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perlmodlib - constructing new Perl modules and finding existing ones |
perlmodlib - constructing new Perl modules and finding existing ones
Many modules are included the Perl distribution. These are described below, and all end in .pm. You may discover compiled library file (usually ending in .so) or small pieces of modules to be autoloaded (ending in .al); these were automatically generated by the installation process. You may also discover files in the library directory that end in either .pl or .ph. These are old libraries supplied so that old programs that use them still run. The .pl files will all eventually be converted into standard modules, and the .ph files made by h2ph will probably end up as extension modules made by h2xs. (Some .ph values may already be available through the POSIX, Errno, or Fcntl modules.) The pl2pm file in the distribution may help in your conversion, but it's just a mechanical process and therefore far from bulletproof.
They work somewhat like compiler directives (pragmata) in that they
tend to affect the compilation of your program, and thus will usually
work well only when used within a use, or no. Most of these
are lexically scoped, so an inner BLOCK may countermand them
by saying:
no integer;
no strict 'refs';
no warnings;
which lasts until the end of that BLOCK.
Some pragmas are lexically scoped--typically those that affect the
$^H hints variable. Others affect the current package instead,
like use vars and use subs, which allow you to predeclare a
variables or subroutines within a particular file rather than
just a block. Such declarations are effective for the entire file
for which they were declared. You cannot rescind them with no
vars or no subs.
The following pragmas are defined (and have their own documentation).
\N{named} string literal escape.
-r, -w for AFS, etc.
our())
Standard, bundled modules are all expected to behave in a well-defined manner with respect to namespace pollution because they use the Exporter module. See their own documentation for details.
B::Stash -- XXX NFI XXX
ExtUtils::Miniperl, writemain - Write the C code for perlmain.c
stat() functions
syslog(3) calls
Text::Tabs -- expand and unexpand tabs per expand(1) and unexpand(1)
gmtime() function
localtime() function
To find out all modules installed on your system, including those without documentation or outside the standard release, just do this:
% find `perl -e 'print "@INC"'` -name '*.pm' -print
To get a log of all module distributions which have been installed since perl was installed, just do:
% perldoc perllocal
Modules should all have their own documentation installed and accessible
via your system man(1) command, or via the perldoc program. If you do
not have a find
program, you can use the Perl find2perl program instead, which
generates Perl code as output you can run through perl. If you
have a man program but it doesn't find your modules, you'll have
to fix your manpath. See the perl manpage for details.
Extension modules are written in C (or a mix of Perl and C). They are usually dynamically loaded into Perl if and when you need them, but may also be be linked in statically. Supported extension modules include Socket, Fcntl, and POSIX.
Many popular C extension modules do not come bundled (at least, not completely) due to their sizes, volatility, or simply lack of time for adequate testing and configuration across the multitude of platforms on which Perl was beta-tested. You are encouraged to look for them on CPAN (described below), or using web search engines like Alta Vista or Deja News.
CPAN stands for Comprehensive Perl Archive Network; it's a globally replicated trove of Perl materials, including documentation, style guides, tricks and trap, alternate ports to non-Unix systems and occasional binary distributions for these. Search engines for CPAN can be found at http://cpan.perl.com/ and at http://theory.uwinnipeg.ca/mod_perl/cpan-search.pl .
Most importantly, CPAN includes around a thousand unbundled modules, some of which require a C compiler to build. Major categories of modules are:
Registered CPAN sites as of this writing include the following. You should try to choose one close to you:
South Africa ftp://ftp.is.co.za/programming/perl/CPAN/
ftp://ftp.saix.net/pub/CPAN/
ftp://ftp.sun.ac.za/CPAN/
ftp://ftpza.co.za/pub/mirrors/cpan/
China ftp://freesoft.cei.gov.cn/pub/languages/perl/CPAN/
Hong Kong ftp://ftp.pacific.net.hk/pub/mirror/CPAN/
Indonesia ftp://malone.piksi.itb.ac.id/pub/CPAN/
Israel ftp://bioinfo.weizmann.ac.il/pub/software/perl/CPAN/
Japan ftp://ftp.dti.ad.jp/pub/lang/CPAN/
ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/
ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/
ftp://ftp.meisei-u.ac.jp/pub/CPAN/
ftp://ftp.ring.gr.jp/pub/lang/perl/CPAN/
ftp://mirror.nucba.ac.jp/mirror/Perl/
Saudi-Arabia ftp://ftp.isu.net.sa/pub/CPAN/
Singapore ftp://ftp.nus.edu.sg/pub/unix/perl/CPAN/
South Korea ftp://ftp.bora.net/pub/CPAN/
ftp://ftp.kornet.net/pub/CPAN/
ftp://ftp.nuri.net/pub/CPAN/
Taiwan ftp://coda.nctu.edu.tw/computer-languages/perl/CPAN/
ftp://ftp.ee.ncku.edu.tw/pub3/perl/CPAN/
ftp://ftp1.sinica.edu.tw/pub1/perl/CPAN/
Thailand ftp://ftp.nectec.or.th/pub/mirrors/CPAN/
Australia ftp://cpan.topend.com.au/pub/CPAN/
ftp://ftp.labyrinth.net.au/pub/perl-CPAN/
ftp://ftp.sage-au.org.au/pub/compilers/perl/CPAN/
ftp://mirror.aarnet.edu.au/pub/perl/CPAN/
New Zealand ftp://ftp.auckland.ac.nz/pub/perl/CPAN/
ftp://sunsite.net.nz/pub/languages/perl/CPAN/
Costa Rica ftp://ftp.ucr.ac.cr/pub/Unix/CPAN/
Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/
Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/
Bulgaria ftp://ftp.ntrl.net/pub/mirrors/CPAN/
Croatia ftp://ftp.linux.hr/pub/CPAN/
Czech Republic ftp://ftp.fi.muni.cz/pub/perl/
ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/
Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/
Estonia ftp://ftp.ut.ee/pub/languages/perl/CPAN/
Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/
France ftp://ftp.grolier.fr/pub/perl/CPAN/
ftp://ftp.lip6.fr/pub/perl/CPAN/
ftp://ftp.oleane.net/pub/mirrors/CPAN/
ftp://ftp.pasteur.fr/pub/computing/CPAN/
ftp://ftp.uvsq.fr/pub/perl/CPAN/
German ftp://ftp.gigabell.net/pub/CPAN/
Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/
ftp://ftp.gmd.de/packages/CPAN/
ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/
ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
ftp://ftp.uni-erlangen.de/pub/source/CPAN/
ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
ftp://ftp.freenet.de/pub/ftp.cpan.org/pub/
ftp://ftp.gmd.de/packages/CPAN/
ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
ftp://ftp.leo.org/pub/comp/general/programming/languages/script/perl/CPAN/
ftp://ftp.mpi-sb.mpg.de/pub/perl/CPAN/
ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/
ftp://ftp.uni-erlangen.de/pub/source/CPAN/
ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/
Greece ftp://ftp.ntua.gr/pub/lang/perl/
Hungary ftp://ftp.kfki.hu/pub/packages/perl/CPAN/
Iceland ftp://ftp.gm.is/pub/CPAN/
Ireland ftp://cpan.indigo.ie/pub/CPAN/
ftp://sunsite.compapp.dcu.ie/pub/perl/
Italy ftp://cis.uniRoma2.it/CPAN/
ftp://ftp.flashnet.it/pub/CPAN/
ftp://ftp.unina.it/pub/Other/CPAN/
ftp://ftp.unipi.it/pub/mirror/perl/CPAN/
Netherlands ftp://ftp.cs.uu.nl/mirror/CPAN/
ftp://ftp.nluug.nl/pub/languages/perl/CPAN/
Norway ftp://ftp.uit.no/pub/languages/perl/cpan/
ftp://sunsite.uio.no/pub/languages/perl/CPAN/
Poland ftp://ftp.man.torun.pl/pub/CPAN/
ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/
ftp://sunsite.icm.edu.pl/pub/CPAN/
Portugal ftp://ftp.ci.uminho.pt/pub/mirrors/cpan/
ftp://ftp.ist.utl.pt/pub/CPAN/
ftp://ftp.ua.pt/pub/CPAN/
Romania ftp://ftp.dnttm.ro/pub/CPAN/
Russia ftp://ftp.chg.ru/pub/lang/perl/CPAN/
ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/
Slovakia ftp://ftp.entry.sk/pub/languages/perl/CPAN/
Slovenia ftp://ftp.arnes.si/software/perl/CPAN/
Spain ftp://ftp.etse.urv.es/pub/perl/
ftp://ftp.rediris.es/mirror/CPAN/
Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/
Switzerland ftp://sunsite.cnlab-switch.ch/mirror/CPAN/
Turkey ftp://sunsite.bilkent.edu.tr/pub/languages/CPAN/
United Kingdom ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/
ftp://ftp.flirble.org/pub/languages/perl/CPAN/
ftp://ftp.mirror.ac.uk/sites/ftp.funet.fi/pub/languages/perl/CPAN/
ftp://ftp.plig.org/pub/CPAN/
ftp://sunsite.doc.ic.ac.uk/packages/CPAN/
Alberta ftp://sunsite.ualberta.ca/pub/Mirror/CPAN/
California ftp://cpan.nas.nasa.gov/pub/perl/CPAN/
ftp://cpan.valueclick.com/CPAN/
ftp://ftp.cdrom.com/pub/perl/CPAN/
http://download.sourceforge.net/mirrors/CPAN/
Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/
Florida ftp://ftp.cise.ufl.edu/pub/perl/CPAN/
Georgia ftp://ftp.twoguys.org/CPAN/
Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/
Indiana ftp://csociety-ftp.ecn.purdue.edu/pub/CPAN/
ftp://ftp.uwsg.indiana.edu/pub/perl/CPAN/
Kentucky ftp://ftp.uky.edu/CPAN/
Manitoba ftp://theoryx5.uwinnipeg.ca/pub/CPAN/
Massachusetts ftp://ftp.ccs.neu.edu/net/mirrors/ftp.funet.fi/pub/languages/perl/CPAN/
ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/
Mexico ftp://ftp.msg.com.mx/pub/CPAN/
New York ftp://ftp.deao.net/pub/CPAN/
ftp://ftp.rge.com/pub/languages/perl/
North Carolina ftp://ftp.duke.edu/pub/perl/
Nova Scotia ftp://cpan.chebucto.ns.ca/pub/CPAN/
Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/
Ontario ftp://ftp.crc.ca/pub/packages/lang/perl/CPAN/
Oregon ftp://ftp.orst.edu/pub/packages/CPAN/
Pennsylvania ftp://ftp.epix.net/pub/languages/perl/
Tennessee ftp://ftp.sunsite.utk.edu/pub/CPAN/
Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/
ftp://jhcloos.com/pub/mirror/CPAN/
Utah ftp://mirror.xmission.com/CPAN/
Virginia ftp://ftp.perl.org/pub/perl/CPAN/
ftp://ruff.cs.jmu.edu/pub/CPAN/
Washington ftp://ftp-mirror.internap.com/pub/CPAN/
ftp://ftp.llarian.net/pub/CPAN/
ftp://ftp.spu.edu/pub/CPAN/
Brazil ftp://cpan.if.usp.br/pub/mirror/CPAN/
ftp://ftp.matrix.com.br/pub/perl/
Chile ftp://sunsite.dcc.uchile.cl/pub/Lang/PERL/
For an up-to-date listing of CPAN sites, see http://www.perl.com/perl/CPAN/SITES or ftp://www.perl.com/CPAN/SITES .
(The following section is borrowed directly from Tim Bunce's modules file, available at your nearest CPAN site.)
Perl implements a class using a package, but the presence of a package doesn't imply the presence of a class. A package is just a namespace. A class is a package that provides subroutines that can be used as methods. A method is just a subroutine that expects, as its first argument, either the name of a package (for ``static'' methods), or a reference to something (for ``virtual'' methods).
A module is a file that (by convention) provides a class of the same name (sans the .pm), plus an import method in that class that can be called to fetch exported symbols. This module may implement some of its methods by loading dynamic C or C++ objects, but that should be totally transparent to the user of the module. Likewise, the module might set up an AUTOLOAD function to slurp in subroutine definitions on demand, but this is also transparent. Only the .pm file is required to exist. See the perlsub manpage, the perltoot manpage, and the AutoLoader manpage for details about the AUTOLOAD mechanism.
If you are writing a module to expand an already existing set of modules, please coordinate with the author of the package. It helps if you follow the same naming scheme and module interaction scheme as the original author.
use warnings; (or use warnings qw(...);).
Remember that you can add no warnings qw(...); to individual blocks
of code that need less warnings.
Use blessed references. Use the two argument form of bless to bless into the class name given as the first parameter of the constructor, e.g.,:
sub new {
my $class = shift;
return bless {}, $class;
}
or even this if you'd like it to be used as either a static or a virtual method.
sub new {
my $self = shift;
my $class = ref($self) || $self;
return bless {}, $class;
}
Pass arrays as references so more parameters can be added later (it's also faster). Convert functions into methods where appropriate. Split large methods into smaller more flexible ones. Inherit methods from other modules if appropriate.
Avoid class name tests like: die "Invalid" unless ref $ref eq 'FOO'.
Generally you can delete the eq 'FOO' part with no harm at all.
Let the objects look after themselves! Generally, avoid hard-wired
class names as far as possible.
Avoid $r->Class::func() where using @ISA=qw(... Class ...) and
$r->func() would work (see the perlbot manpage for more details).
Use autosplit so little used or newly added functions won't be a burden to programs that don't use them. Add test functions to the module after __END__ either using AutoSplit or by saying:
eval join('',<main::DATA>) || die $@ unless caller();
Does your module pass the 'empty subclass' test? If you say
@SUBCLASS::ISA = qw(YOURCLASS); your applications should be able
to use SUBCLASS in exactly the same way as YOURCLASS. For example,
does your application still work if you change: $obj = new YOURCLASS;
into: $obj = new SUBCLASS; ?
Avoid keeping any state information in your packages. It makes it difficult for multiple other packages to use yours. Keep state information in objects.
Always use -w.
Try to use strict; (or use strict qw(...);).
Remember that you can add no strict qw(...); to individual blocks
of code that need less strictness.
Always use -w.
Follow the guidelines in the perlstyle(1) manual.
Always use -w.
Coding style is a matter of personal taste. Many people evolve their style over several years as they learn what helps them write and maintain good code. Here's one set of assorted suggestions that seem to be widely used by experienced developers:
Use underscores to separate words. It is generally easier to read $var_names_like_this than $VarNamesLikeThis, especially for non-native speakers of English. It's also a simple rule that works consistently with VAR_NAMES_LIKE_THIS.
Package/Module names are an exception to this rule. Perl informally reserves lowercase module names for 'pragma' modules like integer and strict. Other modules normally begin with a capital letter and use mixed case with no underscores (need to be short and portable).
You may find it helpful to use letter case to indicate the scope or nature of a variable. For example:
$ALL_CAPS_HERE constants only (beware clashes with Perl vars) $Some_Caps_Here package-wide global/static $no_caps_here function scope my() or local() variables
Function and method names seem to work best as all lowercase.
e.g., $obj->as_string().
You can use a leading underscore to indicate that a variable or function should not be used outside the package that defined it.
Do NOT export anything else by default without a good reason!
Exports pollute the namespace of the module user. If you must export try to use @EXPORT_OK in preference to @EXPORT and avoid short or common names to reduce the risk of name clashes.
Generally anything not exported is still accessible from outside the
module using the ModuleName::item_name (or $blessed_ref->method)
syntax. By convention you can use a leading underscore on names to
indicate informally that they are 'internal' and not for public use.
(It is actually possible to get private functions by saying:
my $subref = sub { ... }; &$subref;. But there's no way to call that
directly as a method, because a method must have a name in the symbol
table.)
As a general rule, if the module is trying to be object oriented then export nothing. If it's just a collection of functions then @EXPORT_OK anything but use @EXPORT with caution.
Having 57 modules all called Sort will not make life easy for anyone (though having 23 called Sort::Quick is only marginally better :-). Imagine someone trying to install your module alongside many others. If in any doubt ask for suggestions in comp.lang.perl.misc.
If you are developing a suite of related modules/classes it's good practice to use nested classes with a common prefix as this will avoid namespace clashes. For example: Xyz::Control, Xyz::View, Xyz::Model etc. Use the modules in this list as a naming guide.
If adding a new module to a set, follow the original author's standards for naming modules and the interface to methods in those modules.
To be portable each component of a module name should be limited to 11 characters. If it might be used on MS-DOS then try to ensure each is unique in the first 8 characters. Nested modules make this easier.
The best way to know for sure, and pick up many helpful suggestions, is to ask someone who knows. Comp.lang.perl.misc is read by just about all the people who develop modules and it's the best place to ask.
All you need to do is post a short summary of the module, its purpose and interfaces. A few lines on each of the main methods is probably enough. (If you post the whole module it might be ignored by busy people - generally the very people you want to read it!)
Don't worry about posting if you can't say when the module will be ready - just say so in the message. It might be worth inviting others to help you, they may be able to complete it for you!
If the README file seems to be getting too large you may wish to split out some of the sections into separate files: INSTALL, Copying, ToDo etc.
Perl, for example, is supplied with two types of licence: The GNU GPL and The Artistic Licence (see the files README, Copying, and Artistic). Larry has good reasons for NOT just using the GNU GPL.
My personal recommendation, out of respect for Larry, Perl, and the Perl community at large is to state something simply like:
Copyright (c) 1995 Your Name. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
This statement should at least appear in the README file. You may also wish to include it in a Copying file and your source files. Remember to include the other words in addition to the Copyright.
$VERSION = "0.01"). Don't use a ``1.3.2'' style version.
See the Exporter manpage for details.
It may be handy to add a function or method to retrieve the number. Use the number in announcements and archive file names when releasing the module (ModuleName-1.02.tar.Z). See perldoc ExtUtils::MakeMaker.pm for details.
If possible, register the module with CPAN. You should include details of its location in your announcement.
Some notes about ftp archives: Please use a long descriptive file name that includes the version number. Most incoming directories will not be readable/listable, i.e., you won't be able to see your file after uploading it. Remember to send your email notification message as soon as possible after uploading else your file may get deleted automatically. Allow time for the file to be processed and/or check the file has been processed before announcing its location.
FTP Archives for Perl Modules:
Follow the instructions and links on:
http://www.perl.com/CPAN/modules/00modlist.long.html http://www.perl.com/CPAN/modules/04pause.html
or upload to one of these sites:
https://pause.kbx.de/pause/ http://pause.perl.org/pause/
and notify <modules@perl.org>.
By using the WWW interface you can ask the Upload Server to mirror your modules from your ftp or WWW site into your own directory on CPAN!
Please remember to send me an updated entry for the Module list!
die(...) to croak(...)Being a mechanical process pl2pm is not bullet proof. The converted code will need careful checking, especially any package statements. Don't delete the original .pl file till the new .pm one works!
% perl -e 'use Module::Name; method(@ARGV)' ...
or
% perl -mModule::Name ... (in perl5.002 or higher)
Perl does not enforce private and public parts of its modules as you may have been used to in other languages like C++, Ada, or Modula-17. Perl doesn't have an infatuation with enforced privacy. It would prefer that you stayed out of its living room because you weren't invited, not because it has a shotgun.
The module and its user have a contract, part of which is common law,
and part of which is ``written''. Part of the common law contract is
that a module doesn't pollute any namespace it wasn't asked to. The
written contract for the module (A.K.A. documentation) may make other
provisions. But then you know when you use RedefineTheWorld that
you're redefining the world and willing to take the consequences.
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perlmodlib - constructing new Perl modules and finding existing ones |