3 perlmod - Perl modules (packages)
9 Perl provides a mechanism for alternative namespaces to protect packages
10 from stomping on each others variables. In fact, apart from certain
11 magical variables, there's really no such thing as a global variable in
12 Perl. The package statement declares the compilation unit as being in the
13 given namespace. The scope of the package declaration is from the
14 declaration itself through the end of the enclosing block (the same scope
15 as the local() operator). All further unqualified dynamic identifiers
16 will be in this namespace. A package statement only affects dynamic
17 variables--including those you've used local() on--but I<not> lexical
18 variables created with my(). Typically it would be the first declaration
19 in a file to be included by the C<require> or C<use> operator. You can
20 switch into a package in more than one place; it merely influences which
21 symbol table is used by the compiler for the rest of that block. You can
22 refer to variables and filehandles in other packages by prefixing the
23 identifier with the package name and a double colon:
24 C<$Package::Variable>. If the package name is null, the C<main> package
25 as assumed. That is, C<$::sail> is equivalent to C<$main::sail>.
27 (The old package delimiter was a single quote, but double colon
28 is now the preferred delimiter, in part because it's more readable
29 to humans, and in part because it's more readable to B<emacs> macros.
30 It also makes C++ programmers feel like they know what's going on.)
32 Packages may be nested inside other packages: C<$OUTER::INNER::var>. This
33 implies nothing about the order of name lookups, however. All symbols
34 are either local to the current package, or must be fully qualified
35 from the outer package name down. For instance, there is nowhere
36 within package C<OUTER> that C<$INNER::var> refers to C<$OUTER::INNER::var>.
37 It would treat package C<INNER> as a totally separate global package.
39 Only identifiers starting with letters (or underscore) are stored in a
40 package's symbol table. All other symbols are kept in package C<main>,
41 including all of the punctuation variables like $_. In addition, the
42 identifiers STDIN, STDOUT, STDERR, ARGV, ARGVOUT, ENV, INC and SIG are
43 forced to be in package C<main>, even when used for other purposes than
44 their built-in one. Note also that, if you have a package called C<m>,
45 C<s> or C<y>, then you can't use the qualified form of an identifier
46 because it will be interpreted instead as a pattern match, a substitution,
49 (Variables beginning with underscore used to be forced into package
50 main, but we decided it was more useful for package writers to be able
51 to use leading underscore to indicate private variables and method names.
52 $_ is still global though.)
54 Eval()ed strings are compiled in the package in which the eval() was
55 compiled. (Assignments to C<$SIG{}>, however, assume the signal
56 handler specified is in the C<main> package. Qualify the signal handler
57 name if you wish to have a signal handler in a package.) For an
58 example, examine F<perldb.pl> in the Perl library. It initially switches
59 to the C<DB> package so that the debugger doesn't interfere with variables
60 in the script you are trying to debug. At various points, however, it
61 temporarily switches back to the C<main> package to evaluate various
62 expressions in the context of the C<main> package (or wherever you came
63 from). See L<perldebug>.
65 See L<perlsub> for other scoping issues related to my() and local(),
66 or L<perlref> regarding closures.
70 The symbol table for a package happens to be stored in the associative
71 array of that name appended with two colons. The main symbol table's
72 name is thus C<%main::>, or C<%::> for short. Likewise the nested package
73 mentioned earlier is named C<%OUTER::INNER::>.
75 The value in each entry of the associative array is what you are referring
76 to when you use the C<*name> typeglob notation. In fact, the following
77 have the same effect, though the first is more efficient because it does
78 the symbol table lookups at compile time:
80 local(*main::foo) = *main::bar; local($main::{'foo'}) =
83 You can use this to print out all the variables in a package, for
84 instance. Here is F<dumpvar.pl> from the Perl library:
89 local(*stab) = eval("*${package}::");
90 while (($key,$val) = each(%stab)) {
93 print "\$$key = '$entry'\n";
98 foreach $num ($[ .. $#entry) {
99 print " $num\t'",$entry[$num],"'\n";
104 if ($key ne "${package}::" && defined %entry) {
105 print "\%$key = (\n";
106 foreach $key (sort keys(%entry)) {
107 print " $key\t'",$entry{$key},"'\n";
114 Note that even though the subroutine is compiled in package C<dumpvar>,
115 the name of the subroutine is qualified so that its name is inserted
116 into package C<main>.
118 Assignment to a typeglob performs an aliasing operation, i.e.,
122 causes variables, subroutines and file handles accessible via the
123 identifier C<richard> to also be accessible via the symbol C<dick>. If
124 you only want to alias a particular variable or subroutine, you can
125 assign a reference instead:
129 makes $richard and $dick the same variable, but leaves
130 @richard and @dick as separate arrays. Tricky, eh?
132 This mechanism may be used to pass and return cheap references
133 into or from subroutines if you won't want to copy the whole
137 *some_hash = fn( \%another_hash );
139 local *hashsym = shift;
140 # now use %hashsym normally, and you
141 # will affect the caller's %another_hash
142 my %nhash = (); # do what you want
146 On return, the reference wil overwrite the hash slot in the
147 symbol table specified by the *some_hash typeglob. This
148 is a somewhat tricky way of passing around refernces cheaply
149 when you won't want to have to remember to dereference variables
152 Another use of symbol tables is for making "constant" scalars.
154 *PI = \3.14159265358979;
156 Now you cannot alter $PI, which is probably a good thing all in all.
158 =head2 Package Constructors and Destructors
160 There are two special subroutine definitions that function as package
161 constructors and destructors. These are the C<BEGIN> and C<END>
162 routines. The C<sub> is optional for these routines.
164 A C<BEGIN> subroutine is executed as soon as possible, that is, the
165 moment it is completely defined, even before the rest of the containing
166 file is parsed. You may have multiple C<BEGIN> blocks within a
167 file--they will execute in order of definition. Because a C<BEGIN>
168 block executes immediately, it can pull in definitions of subroutines
169 and such from other files in time to be visible to the rest of the
172 An C<END> subroutine is executed as late as possible, that is, when the
173 interpreter is being exited, even if it is exiting as a result of a
174 die() function. (But not if it's is being blown out of the water by a
175 signal--you have to trap that yourself (if you can).) You may have
176 multiple C<END> blocks within a file--they will execute in reverse
177 order of definition; that is: last in, first out (LIFO).
179 Note that when you use the B<-n> and B<-p> switches to Perl, C<BEGIN>
180 and C<END> work just as they do in B<awk>, as a degenerate case.
184 There is no special class syntax in Perl, but a package may function
185 as a class if it provides subroutines that function as methods. Such a
186 package may also derive some of its methods from another class package
187 by listing the other package name in its @ISA array.
189 For more on this, see L<perlobj>.
193 A module is just a package that is defined in a library file of
194 the same name, and is designed to be reusable. It may do this by
195 providing a mechanism for exporting some of its symbols into the symbol
196 table of any package using it. Or it may function as a class
197 definition and make its semantics available implicitly through method
198 calls on the class and its objects, without explicit exportation of any
199 symbols. Or it can do a little of both.
201 For example, to start a normal module called Fred, create
202 a file called Fred.pm and put this at the start of it:
207 @EXPORT = qw(func1 func2);
208 @EXPORT_OK = qw($sally @listabob %harry func3);
210 Then go on to declare and use your variables in functions
211 without any qualifications.
212 See L<Exporter> and the I<Perl Modules File> for details on
213 mechanics and style issues in module creation.
215 Perl modules are included into your program by saying
223 This is exactly equivalent to
225 BEGIN { require "Module.pm"; import Module; }
229 BEGIN { require "Module.pm"; import Module LIST; }
235 is exactly equivalent to
237 BEGIN { require "Module.pm"; }
239 All Perl module files have the extension F<.pm>. C<use> assumes this so
240 that you don't have to spell out "F<Module.pm>" in quotes. This also
241 helps to differentiate new modules from old F<.pl> and F<.ph> files.
242 Module names are also capitalized unless they're functioning as pragmas,
243 "Pragmas" are in effect compiler directives, and are sometimes called
244 "pragmatic modules" (or even "pragmata" if you're a classicist).
246 Because the C<use> statement implies a C<BEGIN> block, the importation
247 of semantics happens at the moment the C<use> statement is compiled,
248 before the rest of the file is compiled. This is how it is able
249 to function as a pragma mechanism, and also how modules are able to
250 declare subroutines that are then visible as list operators for
251 the rest of the current file. This will not work if you use C<require>
252 instead of C<use>. With require you can get into this problem:
254 require Cwd; # make Cwd:: accessible
255 $here = Cwd::getcwd();
257 use Cwd; # import names from Cwd::
260 require Cwd; # make Cwd:: accessible
261 $here = getcwd(); # oops! no main::getcwd()
263 In general C<use Module ();> is recommended over C<require Module;>.
265 Perl packages may be nested inside other package names, so we can have
266 package names containing C<::>. But if we used that package name
267 directly as a filename it would makes for unwieldy or impossible
268 filenames on some systems. Therefore, if a module's name is, say,
269 C<Text::Soundex>, then its definition is actually found in the library
270 file F<Text/Soundex.pm>.
272 Perl modules always have a F<.pm> file, but there may also be dynamically
273 linked executables or autoloaded subroutine definitions associated with
274 the module. If so, these will be entirely transparent to the user of
275 the module. It is the responsibility of the F<.pm> file to load (or
276 arrange to autoload) any additional functionality. The POSIX module
277 happens to do both dynamic loading and autoloading, but the user can
278 just say C<use POSIX> to get it all.
280 For more information on writing extension modules, see L<perlxs>
285 Perl does not enforce private and public parts of its modules as you may
286 have been used to in other languages like C++, Ada, or Modula-17. Perl
287 doesn't have an infatuation with enforced privacy. It would prefer
288 that you stayed out of its living room because you weren't invited, not
289 because it has a shotgun.
291 The module and its user have a contract, part of which is common law,
292 and part of which is "written". Part of the common law contract is
293 that a module doesn't pollute any namespace it wasn't asked to. The
294 written contract for the module (AKA documentation) may make other
295 provisions. But then you know when you C<use RedefineTheWorld> that
296 you're redefining the world and willing to take the consequences.
298 =head1 THE PERL MODULE LIBRARY
300 A number of modules are included the the Perl distribution. These are
301 described below, and all end in F<.pm>. You may also discover files in
302 the library directory that end in either F<.pl> or F<.ph>. These are old
303 libraries supplied so that old programs that use them still run. The
304 F<.pl> files will all eventually be converted into standard modules, and
305 the F<.ph> files made by B<h2ph> will probably end up as extension modules
306 made by B<h2xs>. (Some F<.ph> values may already be available through the
307 POSIX module.) The B<pl2pm> file in the distribution may help in your
308 conversion, but it's just a mechanical process, so is far from bullet proof.
310 =head2 Pragmatic Modules
312 They work somewhat like pragmas in that they tend to affect the compilation of
313 your program, and thus will usually only work well when used within a
314 C<use>, or C<no>. These are locally scoped, so an inner BLOCK
315 may countermand any of these by saying
320 which lasts until the end of that BLOCK.
322 The following programs are defined (and have their own documentation).
328 Pragma to produce enhanced diagnostics
332 Pragma to compute arithmetic in integer instead of double
336 Pragma to request less of something from the compiler
340 Pragma for overloading operators
344 Pragma to enable stack backtrace on unexpected signals
348 Pragma to restrict unsafe constructs
352 Pragma to predeclare sub names
356 =head2 Standard Modules
358 Standard, bundled modules are all expected to behave in a well-defined
359 manner with respect to namespace pollution because they use the
360 Exporter module. See their own documentation for details.
366 provide framework for multiple DBMs
370 load functions only on demand
374 split a package for autoloading
378 benchmark running times of code
382 warn of errors (from perspective of caller)
386 access Perl configuration option
390 get pathname of current working directory
394 Perl access to Berkeley DB
396 =item Devel::SelfStubber
398 generate stubs for a SelfLoading module
402 Dynamically load C libraries into Perl code
406 use nice English (or awk) names for ugly punctuation variables
410 perl module that imports environment variables
414 provide inport/export controls for Perl modules
416 =item ExtUtils::Liblist
418 determine libraries to use and how to use them
420 =item ExtUtils::MakeMaker
422 create an extension Makefile
424 =item ExtUtils::Manifest
426 utilities to write and check a MANIFEST file
428 =item ExtUtils::Mkbootstrap
430 make a bootstrap file for use by DynaLoader
432 =item ExtUtils::Miniperl
438 load the C Fcntl.h defines
442 parse file specifications
444 =item File::CheckTree
446 run many filetest checks on a tree
454 supply object methods for filehandles
458 create or remove a series of directories
462 extended getopt processing
466 Process single-character switches with switch clustering
470 compare 8-bit scalar data according to the current locale
474 a process for both reading and writing
478 open a process for reading, writing, and error handling
482 check a host for upness
486 Perl interface to IEEE Std 1003.1
490 load functions only on demand
494 Creation controlled compartments in which perl code can be evaluated.
498 load the C socket.h defines and structure manipulators
502 run perl standard test scripts with statistics
506 rceate an abbreviation table from a list
510 To find out I<all> the modules installed on your system, including
511 those without documentation or outside the standard release, do this:
513 find `perl -e 'print "@INC"'` -name '*.pm' -print
515 They should all have their own documentation installed and accessible via
516 your system man(1) command. If that fails, try the I<perldoc> program.
518 =head2 Extension Modules
520 Extension modules are written in C (or a mix of Perl and C) and get
521 dynamically loaded into Perl if and when you need them. Supported
522 extension modules include the Socket, Fcntl, and POSIX modules.
524 Many popular C extension modules do not come bundled (at least, not
525 completely) due to their size, volatility, or simply lack of time for
526 adequate testing and configuration across the multitude of platforms on
527 which Perl was beta-tested. You are encouraged to look for them in
528 archie(1L), the Perl FAQ or Meta-FAQ, the WWW page, and even with their
529 authors before randomly posting asking for their present condition and
534 CPAN stands for the Comprehensive Perl Archive Network. This is a globally
535 replicated collection of all known Perl materials, including hundreds
536 of unbunded modules. Here are the major categories of modules:
541 Language Extensions and Documentation Tools
547 Operating System Interfaces
550 Networking, Device Control (modems) and InterProcess Communication
553 Data Types and Data Type Utilities
562 Interfaces to / Emulations of Other Programming Languages
565 File Names, File Systems and File Locking (see also File Handles)
568 String Processing, Language Text Processing, Parsing and Searching
571 Option, Argument, Parameter and Configuration File Processing
574 Internationalization and Locale
577 Authentication, Security and Encryption
580 World Wide Web, HTML, HTTP, CGI, MIME
583 Server and Daemon Utilities
586 Archiving and Compression
589 Images, Pixmap and Bitmap Manipulation, Drawing and Graphing
595 Control Flow Utilities (callbacks and exceptions etc)
598 File Handle and Input/Output Stream Utilities
601 Miscellaneous Modules
605 Some of the reguster CPAN sites as of this writing include the following.
606 You should try to choose one close to you:
611 ftp://ftp.sterling.com/programming/languages/perl/
614 ftp://ftp.sedl.org/pub/mirrors/CPAN/
617 ftp://ftp.uoknor.edu/mirrors/CPAN/
620 ftp://ftp.delphi.com/pub/mirrors/packages/perl/CPAN/
623 ftp://uiarchive.cso.uiuc.edu/pub/lang/perl/CPAN/
626 ftp://ftp.cis.ufl.edu/pub/perl/CPAN/
629 ftp://ftp.switch.ch/mirror/CPAN/
632 ftp://ftp.sunet.se/pub/lang/perl/CPAN/
635 ftp://ftp.ci.uminho.pt/pub/lang/perl/
638 ftp://ftp.cs.ruu.nl/pub/PERL/CPAN/
641 ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/
644 ftp://ftp.rz.ruhr-uni-bochum.de/pub/programming/languages/perl/CPAN/
647 ftp://ftp.leo.org/pub/comp/programming/languages/perl/CPAN/
650 ftp://ftp.pasteur.fr/pub/computing/unix/perl/CPAN/
653 ftp://ftp.ibp.fr/pub/perl/CPAN/
656 ftp://ftp.funet.fi/pub/languages/perl/CPAN/
659 ftp://ftp.tekotago.ac.nz/pub/perl/CPAN/
662 ftp://ftp.mame.mu.oz.au/pub/perl/CPAN/
665 ftp://coombs.anu.edu.au/pub/perl/
668 ftp://dongpo.math.ncu.edu.tw/perl/CPAN/
671 ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/
674 ftp://ftp.is.co.za/programming/perl/CPAN/
678 For an up-to-date listing of CPAN sites,
679 see http://www.perl.com/perl/ or ftp://ftp.perl.com/perl/ .
681 =head1 Modules: Creation, Use and Abuse
683 (The following section is borrowed directly from Tim Bunce's modules
684 file, available at your nearest CPAN site.)
686 Perl 5 implements a class using a package, but the presence of a
687 package doesn't imply the presence of a class. A package is just a
688 namespace. A class is a package that provides subroutines that can be
689 used as methods. A method is just a subroutine that expects, as its
690 first argument, either the name of a package (for "static" methods),
691 or a reference to something (for "virtual" methods).
693 A module is a file that (by convention) provides a class of the same
694 name (sans the .pm), plus an import method in that class that can be
695 called to fetch exported symbols. This module may implement some of
696 its methods by loading dynamic C or C++ objects, but that should be
697 totally transparent to the user of the module. Likewise, the module
698 might set up an AUTOLOAD function to slurp in subroutine definitions on
699 demand, but this is also transparent. Only the .pm file is required to
702 =head2 Guidelines for Module Creation
706 =item Do similar modules already exist in some form?
708 If so, please try to reuse the existing modules either in whole or
709 by inheriting useful features into a new class. If this is not
710 practical try to get together with the module authors to work on
711 extending or enhancing the functionality of the existing modules.
712 A perfect example is the plethora of packages in perl4 for dealing
713 with command line options.
715 If you are writing a module to expand an already existing set of
716 modules, please coordinate with the author of the package. It
717 helps if you follow the same naming scheme and module interaction
718 scheme as the original author.
720 =item Try to design the new module to be easy to extend and reuse.
722 Use blessed references. Use the two argument form of bless to bless
723 into the class name given as the first parameter of the constructor,
728 return bless {}, $class;
731 or even this if you'd like it to be used as either a static
736 my $class = ref($self) || $self;
737 return bless {}, $class;
740 Pass arrays as references so more parameters can be added later
741 (it's also faster). Convert functions into methods where
742 appropriate. Split large methods into smaller more flexible ones.
743 Inherit methods from other modules if appropriate.
745 Avoid class name tests like: die "Invalid" unless ref $ref eq 'FOO'.
746 Generally you can delete the "eq 'FOO'" part with no harm at all.
747 Let the objects look after themselves! Generally, avoid hardwired
748 class names as far as possible.
750 Avoid $r->Class::func() where using @ISA=qw(... Class ...) and
751 $r->func() would work (see perlbot man page for more details).
753 Use autosplit so little used or newly added functions won't be a
754 burden to programs which don't use them. Add test functions to
755 the module after __END__ either using AutoSplit or by saying:
757 eval join('',<main::DATA>) || die $@ unless caller();
759 Does your module pass the 'empty sub-class' test? If you say
760 "@SUBCLASS::ISA = qw(YOURCLASS);" your applications should be able
761 to use SUBCLASS in exactly the same way as YOURCLASS. For example,
762 does your application still work if you change: $obj = new YOURCLASS;
763 into: $obj = new SUBCLASS; ?
765 Avoid keeping any state information in your packages. It makes it
766 difficult for multiple other packages to use yours. Keep state
767 information in objects.
769 Always use C<-w>. Try to C<use strict;> (or C<use strict qw(...);>).
770 Remember that you can add C<no strict qw(...);> to individual blocks
771 of code which need less strictness. Always use C<-w>. Always use C<-w>!
772 Follow the guidelines in the perlstyle(1) manual.
774 =item Some simple style guidelines
776 The perlstyle manual supplied with perl has many helpful points.
778 Coding style is a matter of personal taste. Many people evolve their
779 style over several years as they learn what helps them write and
780 maintain good code. Here's one set of assorted suggestions that
781 seem to be widely used by experienced developers:
783 Use underscores to separate words. It is generally easier to read
784 $var_names_like_this than $VarNamesLikeThis, especially for
785 non-native speakers of English. It's also a simple rule that works
786 consistently with VAR_NAMES_LIKE_THIS.
788 Package/Module names are an exception to this rule. Perl informally
789 reserves lowercase module names for 'pragma' modules like integer
790 and strict. Other modules normally begin with a capital letter and
791 use mixed case with no underscores (need to be short and portable).
793 You may find it helpful to use letter case to indicate the scope
794 or nature of a variable. For example:
796 $ALL_CAPS_HERE constants only (beware clashes with perl vars)
797 $Some_Caps_Here package-wide global/static
798 $no_caps_here function scope my() or local() variables
800 Function and method names seem to work best as all lowercase.
801 E.g., $obj->as_string().
803 You can use a leading underscore to indicate that a variable or
804 function should not be used outside the package that defined it.
806 =item Select what to export.
808 Do NOT export method names!
810 Do NOT export anything else by default without a good reason!
812 Exports pollute the namespace of the module user. If you must
813 export try to use @EXPORT_OK in preference to @EXPORT and avoid
814 short or common names to reduce the risk of name clashes.
816 Generally anything not exported is still accessible from outside the
817 module using the ModuleName::item_name (or $blessed_ref->method)
818 syntax. By convention you can use a leading underscore on names to
819 informally indicate that they are 'internal' and not for public use.
821 (It is actually possible to get private functions by saying:
822 my $subref = sub { ... }; &$subref; But there's no way to call that
823 directly as a method, since a method must have a name in the symbol
826 As a general rule, if the module is trying to be object oriented
827 then export nothing. If it's just a collection of functions then
828 @EXPORT_OK anything but use @EXPORT with caution.
830 =item Select a name for the module.
832 This name should be as descriptive, accurate and complete as
833 possible. Avoid any risk of ambiguity. Always try to use two or
834 more whole words. Generally the name should reflect what is special
835 about what the module does rather than how it does it. Please use
836 nested module names to informally group or categorise a module.
837 A module should have a very good reason not to have a nested name.
838 Module names should begin with a capital letter.
840 Having 57 modules all called Sort will not make life easy for anyone
841 (though having 23 called Sort::Quick is only marginally better :-).
842 Imagine someone trying to install your module alongside many others.
843 If in any doubt ask for suggestions in comp.lang.perl.misc.
845 If you are developing a suite of related modules/classes it's good
846 practice to use nested classes with a common prefix as this will
847 avoid namespace clashes. For example: Xyz::Control, Xyz::View,
848 Xyz::Model etc. Use the modules in this list as a naming guide.
850 If adding a new module to a set, follow the original author's
851 standards for naming modules and the interface to methods in
854 To be portable each component of a module name should be limited to
855 11 characters. If it might be used on DOS then try to ensure each is
856 unique in the first 8 characters. Nested modules make this easier.
858 =item Have you got it right?
860 How do you know that you've made the right decisions? Have you
861 picked an interface design that will cause problems later? Have
862 you picked the most appropriate name? Do you have any questions?
864 The best way to know for sure, and pick up many helpful suggestions,
865 is to ask someone who knows. Comp.lang.perl.misc is read by just about
866 all the people who develop modules and it's the best place to ask.
868 All you need to do is post a short summary of the module, its
869 purpose and interfaces. A few lines on each of the main methods is
870 probably enough. (If you post the whole module it might be ignored
871 by busy people - generally the very people you want to read it!)
873 Don't worry about posting if you can't say when the module will be
874 ready - just say so in the message. It might be worth inviting
875 others to help you, they may be able to complete it for you!
877 =item README and other Additional Files.
879 It's well known that software developers usually fully document the
880 software they write. If, however, the world is in urgent need of
881 your software and there is not enough time to write the full
882 documentation please at least provide a README file containing:
887 A description of the module/package/extension etc.
890 A copyright notice - see below.
893 Prerequisites - what else you may need to have.
896 How to build it - possible changes to Makefile.PL etc.
902 Recent changes in this release, especially incompatibilities
905 Changes / enhancements you plan to make in the future.
909 If the README file seems to be getting too large you may wish to
910 split out some of the sections into separate files: INSTALL,
913 =item Adding a Copyright Notice.
915 How you choose to licence your work is a personal decision.
916 The general mechanism is to assert your Copyright and then make
917 a declaration of how others may copy/use/modify your work.
919 Perl, for example, is supplied with two types of licence: The GNU
920 GPL and The Artistic License (see the files README, Copying and
921 Artistic). Larry has good reasons for NOT just using the GNU GPL.
923 My personal recommendation, out of respect for Larry, Perl and the
924 perl community at large is to simply state something like:
926 Copyright (c) 1995 Your Name. All rights reserved.
927 This program is free software; you can redistribute it and/or
928 modify it under the same terms as Perl itself.
930 This statement should at least appear in the README file. You may
931 also wish to include it in a Copying file and your source files.
932 Remember to include the other words in addition to the Copyright.
934 =item Give the module a version/issue/release number.
936 To be fully compatible with the Exporter and MakeMaker modules you
937 should store your module's version number in a non-my package
938 variable called $VERSION. This should be a valid floating point
939 number with at least two digits after the decimal (ie hundredths,
940 e.g, $VERSION = "0.01"). Don't use a "1.3.2" style version.
941 See Exporter.pm in Perl5.001m or later for details.
943 It may be handy to add a function or method to retrieve the number.
944 Use the number in announcements and archive file names when
945 releasing the module (ModuleName-1.02.tar.Z).
946 See perldoc ExtUtils::MakeMaker.pm for details.
948 =item How to release and distribute a module.
950 It's good idea to post an announcement of the availability of your
951 module (or the module itself if small) to the comp.lang.perl.announce
952 Usenet newsgroup. This will at least ensure very wide once-off
955 If possible you should place the module into a major ftp archive and
956 include details of it's location in your announcement.
958 Some notes about ftp archives: Please use a long descriptive file
959 name which includes the version number. Most incoming directories
960 will not be readable/listable, i.e., you won't be able to see your
961 file after uploading it. Remember to send your email notification
962 message as soon as possible after uploading else your file may get
963 deleted automatically. Allow time for the file to be processed
964 and/or check the file has been processed before announcing its
967 FTP Archives for Perl Modules:
969 Follow the instructions and links on
971 http://franz.ww.tu-berlin.de/modulelist
973 or upload to one of these sites:
975 ftp://franz.ww.tu-berlin.de/incoming
976 ftp://ftp.cis.ufl.edu/incoming
978 and notify upload@franz.ww.tu-berlin.de.
980 By using the WWW interface you can ask the Upload Server to mirror
981 your modules from your ftp or WWW site into your own directory on
984 Please remember to send me an updated entry for the Module list!
986 =item Take care when changing a released module.
988 Always strive to remain compatible with previous released versions
989 (see 2.2 above) Otherwise try to add a mechanism to revert to the
990 old behaviour if people rely on it. Document incompatible changes.
994 =head2 Guidelines for Converting Perl 4 Library Scripts into Modules
998 =item There is no requirement to convert anything.
1000 If it ain't broke, don't fix it! Perl 4 library scripts should
1001 continue to work with no problems. You may need to make some minor
1002 changes (like escaping non-array @'s in double quoted strings) but
1003 there is no need to convert a .pl file into a Module for just that.
1005 =item Consider the implications.
1007 All the perl applications which make use of the script will need to
1008 be changed (slightly) if the script is converted into a module. Is
1009 it worth it unless you plan to make other changes at the same time?
1011 =item Make the most of the opportunity.
1013 If you are going to convert the script to a module you can use the
1014 opportunity to redesign the interface. The 'Guidelines for Module
1015 Creation' above include many of the issues you should consider.
1017 =item The pl2pm utility will get you started.
1019 This utility will read *.pl files (given as parameters) and write
1020 corresponding *.pm files. The pl2pm utilities does the following:
1025 Adds the standard Module prologue lines
1028 Converts package specifiers from ' to ::
1031 Converts die(...) to croak(...)
1034 Several other minor changes
1038 Being a mechanical process pl2pm is not bullet proof. The converted
1039 code will need careful checking, especially any package statements.
1040 Don't delete the original .pl file till the new .pm one works!
1044 =head2 Guidelines for Reusing Application Code
1048 =item Complete applications rarely belong in the Perl Module Library.
1050 =item Many applications contain some perl code which could be reused.
1052 Help save the world! Share your code in a form that makes it easy
1055 =item Break-out the reusable code into one or more separate module files.
1057 =item Take the opportunity to reconsider and redesign the interfaces.
1059 =item In some cases the 'application' can then be reduced to a small
1061 fragment of code built on top of the reusable modules. In these cases
1062 the application could invoked as:
1064 perl -e 'use Module::Name; method(@ARGV)' ...
1066 perl -mModule::Name ... (in perl5.002?)