1. It depends on you needs. If there is a subroutine you are using in several scripts you should put it in a module.
2. Probably. Loading a module will usually require a little more overhead than including all the code in your script.
3. I may be missing something here, but I have never used, nor seen anyone else use, an include file in perl (one that wasn't a module, that is). I imagine you could do neat tricks with eval to include files in a script, though.
4. Reusability. We are lazy and prefer to only type our code once, then use it whenever we like. Using the module system is the standard way of writing software components in perl and it provides (among other things) support for locating modules in shared (/usr/lib/perl) or private (~/my/perl) directories, namespace protection and version numbers for your modules.

Cheers,
--Moodster

3 I may be missing something here, but I have never used, nor seen anyone else use, an include file in perl (one that wasn't a module, that is). I imagine you could do neat tricks with eval to include files in a script, though.

You are missing something:

require "c:/some_script.pl";
print some_func_from_some_script();
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use Foo::Bar; is like BEGIN { require Foo::Bar } ie use is compile time, require is run time. You are just requiring in a file (the .pm is implicit as is the path which is assumed to be in @INC). See the docs.

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

Every day, you learn something new. :)

But to be honest, I don't see why this should be better than putting your code in a proper module. It saves you the bother of messing around with Exporter, yes, but Exporter is your friend. Exporter wants to cuddle you and keep you safe from harm.

Cheers,
--Moodster

1. I commonly use modules (so *.pm files) for anything that loads perl code (except sometimes configuration files created with Data::Dumper and the like)

2. Modules are probably a little slower (but i'd be surprised if it's significant).

3. If you load modules using the use MODULE statement, the file is loaded eval'ed at compile time, so syntax errors in the loaded files abort the script before running. Also, if you include an import routine in your module, it will be called whenever a use MODULE statement is found. (but the module itself will only be loaded and eval'ed once: when the first use is found.)

4. The main reason to declare functions and variables in different packages, is to make sure you don't override some other (global) vars or subroutines, and so you can create objects from them (object classes all need their own package name). In the end though, the *.pm extention is not really needed for all this, it just makes the whole process a little easier and less error-prone, because you can use *.pm files . (see 3.)

See also:

perldoc -f use
perldoc -f require
perldoc perlobj
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Joost.

Also, there is no speed difference. A module is just an include file that declares a package name.