perlmodlib
Current Perl documentation can be found at
perldoc.perl.org.
Here is our local, out-dated (pre-5.6) version:
perlmodlib - constructing new Perl modules and finding existing ones
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.
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 locally 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
- 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, 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
- 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
- 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::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
- 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
- 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
- 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 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-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 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:
- Language Extensions and Documentation Tools
- Development Support
- Operating System Interfaces
- Networking, Device Control (modems) and InterProcess Communication
- Data Types and Data Type Utilities
- Database Interfaces
- User Interfaces
- Interfaces to / Emulations of Other Programming Languages
- File Names, File Systems and File Locking (see also File Handles)
- String Processing, Language Text Processing, Parsing, and Searching
- Option, Argument, Parameter, and Configuration File Processing
- Internationalization and Locale
- Authentication, Security, and Encryption
- World Wide Web, HTML, HTTP, CGI, MIME
- Server and Daemon Utilities
- Archiving and Compression
- Images, Pixmap and Bitmap Manipulation, Drawing, and Graphing
- Mail and Usenet News
- Control Flow Utilities (callbacks and exceptions etc)
- File Handle and Input/Output Stream Utilities
- Miscellaneous Modules
The registered
CPAN sites as of this writing include the following.
You should try to choose one close to you:
- Africa
South Africa ftp://ftp.is.co.za/programming/perl/CPAN/
- Asia
Hong Kong ftp://ftp.hkstar.com/pub/CPAN/
Japan ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/
ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/
South Korea ftp://ftp.nuri.net/pub/CPAN/
Taiwan ftp://dongpo.math.ncu.edu.tw/perl/CPAN/
ftp://ftp.wownet.net/pub2/PERL/
- Australasia
Australia ftp://ftp.netinfo.com.au/pub/perl/CPAN/
New Zealand ftp://ftp.tekotago.ac.nz/pub/perl/CPAN/
- Europe
Austria ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/
Belgium ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/
Czech Republic ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/
Denmark ftp://sunsite.auc.dk/pub/languages/perl/CPAN/
Finland ftp://ftp.funet.fi/pub/languages/perl/CPAN/
France ftp://ftp.ibp.fr/pub/perl/CPAN/
ftp://ftp.pasteur.fr/pub/computing/unix/perl/CPAN/
Germany ftp://ftp.gmd.de/packages/CPAN/
ftp://ftp.leo.org/pub/comp/programming/languages/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/Perl/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/
Italy ftp://cis.utovrm.it/CPAN/
the Netherlands ftp://ftp.cs.ruu.nl/pub/PERL/CPAN/
ftp://ftp.EU.net/packages/cpan/
Norway ftp://ftp.uit.no/pub/languages/perl/cpan/
Poland ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/
ftp://sunsite.icm.edu.pl/pub/CPAN/
Portugal ftp://ftp.ci.uminho.pt/pub/lang/perl/
ftp://ftp.telepac.pt/pub/CPAN/
Russia ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/
Slovenia ftp://ftp.arnes.si/software/perl/CPAN/
Spain ftp://ftp.etse.urv.es/pub/mirror/perl/
ftp://ftp.rediris.es/mirror/CPAN/
Sweden ftp://ftp.sunet.se/pub/lang/perl/CPAN/
UK ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/
ftp://sunsite.doc.ic.ac.uk/packages/CPAN/
ftp://unix.hensa.ac.uk/mirrors/perl-CPAN/
- North America
Ontario ftp://ftp.utilis.com/public/CPAN/
ftp://enterprise.ic.gc.ca/pub/perl/CPAN/
Manitoba ftp://theory.uwinnipeg.ca/pub/CPAN/
California ftp://ftp.digital.com/pub/plan/perl/CPAN/
ftp://ftp.cdrom.com/pub/perl/CPAN/
Colorado ftp://ftp.cs.colorado.edu/pub/perl/CPAN/
Florida ftp://ftp.cis.ufl.edu/pub/perl/CPAN/
Illinois ftp://uiarchive.uiuc.edu/pub/lang/perl/CPAN/
Massachusetts ftp://ftp.iguide.com/pub/mirrors/packages/perl/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/
Oregon http://www.perl.org/CPAN/
ftp://ftp.orst.edu/pub/packages/CPAN/
Pennsylvania ftp://ftp.epix.net/pub/languages/perl/
Texas ftp://ftp.sedl.org/pub/mirrors/CPAN/
ftp://ftp.metronet.com/pub/perl/
- South America
Chile 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/.
(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.
- 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.
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 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
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 at least provide a
README file containing:
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 ``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 mechanism to revert to the old behaviour if people
rely on it. Document incompatible changes.
- 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:
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!
- Complete applications rarely belong in the Perl Module Library.
-
- Many applications contain some Perl code that could be reused.
-
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)
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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