PERLMODLIB(1) Perl Programmers Reference Guide PERLMODLIB(1)NAMEperlmodlib - constructing new Perl modules and finding
existing ones
DESCRIPTIONTHE PERL MODULE LIBRARY
A number of modules are included the Perl distribution.
These are described below, and all end in .pm. 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 module.) The pl2pm
file in the distribution may help in your conversion, but
it's just a mechanical process and therefore far from
bulletproof.
Pragmatic Modules
They work somewhat like pragmas 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 any of these by saying:
no integer;
no strict 'refs';
which lasts until the end of that BLOCK.
Unlike the pragmas that effect the $^H hints variable, the
use vars and use subs declarations are not BLOCK-scoped.
They 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).
use autouse MODULE => qw(sub1 sub2 sub3)
Defers require MODULE until someone calls one
of the specified subroutines (which must be
exported by MODULE). This pragma should be
used with caution, and only when necessary.
blib manipulate @INC at compile time to use
MakeMaker's uninstalled version of a package
diagnostics force verbose warning diagnostics
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integer compute arithmetic in integer instead of
double
less request less of something from the compiler
lib manipulate @INC at compile time
locale use or ignore current locale for builtin
operations (see the perllocale manpage)
ops restrict named opcodes when compiling or
running Perl code
overload overload basic Perl operations
re alter behaviour of regular expressions
sigtrap enable simple signal handling
strict restrict unsafe constructs
subs predeclare sub names
vmsish adopt certain VMS-specific behaviors
vars predeclare global variable names
Standard Modules
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.
AnyDBM_File provide framework for multiple DBMs
AutoLoader load functions only on demand
AutoSplit split a package for autoloading
Benchmark benchmark running times of code
CPAN interface to Comprehensive Perl Archive
Network
CPAN::FirstTime
create a CPAN configuration file
CPAN::Nox run CPAN while avoiding compiled extensions
Carp warn of errors (from perspective of caller)
Class::Struct
declare struct-like datatypes
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Config access Perl configuration information
Cwd get pathname of current working directory
DB_File access to Berkeley DB
Devel::SelfStubber
generate stubs for a SelfLoading module
DirHandle supply object methods for directory handles
DynaLoader dynamically load C libraries into Perl code
English use nice English (or awk) names for ugly
punctuation variables
Env import environment variables
Exporter implements default import method for modules
ExtUtils::Embed
utilities for embedding Perl in C/C++
applications
ExtUtils::Install
install files from here to there
ExtUtils::Liblist
determine libraries to use and how to use them
ExtUtils::MM_OS2
methods to override Unix behaviour in
ExtUtils::MakeMaker
ExtUtils::MM_Unix
methods used by ExtUtils::MakeMaker
ExtUtils::MM_VMS
methods to override Unix behaviour in
ExtUtils::MakeMaker
ExtUtils::MakeMaker
create an extension Makefile
ExtUtils::Manifest
utilities to write and check a MANIFEST file
ExtUtils::Mkbootstrap
make a bootstrap file for use by DynaLoader
ExtUtils::Mksymlists
write linker options files for dynamic
extension
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ExtUtils::testlib
add blib/* directories to @INC
Fatal make errors in builtins or Perl functions
fatal
Fcntl load the C Fcntl.h defines
File::Basename
split a pathname into pieces
File::CheckTree
run many filetest checks on a tree
File::Compare
compare files or filehandles
File::Copy copy files or filehandles
File::Find traverse a file tree
File::Path create or remove a series of directories
File::Spec portably perform operations on file names
File::Spec::Functions
function call interface to File::Spec module
File::stat by-name interface to Perl's builtin stat()
functions
FileCache keep more files open than the system permits
FileHandle supply object methods for filehandles
FindBin locate directory of original Perl script
GDBM_File access to the gdbm library
Getopt::Long
extended processing of command line options
Getopt::Std process single-character switches with switch
clustering
I18N::Collate
compare 8-bit scalar data according to the
current locale
IO load various IO modules
IO::File supply object methods for filehandles
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IO::Handle supply object methods for I/O handles
IO::Pipe supply object methods for pipes
IO::Seekable
supply seek based methods for I/O objects
IO::Select OO interface to the select system call
IO::Socket object interface to socket communications
IPC::Open2 open a process for both reading and writing
IPC::Open3 open a process for reading, writing, and error
handling
Math::BigFloat
arbitrary length float math package
Math::BigInt
arbitrary size integer math package
Math::Complex
complex numbers and associated mathematical
functions
Math::Trig simple interface to parts of Math::Complex for
those who need trigonometric functions only
for real numbers
NDBM_File tied access to ndbm files
Net::Ping Hello, anybody home?
Net::hostent
by-name interface to Perl's builtin gethost*()
functions
Net::netent by-name interface to Perl's builtin getnet*()
functions
Net::protoent
by-name interface to Perl's builtin
getproto*() functions
Net::servent
by-name interface to Perl's builtin getserv*()
functions
Opcode disable named opcodes when compiling or
running Perl code
Pod::Text convert POD data to formatted ASCII text
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POSIX interface to IEEE Standard 1003.1
SDBM_File tied access to sdbm files
Safe compile and execute code in restricted
compartments
Search::Dict
search for key in dictionary file
SelectSaver save and restore selected file handle
SelfLoader load functions only on demand
Shell run shell commands transparently within Perl
Socket load the C socket.h defines and structure
manipulators
Symbol manipulate Perl symbols and their names
Sys::Hostname
try every conceivable way to get hostname
Sys::Syslog interface to the Unix syslog(3) calls
Term::Cap termcap interface
Term::Complete
word completion module
Term::ReadLine
interface to various readline packages
Test::Harness
run Perl standard test scripts with statistics
Text::Abbrev
create an abbreviation table from a list
Text::ParseWords
parse text into an array of tokens
Text::Soundex
implementation of the Soundex Algorithm as
described by Knuth
Text::Tabs expand and unexpand tabs per the Unix
expand(1) and unexpand(1)
Text::Wrap line wrapping to form simple paragraphs
Tie::Hash base class definitions for tied hashes
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Tie::RefHash
base class definitions for tied hashes with
references as keys
Tie::Scalar base class definitions for tied scalars
Tie::SubstrHash
fixed-table-size, fixed-key-length hashing
Time::Local efficiently compute time from local and GMT
time
Time::gmtime
by-name interface to Perl's builtin gmtime()
function
Time::localtime
by-name interface to Perl's builtin
localtime() function
Time::tm internal object used by Time::gmtime and
Time::localtime
UNIVERSAL base class for ALL classes (blessed
references)
User::grent by-name interface to Perl's builtin getgr*()
functions
User::pwent by-name interface to Perl's builtin getpw*()
functions
To find out all the modules installed on your system,
including those without documentation or outside the
standard release, do this:
% find `perl -e 'print "@INC"'` -name '*.pm' -print
They should all have their own documentation installed and
accessible via your system man(1) command. If that fails,
try the perldoc program.
Extension Modules
Extension modules are written in C (or a mix of Perl and
C) and may be statically linked or in general are
dynamically loaded into Perl if and when you need them.
Supported extension modules include the Socket, Fcntl, and
POSIX modules.
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-
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tested. You are encouraged to look for them in
archie(1L), the Perl FAQ or Meta-FAQ, the WWW page, and
even with their authors before randomly posting asking for
their present condition and disposition.
CPAN
CPAN stands for the Comprehensive Perl Archive Network.
This is a globally replicated collection of all known Perl
materials, including hundreds of unbundled modules. Here
are the major categories of modules:
o Language Extensions and Documentation Tools
o Development Support
o Operating System Interfaces
o Networking, Device Control (modems) and InterProcess
Communication
o Data Types and Data Type Utilities
o Database Interfaces
o User Interfaces
o Interfaces to / Emulations of Other Programming
Languages
o File Names, File Systems and File Locking (see also File
Handles)
o String Processing, Language Text Processing, Parsing,
and Searching
o Option, Argument, Parameter, and Configuration File
Processing
o Internationalization and Locale
o Authentication, Security, and Encryption
o World Wide Web, HTML, HTTP, CGI, MIME
o Server and Daemon Utilities
o Archiving and Compression
o Images, Pixmap and Bitmap Manipulation, Drawing, and
Graphing
o Mail and Usenet News
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o Control Flow Utilities (callbacks and exceptions etc)
o File Handle and Input/Output Stream Utilities
o Miscellaneous Modules
The registered CPAN sites as of this writing include the
following. You should try to choose one close to you:
o Africa
South Africa ftp://ftp.is.co.za/programming/perl/CPAN/
ftp://ftpza.co.za/pub/mirrors/cpan/
o Asia
Armenia ftp://sunsite.aua.am/pub/CPAN/
China ftp://freesoft.cei.gov.cn/pub/languages/perl/CPAN/
Hong Kong ftp://ftp.hkstar.com/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://mirror.nucba.ac.jp/mirror/Perl/
Singapore ftp://ftp.nus.edu.sg/pub/unix/perl/CPAN/
South Korea ftp://ftp.bora.net/pub/CPAN/
ftp://ftp.nuri.net/pub/CPAN/
Taiwan ftp://ftp.wownet.net/pub2/PERL/
ftp://ftp1.sinica.edu.tw/pub1/perl/CPAN/
Thailand ftp://ftp.cs.riubon.ac.th/pub/mirrors/CPAN/
ftp://ftp.nectec.or.th/pub/mirrors/CPAN/
o Australasia
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/
o Central America
Costa Rica ftp://ftp.ucr.ac.cr/pub/Unix/CPAN/
o Europe
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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.lip6.fr/pub/perl/CPAN/
ftp://ftp.oleane.net/pub/mirrors/CPAN/
ftp://ftp.pasteur.fr/pub/computing/CPAN/
Germany ftp://ftp.archive.de.uu.net/pub/CPAN/
ftp://ftp.gmd.de/packages/CPAN/
ftp://ftp.gwdg.de/pub/languages/perl/CPAN/
ftp://ftp.leo.org/pub/comp/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/
Ireland ftp://sunsite.compapp.dcu.ie/pub/perl/
Italy ftp://cis.uniRoma2.it/CPAN/
ftp://ftp.flashnet.it/pub/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.szczecin.pl/pub/perl/CPAN/
ftp://ftp.man.torun.pl/pub/doc/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.ua.pt/pub/CPAN/
Romania ftp://ftp.dntis.ro/pub/mirrors/perl-cpan/
ftp://ftp.dnttm.ro/pub/CPAN/
Russia ftp://cpan.npi.msu.su/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.plig.org/pub/CPAN/
ftp://sunsite.doc.ic.ac.uk/packages/CPAN/
ftp://unix.hensa.ac.uk/mirrors/perl-CPAN/
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o North America
Alberta ftp://sunsite.ualberta.ca/pub/Mirror/CPAN/
California ftp://ftp.cdrom.com/pub/perl/CPAN/
ftp://ftp.digital.com/pub/plan/perl/CPAN/
Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/
Florida ftp://ftp.cise.ufl.edu/pub/perl/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/
Manitoba ftp://theory.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 D.F. ftp://ftp.msg.com.mx/pub/CPAN/
New York ftp://ftp.rge.com/pub/languages/perl/
North Carolina ftp://ftp.duke.edu/pub/perl/
Oklahoma ftp://ftp.ou.edu/mirrors/CPAN/
Ontario ftp://ftp.crc.ca/pub/packages/perl/CPAN/
Oregon ftp://ftp.orst.edu/pub/packages/CPAN/
Pennsylvania ftp://ftp.epix.net/pub/languages/perl/
Texas ftp://ftp.sedl.org/pub/mirrors/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.spu.edu/pub/CPAN/
o South America
Brazil ftp://cpan.if.usp.br/pub/mirror/CPAN/
Chile ftp://ftp.ing.puc.cl/pub/unix/perl/CPAN/
ftp://sunsite.dcc.uchile.cl/pub/Lang/perl/CPAN/
For an up-to-date listing of CPAN sites, see
http://www.perl.com/perl/CPAN or ftp://ftp.perl.com/perl/.
Modules: Creation, Use, and Abuse
(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.
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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.
Guidelines for Module Creation
Do similar modules already exist in some form?
If so, please try to reuse the existing modules either
in whole or by inheriting useful features into a new
class. If this is not practical try to get together
with the module authors to work on extending or
enhancing the functionality of the existing modules.
A perfect example is the plethora of packages in perl4
for dealing with command line options.
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.
Try to design the new module to be easy to extend and
reuse.
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.
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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. Always use -w! Follow the
guidelines in the perlstyle(1) manual.
Some simple style guidelines
The perlstyle manual supplied with Perl has many
helpful points.
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
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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.
Select what to export.
Do NOT export method names!
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.
Select a name for the module.
This name should be as descriptive, accurate, and
complete as possible. Avoid any risk of ambiguity.
Always try to use two or more whole words. Generally
the name should reflect what is special about what the
module does rather than how it does it. Please use
nested module names to group informally or categorize
a module. There should be a very good reason for a
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module not to have a nested name. Module names should
begin with a capital letter.
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.
Have you got it right?
How do you know that you've made the right decisions?
Have you picked an interface design that will cause
problems later? Have you picked the most appropriate
name? Do you have any questions?
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!
README and other Additional Files.
It's well known that software developers usually fully
document the software they write. If, however, the
world is in urgent need of your software and there is
not enough time to write the full documentation please
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at least provide a README file containing:
o A description of the module/package/extension etc.
o A copyright notice - see below.
o Prerequisites - what else you may need to have.
o How to build it - possible changes to Makefile.PL etc.
o How to install it.
o Recent changes in this release, especially
incompatibilities
o Changes / enhancements you plan to make in the future.
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.
Adding a Copyright Notice.
How you choose to license your work is a personal
decision. The general mechanism is to assert your
Copyright and then make a declaration of how
others may copy/use/modify your work.
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.
Give the module a version/issue/release number.
To be fully compatible with the Exporter and
MakeMaker modules you should store your module's
version number in a non-my package variable called
$VERSION. This should be a floating point number
with at least two digits after the decimal (i.e.,
hundredths, e.g, $VERSION = "0.01"). Don't use a
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"1.3.2" style version. See Exporter.pm in
Perl5.001m or later 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.
How to release and distribute a module.
It's good idea to post an announcement of the
availability of your module (or the module itself
if small) to the comp.lang.perl.announce Usenet
newsgroup. This will at least ensure very wide
once-off distribution.
If possible you should place the module into a
major ftp archive and 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://franz.ww.tu-berlin.de/modulelist
or upload to one of these sites:
ftp://franz.ww.tu-berlin.de/incoming
ftp://ftp.cis.ufl.edu/incoming
and notify <upload@franz.ww.tu-berlin.de>.
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!
Take care when changing a released module.
Always strive to remain compatible with previous
released versions. Otherwise try to add a
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mechanism to revert to the old behaviour if people
rely on it. Document incompatible changes.
Guidelines for Converting Perl 4 Library Scripts into
Modules
There is no requirement to convert anything.
If it ain't broke, don't fix it! Perl 4 library
scripts should continue to work with no problems. You
may need to make some minor changes (like escaping
non-array @'s in double quoted strings) but there is
no need to convert a .pl file into a Module for just
that.
Consider the implications.
All Perl applications that make use of the script will
need to be changed (slightly) if the script is
converted into a module. Is it worth it unless you
plan to make other changes at the same time?
Make the most of the opportunity.
If you are going to convert the script to a module you
can use the opportunity to redesign the interface. The
'Guidelines for Module Creation' above include many of
the issues you should consider.
The pl2pm utility will get you started.
This utility will read *.pl files (given as
parameters) and write corresponding *.pm files. The
pl2pm utilities does the following:
o Adds the standard Module prologue lines
o Converts package specifiers from ' to ::
o Converts die(...) to croak(...)
o Several other minor changes
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!
Guidelines for Reusing Application Code
Complete applications rarely belong in the Perl Module
Library.
Many applications contain some Perl code that could be
reused.
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Help save the world! Share your code in a form that
makes it easy to reuse.
Break-out the reusable code into one or more separate
module files.
Take the opportunity to reconsider and redesign the
interfaces.
In some cases the 'application' can then be reduced to a
small
fragment of code built on top of the reusable modules.
In these cases the application could invoked as:
% perl -e 'use Module::Name; method(@ARGV)' ...
or
% perl -mModule::Name ... (in perl5.002 or higher)
NOTE
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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