[6466] in Perl-Users-Digest
Perl-Users Digest, Issue: 91 Volume: 8
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Tue Mar 11 19:17:35 1997
Date: Tue, 11 Mar 97 16:01:41 -0800
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Tue, 11 Mar 1997 Volume: 8 Number: 91
Today's topics:
Perl FAQ part 2 of 0..9: Obtaining and Learning about P <tchrist@mox.perl.com>
Perl FAQ part 3 of 0..9: Programming Tools [Periodic Po <tchrist@mox.perl.com>
Digest Administrivia (Last modified: 8 Mar 97) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: 11 Mar 1997 23:23:50 GMT
From: Tom Christiansen <tchrist@mox.perl.com>
Subject: Perl FAQ part 2 of 0..9: Obtaining and Learning about Perl [Periodic Posting]
Message-Id: <5g4pi6$fmh$1@csnews.cs.colorado.edu>
=head1 NAME
perlfaq2 - Obtaining and Learning about Perl ($Revision: 1.12 $)
=head1 DESCRIPTION
This section of the FAQ answers questions about where to find
source and documentation for Perl, support and training, and
related matters.
=head2 What machines support Perl? Where do I get it?
The standard release of Perl (the one maintained by the perl development
team) is distributed only in source code form. You can find this at
http://www.perl.com/CPAN/src/latest.tar.gz, which is a gzipped archive
in POSIX format. This source builds with no porting whatsoever on most
Unix systems (Perl's native environment), as well as Plan 9, VMS, QNX,
OS/2, and the Amiga.
Although it's rumored that the (imminent) 5.004 release may build
on Windows NT, this is yet to be proven. Binary distributions
for 32-bit Microsoft systems and for Apple systems can be found
http://www.perl.com/CPAN/ports/ directory. Because these are not part of
the standard distribution, they may and in fact do differ from the base
Perl port in a variety of ways. You'll have to check their respective
release notes to see just what the differences are. These differences
can be either positive (e.g. extensions for the features of the particular
platform that are not supported in the source release of perl) or negative
(e.g. might be based upon a less current source release of perl).
A useful FAQ for Win32 Perl users is
http://www.endcontsw.com/people/evangelo/Perl_for_Win32_FAQ.html
=head2 How can I get a binary version of Perl?
If you don't have a C compiler because for whatever reasons your
vendor did not include one with your system, the best thing to do is
grab a binary version of gcc from the net and use that to compile perl
with. CPAN only has binaries for systems that are terribly hard to
get free compilers for, not for Unix systems.
=head2 I copied the Perl binary from one machine to another, but scripts don't work.
That's probably because you forgot libraries, or library paths differ.
You really should build the whole distribution on the machine it will
eventually live on, and then type C<make install>. Most other
approaches are doomed to failure.
One simple way to check that things are in the right place is to print out
the hard-coded @INC which perl is looking for.
perl -e 'print join("\n",@INC)'
If this command lists any paths which don't exist on your system, then you
may need to move the appropriate libraries to these locations, or create
symlinks, aliases, or shortcuts appropriately.
=head2 I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work?
Read the F<INSTALL> file, which is part of the source distribution.
It describes in detail how to cope with most idiosyncracies that the
Configure script can't work around for any given system or
architecture.
=head2 What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean?
CPAN stands for Comprehensive Perl Archive Network, a huge archive
replicated on dozens of machines all over the world. CPAN contains
source code, non-native ports, documentation, scripts, and many
third-party modules and extensions, designed for everything from
commercial database interfaces to keyboard/screen control to web
walking and CGI scripts. The master machine for CPAN is
ftp://ftp.funet.fi/pub/languages/perl/CPAN/, but you can use the
address http://www.perl.com/CPAN/CPAN.html to fetch a copy from a
"site near you". See http://www.perl.com/CPAN (without a slash at the
end) for how this process works.
CPAN/path/... is a naming convention for files available on CPAN
sites. CPAN indicates the base directory of a CPAN mirror, and the
rest of the path is the path from that directory to the file. For
instance, if you're using ftp://ftp.funet.fi/pub/languages/perl/CPAN
as your CPAN site, the file CPAN/misc/japh file is downloadable as
ftp://ftp.funet.fi/pub/languages/perl/CPAN/misc/japh .
Considering that there are hundreds of existing modules in the
archive, one probably exists to do nearly anything you can think of.
Current categories under CPAN/modules/by-category/ include perl core
modules; development support; operating system interfaces; networking,
devices, and interprocess communication; data type utilities; database
interfaces; user interfaces; interfaces to other languages; filenames,
file systems, and file locking; internationalization and locale; world
wide web support; server and daemon utilities; archiving and
compression; image manipulation; mail and news; control flow
utilities; filehandle and I/O; Microsoft Windows modules; and
miscellaneous modules.
=head2 Is there an ISO or ANSI certified version of Perl?
Certainly not. Larry expects that he'll be certified before Perl is.
=head2 Where can I get information on Perl?
The complete Perl documentation is available with the perl
distribution. If you have perl installed locally, you probably have
the documentation installed as well: type C<man perl> if you're on a
system resembling Unix. This will lead you to other important man
pages. If you're not on a Unix system, access to the documentation
will be different; for example, it might be only in HTML format. But
all proper perl installations have fully-accessible documentation.
You might also try C<perldoc perl> in case your system doesn't
have a proper man command, or it's been misinstalled. If that doesn't
work, try looking in /usr/local/lib/perl5/pod for documentation.
If all else fails, consult the CPAN/doc directory, which contains the
complete documentation in various formats, including native pod,
troff, html, and plain text. There's also a web page at
http://www.perl.com/perl/info/documentation.html that might help.
It's also worth noting that there's a PDF version of the complete
documentation for perl available in the CPAN/authors/id/BMIDD
directory.
Many good books have been written about Perl -- see the section below
for more details.
=head2 What are the Perl newsgroups on USENET? Where do I post questions?
The now defunct comp.lang.perl newsgroup has been superseded by the
following groups:
comp.lang.perl.announce Moderated announcement group
comp.lang.perl.misc Very busy group about Perl in general
comp.lang.perl.modules Use and development of Perl modules
comp.lang.perl.tk Using Tk (and X) from Perl
comp.infosystems.www.authoring.cgi Writing CGI scripts for the Web.
There is also USENET gateway to the mailing list used by the crack
Perl development team (perl5-porters) at
news://genetics.upenn.edu/perl.porters-gw/ .
=head2 Where should I post source code?
You should post source code to whichever group is most appropriate,
but feel free to cross-post to comp.lang.perl.misc. If you want to
cross-post to alt.sources, please make sure it follows their posting
standards, including setting the Followup-To header line to NOT
include alt.sources; see their FAQ for details.
=head2 Perl Books
A number books on Perl and/or CGI programming are available. A few of
these are good, some are ok, but many aren't worth your money. Tom
Christiansen maintains a list of these books, some with extensive
reviews, at http://www.perl.com/perl/critiques/index.html.
The incontestably definitive reference book on Perl, written by the
creator of Perl and his apostles, is now in its second edition and
fourth printing.
Programming Perl (the "Camel Book"):
Authors: Larry Wall, Tom Christiansen, and Randal Schwartz
ISBN 1-56592-149-6 (English)
ISBN 4-89052-384-7 (Japanese)
(French and German translations in progress)
Note that O'Reilly books are color-coded: turquoise (some would call
it teal) covers indicate perl5 coverage, while magenta (some would
call it pink) covers indicate perl4 only. Check the cover color
before you buy!
What follows is a list of the books that the FAQ authors found personally
useful. Your mileage may (but, we hope, probably won't) vary.
If you're already a hard-core systems programmer, then the Camel Book
just might suffice for you to learn Perl from. But if you're not,
check out the "Llama Book". It currently doesn't cover perl5, but the
2nd edition is nearly done and should be out by summer 97:
Learning Perl (the Llama Book):
Author: Randal Schwartz, with intro by Larry Wall
ISBN 1-56592-042-2 (English)
ISBN 4-89502-678-1 (Japanese)
ISBN 2-84177-005-2 (French)
ISBN 3-930673-08-8 (German)
Another stand-out book in the turquoise O'Reilly Perl line is the "Hip
Owls" book. It covers regular expressions inside and out, with quite a
bit devoted exclusively to Perl:
Mastering Regular Expressions (the Cute Owls Book):
Author: Jeffrey Friedl
ISBN 1-56592-257-3
You can order any of these books from O'Reilly & Associates,
1-800-998-9938. Local/overseas is 1-707-829-0515. If you can locate
an O'Reilly order form, you can also fax to 1-707-829-0104. See
http://www.ora.com/ on the Web.
Recommended Perl books that are not from O'Reilly are the following:
Cross-Platform Perl, (for Unix and Windows NT)
Author: Eric F. Johnson
ISBN: 1-55851-483-X
How to Set up and Maintain a World Wide Web Site, (2nd edition)
Author: Lincoln Stein, M.D., Ph.D.
ISBN: 0-201-63462-7
CGI Programming in C & Perl,
Author: Thomas Boutell
ISBN: 0-201-42219-0
Note that some of these address specific application areas (e.g. the
Web) and are not general-purpose programming books.
=head2 Perl in Magazines
The Perl Journal is the first and only magazine dedicated to Perl.
It is published (on paper, not online) quarterly by Jon Orwant
(orwant@tpj.com), editor. Subscription information is at http://tpj.com
or via email to subscriptions@tpj.com.
Beyond this, two other magazines that frequently carry high-quality articles
on Perl are Web Techniques (see http://www.webtechniques.com/) and
Unix Review (http://www.unixreview.com/).
=head2 Perl on the Net: FTP and WWW Access
To get the best (and possibly cheapest) performance, pick a site from
the list below and use it to grab the complete list of mirror sites.
>From there you can find the quickest site for you. Remember, the
following list is I<not> the complete list of CPAN mirrors.
http://www.perl.com/CPAN (redirects to another mirror)
http://www.perl.org/CPAN
ftp://ftp.funet.fi/pub/languages/perl/CPAN/
http://www.cs.ruu.nl/pub/PERL/CPAN/
ftp://ftp.cs.colorado.edu/pub/perl/CPAN/
=head2 What mailing lists are there for perl?
Most of the major modules (tk, CGI, libwww-perl) have their own
mailing lists. Consult the documentation that came with the module for
subscription information. The following are a list of mailing lists
related to perl itself.
If you subscribe to a mailing list, it behooves you to know how to
unsubscribe from it. Strident pleas to the list itself to get you off
will not be favorably received.
=over 4
=item MacPerl
There is a mailing list for discussing Macintosh Perl. Contact
"mac-perl-request@iis.ee.ethz.ch".
Also see Matthias Neeracher's (the creator and maintainer of MacPerl)
webpage at http://www.iis.ee.ethz.ch/~neeri/macintosh/perl.html for
many links to interesting MacPerl sites, and the applications/MPW
tools, precompiled.
=item Perl5-Porters
The core development team have a mailing list for discussing fixes and
changes to the language. Send mail to
"perl5-porters-request@perl.org" with help in the body of the message
for information on subscribing.
=item NTPerl
This list is used to discuss issues involving Win32 Perl 5 (Windows NT
and Win95). Subscribe by emailing ListManager@ActiveWare.com with the
message body:
subscribe Perl-Win32-Users
The list software, also written in perl, will automatically determine
your address, and subscribe you automatically. To unsubscribe, email
the following in the message body to the same address like so:
unsubscribe Perl-Win32-Users
You can also check http://www.activeware.com/ and select "Mailing Lists"
to join or leave this list.
=item Perl-Packrats
Discussion related to archiving of perl materials, particularly the
Comprehensive PerlArchive Network (CPAN). Subscribe by emailing
majordomo@cis.ufl.edu:
subscribe perl-packrats
The list software, also written in perl, will automatically determine
your address, and subscribe you automatically. To unsubscribe, simple
prepend the same command with an "un", and mail to the same address
like so:
unsubscribe perl-packrats
=back
=head2 Archives of comp.lang.perl.misc
Have you tried Deja News or Alta Vista?
ftp.cis.ufl.edu:/pub/perl/comp.lang.perl.*/monthly has an almost
complete collection dating back to 12/89 (missing 08/91 through
12/93). They are kept as one large file for each month.
You'll probably want more a sophisticated query and retrieval mechanism
than a file listing, preferably one that allows you to retrieve
articles using a fast-access indices, keyed on at least author, date,
subject, thread (as in "trn") and probably keywords. The best
solution the FAQ authors know of is the MH pick command, but it is
very slow to select on 18000 articles.
If you have, or know where can be found, the missing sections, please
let perlfaq-suggestions@perl.com know.
=head2 Perl Training
While some large training companies offer their own courses on Perl,
you may prefer to contact individuals near and dear to the heart of
Perl development. Two well-known members of the Perl development team
who offer such things are Tom Christiansen <perl-classes@perl.com>
and Randal Schwartz <perl-training-info@stonehenge.com>, plus their
respective minions, who offer a variety of professional tutorials
and seminars on Perl. These courses include large public seminars,
private corporate training, and fly-ins to Colorado and Oregon.
See http://www.perl.com/perl/info/training.html for more details.
=head2 Where can I buy a commercial version of Perl?
In a sense, Perl already I<is> commercial software: It has a licence
that you can grab and carefully read to your manager. It is
distributed in releases and comes in well-defined packages. There is a
very large user community and an extensive literature. The
comp.lang.perl.* newsgroups and several of the mailing lists provide
free answers to your questions in near real-time. Perl has
traditionally been supported by Larry, dozens of software designers
and developers, and thousands of programmers, all working for free
to create a useful thing to make life better for everyone.
However, these answers may not suffice for managers who require a
purchase order from a company whom they can sue should anything go
wrong. Or maybe they need very serious hand-holding and contractual
obligations. Shrink-wrapped CDs with perl on them are available from
several sources if that will help.
Or you can purchase a real support contract. Although Cygnus historically
provided this service, they no longer sell support contracts for Perl.
Instead, the Paul Ingram Group will be taking up the slack through The
Perl Clinic. The following is a commercial from them:
"Do you need professional support for Perl and/or Oraperl? Do you need
a support contract with defined levels of service? Do you want to pay
only for what you need?
"The Paul Ingram Group has provided quality software development and
support services to some of the world's largest corporations for ten
years. We are now offering the same quality support services for Perl
at The Perl Clinic. This service is led by Tim Bunce, an active perl
porter since 1994 and well known as the author and maintainer of the
DBI, DBD::Oracle, and Oraperl modules and author/co-maintainer of The
Perl 5 Module List. We also offer Oracle users support for Perl5
Oraperl and related modules (which Oracle is planning to ship as part
of Oracle Web Server 3). 20% of the profit from our Perl support work
will be donated to The Perl Institute."
For more information, contact the The Perl Clinic:
Tel: +44 1483 424424
Fax: +44 1483 419419
Web: http://www.perl.co.uk/
Email: perl-support-info@perl.co.uk or Tim.Bunce@ig.co.uk
=head2 Where do I send bug reports?
If you are reporting a bug in the perl interpreter or the modules
shipped with perl, use the perlbug program in the perl distribution or
email your report to perlbug@perl.com.
If you are posting a bug with a non-standard port (see the answer to
"What platforms is Perl available for?"), a binary distribution, or a
non-standard module (such as Tk, CGI, etc), then please see the
documentation that came with it to determine the correct place to post
bugs.
Read the perlbug man page (perl5.004 or later) for more information.
=head2 What is perl.com? perl.org? The Perl Institute?
perl.org is the official vehicle for The Perl Institute. The motto of
TPI is "helping people help Perl help people" (or something like
that). It's a non-profit organization supporting development,
documentation, and dissemination of perl. Current directors of TPI
include Larry Wall, Tom Christiansen, and Randal Schwartz, whom you
may have heard of somewhere else around here.
The perl.com domain is Tom Christiansen's domain. He created it as a
public service long before perl.org came about. It's the original PBS
of the Perl world, a clearinghouse for information about all things
Perlian, accepting no paid advertisements, glossy gifs, or (gasp!)
java applets on its pages.
=head2 How do I learn about object-oriented Perl programming?
L<perltoot> (distributed with 5.004 or later) is a good place to start.
Also, L<perlobj>, L<perlref>, and L<perlmod> are useful references,
while L<perlbot> has some excellent tips and tricks.
=head1 AUTHOR AND COPYRIGHT
Copyright (c) 1997 Tom Christiansen and Nathan Torkington.
All rights reserved. See L<perlfaq> for distribution information.
--
Tom Christiansen tchrist@jhereg.perl.com
And don't tell me there isn't one bit of difference between null and space,
because that's exactly how much difference there is. :-)
--Larry Wall in <10209@jpl-devvax.JPL.NASA.GOV>
------------------------------
Date: 11 Mar 1997 23:24:35 GMT
From: Tom Christiansen <tchrist@mox.perl.com>
Subject: Perl FAQ part 3 of 0..9: Programming Tools [Periodic Posting]
Message-Id: <5g4pjj$fp9$1@csnews.cs.colorado.edu>
=head1 NAME
perlfaq3 - Programming Tools ($Revision: 1.17 $)
=head1 DESCRIPTION
This section of the FAQ answers questions related to programmer tools
and programming support.
=head2 How do I do (anything)?
Have you looked at CPAN (see L<perlfaq2>)? The chances are that
someone has already written a module that can solve your problem.
Have you read the appropriate man pages? Here's a brief index:
Objects perlref, perlmod, perlobj, perltie
Data Structures perlref, perllol, perldsc
Modules perlmod, perlsub
Regexps perlre, perlfunc, perlop
Moving to perl5 perltrap, perl
Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed
Various http://www.perl.com/CPAN/doc/FMTEYEWTK/index.html
(not a man-page but still useful)
L<perltoc> provides a crude table of contents for the perl man page set.
=head2 How can I use Perl interactively?
The typical approach uses the Perl debugger, described in the
perldebug(1) man page, on an "empty" program, like this:
perl -de 42
Now just type in any legal Perl code, and it will be immediately
evaluated. You can also examine the symbol table, get stack
backtraces, check variable values, set breakpoints, and other
operations typically found in symbolic debuggers
=head2 Is there a Perl shell?
In general, no. The Shell.pm module (distributed with perl) makes
perl try commands which aren't part of the Perl language as shell
commands. perlsh from the source distribution is simplistic and
uninteresting, but may still be what you want.
=head2 How do I debug my Perl programs?
Have you used C<-w>?
Have you tried C<use strict>?
Did you check the returns of each and every system call?
Did you read L<perltrap>?
Have you tried the Perl debugger, described in L<perldebug>?
=head2 How do I profile my Perl programs?
You should get the Devel::DProf module from CPAN, and also use
Benchmark.pm from the standard distribution. Benchmark lets you time
specific portions of your code, while Devel::DProf gives detailed
breakdowns of where your code spends its time.
=head2 How do I cross-reference my Perl programs?
The B::Xref module, shipped with the new, alpha-release Perl compiler
(not the general distribution), can be used to generate
cross-reference reports for Perl programs.
perl -MO=Xref[,OPTIONS] foo.pl
=head2 Is there a pretty-printer (formatter) for Perl?
There is no program that will reformat Perl as much as indent(1) will
do for C. The complex feedback between the scanner and the parser
(this feedback is what confuses the vgrind and emacs programs) makes it
challenging at best to write a stand-alone Perl parser.
Of course, if you simply follow the guidelines in L<perlstyle>, you
shouldn't need to reformat.
Your editor can and should help you with source formatting. The
perl-mode for emacs can provide a remarkable amount of help with most
(but not all) codes, and even less programmable editors can provide
significant assistance.
If you are using to using vgrind program for printing out nice code to
a laser print, you can take a stab at this using
http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the
results are not particularly satisfying for sophisticated code.
=head2 Is there a ctags for Perl?
There's a simple one at
http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do
the trick.
=head2 Where can I get Perl macros for vi?
For a complete version of Tom Christiansen's vi configuration file,
see ftp://ftp.perl.com/pub/vi/toms.exrc, the standard benchmark file
for vi emulators. This runs best with nvi, the current version of vi
out of Berkeley, which incidentally can be built with an embedded Perl
interpreter -- see http://www.perl.com/CPAN/src/misc .
=head2 Where can I get perl-mode for emacs?
Since Emacs version 19 patchlevel 22 or so, there have been both a
perl-mode.el and support for the perl debugger built in. These should
come with the standard Emacs 19 distribution.
In the perl source directory, you'll find a directory called "emacs",
which contains a cperl-mode that color-codes keywords, provides
context-sensitive help, and other nifty things.
Note that the perl-mode of emacs will have fits with "main'foo"
(single quote), and mess up the indentation and hilighting. You
should be using "main::foo", anyway.
=head2 How can I use curses with Perl?
The Curses module from CPAN provides a dynamically loadable object
module interface to a curses library.
=head2 How can I use X or Tk with Perl?
Tk is a completely Perl-based, object-oriented interface to the Tk
toolkit that doesn't force you to use Tcl just to get at Tk. Sx is an
interface to the Athena Widget set. Both are available from CPAN.
=head2 How can I generate simple menus without using CGI or Tk?
The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
module, which is curses-based, can help with this.
=head2 Can I dynamically load C routines into Perl?
If your system architecture supports it, then the standard perl
on your system should also provide you with this via the
DynaLoader module. Read L<perlxstut> for details.
=head2 What is undump?
See the next questions.
=head2 How can I make my Perl program run faster?
The best way to do this is to come up with a better algorithm.
This can often make a dramatic difference. Chapter 8 in the Camel
has some efficiency tips in it you might want to look at.
Other approaches include autoloading seldom-used Perl code. See the
AutoSplit and AutoLoader modules in the standard distribution for
that. Or you could locate the bottleneck and think about writing just
that part in C, the way we used to take bottlenecks in C code and
write them in assembler. Similar to rewriting in C is the use of
modules that have critical sections written in C (for instance, the
PDL module from CPAN).
In some cases, it may be worth it to use the backend compiler to
produce byte code (saving compilation time) or compile into C, which
will certainly save compilation time and sometimes a small amount (but
not much) execution time. See the question about compiling your Perl
programs.
If you're currently linking your perl executable to a shared libc.so,
you can often gain a 10-25% performance benefit by rebuilding it to
link with a static libc.a instead. This will make a bigger perl
executable, but your Perl programs (and programmers) may thank you for
it. See the F<INSTALL> file in the source distribution for more
information.
Unsubstantiated reports allege that Perl interpreters that use sfio
outperform those that don't (for IO intensive applications). To try
this, see the F<INSTALL> file in the source distribution, especially
the "Selecting File IO mechanisms" section.
The undump program was an old attempt to speed up your Perl program
by storing the already-compiled form to disk. This is no longer
a viable option, as it only worked on a few architectures, and
wasn't a good solution anyway.
=head2 How can I make my Perl program take less memory?
When it comes to time-space tradeoffs, Perl nearly always prefers to
throw memory at a problem. Scalars in Perl use more memory than
strings in C, arrays take more that, and hashes use even more. While
there's still a lot to be done, recent releases have been addressing
these issues. For example, as of 5.004, duplicate hash keys are
shared amongst all hashes using them, so require no reallocation.
In some cases, using substr() or vec() to simulate arrays can be
highly beneficial. For example, an array of a thousand booleans will
take at least 20,000 bytes of space, but it can be turned into one
125-byte bit vector for a considerable memory savings. The standard
Tie::SubstrHash module can also help for certain types of data
structure. If you're working with specialist data structures
(matrices, for instance) modules that implement these in C may use
less memory than equivalent Perl modules.
Another thing to try is learning whether your Perl was compiled with
the system malloc or with Perl's built-in malloc. Whichever one it
is, try using the other one and see whether this makes a difference.
Information about malloc is in the F<INSTALL> file in the source
distribution. You can find out whether you are using perl's malloc by
typing C<perl -V:usemymalloc>.
=head2 Is it unsafe to return a pointer to local data?
No, Perl's garbage collection system takes care of this.
sub makeone {
my @a = ( 1 .. 10 );
return \@a;
}
for $i ( 1 .. 10 ) {
push @many, makeone();
}
print $many[4][5], "\n";
print "@many\n";
=head2 How can I free an array or hash so my program shrinks?
You can't. Memory the system allocates to a program will never be
returned to the system. That's why long-running programs sometimes
re-exec themselves.
However, judicious use of my() on your variables will help make sure
that they go out of scope so that Perl can free up their storage for
use in other parts of your program. (NB: my() variables also execute
about 10% faster than globals.) A global variable, of course, never
goes out of scope, so you can't get its space automatically reclaimed,
although undef()ing and/or delete()ing it will achieve the same effect.
In general, memory allocation and de-allocation isn't something you can
or should be worrying about much in Perl, but even this capability
(preallocation of data types) is in the works.
=head2 How can I make my CGI script more efficient?
Beyond the normal measures described to make general Perl programs
faster or smaller, a CGI program has additional issues. It may be run
several times per second. Given that each time it runs it will need
to be re-compiled and will often allocate a megabyte or more of system
memory, this can be a killer. Compiling into C B<isn't going to help
you> because the process start-up overhead is where the bottleneck is.
There are at least two popular ways to avoid this overhead. One
solution involves running the Apache HTTP server (available from
http://www.apache.org/) with either of the mod_perl or mod_fastcgi
plugin modules. With mod_perl and the Apache::* modules (from CPAN),
httpd will run with an embedded Perl interpreter which pre-compiles
your script and then executes it within the same address space without
forking. The Apache extension also gives Perl access to the internal
server API, so modules written in Perl can do just about anything a
module written in C can. With the FCGI module (from CPAN), a Perl
executable compiled with sfio (see the F<INSTALL> file in the
distribution) and the mod_fastcgi module (available from
http://www.fastcgi.com/) each of your perl scripts becomes a permanent
CGI daemon processes.
Both of these solutions can have far-reaching effects on your system
and on the way you write your CGI scripts, so investigate them with
care.
=head2 How can I hide the source for my Perl program?
Delete it. :-) Seriously, there are a number of (mostly
unsatisfactory) solutions with varying levels of "security".
First of all, however, you I<can't> take away read permission, because
the source code has to be readable in order to be compiled and
interpreted. (That doesn't mean that a CGI script's source is
readable by people on the web, though.) So you have to leave the
permissions at the socially friendly 0755 level.
Some people regard this as a security problem. If your program does
insecure things, and relies on people not knowing how to exploit those
insecurities, it is not secure. It is often possible for someone to
determine the insecure things and exploit them without viewing the
source. Security through obscurity, the name for hiding your bugs
instead of fixing them, is little security indeed.
You can try using encryption via source filters (Filter::* from CPAN).
But crackers might be able to decrypt it. You can try using the
byte-code compiler and interpreter described below, but crackers might
be able to de-compile it. You can try using the native-code compiler
described below, but crackers might be able to disassemble it. These
pose varying degrees of difficulty to people wanting to get at your
code, but none can definitively conceal it (this is true of every
language, not just Perl).
If you're concerned about people profiting from your code, then the
bottom line is that nothing but a restrictive licence will give you
legal security. License your software and pepper it with threatening
statements like "This is unpublished proprietary software of XYZ Corp.
Your access to it does not give you permission to use it blah blah
blah." We are not lawyers, of course, so you should see a lawyer if
you want to be sure your licence's wording will stand up in court.
=head2 How can I compile my Perl program into byte-code or C?
Malcolm Beattie has written a multifunction backend compiler,
available from CPAN, that can do both these things. It is as of
Feb-1997 in late alpha release, which means it's fun to play with if
you're a programmer but not really for people looking for turn-key
solutions.
I<Please> understand that merely compiling into C does not in and of
itself guarantee that your code will run very much faster. That's
because except for lucky cases where a lot of native type inferencing
is possible, the normal Perl run time system is still present and thus
will still take just as long to run and be just as big. Most programs
save little more than compilation time, leaving execution no more than
10-30% faster. A few rare programs actually benefit significantly
(like several times faster), but this takes some tweaking of your
code.
Malcolm will be in charge of the 5.005 release of Perl itself
to try to unify and merge his compiler and multithreading work into
the main release.
You'll probably be astonished to learn that the current version of the
compiler generates a compiled form of your script whose executable is
just as big as the original perl executable, and then some. That's
because as currently written, all programs are prepared for a full
eval() statement. You can tremendously reduce this cost by building a
shared libperl.so library and linking against that. See the
F<INSTALL> podfile in the perl source distribution for details. If
you link your main perl binary with this, it will make it miniscule.
For example, on one author's system, /usr/bin/perl is only 11k in
size!
=head2 How can I get '#!perl' to work on [MSDOS,NT,...]?
For OS/2 just use
extproc perl -S -your_switches
as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
`extproc' handling). For DOS one should first invent a corresponding
batch file, and codify it in C<ALTERNATIVE_SHEBANG> (see the
F<INSTALL> file in the source distribution for more information).
The Win95/NT installation, when using the Activeware port of Perl,
will modify the Registry to associate the .pl extension with the perl
interpreter. If you install another port, or (eventually) build your
own Win95/NT Perl using WinGCC, then you'll have to modify the
Registry yourself.
Macintosh perl scripts will have the the appropriate Creator and
Type, so that double-clicking them will invoke the perl application.
I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
throw the perl interpreter into your cgi-bin directory, in order to
get your scripts working for a web server. This is an EXTREMELY big
security risk. Take the time to figure out how to do it correctly.
=head2 Can I write useful perl programs on the command line?
Yes. Read L<perlrun> for more information. Some examples follow.
(These assume standard Unix shell quoting rules.)
# sum first and last fields
perl -lane 'print $F[0] + $F[-1]'
# identify text files
perl -le 'for(@ARGV) {print if -f && -T}' *
# remove comments from C program
perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
# make file a month younger than today, defeating reaper daemons
perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
# find first unused uid
perl -le '$i++ while getpwuid($i); print $i'
# display reasonable manpath
echo $PATH | perl -nl -072 -e '
s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
Ok, the last one was actually an obfuscated perl entry. :-)
=head2 Why don't perl one-liners work on my DOS/Mac/VMS system?
The problem is usually that the command interpreters on those systems
have rather different ideas about quoting than the Unix shells under
which the one-liners were created. On some systems, you may have to
change single-quotes to double ones, which you must I<NOT> do on Unix
or Plan9 systems. You might also have to change a single % to a %%.
For example:
# Unix
perl -e 'print "Hello world\n"'
# DOS, etc.
perl -e "print \"Hello world\n\""
# Mac
print "Hello world\n"
(then Run "Myscript" or Shift-Command-R)
# VMS
perl -e "print ""Hello world\n"""
The problem is that none of this is reliable: it depends on the command
interpreter. Under Unix, the first two often work. Under DOS, it's
entirely possible neither works. If 4DOS was the command shell, I'd
probably have better luck like this:
perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
And don't even try to explain the default command processors --
CMD.EXE in Windows NT slipped a lot of standard Unix functionality in
when nobody was looking, but just try to find documentation for its
quoting rules.
Under the Mac, it depends which environment you are using. The MacPerl
shell, or MPW, is much like Unix shells in its support for several
quoting variants, except that it makes free use of the Mac's non-ASCII
characters as control characters.
I'm afraid that there is no general solution to all of this. It is a
mess, pure and simple.
[Some of this answer was contributed by Kenneth Albanowski.]
=head2 Where can I learn about CGI or Web programming in Perl?
For modules, get the CGI or LWP modules from CPAN. For textbooks,
see the two especially dedicated to web stuff in the question on
books. For problems and questions related to the web, like "Why
do I get 500 Errors" or "Why doesn't it run from the browser right
when it runs fine on the command line", see these sources:
The Idiot's Guide to Solving Perl/CGI Problems, by Tom Christiansen
http://www.perl.com/perl/faq/idiots-guide.html
Frequently Asked Questions about CGI Programming, by Nick Kew
ftp://rtfm.mit.edu/pub/usenet/news.answers/www/cgi-faq
http://www3.pair.com/webthing/docs/cgi/faqs/cgifaq.shtml
Perl/CGI programming FAQ, by Shishir Gundavaram and Tom Christiansen
http://www.perl.com/perl/faq/perl-cgi-faq.html
The WWW Security FAQ, by Lincoln Stein
http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html
World Wide Web FAQ, by Thomas Boutell
http://www.boutell.com/faq/
=head2 Where can I learn about object-oriented Perl programming?
L<perltoot> is a good place to start, and you can use L<perlobj> and
L<perlbot> for reference. Perltoot didn't come out until the 5.004
release, but you can get a copy (in pod, html, or postscript) from
http://www.perl.com/CPAN/doc/FMTEYEWTK/ .
=head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
If you want to call C from Perl, start with L<perlxstut> man page,
moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
call Perl from C, then read L<perlembed>, L<perlcall>, and
L<perlguts>. Don't forget that you can learn a lot from looking at
how the authors of existing extension modules wrote their code and
solved their problems.
=head2 I've read perlembed, perlguts, etc., but I can't embed perl in
my C program, what am I doing wrong?
Download the ExtUtils::Embed kit from CPAN and run `make test'. If
the tests pass, read the pods again and again and again. If they
fail, see L<perlbug> and send a bugreport with the output of
C<make test TEST_VERBOSE=1> along with C<perl -V>.
=head2 When I tried to run my script, I got this message. What does it
mean?
L<perldiag> has a complete list of perl's error messages and warnings,
with explanatory text. You can also use the splain program (distributed
with perl) to explain the error messages:
perl program 2>diag.out
splain [-v] [-p] diag.out
or change your program to explain the messages for you:
use diagnostics;
or
use diagnostics -verbose;
=head2 What's MakeMaker?
This module (part of the standard perl distribution) is designed to
write a Makefile for an extension module from a Makefile.PL. For more
information, see L<ExtUtils::MakeMaker>.
=head1 AUTHOR AND COPYRIGHT
Copyright (c) 1997 Tom Christiansen and Nathan Torkington.
All rights reserved. See L<perlfaq> for distribution information.
--
Tom Christiansen tchrist@jhereg.perl.com
"A journey of a thousand miles continues with the second step." --Larry Wall
------------------------------
Date: 8 Mar 97 21:33:47 GMT (Last modified)
From: Perl-Request@ruby.oce.orst.edu (Perl-Users-Digest Admin)
Subject: Digest Administrivia (Last modified: 8 Mar 97)
Message-Id: <null>
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