CPAN Module Distributions

This code will work fine under UNIX and MacOS, but may result in a corrupted 

image under Windows. The reason is that by default Windows handles files in text 

mode. That means translating all CRLFs into CRs on input and the reverse on output. 

The problem is that since image.jpg is a binary file, it might well have CRLF sequences 

that aren't meant to be line endings. To safely handle binary data, you need to use 

the binmode() function:

open(IMAGE, "image.jpg") or die $!; # open the image file

binmode(IMAGE);                     # the image file is binary data

my $image = join(  ,);       # read the image data into $image

smooth($image);                     # smooth the image

binmode(STDOUT);                    # about to print binary data on STDOUT

print STDOUT $image;                # print out the image to the client

Notice that in this case binmode() is necessary on both IMAGE and STDOUT to avoid 

corrupting text mode translations.

Another place where line endings rear their ugly heads is in network pro 

gramming. Many network protocols state that lines must end in CRLF. The only way to 

be sure that you're ending your lines properly is to explicitly add the line ending bytes:

print SOCK "GET / HTTP/1.1\015\012";

In particular, using \r\n will not work since the setting for \n varies from system 

to system.

File Systems

Nothing varies as much between operating systems as file system usage. Every 

thing is up for grabs the path separator, maximum size of filenames, characters 

allowed in filenames, the number of  root  directories or  volumes,  the way 

network resources are named in the file system, and so on. Listing out all the vari 

ations would only serve to convince you that producing portable code that 

accesses the file system is impossible. Instead I'll just cut to the good news it is 

possible and it's not very hard at all.

Perl comes with a module called File::Spec

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 that provides functions for 

manipulating filenames and paths. To get a list of available methods, read the

 documentation for the File::Spec::Unix module all the available subclasses 

support the same methods.

23. This module comes with Perl and was written by Kenneth Albanowski, Andy Dougherty, 

Andreas Koenig, Tim Bunce, Charles Bailey, Ilya Zakharevich, Paul Schinder, Shigio 

Yamaguchi, and Barrie Slaymaker.

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