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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 classic (Mac OS 9 and earlier) used ":" as path separator, but not in
       the same way as a generic URI. ":foo" was a relative name.  "foo:bar" was an absolute
       name.  Also, path segments could contain the "/" character as well as the literal "." or
       "..".  So the mapping looks like this:

	 Mac classic	       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 "\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:/

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 v5.16.3				    2012-02-11				     URI::file(3)
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