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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" construc-
tors:
$u = URI::file->new( $filename, [$os] )
Maps a file name to the file: URI name space, creates a URI object and returns
it. The $filename is interpreted as belonging to the indicated operating sys-
tem ($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 algo-
rithm 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 seg-
ments 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 "\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 ear-
lier. 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 v5.8.6 2004-01-14 URI::file(3)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
Under GNU General Public License
2009-01-09 01:02 @38.103.63.58 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)