perlfaq9.pod

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    HTTPD::UserAdmin
	  ->new(DB => "/foo/.htpasswd")
	  ->add($username => $password);

=head2 How do I make sure users can't enter values into a form that cause my CGI script to do bad things?

See the security references listed in the CGI Meta FAQ

	http://www.perl.org/CGI_MetaFAQ.html

=head2 How do I parse a mail header?

For a quick-and-dirty solution, try this solution derived
from L<perlfunc/split>:

    $/ = '';
    $header = <MSG>;
    $header =~ s/\n\s+/ /g;	 # merge continuation lines
    %head = ( UNIX_FROM_LINE, split /^([-\w]+):\s*/m, $header );

That solution doesn't do well if, for example, you're trying to
maintain all the Received lines.  A more complete approach is to use
the Mail::Header module from CPAN (part of the MailTools package).

=head2 How do I decode a CGI form?

(contributed by brian d foy)

Use the CGI.pm module that comes with Perl.  It's quick,
it's easy, and it actually does quite a bit of work to
ensure things happen correctly.  It handles GET, POST, and
HEAD requests, multipart forms, multivalued fields, query
string and message body combinations, and many other things
you probably don't want to think about.

It doesn't get much easier: the CGI module automatically
parses the input and makes each value available through the
C<param()> function.

	use CGI qw(:standard);

	my $total = param( 'price' ) + param( 'shipping' );

	my @items = param( 'item' ); # multiple values, same field name

If you want an object-oriented approach, CGI.pm can do that too.

	use CGI;

	my $cgi = CGI->new();

	my $total = $cgi->param( 'price' ) + $cgi->param( 'shipping' );

	my @items = $cgi->param( 'item' );

You might also try CGI::Minimal which is a lightweight version
of the same thing.  Other CGI::* modules on CPAN might work better
for you, too.

Many people try to write their own decoder (or copy one from
another program) and then run into one of the many "gotchas"
of the task.  It's much easier and less hassle to use CGI.pm.

=head2 How do I check a valid mail address?

(partly contributed by Aaron Sherman)

This isn't as simple a question as it sounds.  There are two parts:

a) How do I verify that an email address is correctly formatted?

b) How do I verify that an email address targets a valid recipient?

Without sending mail to the address and seeing whether there's a human
on the other end to answer you, you cannot fully answer part I<b>, but
either the C<Email::Valid> or the C<RFC::RFC822::Address> module will do
both part I<a> and part I<b> as far as you can in real-time.

If you want to just check part I<a> to see that the address is valid
according to the mail header standard with a simple regular expression,
you can have problems, because there are deliverable addresses that
aren't RFC-2822 (the latest mail header standard) compliant, and
addresses that aren't deliverable which, are compliant.  However,  the
following will match valid RFC-2822 addresses that do not have comments,
folding whitespace, or any other obsolete or non-essential elements.
This I<just> matches the address itself:

    my $atom       = qr{[a-zA-Z0-9_!#\$\%&'*+/=?\^`{}~|\-]+};
    my $dot_atom   = qr{$atom(?:\.$atom)*};
    my $quoted     = qr{"(?:\\[^\r\n]|[^\\"])*"};
    my $local      = qr{(?:$dot_atom|$quoted)};
    my $domain_lit = qr{\[(?:\\\S|[\x21-\x5a\x5e-\x7e])*\]};
    my $domain     = qr{(?:$dot_atom|$domain_lit)};
    my $addr_spec  = qr{$local\@$domain};

Just match an address against C</^${addr_spec}$/> to see if it follows
the RFC2822 specification.  However, because it is impossible to be
sure that such a correctly formed address is actually the correct way
to reach a particular person or even has a mailbox associated with it,
you must be very careful about how you use this.

Our best advice for verifying a person's mail address is to have them
enter their address twice, just as you normally do to change a
password. This usually weeds out typos. If both versions match, send
mail to that address with a personal message. If you get the message
back and they've followed your directions, you can be reasonably
assured that it's real.

A related strategy that's less open to forgery is to give them a PIN
(personal ID number).  Record the address and PIN (best that it be a
random one) for later processing. In the mail you send, ask them to
include the PIN in their reply.  But if it bounces, or the message is
included via a "vacation" script, it'll be there anyway.  So it's
best to ask them to mail back a slight alteration of the PIN, such as
with the characters reversed, one added or subtracted to each digit, etc.

=head2 How do I decode a MIME/BASE64 string?

The MIME-Base64 package (available from CPAN) handles this as well as
the MIME/QP encoding.  Decoding BASE64 becomes as simple as:

    use MIME::Base64;
    $decoded = decode_base64($encoded);

The MIME-Tools package (available from CPAN) supports extraction with
decoding of BASE64 encoded attachments and content directly from email
messages.

If the string to decode is short (less than 84 bytes long)
a more direct approach is to use the unpack() function's "u"
format after minor transliterations:

    tr#A-Za-z0-9+/##cd;                   # remove non-base64 chars
    tr#A-Za-z0-9+/# -_#;                  # convert to uuencoded format
    $len = pack("c", 32 + 0.75*length);   # compute length byte
    print unpack("u", $len . $_);         # uudecode and print

=head2 How do I return the user's mail address?

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:

    use Sys::Hostname;
    $address = sprintf('%s@%s', scalar getpwuid($<), hostname);

Company policies on mail address can mean that this generates addresses
that the company's mail system will not accept, so you should ask for
users' mail addresses when this matters.  Furthermore, not all systems
on which Perl runs are so forthcoming with this information as is Unix.

The Mail::Util module from CPAN (part of the MailTools package) provides a
mailaddress() function that tries to guess the mail address of the user.
It makes a more intelligent guess than the code above, using information
given when the module was installed, but it could still be incorrect.
Again, the best way is often just to ask the user.

=head2 How do I send mail?

Use the C<sendmail> program directly:

    open(SENDMAIL, "|/usr/lib/sendmail -oi -t -odq")
                        or die "Can't fork for sendmail: $!\n";
    print SENDMAIL <<"EOF";
    From: User Originating Mail <me\@host>
    To: Final Destination <you\@otherhost>
    Subject: A relevant subject line

    Body of the message goes here after the blank line
    in as many lines as you like.
    EOF
    close(SENDMAIL)     or warn "sendmail didn't close nicely";

The B<-oi> option prevents sendmail from interpreting a line consisting
of a single dot as "end of message".  The B<-t> option says to use the
headers to decide who to send the message to, and B<-odq> says to put
the message into the queue.  This last option means your message won't
be immediately delivered, so leave it out if you want immediate
delivery.

Alternate, less convenient approaches include calling mail (sometimes
called mailx) directly or simply opening up port 25 have having an
intimate conversation between just you and the remote SMTP daemon,
probably sendmail.

Or you might be able use the CPAN module Mail::Mailer:

    use Mail::Mailer;

    $mailer = Mail::Mailer->new();
    $mailer->open({ From    => $from_address,
                    To      => $to_address,
                    Subject => $subject,
                  })
        or die "Can't open: $!\n";
    print $mailer $body;
    $mailer->close();

The Mail::Internet module uses Net::SMTP which is less Unix-centric than
Mail::Mailer, but less reliable.  Avoid raw SMTP commands.  There
are many reasons to use a mail transport agent like sendmail.  These
include queuing, 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    =>'[e-mail]',
                 To      =>'[e-mail]',
                 Cc      =>'[e-mail], [e-mail]',
                 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> 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 (part
of the MailTools package), often a module is overkill.  Here's a
mail sorter.

    #!/usr/bin/perl

    my(@msgs, @sub);
    my $msgno = -1;
    $/ = '';                    # paragraph reads
    while (<>) {
        if (/^From /m) {
            /^Subject:\s*(?:Re:\s*)*(.*)/mi;
            $sub[++$msgno] = lc($1) || '';
        }
        $msgs[$msgno] .= $_;
    }
    for my $i (sort { $sub[$a] cmp $sub[$b] || $a <=> $b } (0 .. $#msgs)) {
        print $msgs[$i];
    }

Or more succinctly,

    #!/usr/bin/perl -n00
    # bysub2 - awkish sort-by-subject
    BEGIN { $msgno = -1 }
    $sub[++$msgno] = (/^Subject:\s*(?:Re:\s*)*(.*)/mi)[0] if /^From/m;
    $msg[$msgno] .= $_;
    END { print @msg[ sort { $sub[$a] cmp $sub[$b] || $a <=> $b } (0 .. $#msg) ] }

=head2 How do I find out my hostname, domainname, or IP address?
X<hostname, domainname, IP address, host, domain, hostfqdn, inet_ntoa,
gethostbyname, Socket, Net::Domain, Sys::Hostname>

(contributed by brian d foy)

The Net::Domain module, which is part of the standard distribution starting
in perl5.7.3, can get you the fully qualified domain name (FQDN), the host
name, or the domain name.

	use Net::Domain qw(hostname hostfqdn hostdomain);

	my $host = hostfqdn();

The C<Sys::Hostname> module, included in the standard distribution since
perl5.6, can also get the hostname.

	use Sys::Hostname;

	$host = hostname();

To get the IP address, you can use the C<gethostbyname> built-in function
to turn the name into a number. To turn that number into the dotted octet
form (a.b.c.d) that most people expect, use the C<inet_ntoa> function
from the <Socket> module, which also comes with perl.

    use Socket;

    my $address = inet_ntoa(
    	scalar gethostbyname( $host || 'localhost' )
    	);

=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

    perl -MNews::NNTPClient
      -e 'print News::NNTPClient->new->list("newsgroups")'

=head2 How do I fetch/put an FTP file?

LWP::Simple (available from CPAN) can fetch but not put.  Net::FTP (also
available from CPAN) is more complex but can put as well as fetch.

=head2 How can I do RPC in Perl?

(Contributed by brian d foy)

Use one of the RPC modules you can find on CPAN (
http://search.cpan.org/search?query=RPC&mode=all ).

=head1 REVISION

Revision: $Revision: 8539 $

Date: $Date: 2007-01-11 00:07:14 +0100 (Thu, 11 Jan 2007) $

See L<perlfaq> for source control details and availability.

=head1 AUTHOR AND COPYRIGHT

Copyright (c) 1997-2007 Tom Christiansen, Nathan Torkington, and
other authors as noted. All rights reserved.

This documentation is free; you can redistribute it and/or modify it
under the same terms as Perl itself.

Irrespective of its distribution, all code examples in this file
are hereby placed into the public domain.  You are permitted and
encouraged to use this code in your own programs for fun
or for profit as you see fit.  A simple comment in the code giving
credit would be courteous but is not required.