URI::file(3)						User Contributed Perl Documentation					      URI::file(3)

NAME

       URI::file - URI that maps to local file names

SYNOPSIS

	use URI::file;

	$u1 = URI->new("file:/foo/bar");
	$u2 = URI->new("foo/bar", "file");

	$u3 = URI::file->new($path);
	$u4 = URI::file->new("c:\windows\", "win32");

	$u1->file;
	$u1->file("mac");

DESCRIPTION

       The "URI::file" class supports "URI" objects belonging to the file URI scheme.  This scheme allows us to map the conventional file names
       found on various computer systems to the URI name space.  An old specification of the file URI scheme is found in RFC 1738.  Some older
       background information is also in RFC 1630. There are no newer specifications as far as I know.

       If you simply want to construct file URI objects from URI strings, use the normal "URI" constructor.  If you want to construct file URI
       objects from the actual file names used by various systems, then use one of the following "URI::file" constructors:

       $u = URI::file->new( $filename, [$os] )
	   Maps a file name to the file: URI name space, creates a URI object and returns it.  The $filename is interpreted as belonging to the
	   indicated operating system ($os), which defaults to the value of the $^O variable.  The $filename can be either absolute or relative,
	   and the corresponding type of URI object for $os is returned.

       $u = URI::file->new_abs( $filename, [$os] )
	   Same as URI::file->new, but makes sure that the URI returned represents an absolute file name.  If the $filename argument is relative,
	   then the name is resolved relative to the current directory, i.e. this constructor is really the same as:

	     URI::file->new($filename)->abs(URI::file->cwd);

       $u = URI::file->cwd
	   Returns a file URI that represents the current working directory.  See Cwd.

       The following methods are supported for file URI (in addition to the common and generic methods described in URI):

       $u->file( [$os] )
	   Returns a file name.  It maps from the URI name space to the file name space of the indicated operating system.

	   It might return "undef" if the name can not be represented in the indicated file system.

       $u->dir( [$os] )
	   Some systems use a different form for names of directories than for plain files.  Use this method if you know you want to use the name
	   for a directory.

       The "URI::file" module can be used to map generic file names to names suitable for the current system.  As such, it can work as a nice
       replacement for the "File::Spec" module.  For instance, the following code translates the UNIX-style file name Foo/Bar.pm to a name
       suitable for the local system:

	 $file = URI::file->new("Foo/Bar.pm", "unix")->file;
	 die "Can't map filename Foo/Bar.pm for $^O" unless defined $file;
	 open(FILE, $file) || die "Can't open '$file': $!";
	 # do something with FILE

MAPPING NOTES

       Most computer systems today have hierarchically organized file systems.	Mapping the names used in these systems to the generic URI syntax
       allows us to work with relative file URIs that behave as they should when resolved using the generic algorithm for URIs (specified in RFC
       2396).  Mapping a file name to the generic URI syntax involves mapping the path separator character to "/" and encoding any reserved
       characters that appear in the path segments of the file name.  If path segments consisting of the strings "." or ".." have a different
       meaning than what is specified for generic URIs, then these must be encoded as well.

       If the file system has device, volume or drive specifications as the root of the name space, then it makes sense to map them to the
       authority field of the generic URI syntax.  This makes sure that relative URIs can not be resolved "above" them, i.e. generally how
       relative file names work in those systems.

       Another common use of the authority field is to encode the host on which this file name is valid.  The host name "localhost" is special and
       generally has the same meaning as a missing or empty authority field.  This use is in conflict with using it as a device specification, but
       can often be resolved for device specifications having characters not legal in plain host names.

       File name to URI mapping in normally not one-to-one.  There are usually many URIs that map to any given file name.  For instance, an
       authority of "localhost" maps the same as a URI with a missing or empty authority.

       Example 1: The Mac uses ":" as path separator, but not in the same way as a generic URI. ":foo" is a relative name.  "foo:bar" is an
       absolute name.  Also, path segments can contain the "/" character as well as the literal "." or "..".  So the mapping looks like this:

	 Mac		       URI
	 ----------	       -------------------
	 :foo:bar     <==>     foo/bar
	 :	      <==>     ./
	 ::foo:bar    <==>     ../foo/bar
	 :::	      <==>     ../../
	 foo:bar      <==>     file:/foo/bar
	 foo:bar:     <==>     file:/foo/bar/
	 ..	      <==>     %2E%2E
	 <undef>      <==      /
	 foo/	      <==      file:/foo%2F
	 ./foo.txt    <==      file:/.%2Ffoo.txt

       Note that if you want a relative URL, you *must* begin the path with a :.  Any path that begins with [^:] is treated as absolute.

       Example 2: The UNIX file system is easy to map, as it uses the same path separator as URIs, has a single root, and segments of "." and ".."
       have the same meaning.  URIs that have the character "" or "/" as part of any path segment can not be turned into valid UNIX file names.

	 UNIX		       URI
	 ----------	       ------------------
	 foo/bar      <==>     foo/bar
	 /foo/bar     <==>     file:/foo/bar
	 /foo/bar     <==      file://localhost/foo/bar
	 file:	       ==>     ./file:
	 <undef>      <==      file:/fo%00/bar
	 /	      <==>     file:/

CONFIGURATION VARIABLES

       The following configuration variables influence how the class and its methods behave:

       %URI::file::OS_CLASS
	   This hash maps OS identifiers to implementation classes.  You might want to add or modify this if you want to plug in your own file
	   handler class.  Normally the keys should match the $^O values in use.

	   If there is no mapping then the "Unix" implementation is used.

       $URI::file::DEFAULT_AUTHORITY
	   This determine what "authority" string to include in absolute file URIs.  It defaults to "".  If you prefer verbose URIs you might set
	   it to be "localhost".

	   Setting this value to "undef" force behaviour compatible to URI v1.31 and earlier.  In this mode host names in UNC paths and drive
	   letters are mapped to the authority component on Windows, while we produce authority-less URIs on Unix.

SEE ALSO

       URI, File::Spec, perlport

COPYRIGHT

       Copyright 1995-1998,2004 Gisle Aas.

       This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.12.1							    2009-05-28							      URI::file(3)