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URI::file(3pm) User Contributed Perl Documentation URI::file(3pm)
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 v5.32.1 2021-10-26 URI::file(3pm)
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On Apache
Under GNU General Public License
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