This section deals with questions related to networking, the internet,
and a few on the web.
-=head2 My CGI script runs from the command line but not the browser. (500 Server Error)
+=head2 My CGI script runs from the command line but not the browser. (500 Server Error)
If you can demonstrate that you've read the following FAQs and that
your problem isn't something simple that can be easily answered, you'll
The useful FAQs and related documents are:
CGI FAQ
- http://www.webthing.com/page.cgi/cgifaq
+ http://www.webthing.com/tutorials/cgifaq.html
Web FAQ
http://www.boutell.com/faq/
=head2 How do I remove HTML from a string?
The most correct way (albeit not the fastest) is to use HTML::Parser
-from CPAN (part of the HTML-Tree package on CPAN). Another correct
+from CPAN. Another mostly correct
way is to use HTML::FormatText which not only removes HTML but also
attempts to do a little simple formatting of the resulting plain text.
Many folks attempt a simple-minded regular expression approach, like
-C<s/E<lt>.*?E<gt>//g>, but that fails in many cases because the tags
+C<< s/<.*?>//g >>, but that fails in many cases because the tags
may continue over line breaks, they may contain quoted angle-brackets,
-or HTML comment may be present. Plus folks forget to convert
-entities, like C<<> for example.
+or HTML comment may be present. Plus, folks forget to convert
+entities--like C<<> for example.
Here's one "simple-minded" approach, that works for most files:
=head2 How do I make a pop-up menu in HTML?
-Use the B<E<lt>SELECTE<gt>> and B<E<lt>OPTIONE<gt>> tags. The CGI.pm
+Use the B<< <SELECT> >> and B<< <OPTION> >> tags. The CGI.pm
module (available from CPAN) supports this widget, as well as many
others, including some that it cleverly synthesizes on its own.
# or print HTML from a URL
use LWP::Simple;
- getprint "http://www.sn.no/libwww-perl/";
+ getprint "http://www.linpro.no/lwp/";
# or print ASCII from HTML from a URL
# also need HTML-Tree package from CPAN
=head2 How do I decode or create those %-encodings on the web?
-Here's an example of decoding:
- $string = "http://altavista.digital.com/cgi-bin/query?pg=q&what=news&fmt=.&q=%2Bcgi-bin+%2Bperl.exe";
- $string =~ s/%([a-fA-F0-9]{2})/chr(hex($1))/ge;
+If you are writing a CGI script, you should be using the CGI.pm module
+that comes with perl, or some other equivalent module. The CGI module
+automatically decodes queries for you, and provides an escape()
+function to handle encoding.
-Encoding is a bit harder, because you can't just blindly change
-all the non-alphanumunder character (C<\W>) into their hex escapes.
-It's important that characters with special meaning like C</> and C<?>
-I<not> be translated. Probably the easiest way to get this right is
-to avoid reinventing the wheel and just use the URI::Escape module,
-which is part of the libwww-perl package (LWP) available from CPAN.
+
+The best source of detailed information on URI encoding is RFC 2396.
+Basically, the following substitutions do it:
+
+ s/([^\w()'*~!.-])/sprintf '%%%02x', $1/eg; # encode
+
+ s/%([A-Fa-f\d]{2})/chr hex $1/eg; # decode
+
+However, you should only apply them to individual URI components, not
+the entire URI, otherwise you'll lose information and generally mess
+things up. If that didn't explain it, don't worry. Just go read
+section 2 of the RFC, it's probably the best explanation there is.
+
+RFC 2396 also contains a lot of other useful information, including a
+regexp for breaking any arbitrary URI into components (Appendix B).
=head2 How do I redirect to another page?
-Instead of sending back a C<Content-Type> as the headers of your
-reply, send back a C<Location:> header. Officially this should be a
-C<URI:> header, so the CGI.pm module (available from CPAN) sends back
-both:
+According to RFC 2616, "Hypertext Transfer Protocol -- HTTP/1.1", the
+preferred method is to send a C<Location:> header instead of a
+C<Content-Type:> header:
Location: http://www.domain.com/newpage
- URI: http://www.domain.com/newpage
Note that relative URLs in these headers can cause strange effects
because of "optimizations" that servers do.
EOF
-To be correct to the spec, each of those virtual newlines should really be
-physical C<"\015\012"> sequences by the time you hit the client browser.
-Except for NPH scripts, though, that local newline should get translated
-by your server into standard form, so you shouldn't have a problem
-here, even if you are stuck on MacOS. Everybody else probably won't
-even notice.
+To be correct to the spec, each of those virtual newlines should
+really be physical C<"\015\012"> sequences by the time your message is
+received by the client browser. Except for NPH scripts, though, that
+local newline should get translated by your server into standard form,
+so you shouldn't have a problem here, even if you are stuck on MacOS.
+Everybody else probably won't even notice.
=head2 How do I put a password on my web pages?
=head2 How do I make sure users can't enter values into a form that cause my CGI script to do bad things?
Read the CGI security FAQ, at
-http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html, and the
+http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html , and the
Perl/CGI FAQ at
-http://www.perl.com/CPAN/doc/FAQs/cgi/perl-cgi-faq.html.
+http://www.perl.com/CPAN/doc/FAQs/cgi/perl-cgi-faq.html .
In brief: use tainting (see L<perlsec>), which makes sure that data
from outside your script (eg, CGI parameters) are never used in
=head2 How do I parse a mail header?
For a quick-and-dirty solution, try this solution derived
-from page 222 of the 2nd edition of "Programming Perl":
+from L<perlfunc/split>:
$/ = '';
$header = <MSG>;
Many are tempted to try to eliminate many frequently-invalid
mail addresses with a simple regex, such as
-C</^[\w.-]+\@([\w.-]\.)+\w+$/>. It's a very bad idea. However,
+C</^[\w.-]+\@(?:[\w-]+\.)+\w+$/>. It's a very bad idea. However,
this also throws out many valid ones, and says nothing about
-potential deliverability, so is not suggested. Instead, see
-http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/ckaddr.gz ,
+potential deliverability, so it is not suggested. Instead, see
+http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/ckaddr.gz,
which actually checks against the full RFC spec (except for nested
comments), looks for addresses you may not wish to accept mail to
(say, Bill Clinton or your postmaster), and then makes sure that the
=head2 How do I return the user's mail address?
-On systems that support getpwuid, the $E<lt> variable and the
+On systems that support getpwuid, the $< variable, and the
Sys::Hostname module (which is part of the standard perl distribution),
you can probably try using something like this:
are many reasons to use a mail transport agent like sendmail. These
include queueing, MX records, and security.
+=head2 How do I use MIME to make an attachment to a mail message?
+
+This answer is extracted directly from the MIME::Lite documentation.
+Create a multipart message (i.e., one with attachments).
+
+ use MIME::Lite;
+
+ ### Create a new multipart message:
+ $msg = MIME::Lite->new(
+ From =>'me@myhost.com',
+ To =>'you@yourhost.com',
+ Cc =>'some@other.com, some@more.com',
+ Subject =>'A message with 2 parts...',
+ Type =>'multipart/mixed'
+ );
+
+ ### Add parts (each "attach" has same arguments as "new"):
+ $msg->attach(Type =>'TEXT',
+ Data =>"Here's the GIF file you wanted"
+ );
+ $msg->attach(Type =>'image/gif',
+ Path =>'aaa000123.gif',
+ Filename =>'logo.gif'
+ );
+
+ $text = $msg->as_string;
+
+MIME::Lite also includes a method for sending these things.
+
+ $msg->send;
+
+This defaults to using L<sendmail(1)> but can be customized to use
+SMTP via L<Net::SMTP>.
+
=head2 How do I read mail?
While you could use the Mail::Folder module from CPAN (part of the
MailFolder package) or the Mail::Internet module from CPAN (also part
-of the MailTools package), often a module is overkill, though. Here's a
+of the MailTools package), often a module is overkill. Here's a
mail sorter.
#!/usr/bin/perl
=head2 How do I fetch a news article or the active newsgroups?
Use the Net::NNTP or News::NNTPClient modules, both available from CPAN.
-This can make tasks like fetching the newsgroup list as simple as:
+This can make tasks like fetching the newsgroup list as simple as
perl -MNews::NNTPClient
-e 'print News::NNTPClient->new->list("newsgroups")'
=head2 How can I do RPC in Perl?
-A DCE::RPC module is being developed (but is not yet available), and
+A DCE::RPC module is being developed (but is not yet available) and
will be released as part of the DCE-Perl package (available from
CPAN). The rpcgen suite, available from CPAN/authors/id/JAKE/, is
an RPC stub generator and includes an RPC::ONC module.
https://perl5.git.perl.org / perl5.git / blobdiff