URI::file
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 specifica-
tion of the file URI scheme is found in RFC 1738. Some older back-
ground information is also in RFC 1630. There are no newer specifica-
tions 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 rela-
tive, 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 repre-
sents an absolute file name. If the $filename argument is rela-
tive, then the name is resolved relative to the current directory,
i.e. this constructor is really the same as:
URI::file->new($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 charac-
ters that appear in the path segments of the file name. If path seg-
ments 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 author-
ity 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 specifica-
tion, but can often be resolved for device specifications having char-
acters 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 author-
ity.
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 "\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 v5.8.6 2004-01-14 URI::file(3)
