CPAN Module Distributions

OS you're running under

25

 and loads the appropriate File::Spec subclass, be it 

File::Spec::Unix or File::Spec::OS2. This pattern, breaking out OS specific 

implementations of a standard API, is an excellent one for portable code. One 

major advantage is that it allows the code to start small supporting only a few 

systems and grow in portability as additional subclasses are added.

Be Explicit

It's good to be portable; but if you can't, then you should be explicit about it. One 

way to do this is to put code in your Makefile.PL that explicitly checks the OS at 

installation. For example, if you know that your module can't possibly work under 

Microsoft Windows, you could use code like this:

if ($^O eq  MSWin32 ) {

   die "Sorry, the Data::Counter module doesn t support Windows yet!\n";

}

This is much nicer than allowing a user to install your module and realize that it 

doesn't work later. That said, this technique is hard to get right since you have to 

either know all the $^O strings where your module will work or all the $^O strings 

where it won't work. Neither piece of knowledge is easy to come by considering the 

large number of possibilities.

Perl Version Independence

Another type of portability is compatibility with older versions of Perl. There are 

many reasons why people don't upgrade their Perl, some good and some bad. 

Ignore older versions of Perl at your own peril you never know when you'll end 

up in a job where the hoary old sys admin insists that Perl 5.004 is as good today as 

the day it was born!

Supporting older versions of Perl means avoiding new Perl features like the 

plague. In particular, you'll need to watch out for using the newer syntactic 

features of modern Perl our, use warnings, v strings (numbers of the form 1.2.3), 

unquoted hash strings, unquoted strings on the left hand side of a =>, new fangled 

regex extensions, and much more. Some of these will merely cause warnings 

under old versions of Perl, but many will break the module unequivocally.

25. Using the $^O variable, which carries a short identifier specifying the OS. See the perlport 

documentation for a complete list.

12

125

5