 | C</^[\w.-]+\@([\w.-]\.)+\w+$/>. It's a very bad idea. However, |
c8db1d39 TC |
347 | this also throws out many valid ones, and says nothing about |
348 | potential deliverability, so is not suggested. Instead, see | |
68dc0745 | 349 | http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/ckaddr.gz , |
350 | which actually checks against the full RFC spec (except for nested | |
5a964f20 | 351 | comments), looks for addresses you may not wish to accept mail to |
68dc0745 | 352 | (say, Bill Clinton or your postmaster), and then makes sure that the |
c8db1d39 TC |
353 | hostname given can be looked up in the DNS MX records. It's not fast, |
354 | but it works for what it tries to do. | |
355 | ||
356 | Our best advice for verifying a person's mail address is to have them | |
357 | enter their address twice, just as you normally do to change a password. | |
358 | This usually weeds out typos. If both versions match, send | |
359 | mail to that address with a personal message that looks somewhat like: | |
360 | ||
361 | Dear someuser@host.com, | |
362 | ||
363 | Please confirm the mail address you gave us Wed May 6 09:38:41 | |
364 | MDT 1998 by replying to this message. Include the string | |
365 | "Rumpelstiltskin" in that reply, but spelled in reverse; that is, | |
366 | start with "Nik...". Once this is done, your confirmed address will | |
367 | be entered into our records. | |
368 | ||
369 | If you get the message back and they've followed your directions, | |
370 | you can be reasonably assured that it's real. | |
68dc0745 | 371 | |
c8db1d39 TC |
372 | A related strategy that's less open to forgery is to give them a PIN |
373 | (personal ID number). Record the address and PIN (best that it be a | |
374 | random one) for later processing. In the mail you send, ask them to | |
375 | include the PIN in their reply. But if it bounces, or the message is | |
376 | included via a ``vacation'' script, it'll be there anyway. So it's | |
377 | best to ask them to mail back a slight alteration of the PIN, such as | |
378 | with the characters reversed, one added or subtracted to each digit, etc. | |
46fc3d4c | 379 | |
68dc0745 | 380 | =head2 How do I decode a MIME/BASE64 string? |
381 | ||
382 | The MIME-tools package (available from CPAN) handles this and a lot | |
383 | more. Decoding BASE64 becomes as simple as: | |
384 | ||
385 | use MIME::base64; | |
386 | $decoded = decode_base64($encoded); | |
387 | ||
388 | A more direct approach is to use the unpack() function's "u" | |
389 | format after minor transliterations: | |
390 | ||
391 | tr#A-Za-z0-9+/##cd; # remove non-base64 chars | |
392 | tr#A-Za-z0-9+/# -_#; # convert to uuencoded format | |
393 | $len = pack("c", 32 + 0.75*length); # compute length byte | |
394 | print unpack("u", $len . $_); # uudecode and print | |
395 | ||
5a964f20 | 396 | =head2 How do I return the user's mail address? |
68dc0745 | 397 | |
bd3a7847 | 398 | On systems that support getpwuid, the $< variable, and the |
68dc0745 | 399 | Sys::Hostname module (which is part of the standard perl distribution), |
400 | you can probably try using something like this: | |
401 | ||
402 | use Sys::Hostname; | |
231ab6d1 | 403 | $address = sprintf('%s@%s', scalar getpwuid($<), hostname); |
68dc0745 | 404 | |
5a964f20 TC |
405 | Company policies on mail address can mean that this generates addresses |
406 | that the company's mail system will not accept, so you should ask for | |
407 | users' mail addresses when this matters. Furthermore, not all systems | |
68dc0745 | 408 | on which Perl runs are so forthcoming with this information as is Unix. |
409 | ||
410 | The Mail::Util module from CPAN (part of the MailTools package) provides a | |
411 | mailaddress() function that tries to guess the mail address of the user. | |
412 | It makes a more intelligent guess than the code above, using information | |
413 | given when the module was installed, but it could still be incorrect. | |
414 | Again, the best way is often just to ask the user. | |
415 | ||
c8db1d39 | 416 | =head2 How do I send mail? |
68dc0745 | 417 | |
c8db1d39 TC |
418 | Use the C<sendmail> program directly: |
419 | ||
420 | open(SENDMAIL, "|/usr/lib/sendmail -oi -t -odq") | |
421 | or die "Can't fork for sendmail: $!\n"; | |
422 | print SENDMAIL <<"EOF"; | |
423 | From: User Originating Mail <me\@host> | |
424 | To: Final Destination <you\@otherhost> | |
425 | Subject: A relevant subject line | |
426 | ||
65acb1b1 TC |
427 | Body of the message goes here after the blank line |
428 | in as many lines as you like. | |
c8db1d39 TC |
429 | EOF |
430 | close(SENDMAIL) or warn "sendmail didn't close nicely"; | |
431 | ||
432 | The B<-oi> option prevents sendmail from interpreting a line consisting | |
433 | of a single dot as "end of message". The B<-t> option says to use the | |
434 | headers to decide who to send the message to, and B<-odq> says to put | |
435 | the message into the queue. This last option means your message won't | |
436 | be immediately delivered, so leave it out if you want immediate | |
437 | delivery. | |
438 | ||
d92eb7b0 GS |
439 | Alternate, less convenient approaches include calling mail (sometimes |
440 | called mailx) directly or simply opening up port 25 have having an | |
441 | intimate conversation between just you and the remote SMTP daemon, | |
442 | probably sendmail. | |
443 | ||
444 | Or you might be able use the CPAN module Mail::Mailer: | |
c8db1d39 TC |
445 | |
446 | use Mail::Mailer; | |
447 | ||
448 | $mailer = Mail::Mailer->new(); | |
449 | $mailer->open({ From => $from_address, | |
450 | To => $to_address, | |
451 | Subject => $subject, | |
452 | }) | |
453 | or die "Can't open: $!\n"; | |
454 | print $mailer $body; | |
455 | $mailer->close(); | |
456 | ||
457 | The Mail::Internet module uses Net::SMTP which is less Unix-centric than | |
458 | Mail::Mailer, but less reliable. Avoid raw SMTP commands. There | |
d92eb7b0 | 459 | are many reasons to use a mail transport agent like sendmail. These |
c8db1d39 TC |
460 | include queueing, MX records, and security. |
461 | ||
462 | =head2 How do I read mail? | |
463 | ||
d92eb7b0 GS |
464 | While you could use the Mail::Folder module from CPAN (part of the |
465 | MailFolder package) or the Mail::Internet module from CPAN (also part | |
bd3a7847 | 466 | of the MailTools package), often a module is overkill. Here's a |
d92eb7b0 GS |
467 | mail sorter. |
468 | ||
469 | #!/usr/bin/perl | |
c8db1d39 TC |
470 | # bysub1 - simple sort by subject |
471 | my(@msgs, @sub); | |
472 | my $msgno = -1; | |
473 | $/ = ''; # paragraph reads | |
474 | while (<>) { | |
475 | if (/^From/m) { | |
476 | /^Subject:\s*(?:Re:\s*)*(.*)/mi; | |
477 | $sub[++$msgno] = lc($1) || ''; | |
478 | } | |
479 | $msgs[$msgno] .= $_; | |
d92eb7b0 | 480 | } |
c8db1d39 TC |
481 | for my $i (sort { $sub[$a] cmp $sub[$b] || $a <=> $b } (0 .. $#msgs)) { |
482 | print $msgs[$i]; | |
483 | } | |
484 | ||
d92eb7b0 | 485 | Or more succinctly, |
c8db1d39 TC |
486 | |
487 | #!/usr/bin/perl -n00 | |
488 | # bysub2 - awkish sort-by-subject | |
489 | BEGIN { $msgno = -1 } | |
490 | $sub[++$msgno] = (/^Subject:\s*(?:Re:\s*)*(.*)/mi)[0] if /^From/m; | |
491 | $msg[$msgno] .= $_; | |
492 | END { print @msg[ sort { $sub[$a] cmp $sub[$b] || $a <=> $b } (0 .. $#msg) ] } | |
493 | ||
68dc0745 | 494 | =head2 How do I find out my hostname/domainname/IP address? |
495 | ||
c8db1d39 TC |
496 | The normal way to find your own hostname is to call the C<`hostname`> |
497 | program. While sometimes expedient, this has some problems, such as | |
498 | not knowing whether you've got the canonical name or not. It's one of | |
499 | those tradeoffs of convenience versus portability. | |
68dc0745 | 500 | |
501 | The Sys::Hostname module (part of the standard perl distribution) will | |
502 | give you the hostname after which you can find out the IP address | |
503 | (assuming you have working DNS) with a gethostbyname() call. | |
504 | ||
505 | use Socket; | |
506 | use Sys::Hostname; | |
507 | my $host = hostname(); | |
65acb1b1 | 508 | my $addr = inet_ntoa(scalar gethostbyname($host || 'localhost')); |
68dc0745 | 509 | |
510 | Probably the simplest way to learn your DNS domain name is to grok | |
511 | it out of /etc/resolv.conf, at least under Unix. Of course, this | |
512 | assumes several things about your resolv.conf configuration, including | |
513 | that it exists. | |
514 | ||
515 | (We still need a good DNS domain name-learning method for non-Unix | |
516 | systems.) | |
517 | ||
518 | =head2 How do I fetch a news article or the active newsgroups? | |
519 | ||
520 | Use the Net::NNTP or News::NNTPClient modules, both available from CPAN. | |
bd3a7847 | 521 | This can make tasks like fetching the newsgroup list as simple as |
68dc0745 | 522 | |
523 | perl -MNews::NNTPClient | |
524 | -e 'print News::NNTPClient->new->list("newsgroups")' | |
525 | ||
526 | =head2 How do I fetch/put an FTP file? | |
527 | ||
528 | LWP::Simple (available from CPAN) can fetch but not put. Net::FTP (also | |
529 | available from CPAN) is more complex but can put as well as fetch. | |
530 | ||
531 | =head2 How can I do RPC in Perl? | |
532 | ||
bd3a7847 | 533 | A DCE::RPC module is being developed (but is not yet available) and |
68dc0745 | 534 | will be released as part of the DCE-Perl package (available from |
65acb1b1 TC |
535 | CPAN). The rpcgen suite, available from CPAN/authors/id/JAKE/, is |
536 | an RPC stub generator and includes an RPC::ONC module. | |
68dc0745 | 537 | |
538 | =head1 AUTHOR AND COPYRIGHT | |
539 | ||
65acb1b1 | 540 | Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington. |
5a964f20 TC |
541 | All rights reserved. |
542 | ||
543 | When included as part of the Standard Version of Perl, or as part of | |
544 | its complete documentation whether printed or otherwise, this work | |
d92eb7b0 | 545 | may be distributed only under the terms of Perl's Artistic License. |
5a964f20 TC |
546 | Any distribution of this file or derivatives thereof I<outside> |
547 | of that package require that special arrangements be made with | |
548 | copyright holder. | |
549 | ||
550 | Irrespective of its distribution, all code examples in this file | |
551 | are hereby placed into the public domain. You are permitted and | |
552 | encouraged to use this code in your own programs for fun | |
553 | or for profit as you see fit. A simple comment in the code giving | |
554 | credit would be courteous but is not required. |