-'\"
.\" (C) Copyright 1999-2000 David A. Wheeler (dwheeler@dwheeler.com)
.\"
-.\" Permission is granted to make and distribute verbatim copies of this
-.\" manual provided the copyright notice and this permission notice are
-.\" preserved on all copies.
-.\"
-.\" Permission is granted to copy and distribute modified versions of this
-.\" manual under the conditions for verbatim copying, provided that the
-.\" entire resulting derived work is distributed under the terms of a
-.\" permission notice identical to this one.
-.\"
-.\" Since the Linux kernel and libraries are constantly changing, this
-.\" manual page may be incorrect or out-of-date. The author(s) assume no
-.\" responsibility for errors or omissions, or for damages resulting from
-.\" the use of the information contained herein. The author(s) may not
-.\" have taken the same level of care in the production of this manual,
-.\" which is licensed free of charge, as they might when working
-.\" professionally.
-.\"
-.\" Formatted or processed versions of this manual, if unaccompanied by
-.\" the source, must acknowledge the copyright and authors of this work.
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" Fragments of this document are directly derived from IETF standards.
.\" For those fragments which are directly derived from such standards,
.\" Modified Fri Aug 21 23:00:00 1999 by David A. Wheeler (dwheeler@dwheeler.com)
.\" Modified Tue Mar 14 2000 by David A. Wheeler (dwheeler@dwheeler.com)
.\"
-.\" FIXME Section titles and orderings in this page are very inconsistent
-.TH URI 7 2000-03-14 "Linux" "Linux Programmer's Manual"
+.TH uri 7 (date) "Linux man-pages (unreleased)"
.SH NAME
uri, url, urn \- uniform resource identifier (URI), including a URL or URN
.SH SYNOPSIS
.HP
relativeURI = ( net_path | absolute_path | relative_path ) [ "?" query ]
.HP
-scheme = "http" | "ftp" | "gopher" | "mailto" | "news" | "telnet" | "file" | "man" | "info" | "whatis" | "ldap" | "wais" | \&...
+scheme = "http" | "ftp" | "gopher" | "mailto" | "news" | "telnet" |
+ "file" | "man" | "info" | "whatis" | "ldap" | "wais" | \&...
.HP
hierarchical_part = ( net_path | absolute_path ) [ "?" query ]
.HP
relative_path = relative_segment [ absolute_path ]
.fi
.SH DESCRIPTION
-.PP
A Uniform Resource Identifier (URI) is a short string of characters
identifying an abstract or physical resource (for example, a web page).
A Uniform Resource Locator (URL) is a URI
.PP
URIs are the standard way to name hypertext link destinations
for tools such as web browsers.
-The string "http://www.kernelnotes.org" is a URL (and thus it's a URI).
+The string "http://www.kernel.org" is a URL (and thus it
+is also a URI).
Many people use the term URL loosely as a synonym for URI
(though technically URLs are a subset of URIs).
.PP
Within a relative path reference, the complete path segments "." and
".." have special meanings: "the current hierarchy level" and "the
level above this hierarchy level", respectively, just like they do in
-Unix-like systems.
+UNIX-like systems.
A path segment which contains a colon
character can't be used as the first segment of a relative URI path
(e.g., "this:that"), because it would be mistaken for a scheme name;
devicename colons with the vertical bar ("|") in URIs, so "C:" becomes "C|".
.PP
A fragment identifier, if included, refers to a particular named portion
-(fragment) of a resource; text after a '#' identifies the fragment.
-A URI beginning with '#' refers to that fragment in the current resource.
-.SH USAGE
+(fragment) of a resource; text after a \[aq]#\[aq] identifies the fragment.
+A URI beginning with \[aq]#\[aq] refers to that fragment in the current resource.
+.SS Usage
There are many different URI schemes, each with specific
additional rules and meanings, but they are intentionally made to be
as similar as possible.
.HP
.IR "ip_server = " [ user " [ : " password " ] @ ] " host " [ : " port ]
.PP
-This format allows you to optionally insert a user name,
+This format allows you to optionally insert a username,
a user plus password, and/or a port number.
The
.I host
is the name of the host computer, either its name as determined by DNS
or an IP address (numbers separated by periods).
Thus the URI
-<http://fred:fredpassword@xyz.com:8080/>
-logs into a web server on host xyz.com
+<http://fred:fredpassword@example.com:8080/>
+logs into a web server on host example.com
as fred (using fredpassword) using port 8080.
Avoid including a password in a URI if possible because of the many
security risks of having a password written down.
-If the URL supplies a user name but no password, and the remote
+If the URL supplies a username but no password, and the remote
server requests a password, the program interpreting the URL
should request one from the user.
.PP
-Here are some of the most common schemes in use on Unix-like systems
+Here are some of the most common schemes in use on UNIX-like systems
that are understood by many tools.
Note that many tools using URIs also have internal schemes or specialized
schemes; see those tools' documentation for information on those schemes.
-.SS "http \- Web (HTTP) server"
+.PP
+.B "http \- Web (HTTP) server"
+.PP
.RI http:// ip_server / path
.br
.RI http:// ip_server / path ? query
(&) has to be rewritten as &.
Note that not all queries use this format; larger forms
may be too long to store as a URI, so they use a different
-interaction mechanism (called POST) which does not include the data in the URI.
+interaction mechanism (called POST) which does
+not include the data in the URI.
See the Common Gateway Interface specification at
-<http://www.w3.org/CGI> for more information.
-.SS "ftp \- File Transfer Protocol (FTP)"
+.UR http://www.w3.org\:/CGI
+.UE
+for more information.
+.PP
+.B "ftp \- File Transfer Protocol (FTP)"
+.PP
.RI ftp:// ip_server / path
.PP
This is a URL accessing a file through the file transfer protocol (FTP).
The default port (for control) is 21.
-If no username is included, the user name "anonymous" is supplied, and
+If no username is included, the username "anonymous" is supplied, and
in that case many clients provide as the password the requestor's
Internet email address.
An example is
<ftp://ftp.is.co.za/rfc/rfc1808.txt>.
-.SS "gopher \- Gopher server"
+.PP
+.B "gopher \- Gopher server"
+.PP
.RI gopher:// ip_server / "gophertype selector"
.br
.RI gopher:// ip_server / "gophertype selector" %09 search
Gopher selector strings are a sequence of octets which may contain
any octets except 09 hexadecimal (US-ASCII HT or tab), 0A hexadecimal
(US-ASCII character LF), and 0D (US-ASCII character CR).
-.SS "mailto \- Email address"
+.PP
+.B "mailto \- Email address"
+.PP
.RI mailto: email-address
.PP
This is an email address, usually of the form
for more information on the correct format of an email address.
Note that any % character must be rewritten as %25.
An example is <mailto:dwheeler@dwheeler.com>.
-.SS "news \- Newsgroup or News message"
+.PP
+.B "news \- Newsgroup or News message"
+.PP
.RI news: newsgroup-name
.br
.RI news: message-id
A
.I message-id
corresponds to the Message-ID of
-.URL http://www.ietf.org/rfc/rfc1036.txt
+.UR http://www.ietf.org\:/rfc\:/rfc1036.txt
IETF RFC\ 1036,
.UE
without the enclosing "<"
.IR unique @ full_domain_name .
A message identifier may be distinguished from a news group name by the
presence of the "@" character.
-.SS "telnet \- Telnet login"
+.PP
+.B "telnet \- Telnet login"
+.PP
.RI telnet:// ip_server /
.PP
The Telnet URL scheme is used to designate interactive text services that
The final "/" character may be omitted.
The default port is 23.
An example is <telnet://melvyl.ucop.edu/>.
-.SS "file \- Normal file"
+.PP
+.B "file \- Normal file"
+.PP
.RI file:// ip_server / path_segments
.br
.RI file: path_segments
.PP
This represents a file or directory accessible locally.
As a special case,
-.I host
+.I ip_server
can be the string "localhost" or the empty
-string; this is interpreted as `the machine from which the URL is
-being interpreted'.
+string; this is interpreted as "the machine from which the URL is
+being interpreted".
If the path is to a directory, the viewer should display the
directory's contents with links to each containee;
not all viewers currently do this.
a local file.
However, older standards did not permit this format,
and some programs don't recognize this as a URI.
-A more portable syntax is to use an empty string as the server name, e.g.,
+A more portable syntax is to use an empty string as the server name,
+for example,
<file:///etc/passwd>; this form does the same thing
and is easily recognized by pattern matchers and older programs as a URI.
-Note that if you really mean to say "start from the current location," don't
+Note that if you really mean to say "start from the current location", don't
specify the scheme at all; use a relative address like <../test.txt>,
which has the side-effect of being scheme-independent.
An example of this scheme is <file:///etc/passwd>.
-.SS "man \- Man page documentation"
+.PP
+.B "man \- Man page documentation"
+.PP
.RI man: command-name
.br
.RI man: command-name ( section )
.PP
This refers to local online manual (man) reference pages.
-The command name can optionally be followed by a parenthesis and section number;
-see
+The command name can optionally be followed by a
+parenthesis and section number; see
.BR man (7)
for more information on the meaning of the section numbers.
-This URI scheme is unique to Unix-like systems (such as Linux)
+This URI scheme is unique to UNIX-like systems (such as Linux)
and is not currently registered by the IETF.
An example is <man:ls(1)>.
-.SS "info \- Info page documentation"
+.PP
+.B "info \- Info page documentation"
+.PP
.RI info: virtual-filename
.br
.RI info: virtual-filename # nodename
.RI info:( virtual-filename ) nodename
.PP
This scheme refers to online info reference pages (generated from
-texinfo files), a documentation format used by programs such as the GNU tools.
-This URI scheme is unique to Unix-like systems (such as Linux)
+texinfo files),
+a documentation format used by programs such as the GNU tools.
+This URI scheme is unique to UNIX-like systems (such as Linux)
and is not currently registered by the IETF.
As of this writing, GNOME and KDE differ in their URI syntax
and do not accept the other's syntax.
nodename is assumed to be "Top".
Examples of the GNOME format are <info:gcc> and <info:gcc#G++_and_GCC>.
Examples of the KDE format are <info:(gcc)> and <info:(gcc)G++ and GCC>.
-.SS "whatis \- Documentation search"
+.PP
+.B "whatis \- Documentation search"
+.PP
.RI whatis: string
.PP
-This scheme searches the database of short (one-line) descriptions of commands
-and returns a list of descriptions containing that string.
+This scheme searches the database of short (one-line) descriptions of
+commands and returns a list of descriptions containing that string.
Only complete word matches are returned.
See
.BR whatis (1).
-This URI scheme is unique to Unix-like systems (such as Linux)
+This URI scheme is unique to UNIX-like systems (such as Linux)
and is not currently registered by the IETF.
-.SS "ghelp \- GNOME help documentation"
+.PP
+.B "ghelp \- GNOME help documentation"
+.PP
.RI ghelp: name-of-application
.PP
This loads GNOME help for the given application.
Note that not much documentation currently exists in this format.
-.SS "ldap \- Lightweight Directory Access Protocol"
+.PP
+.B "ldap \- Lightweight Directory Access Protocol"
+.PP
.RI ldap:// hostport
.br
.RI ldap:// hostport /
.PP
This scheme supports queries to the
Lightweight Directory Access Protocol (LDAP), a protocol for querying
-a set of servers for hierarchically-organized information
+a set of servers for hierarchically organized information
(such as people and computing resources).
-More information on the LDAP URL scheme is available in
-.UR http://www.ietf.org/rfc/rfc2255.txt
-RFC\ 2255.
+See
+.UR http://www.ietf.org\:/rfc\:/rfc2255.txt
+RFC\ 2255
.UE
+for more information on the LDAP URL scheme.
The components of this URL are:
-.IP hostport 12
+.TP
+hostport
the LDAP server to query, written as a hostname optionally followed by
a colon and the port number.
The default LDAP port is TCP port 389.
If empty, the client determines which the LDAP server to use.
-.IP dn
+.TP
+dn
the LDAP Distinguished Name, which identifies
the base object of the LDAP search (see
-.UR http://www.ietf.org/rfc/rfc2253.txt
+.UR http://www.ietf.org\:/rfc\:/rfc2253.txt
RFC\ 2253
.UE
section 3).
-.IP attributes
+.TP
+attributes
a comma-separated list of attributes to be returned;
see RFC\ 2251 section 4.1.5.
If omitted, all attributes should be returned.
-.IP scope
+.TP
+scope
specifies the scope of the search, which can be one of
"base" (for a base object search), "one" (for a one-level search),
or "sub" (for a subtree search).
If scope is omitted, "base" is assumed.
-.IP filter
+.TP
+filter
specifies the search filter (subset of entries
to return).
If omitted, all entries should be returned.
See
-.UR http://www.ietf.org/rfc/rfc2254.txt
+.UR http://www.ietf.org\:/rfc\:/rfc2254.txt
RFC\ 2254
.UE
section 4.
-.IP extensions
+.TP
+extensions
a comma-separated list of type=value
pairs, where the =value portion may be omitted for options not
requiring it.
-An extension prefixed with a '!' is critical
-(must be supported to be valid), otherwise it's non-critical (optional).
+An extension prefixed with a \[aq]!\[aq] is critical
+(must be supported to be valid), otherwise it is noncritical (optional).
.PP
LDAP queries are easiest to explain by example.
Here's a query that asks ldap.itd.umich.edu for information about
.PP
.nf
ldap://ldap.itd.umich.edu/o=University%20of%20Michigan,c=US
-.nf
+.fi
.PP
To just get its postal address attribute, request:
.PP
.nf
ldap://host.com:6666/o=University%20of%20Michigan,c=US??sub?(cn=Babs%20Jensen)
.fi
-.SS "wais \- Wide Area Information Servers"
+.PP
+.B "wais \- Wide Area Information Servers"
+.PP
.RI wais:// hostport / database
.br
.RI wais:// hostport / database ? search
.PP
This scheme designates a WAIS database, search, or document
(see
-.UR http://www.ietf.org/rfc/rfc1625.txt
+.UR http://www.ietf.org\:/rfc\:/rfc1625.txt
IETF RFC\ 1625
.UE
for more information on WAIS).
is the WAIS designation of the type of the object and
.I wpath
is the WAIS document-id.
-.SS "other schemes"
+.PP
+.B "other schemes"
+.PP
There are many other URI schemes.
Most tools that accept URIs support a set of internal URIs
(e.g., Mozilla has the about: scheme for internal information,
(e.g., urn:ietf:... would identify IETF documents); at this time
URNs are not widely implemented.
Not all tools support all schemes.
-.SH "CHARACTER ENCODING"
-.PP
+.SS Character encoding
URIs use a limited number of characters so that they can be
typed in and used in a variety of situations.
.PP
URI but their use is limited to their reserved purpose
(conflicting data must be escaped before forming the URI):
.IP
- ; / ? : @ & = + $ ,
+.in +4n
+.EX
+; / ? : @ & = + $ ,
+.EE
+.in
.PP
Unreserved characters may be included in a URI.
Unreserved characters
-include upper and lower case English letters,
+include uppercase and lowercase Latin letters,
decimal digits, and the following
limited set of punctuation marks and symbols:
.IP
- \- _ . ! ~ * ' ( )
+.in +4n
+.EX
+\- _ . ! \[ti] * ' ( )
+.EE
+.in
.PP
All other characters must be escaped.
An escaped octet is encoded as a character triplet, consisting of the
percent character "%" followed by the two hexadecimal digits
-representing the octet code (you can use upper or lower case letters
+representing the octet code (you can use uppercase or lowercase letters
for the hexadecimal digits).
For example, a blank space must be escaped
as "%20", a tab character as "%09", and the "&" as "%26".
Unreserved characters can be escaped without changing the semantics
of the URI, but this should not be done unless the URI is being used
in a context that does not allow the unescaped character to appear.
-For example, "%7e" is sometimes used instead of "~" in an http URL
-path, but the two are equivalent for an http URL.
+For example, "%7e" is sometimes used instead of "\[ti]" in an HTTP URL
+path, but the two are equivalent for an HTTP URL.
.PP
For URIs which must handle characters outside the US ASCII character set,
the HTML 4.01 specification (section B.2) and
-IETF RFC\ 2718 (section 2.2.5) recommend the following approach:
-.IP 1. 4
-translate the character sequences into UTF-8 (IETF RFC\ 2279) \(em see
-.BR utf-8 (7)
-\(em and then
-.IP 2.
+IETF RFC\~3986 (last paragraph of section 2.5)
+recommend the following approach:
+.IP (1) 5
+translate the character sequences into UTF-8 (IETF RFC\~3629)\[em]see
+.BR utf\-8 (7)\[em]and
+then
+.IP (2)
use the URI escaping mechanism, that is,
use the %HH encoding for unsafe octets.
-.SH "WRITING A URI"
-When written, URIs should be placed inside doublequotes
-(e.g., "http://www.kernelnotes.org"),
+.SS Writing a URI
+When written, URIs should be placed inside double quotes
+(e.g., "http://www.kernel.org"),
enclosed in angle brackets (e.g., <http://lwn.net>),
or placed on a line by themselves.
A warning for those who use double-quotes:
inside quotation marks.
This latter system, called the 'new' or 'logical' quoting system by
"Hart's Rules" and the "Oxford Dictionary for Writers and Editors",
-is preferred practice in Great Britain and hackers worldwide
-(see the
-Jargon File's section on Hacker Writing Style,
-.IR http://www.fwi.uva.nl/~mes/jargon/h/HackerWritingStyle.html ,
-for more information).
+is preferred practice in Great Britain and in various European languages.
Older documents suggested inserting the prefix "URL:"
just before the URI, but this form has never caught on.
.PP
change over time, particularly when new schemes are introduced.
Since an abbreviated URI has the same syntax as a relative URL path,
abbreviated URI references cannot be used where relative URIs are
-permitted, and can only be used when there is no defined base
+permitted, and can be used only when there is no defined base
(such as in dialog boxes).
Don't use abbreviated URIs as hypertext links inside a document;
use the standard format as described here.
-.SH "CONFORMING TO"
-.PP
-.IR http://www.ietf.org/rfc/rfc2396.txt
-(IETF RFC\ 2396),
-.I http://www.w3.org/TR/REC-html40
-(HTML 4.0).
-.UE
+.SH STANDARDS
+.UR http://www.ietf.org\:/rfc\:/rfc2396.txt
+(IETF RFC\ 2396)
+.UE ,
+.UR http://www.w3.org\:/TR\:/REC\-html40
+(HTML 4.0)
+.UE .
.SH NOTES
Any tool accepting URIs (e.g., a web browser) on a Linux system should
-be able to handle (directly or indirectly) all of the schemes described here,
-including the man: and info: schemes.
-Handling them by invoking some other program is fine and in fact encouraged.
+be able to handle (directly or indirectly) all of the
+schemes described here, including the man: and info: schemes.
+Handling them by invoking some other program is
+fine and in fact encouraged.
.PP
Technically the fragment isn't part of the URI.
.PP
.I text
</A>.
Texinfo files use the format @uref{\fIuri\fP}.
-Man and mdoc have the recently-added UR macro, or just include the
+Man and mdoc have the recently added UR macro, or just include the
URI in the text (viewers should be able to detect :// as part of a URI).
.PP
-The GNOME and KDE desktop environments currently vary in the URIs they accept,
-in particular in their respective help browsers.
+The GNOME and KDE desktop environments currently vary in the URIs
+they accept, in particular in their respective help browsers.
To list man pages, GNOME uses <toc:man> while KDE uses <man:(index)>, and
to list info pages, GNOME uses <toc:info> while KDE uses <info:(dir)>
(the author of this man page prefers the KDE approach here, though a more
Neither browser handles file: references to directories at the time
of this writing, making it difficult to refer to an entire directory with
a browsable URI.
-As noted above, these environments differ in how they handle the info: scheme,
-probably the most important variation.
+As noted above, these environments differ in how they handle the
+info: scheme, probably the most important variation.
It is expected that GNOME and KDE
will converge to common URI formats, and a future
version of this man page will describe the converged result.
Efforts to aid this convergence are encouraged.
.SS Security
-.PP
A URI does not in itself pose a security threat.
There is no general guarantee that a URL, which at one time
located a given resource, will continue to do so.
Nor is there any
guarantee that a URL will not locate a different resource at some
-later point in time; such a guarantee can only be
-obtained from the person(s) controlling that namespace and the
+later point in time; such a guarantee can be
+obtained only from the person(s) controlling that namespace and the
resource in question.
.PP
It is sometimes possible to construct a URL such that an attempt to
It is clearly unwise to use a URI that contains a password which is
intended to be secret.
In particular, the use of a password within
-the 'userinfo' component of a URI is strongly recommended against except
-in those rare cases where the 'password' parameter is intended to be public.
+the "userinfo" component of a URI is strongly recommended against except
+in those rare cases where the "password" parameter is intended to be public.
.SH BUGS
-.PP
Documentation may be placed in a variety of locations, so there
currently isn't a good URI scheme for general online documentation
in arbitrary formats.
<file:///usr/doc/ZZZ> don't work because different distributions and
local installation requirements may place the files in different
directories
-(it may be in /usr/doc, or /usr/local/doc, or /usr/share, or somewhere else).
+(it may be in /usr/doc, or /usr/local/doc, or /usr/share,
+or somewhere else).
Also, the directory ZZZ usually changes when a version changes
(though filename globbing could partially overcome this).
-Finally, using the file: scheme doesn't easily support people who dynamically
-load documentation from the Internet (instead of loading the files
-onto a local filesystem).
+Finally, using the file: scheme doesn't easily support people
+who dynamically load documentation from the Internet (instead of
+loading the files onto a local filesystem).
A future URI scheme may be added (e.g., "userdoc:") to permit
-programs to include cross-references to more detailed documentation without
-having to know the exact location of that documentation.
+programs to include cross-references to more detailed documentation
+without having to know the exact location of that documentation.
Alternatively, a future version of the filesystem specification may
specify file locations sufficiently so that the file: scheme will
be able to locate documentation.
.PP
Many programs can't handle all of these different URI formats; there
should be a standard mechanism to load an arbitrary URI that automatically
-detects the users' environment (e.g., text or graphics, desktop environment,
-local user preferences, and currently-executing tools) and invokes the
-right tool for any URI.
+detects the users' environment (e.g., text or graphics,
+desktop environment, local user preferences, and currently executing
+tools) and invokes the right tool for any URI.
.\" .SH AUTHOR
.\" David A. Wheeler (dwheeler@dwheeler.com) wrote this man page.
-.SH "SEE ALSO"
+.SH SEE ALSO
.BR lynx (1),
.BR man2html (1),
.BR mailaddr (7),
-.BR utf-8 (7),
-.UR http://www.ietf.org/rfc/rfc2255.txt
-IETF RFC\ 2255.
+.BR utf\-8 (7)
+.PP
+.UR http://www.ietf.org\:/rfc\:/rfc2255.txt
+IETF RFC\ 2255
.UE
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