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

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

	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");


       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 want simply 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 an URI object and returns it.
	   The $filename is interpreted as one belonging to the indicated operating system ($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 will make sure that the URI returned represents an abso-
	   lute file name.  If the $filename argument is relative, then the name is resolved rel-
	   ative to the current directory, i.e. this constructor is really the same as:


       $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] )
	   This method return 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 sys-

       $u->dir( [$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 will translate 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

       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 of any reserved characters that appear in the path
       segments of the file names.  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

       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 URI 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 that this file name is
       valid on.  The host name "localhost" is special and generally have the same meaning as an
       missing or empty authority field.  This use will be 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 URI that map
       to the same file name.  For instance an authority of "localhost" maps the same as a URI
       with a missing or empty authority.

       Example 1: The Mac use ":" as path separator, but not in the same way as generic URI.
       ":foo" is a relative name.  "foo:bar" is an absolute name.  Also path segments can contain
       the "/" character as well as be literal "." or "..".  It means that we will map 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 [^:] will be treated as absolute.

       Example 2: The Unix file system is easy to map as it use the same path separator as URIs,
       have a single root, and segments of "." and ".."  have the same meaning.  URIs that have
       the character "\0" 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:/

       URI, File::Spec, perlport

       Copyright 1995-1998 Gisle Aas.

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

perl v5.8.0				    2002-05-10				     URI::file(3)
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