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25.3. Files and Filesystems

File path components are separated with / on Unix,
with \ on Windows, and with : on
Macs. Some systems support neither hard links
(link) nor symbolic links
(symlink, readlink,
lstat). Some systems pay attention to
capitalization of filenames, some don''t, and some pay attention when
creating files but not when reading them.

There are modules that can help. The standard
File::Spec modules provide some functions of the
Right Thing persuasion:

use File::Spec::Functions;
chdir( updir() );        # go up one directory
$file = catfile( curdir(), ''temp'', ''file.txt'' );

The File::Basename module, another
platform-tolerant module bundled with Perl, splits a pathname into its
components: the base filename, the full path to the directory, and the
file suffix.

Here are some tips for writing portable file-manipulating Perl programs:

• 
  

  
  Don''t use two files of the same name with different case, like
  test.pl and Test.pl, since some
  platforms ignore capitalization.



• 
  

  Constrain filenames to the 8.3 convention (eight-letter names and
  three-letter extensions) where possible. You can often get away with longer
  filenames as long as you make sure the filenames will remain unique when
  shoved through an 8.3-sized hole in the wall. (Hey, it''s gotta be easier than
  shoving a camel through the eye of a needle.)



• 
  

  Minimize nonalphanumeric characters in filenames. Using underscores is
  often okay, but it wastes a character that could better be used for uniqueness
  on 8.3 systems. (Remember, that''s why we don''t usually put underscores
  into module names.)



• 
  

  
  Likewise, when using the AutoSplit module, try to constrain your
  subroutine names to eight characters or less, and don''t give two
  subroutines the same name with different case. If you need longer
  subroutine names, make the first eight characters of each unique.



• 
  

  Always use < explicitly to open a file for reading;
  otherwise, on systems that allow punctuation in filenames, a
  file prefixed with a > character could result in a file being
  wiped out, and a file prefixed with a | character could result in a
  pipe open. That''s because the two-argument form of open is magical
  and will interpret characters like >, <, and |, which
  may be the wrong thing to do. (Except when it''s right.)
  

  
  

  open(FILE,      $existing_file)  or die $!;  # wrongish
  open(FILE,    "<$existing_file") or die $!;  # righter
  open(FILE, "<", $existing_file)  or die $!;  # righterer

  
  

  
  



• 
  

  Don''t assume text files will end with a newline. They should, but
  sometimes people forget, especially when their text editor helps them forget.