=head1 NAME
-perlfaq8 - System Interaction ($Revision: 1.17 $, $Date: 1997/03/25 18:17:12 $)
+perlfaq8 - System Interaction ($Revision: 1.21 $, $Date: 1997/04/24 22:44:19 $)
=head1 DESCRIPTION
devices), and most anything else not related to data manipulation.
Read the FAQs and documentation specific to the port of perl to your
-operating system (eg, L<perlvms>, F<REAMDE.os2>, ...). These should
+operating system (eg, L<perlvms>, L<perlplan9>, ...). These should
contain more detailed information on the vagaries of your perl.
=head2 How do I find out which operating system I'm running under?
Even though with normal text files, a "\n" will do the trick, there is
still no unified scheme for terminating a line that is portable
-between Unix, MS-DOS/Windows, and Macintosh, except to terminate I<ALL> line
+between Unix, DOS/Win, and Macintosh, except to terminate I<ALL> line
ends with "\015\012", and strip what you don't need from the output.
This applies especially to socket I/O and autoflushing, discussed
next.
character generates a signal, which you then trap. Signals are
documented in L<perlipc/"Signals"> and chapter 6 of the Camel.
-Be warned that very few C libraries are reentrant. Therefore, if you
+Be warned that very few C libraries are re-entrant. Therefore, if you
attempt to print() in a handler that got invoked during another stdio
operation your internal structures will likely be in an
inconsistent state, and your program will dump core. You can
However, because syscalls restart by default, you'll find that if
you're in a "slow" call, such as E<lt>FHE<gt>, read(), connect(), or
wait(), that the only way to terminate them is by "longjumping" out;
-that is, by raising an exception. See the timeout handler for a
+that is, by raising an exception. See the time-out handler for a
blocking flock() in L<perlipc/"Signals"> or chapter 6 of the Camel.
=head2 How do I modify the shadow password file on a Unix system?
Perl's exception-handling mechanism is its eval() operator. You can
use eval() as setjmp and die() as longjmp. For details of this, see
-the section on signals, especially the timeout handler for a blocking
+the section on signals, especially the time-out handler for a blocking
flock() in L<perlipc/"Signals"> and chapter 6 of the Camel.
If exception handling is all you're interested in, try the
but the hard ones like F<ioctl.h> nearly always need to hand-edited.
Here's how to install the *.ph files:
- 1. become superuser
+ 1. become super-user
2. cd /usr/include
3. h2ph *.h */*.h
=head2 Why can't I get the output of a command with system()?
-You're confusing the purpose of system() and backticks (''). system()
-runs a command and returns exit status information (as a 16 bit value
--- the low 8 bits are the signal the process died from, if any, and
-the high 8 bits are the actual exit value). Backticks ('') run a
+You're confusing the purpose of system() and backticks (``). system()
+runs a command and returns exit status information (as a 16 bit value:
+the low 8 bits are the signal the process died from, if any, and
+the high 8 bits are the actual exit value). Backticks (``) run a
command and return what it sent to STDOUT.
- $status = system("mail-users");
- $output = `ls`;
+ $exit_status = system("mail-users");
+ $output_string = `ls`;
=head2 How can I capture STDERR from an external command?
this very awkwardness is what would make a shell->perl converter
nigh-on impossible to write. By rewriting it, you'll think about what
you're really trying to do, and hopefully will escape the shell's
-pipeline data stream paradigm, which while convenient for some matters,
+pipeline datastream paradigm, which while convenient for some matters,
causes many inefficiencies.
=head2 Can I use perl to run a telnet or ftp session?
-Try the Net::FTP and TCP::Client modules (available from CPAN).
-http://www.perl.com/CPAN/scripts/netstuff/telnet.emul.shar will also
-help for emulating the telnet protocol.
+Try the Net::FTP, TCP::Client, and Net::Telnet modules (available from
+CPAN). http://www.perl.com/CPAN/scripts/netstuff/telnet.emul.shar
+will also help for emulating the telnet protocol, but Net::Telnet is
+quite probably easier to use..
+
+If all you want to do is pretend to be telnet but don't need
+the initial telnet handshaking, then the standard dual-process
+approach will suffice:
+
+ use IO::Socket; # new in 5.004
+ $handle = IO::Socket::INET->new('www.perl.com:80')
+ || die "can't connect to port 80 on www.perl.com: $!";
+ $handle->autoflush(1);
+ if (fork()) { # XXX: undef means failure
+ select($handle);
+ print while <STDIN>; # everything from stdin to socket
+ } else {
+ print while <$handle>; # everything from socket to stdout
+ }
+ close $handle;
+ exit;
=head2 How can I write expect in Perl?
See the F<eg/nih> script (part of the perl source distribution).
-=head2 How do I keep my own module/library directory?
-
-When you build modules, use the PREFIX option when generating
-Makefiles:
-
- perl Makefile.PL PREFIX=/u/mydir/perl
-
-then either set the PERL5LIB environment variable before you run
-scripts that use the modules/libraries (see L<perlrun>) or say
-
- use lib '/u/mydir/perl';
-
-See Perl's L<lib> for more information.
-
=head2 How do I find out if I'm running interactively or not?
Good question. Sometimes C<-t STDIN> and C<-t STDOUT> can give clues,
just need to replace step 3 (B<make>) with B<make perl> and you will
get a new F<perl> binary with your extension linked in.
-See L<ExtUtils::MakeMaker> for more details on building extensions.
+See L<ExtUtils::MakeMaker> for more details on building extensions,
+the question "How do I keep my own module/library directory?"
+
+=head2 How do I keep my own module/library directory?
+
+When you build modules, use the PREFIX option when generating
+Makefiles:
+
+ perl Makefile.PL PREFIX=/u/mydir/perl
+
+then either set the PERL5LIB environment variable before you run
+scripts that use the modules/libraries (see L<perlrun>) or say
+
+ use lib '/u/mydir/perl';
+
+See Perl's L<lib> for more information.
+
+=head2 How do I add the directory my program lives in to the module/library search path?
+
+ use FindBin;
+ use lib "$FindBin:Bin";
+ use your_own_modules;
+
+=head2 How do I add a directory to my include path at runtime?
+
+Here are the suggested ways of modifying your include path:
+
+ the PERLLIB environment variable
+ the PERL5LIB environment variable
+ the perl -Idir commpand line flag
+ the use lib pragma, as in
+ use lib "$ENV{HOME}/myown_perllib";
+
+The latter is particularly useful because it knows about machine
+dependent architectures. The lib.pm pragmatic module was first
+included with the 5.002 release of Perl.
+
+=head1 How do I get one key from the terminal at a time, under POSIX?
+
+ #!/usr/bin/perl -w
+ use strict;
+ $| = 1;
+ for (1..4) {
+ my $got;
+ print "gimme: ";
+ $got = getone();
+ print "--> $got\n";
+ }
+ exit;
+
+ BEGIN {
+ use POSIX qw(:termios_h);
+
+ my ($term, $oterm, $echo, $noecho, $fd_stdin);
+
+ $fd_stdin = fileno(STDIN);
+
+ $term = POSIX::Termios->new();
+ $term->getattr($fd_stdin);
+ $oterm = $term->getlflag();
+
+ $echo = ECHO | ECHOK | ICANON;
+ $noecho = $oterm & ~$echo;
+
+ sub cbreak {
+ $term->setlflag($noecho);
+ $term->setcc(VTIME, 1);
+ $term->setattr($fd_stdin, TCSANOW);
+ }
+
+ sub cooked {
+ $term->setlflag($oterm);
+ $term->setcc(VTIME, 0);
+ $term->setattr($fd_stdin, TCSANOW);
+ }
+
+ sub getone {
+ my $key = '';
+ cbreak();
+ sysread(STDIN, $key, 1);
+ cooked();
+ return $key;
+ }
+
+ }
+ END { cooked() }
+
+=head1 AUTHOR AND COPYRIGHT
+
+Copyright (c) 1997 Tom Christiansen and Nathan Torkington.
+All rights reserved. See L<perlfaq> for distribution information.
+ END-of-perlfaq8.pod
+echo x - perlfaq9.pod
+sed 's/^X//' >perlfaq9.pod << 'END-of-perlfaq9.pod'
+=head1 NAME
+
+perlfaq9 - Networking ($Revision: 1.17 $, $Date: 1997/04/24 22:44:29 $)
+
+=head1 DESCRIPTION
+
+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. Can you help me fix it?
+
+Sure, but you probably can't afford our contracting rates :-)
+
+Seriously, 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 probably receive a courteous and useful reply to your
+question if you post it on comp.infosystems.www.authoring.cgi (if it's
+something to do with HTTP, HTML, or the CGI protocols). Questions that
+appear to be Perl questions but are really CGI ones that are posted to
+comp.lang.perl.misc may not be so well received.
+
+The useful FAQs are:
+
+ http://www.perl.com/perl/faq/idiots-guide.html
+ http://www3.pair.com/webthing/docs/cgi/faqs/cgifaq.shtml
+ http://www.perl.com/perl/faq/perl-cgi-faq.html
+ http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html
+ 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::Parse
+from CPAN (part of the libwww-perl distribution, which is a must-have
+module for all web hackers).
+
+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
+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.
+
+Here's one "simple-minded" approach, that works for most files:
+
+ #!/usr/bin/perl -p0777
+ s/<(?:[^>'"]*|(['"]).*?\1)*>//gs
+
+If you want a more complete solution, see the 3-stage striphtml
+program in
+http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/striphtml.gz
+.
+
+=head2 How do I extract URLs?
+
+A quick but imperfect approach is
+
+ #!/usr/bin/perl -n00
+ # qxurl - tchrist@perl.com
+ print "$2\n" while m{
+ < \s*
+ A \s+ HREF \s* = \s* (["']) (.*?) \1
+ \s* >
+ }gsix;
+
+This version does not adjust relative URLs, understand alternate
+bases, deal with HTML comments, deal with HREF and NAME attributes in
+the same tag, or accept URLs themselves as arguments. It also runs
+about 100x faster than a more "complete" solution using the LWP suite
+of modules, such as the
+http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/xurl.gz
+program.
+
+=head2 How do I download a file from the user's machine? How do I open a file on another machine?
+
+In the context of an HTML form, you can use what's known as
+B<multipart/form-data> encoding. The CGI.pm module (available from
+CPAN) supports this in the start_multipart_form() method, which isn't
+the same as the startform() method.
+
+=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
+module (available from CPAN) supports this widget, as well as many
+others, including some that it cleverly synthesizes on its own.
+
+=head2 How do I fetch an HTML file?
+
+One approach, if you have the lynx text-based HTML browser installed
+on your system, is this:
+
+ $html_code = `lynx -source $url`;
+ $text_data = `lynx -dump $url`;
+
+The libwww-perl (LWP) modules from CPAN provide a more powerful way to
+do this. They work through proxies, and don't require lynx:
+
+ # print HTML from a URL
+ use LWP::Simple;
+ getprint "http://www.sn.no/libwww-perl/";
+
+ # print ASCII from HTML from a URL
+ use LWP::Simple;
+ use HTML::Parse;
+ use HTML::FormatText;
+ my ($html, $ascii);
+ $html = get("http://www.perl.com/");
+ defined $html
+ or die "Can't fetch HTML from http://www.perl.com/";
+ $ascii = HTML::FormatText->new->format(parse_html($html));
+ print $ascii;
+
+=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($1))/ge;
+
+Encoding is a bit harder, because you can't just blindly change
+all the non-alphanumunder character (C<\W>) into their hex escapes.
+It's important that characters with special meaning like C</> and C<?>
+I<not> be translated. Probably the easiest way to get this right is
+to avoid reinventing the wheel and just use the URI::Escape module,
+which is part of the libwww-perl package (LWP) available from CPAN.
+
+=head2 How do I redirect to another page?
+
+Instead of sending back a C<Content-Type> as the headers of your
+reply, send back a C<Location:> header. Officially this should be a
+C<URI:> header, so the CGI.pm module (available from CPAN) sends back
+both:
+
+ Location: http://www.domain.com/newpage
+ URI: http://www.domain.com/newpage
+
+Note that relative URLs in these headers can cause strange effects
+because of "optimizations" that servers do.
+
+=head2 How do I put a password on my web pages?
+
+That depends. You'll need to read the documentation for your web
+server, or perhaps check some of the other FAQs referenced above.
+
+=head2 How do I edit my .htpasswd and .htgroup files with Perl?
+
+The HTTPD::UserAdmin and HTTPD::GroupAdmin modules provide a
+consistent OO interface to these files, regardless of how they're
+stored. Databases may be text, dbm, Berkley DB or any database with a
+DBI compatible driver. HTTPD::UserAdmin supports files used by the
+`Basic' and `Digest' authentication schemes. Here's an example:
+
+ use HTTPD::UserAdmin ();
+ HTTPD::UserAdmin
+ ->new(DB => "/foo/.htpasswd")
+ ->add($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?
+
+Read the CGI security FAQ, at
+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.
+
+In brief: use tainting (see L<perlsec>), which makes sure that data
+from outside your script (eg, CGI parameters) are never used in
+C<eval> or C<system> calls. In addition to tainting, never use the
+single-argument form of system() or exec(). Instead, supply the
+command and arguments as a list, which prevents shell globbing.
+
+=head2 How do I parse an email header?
+
+For a quick-and-dirty solution, try this solution derived
+from page 222 of the 2nd edition of "Programming Perl":
+
+ $/ = '';
+ $header = <MSG>;
+ $header =~ s/\n\s+/ /g; # merge continuation lines
+ %head = ( UNIX_FROM_LINE, split /^([-\w]+):\s*/m, $header );
+
+That solution doesn't do well if, for example, you're trying to
+maintain all the Received lines. A more complete approach is to use
+the Mail::Header module from CPAN (part of the MailTools package).
+
+=head2 How do I decode a CGI form?
+
+A lot of people are tempted to code this up themselves, so you've
+probably all seen a lot of code involving C<$ENV{CONTENT_LENGTH}> and
+C<$ENV{QUERY_STRING}>. It's true that this can work, but there are
+also a lot of versions of this floating around that are quite simply
+broken!
+
+Please do not be tempted to reinvent the wheel. Instead, use the
+CGI.pm or CGI_Lite.pm (available from CPAN), or if you're trapped in
+the module-free land of perl1 .. perl4, you might look into cgi-lib.pl
+(available from http://www.bio.cam.ac.uk/web/form.html).
+
+=head2 How do I check a valid email address?
+
+You can't.
+
+Without sending mail to the address and seeing whether it bounces (and
+even then you face the halting problem), you cannot determine whether
+an email address is valid. Even if you apply the email header
+standard, you can have problems, because there are deliverable
+addresses that aren't RFC-822 (the mail header standard) compliant,
+and addresses that aren't deliverable which are compliant.
+
+Many are tempted to try to eliminate many frequently-invalid email
+addresses with a simple regexp, such as
+C</^[\w.-]+\@([\w.-]\.)+\w+$/>. 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 ,
+which actually checks against the full RFC spec (except for nested
+comments), looks for addresses you may not wish to accept email to
+(say, Bill Clinton or your postmaster), and then makes sure that the
+hostname given can be looked up in DNS. It's not fast, but it works.
+
+Here's an alternative strategy used by many CGI script authors: Check
+the email address with a simple regexp (such as the one above). If
+the regexp matched the address, accept the address. If the regexp
+didn't match the address, request confirmation from the user that the
+email address they entered was correct.
+
+=head2 How do I decode a MIME/BASE64 string?
+
+The MIME-tools package (available from CPAN) handles this and a lot
+more. Decoding BASE64 becomes as simple as:
+
+ use MIME::base64;
+ $decoded = decode_base64($encoded);
+
+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 email address?
+
+On systems that support getpwuid, the $E<lt> 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;
+ $address = sprintf('%s@%s', getpwuid($<), hostname);
+
+Company policies on email address can mean that this generates addresses
+that the company's email system will not accept, so you should ask for
+users' email 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/read mail?
+
+Sending mail: the Mail::Mailer module from CPAN (part of the MailTools
+package) is UNIX-centric, while Mail::Internet uses Net::SMTP which is
+not UNIX-centric. Reading mail: 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).
+
+ # sending mail
+ use Mail::Internet;
+ use Mail::Header;
+ # say which mail host to use
+ $ENV{SMTPHOSTS} = 'mail.frii.com';
+ # create headers
+ $header = new Mail::Header;
+ $header->add('From', 'gnat@frii.com');
+ $header->add('Subject', 'Testing');
+ $header->add('To', 'gnat@frii.com');
+ # create body
+ $body = 'This is a test, ignore';
+ # create mail object
+ $mail = new Mail::Internet(undef, Header => $header, Body => \[$body]);
+ # send it
+ $mail->smtpsend or die;
+
+=head2 How do I find out my hostname/domainname/IP address?
+
+A lot of code has historically cavalierly called the C<`hostname`>
+program. While sometimes expedient, this isn't very portable. It's
+one of those tradeoffs of convenience versus portability.
+
+The Sys::Hostname module (part of the standard perl distribution) will
+give you the hostname after which you can find out the IP address
+(assuming you have working DNS) with a gethostbyname() call.
+
+ use Socket;
+ use Sys::Hostname;
+ my $host = hostname();
+ my $addr = inet_ntoa(scalar(gethostbyname($name)) || 'localhost');
+
+Probably the simplest way to learn your DNS domain name is to grok
+it out of /etc/resolv.conf, at least under Unix. Of course, this
+assumes several things about your resolv.conf configuration, including
+that it exists.
+
+(We still need a good DNS domain name-learning method for non-Unix
+systems.)
+
+=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?
+
+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). No ONC::RPC module is known.
=head1 AUTHOR AND COPYRIGHT
Copyright (c) 1997 Tom Christiansen and Nathan Torkington.
All rights reserved. See L<perlfaq> for distribution information.
+
projects / p5sagit/p5-mst-13.2.git / blobdiff