Chapter 4

Portability

Perl is perhaps the most portable programming language ever created. Perl 

modules can be written to work on virtually every modern computer system.

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Similarly, Perl modules can also be written to work with a range of versions of Perl. 

In general, this is accomplished by limiting your use of certain Perl features be 

they features that work differently on different operating systems or features that 

are broken or nonexistent in older versions of Perl. This section will give you infor 

mation on the most commonly seen portability problems in CPAN modules; for an 

exhaustive list, take a look at the perlport document that comes with Perl.

Operating System Independence

Writing operating system independent code requires you to know which features 

might behave differently when used on different operating systems. This topic 

alone would be enough to fill a book at least as large as this one, but next you'll find 

information on the most commonly encountered portability problems.

Line Endings

Historically operating systems have had different ideas about what to put at the 

end of a line in a text file. UNIX systems use a single byte \012 or LF. MacOS also 

uses a single byte \015 or CR. Microsoft's operating systems (DOS and Windows) 

use 2 bytes \015\012 or CRLF. However, in Microsoft's stdio

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 implementation, 

CRLF is translated into LF on input and back into CRLF on output, but only when 

reading or writing text files. As a result, in memory the lines have UNIX line endings 

but on disk they have the distinctive 2 byte format.

Perl provides the \n escape code for strings and regular expressions that 

matches what the platform thinks of as a line ending be it CR or LF so you usually 

don't need to think about it when reading and writing text files. However, the issue 

has implications for the handling of binary data. Consider the following CGI code 

that reads in a binary image file from disk, smoothes it, and prints it to STDOUT:

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

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

smooth($image);                     # smooth the image

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

21. With the notable exception of small scale embedded systems too small for Perl 5. Perl 6 

aims to address this deficiency. See the perlport documentation for a full list of currently 

supported systems.

22. The system library used by Perl to do file I/O

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