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Edit File: lynx_url_support.html

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<title>URL Schemes Supported in Lynx</title>
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<h1>URL Schemes Supported in Lynx</h1>

Lynx handles a number of URL types, that are enumerated below.
 For more details about URLs (Uniform Resource Locators) see
 RFC1738:

<ul>
 <li><a href=
 "http://www.w3.org/Addressing/rfc1738.txt">http://www.w3.org/Addressing/rfc1738.txt</a></li>

<li><a href=
 "ftp://ftp.rfc-editor.org/in-notes/rfc1738.txt">ftp://ftp.rfc-editor.org/in-notes/rfc1738.txt</a></li>
 </ul>

Lynx resolves partial or relative URLs in documents with
 respect to the BASE if one was specified, otherwise with respect
 to the document's absolute URL, using the rules described in
 RFC1808:

<ul>
 <li><a href=
 "http://www.w3.org/Addressing/rfc1808.txt">http://www.w3.org/Addressing/rfc1808.txt</a></li>

<li><a href=
 "ftp://ftp.rfc-editor.org/in-notes/rfc1808.txt">ftp://ftp.rfc-editor.org/in-notes/rfc1808.txt</a></li>
 </ul>and in subsequent drafts of the IETF:

<ul>
 <li><a href="http://www.ics.uci.edu/pub/ietf/uri/">Uniform
 Resource Identifiers (URI) Working Group</a></li>
 </ul>

When entering a URL on the command line to be used as the
 startfile, or at the prompt for a 'g'oto entry,
 a partial host field can be used and the scheme field can be
 omitted if the scheme and fully qualified domain name can be
 constructed internally by using the URL_DOMAIN_PREFIXES and
 URL_DOMAIN_SUFFIXES definitions in the Lynx configuration file.
 See the explanation of those definitions and their use in your
 lynx.cfg.

For example, wfbr will be treated as
 http://www.wfbr.edu/, and wfbr/dir/lynx will be
 treated as http://www.wfbr.edu/dir/lynx, but
 gopher.wfbr.edu/11/_fileserv/_lynx will be treated as
 gopher://gopher.wfbr.edu/11/_fileserv/_lynx.

For files or directories on the local host, a tilde
 (~) is expanded to the path of the account's login
 directory, e.g., ~/foo will be expanded to
 file://localhost/your/login/directory/foo. The tilde
 expansion is done homologously on Unix and VMS.

On VMS, Lynx also will expand any file or directory spec
 recognizable to DCL into a valid URL, e.g., [] will be
 expanded to
 file://localhost/current/default/directory.

These expansions are SOLELY for startfile or
 'g'oto entries! Any partial or relative URLs within HTML
 documents are resolved according to the rules specified in
 RFC1808 and subsequent IETF drafts.
 <hr>

<h2><a name="http_url">The http and https
 URLs:</a></h2>

Lynx handles http URLs exactly as specified in RFC1738. The
 format is:
 <pre>
 http://host:port/path?searchpart#fragment
</pre>where :port is optional and defaults to
:80, /path if present is a slash-separated series
of symbolic elements, and ?searchpart if present is the
query for an ISINDEX search or the content of a FORM with
METHOD="GET". The #fragment field if present indicates a
location in the document to seek for display, based on a NAME-ed
anchor or an ID attribute within the document, and is technically
an instruction rather than part of the URL. Lynx will treat ID
attributes as NAME-ed anchors for all tags in the BODY of a
document which can correspond to positions in the rendering of the
document.

The https URL has the same format, but the default port is
 :443.
 <hr>

<h2><a name="telnet_url">The telnet, tn3270,
 and rlogin URLs:</a></h2>

A telnet URL generally results in Lynx spawning a
 telnet session. Lynx implements the complete telnet URL scheme,
 i.e.:
 <pre>
 telnet://user:password@host:port
</pre>

The user and/or :password fields may be
 omitted, and the @ should be omitted if neither is
 present. The port defaults to :23 when omitted in the
 URL.

A tn3270 or rlogin URL is specified
 equivalently, and similarly spawns a tn3270 or rlogin session.
 The actual behavior is dependent on the TCP-IP software installed
 on the local and target hosts.

It is unwise to include the :password field except
 for URLs which point to anonymous or other public access
 accounts, and for most TCP-IP software you will be prompted for a
 password whether or not one was included in the URL.
 <hr>

<h2><a name="gopher_url">The gopher URL:</a></h2>

The gopher URL takes the form:
 <pre>
 gopher://host:port/gopher-path
</pre>where :port is optional and defaults to
:70, and the /gopher-path is opaque (not fully
equivalent to the slash-separated series of symbolic elements of
http paths) as explained in RFC1738. Typically, the gopher-path
consists of a <a href=
"keystrokes/gopher_types_help.html">gophertype</a>
indicating the file or service type (e.g., 0 or I
for plain text or an image, respectively, 7 for a search,
or 1 for a directory), followed by a platform-specific
selector. Any reserved characters in the selector should
be hex escaped (%hh), including slashes, although hex
escaping of slashes is not required by Lynx in gopher URLs.

Lynx does not overtly support the gopher+ protocol, and does
 not represent itself as gopher+ capable when communicating with
 gopher servers. Lynx might transmit any
 (hex-escaped-tab-separated) extended gopher+ fields in a URL if
 an author included them in a document, but is likely to mishandle
 what the gopher server returns in such cases, and would not
 generate and transmit them itself. For pre-formed URLs to submit
 gopher searches, it may be better to use a ? rather than
 hex-escaped tab (%09) as the separator for the
 searchpart in the selector, e.g.: 
 gopher://gopher.wfbr.edu/77/_shell/search.shell%20/_shell/walker?lynx*
 Lynx will handle the %09 if you use that instead of
 ?, but other WWW clients may mishandle it.

For the gophertype which signifies HTML (h),
 if the selector begins with GET%20/ Lynx will
 convert the gopher URL to an http URL, e.g.: 
 <pre>
gopher://www.wfbr.edu:80/hGET%20/
</pre>will become: 
 <pre>
http://www.wfbr.edu/
</pre>The port field will be retained if it is not :80,
and will default to :70 if it was defaulted originally.
These conventions were adopted during development of the University
of Minnesota gopher software to facilitate the offering of links to
MIME-capable http servers in the listings returned by gopher
servers, but should be considered Lynxisms and UMN Gopherisms.
 <hr>

The file URL is used to retrieve files or generate a directory
 listing on the local host. The host field can be
 localhost or a domain name for the local host: 
 <pre>
file://localhost/path
</pre>If you do not use localhost or a domain name for the
local host, Lynx will substitute ftp:// for
file:// and treat it as an ftp URL.

The /path is treated as originating at the root,
 unless you include a tilde (~), e.g.:
 <pre>
 file://localhost/~/foo will be converted to:
 file://localhost/your/login/directory/foo
</pre>The latter feature is a Lynxism, is done homologously on Unix
and VMS, and should be used ONLY in local documents intended for
Lynx.

On VMS, the first element of the path, if not a tilde, is
 assumed to be a device, e.g.:
 <pre>
 file://localhost/www_root/directory/filename.suffix
</pre>should be used for:
www_root:[directory]filename.suffix 
 If you are unsure how to specify a file URL in local documents on
 VMS, invoke Lynx with the desired file or directory as the
 startfile using any spec acceptable to DCL, and then use
 the showinfo command (=) to see the file URL
 which Lynx created for it.
 <hr>

The ftp URL has the general format:
 <pre>
 ftp://host:port/path;type=[D,I, or A]
 ftp://username@host:port/path;type=[D,I, or A]
</pre>

The default port is :21 and the default
 username is anonymous. If username is
 included, Lynx will prompt you for the password. For anonymous
 ftp, Lynx uses your personal_mail_address (user@host) as
 the password if it has been defined via the
 'o'ptions menu. Otherwise, Lynx uses the dummy password
 WWWUser. (A password can also be embedded in the URL, by
 replacing username with username:password. This
 is strongly discouraged for 'real' passwords that must be kept
 secret, since URLs with the completely unencrypted
 password may show up on the screen, in HISTORY and LIST
 pages etc., and may even become visible to remote sites for
 example through Referer headers.) Do not include the @
 if neither username nor :password is
 included.

The ;type= parameter can be used with value
 D, I, or A to force handling of the
 URL as, respectively, a directory listing, binary file, or ASCII
 file. The Lynx ftp gateway normally determines this itself, but
 the parameter can be used if the internal procedure draws an
 incorrect inference about the nature of the ftp URL.

The /path is treated according to RFC1738 for VMS and
 VM/CMS ftp servers. The lead slash (/) is treated purely
 as a separator, not as a designator for the root, and the
 path string if present is treated as in or under the
 login directory. For VMS ftp servers, if you wish to have the
 first element treated as a device rather than file or
 subdirectory name, begin it with a hex-escaped slash
 (%2f), e.g.:
 <pre>
 ftp://user@myhost/%2fsys$common/syshlp
</pre>can be used for a listing of sys$common:[syshlp] 
 Also, on VM/CMS ftp servers, if the path string begins
 with vmsysu%3a it receives special handling as an SFS
 path, e.g.:
 <pre>
 ftp://ubvm.cc.buffalo.edu/vmsysu%3alistserv.webshare
</pre>

For Unix and Unix-emulation ftp servers, RFC1738 is not
 respected and the lead slash is treated as the root, i.e., the
 /path is handled equivalently to that in file URLs. The
 distinction is irrelevant for anonymous ftp, but matters when
 using ftp for non-anonymous accounts. If you are using ftp with a
 Unix server and do wish to get a listing of the login directory
 or have the path string treated as a file or path under
 the login directory, include a tilde (~) as for <a href=
 "#file_url">file</a> URLs, e.g.:
 <pre>
 ftp://user@myhost/~
</pre>
 <hr>

The wais URL is used to retrieve resources using the Wide Area
 Information System protocol. The format is:
 <pre>
 wais://host:port/database
 wais://host:port/database?wais_query
 wais://host:port/database/wais_type/wais_path
</pre>where :port defaults to :210

Direct wais support is built into Lynx for VMS, and can be
 compiled into Lynx on Unix.

If only a database is indicated in the URL, Lynx
 returns an ISINDEX cover page for searching that
 database, and will submit your search with the
 wais_query appended. Lynx will convert the server's
 reply into a hit list with URLs that include the
 wais_type and wais_path for retrieving items
 from the hit list.
 <hr>

<h2><a name="news_url">The news, nntp, and
 snews URLs:</a></h2>

The news and nntp URLs are handled by Lynx as specified in
 RFC1738, but for compatibility with other clients, Lynx allows
 inclusion of host and port fields in news URLs, which properly
 should be used only in nntp and snews URLs. If not
 included in news URLs, Lynx will use the nntp server pointed to
 by the NNTPSERVER environment variable or configuration symbol
 (see lynx.cfg), with default port :119. A host field
 must be included in nntp URLs, and the port field is optional
 with the same default.

If the URL requires authentication, lynx will prompt you for
 the username and password. These are cached during a session, for
 reuse on the same host. If $HOME/.newsauth exists, lynx
 initializes its cache from this file. The .newsauth file contents
 are one line per entry: hostname, password and username (in that
 order) separated by a space.

The formats are: 
 <pre>
 news:newsgroup (retrieves list of messages in newsgroup)
 news:messageID (retrieves the message)
 news:* (retrieves list of all available newsgroups)
 nntp://host:port/newsgroup
 nntp://host:port/messageID
 nntp://host:port/*
</pre>(snews same as nntp, but the default port is :563)

The messageID is the message's unique identifier,
 consisting of an identification string and the host of origin for
 the message (ident_string@origin_host).

Lynx also supports wildcarding via an asterisk for listings of
 news hierarchies or sub-hierarchies, e.g.:
 <pre>
 news:comp.infosystems.*
 nntp://host:port/comp.infosystems.*
</pre>(snews same as nntp, but the default port is
:563) 
 This is not in RFC1738 and may not be supported by all other
 clients.

Lynx allows you both to reply to the author of a news
 message via email, and, if news posting has been enabled, to send
 a followup message to the newsgroup (see <a href=
 "#newspost_url">newspost, newsreply, snewspost,
 snewsreply</a>).

Lynx converts any strings in news messages which appear to be
 a URL with a supported scheme into a link for accessing that
 URL.

Lynx also supports the newsgroup and message number URL
 scheme: 
 <pre>
 news:newsgroup/startNo-endNo (lists message range in newsgroup)
 news:newsgroup/messageNo (retrieves the message by number)
 nntp://host:port/newsgroup/startNo-endNo
 nntp://host:port/newsgroup/messageNo
</pre>(snews same as nntp, but the default port is
:563) 
 Use of this scheme is not recommended, because the message
 numbers are specific to each nntp server, unlike the unique
 identifiers for news messages.
 <hr>

<h2><a name="newspost_url">The newspost,
 newsreply, snewspost, and snewsreply
 URLs:</a></h2>

When Lynx receives group listings or articles via
 news, nntp or snews URLs, it also
 checks whether the nntp server supports posting from the Lynx
 user's site, and if so, includes links for posting new messages
 to that server, or for posting followups (replies) to previously
 posted messages. RFC1738, and IETF URL drafts through this
 release of Lynx, do not include any schemes for posting to news
 groups. Lynx has long supported newspost and newreply URL schemes
 for posting new messages or sending followups, respectively, to
 standard nntp servers, with default port :119. Lynx now
 also supports homologous snewspost and snewsreply URLs for use
 with SSL capable nntp servers.

The formats are:
 <pre>
 newspost://host:port/newsgroup(s) (post a new message)
 newsreply://host:port/newsgroup(s) (post a followup message)
</pre>(snewspost and snewsreply have the same formats, but the
default port is :563)

If the host field is omitted, it defaults to that pointed to
 by the NNTPSERVER configuration or environmental variable.
 Inclusion of at least one newsgroup in the URL is required, and
 additional groups can be specified as a comma-separated list.
 Wildcarding of newsgroup names is not supported for these URLs.
 For newsreply and snewsreply URLs, if an external editor has been
 defined via the Options Menu, the user is offered an
 option to include the currently displayed document, which
 presumably is a news article with a followup link that
 was activated, and if confirmed, each line of that document is
 prefixed with a right-angle-bracket. The user is expected to edit
 such an inclusion so that only the passages relevant to the
 followup message are retained.

These URLs can be used as command line startfiles (in which
 case, Lynx will exit after posting the message, and the newreply
 or snewsreply URLs degrade to newspost or snewpost URLs,
 respectively). They also can be used as HREF attribute values in
 any HTML document homologously to <a href=
 "#mailto_url">mailto</a> URLs, with the qualification that they
 presently are supported only by Lynx.
 <hr>

<h2><a name="mailto_url">The mailto URL:</a></h2>

The mailto URL is used to provide links that when activated
 can be used to send a comment or the content of a FORM to an
 Internet email address (user@host). The format is:
 <pre>
 mailto:user@host
</pre>

The description of the mailto URL in RFC1738 has been
 interpreted by some as allowing only a single recipient, but Lynx
 invented the mailto URL, has always supported a series of
 user@host addresses as a comma-separated list, and still does.
 For compatibility with Explorer, Lynx also accepts a
 semi-colon-separated list.

For compatibility with Netscape, Lynx parses any
 ?subject=The%20Subject appended to the URL, trims the
 URL at the ?, and uses the value as the default Subject:
 for the message or FORM content mailing. This is not recommended
 practice. The preferred way to indicate the default Subject: for
 a LINK or Anchor with a mailto HREF, or a FORM with a mailto
 ACTION, is via a TITLE attribute with the subject string as its
 value, e.g.:
 <pre>
 &lt;LINK REV="made"
 HREF="mailto:me@myhost,her@herhost" TITLE="The Subject"&gt;

&lt;A HREF="mailto:user@host" TITLE="The Subject"&gt;...&lt;/A&gt;

&lt;FORM METHOD="post" ENCTYPE="text/plain"
 ACTION="mailto:WebMaster@host" TITLE="The Subject"&gt;
 ...
 &lt;/FORM&gt;
</pre>

Note that a TITLE attribute for FORM is now included in the
 HTML specifications. Some clients use a SUBJECT attribute for
 this purpose in FORM tags, and Lynx recognizes that as a synonym
 for TITLE.

Lynx also will process any to=address(es),
 cc=address(es), keywords=word_list and/or
 body=message fields in ?searchpart tack-ons to
 mailto URLs. The to and/or cc values can be
 single addresses, or comma- or semi-colon-separated lists of
 addresses. All addresses, and any body values, will be
 offered for approval by the user before proceeding with a
 mailing. Any other name=value pairs in the ?searchpart
 will be ignored. Also, if the mailto URL is the ACTION for a
 FORM, any body in a ?searchpart tack-on will be
 ignored, because the body of the mailing must be constructed
 solely from the the FORM's content. Lynx expects multiple
 name=value pairs in a ?searchpart tack-on to be
 separated by ampersands, as in the original Netscape
 implementation, and in an equally ill-advised IETF draft of that
 implementation (<a href=
 "ftp://ftp.isi.edu/internet-drafts/draft-hoffman-mailto-url-03.txt">draft-hoffman-mailto-url-03.txt</a>).
 These should be represented as entities (&amp;amp;) in
 the HTML markup. This functionality is generally desired, but the
 IETF backward compatibility principal normally would lead to a
 new scheme being used (e.g., mail:, or smtp:),
 rather than breaking mailto: implementations.

If ENCTYPE="text/plain" is specified for a FORM with
 a mailto ACTION, Lynx will not hex escape the name=value pairs of
 the FORM's content, and will use physical newlines instead of
 '&amp;' or ';' to separate the pairs, so that
 the content will be readable directly. Otherwise, Lynx will mail
 the content with the default:
 <pre>
 ENCTYPE="application/x-www-form-urlencoded" ('&amp;' separates pairs)
</pre>or:
 <pre>
 ENCTYPE="application/sgml-form-urlencoded" (';' separates pairs)
</pre>if the latter was indicated.

Note that when mailing FORM content Lynx wraps any lines
 longer than 78 characters, to avoid buffer overflows in mail
 software and to ensure reliable transmission across gateways. If
 the ENCTYPE was not text/plain, any script which decodes
 the mailed content should ignore the physical newlines and
 recognize only hex escaped newline characters as intended to be
 present in the decoded content.

If the mailto URL is not the ACTION for a FORM, and if an
 external editor has been defined via the Options Menu,
 the user is offered an option to include the currently displayed
 document. If this option is accepted, each line of that document
 is prefixed with a right-angle-bracket, and the prefixed
 inclusion should be trimmed by the user to just those passages
 relevant to the message which will be sent.
 <hr>

<h2><a name="finger_url">The finger URL:</a></h2>

Lynx has full support for the finger protocol, but a format
 for finger URLs has not yet been adopted by the IETF. The formats
 supported by Lynx therefore include every possibility not
 inconsistent with RFC1738, including:
 <pre>
 finger://host finger://@host
 finger://host/ finger://@host/
 finger://host/%2fw finger://@host/w
 finger://host/w finger://host/w/
 finger://host/username[@host] finger://username@host
 finger://host/username[@host]/ finger://username@host/
 finger://host/w/username[@host] finger://username@host/w
 finger://host/%2fw%20username[@host] finger://host/username[@host]/w
 finger://host/w/username
</pre>

Activating a finger URL will send a request to the finger
 server via port 79 on the host specified. You can include
 :79 in the URL, but no other value is allowed. The
 /w or /%2fw is used to request a full report
 for finger servers which support it, and is not case sensitive
 (i.e., can be /W or /%2fW). Any strings in the
 report which appear to be a URL with a supported scheme will be
 converted into a link for accessing that URL.

An alternative way to access finger servers is via gopher URLs
 with port 79 and the plain text (0) gophertype
 specified: 
 gopher://host:79/0 
 Lynx will handle such URLs equivalently to overt finger URLs,
 including creation of links for any strings which appear to be
 supported URLs.
 <hr>

The cso URL is intended to provide a gateway to CSO/PH (QI)
 servers. The requests are made on port 105 by default
 (:105), with the following overt cso URL format: 
 <pre>
 cso://host
</pre>

You also can use a gopher URL format with port 105 and the CSO
 (2) gophertype specified:
 <pre>
 gopher://host:105/2
</pre>

Lynx will parse the stream returned by the server for the
 above URLs and create a FORM for submitting additional requests
 (searches) to the server. Any strings in the reports returned for
 these requests (searches) which appear to be a URL with a
 supported scheme will be converted into a link for accessing that
 URL.
 <hr>

Lynx provides built-in support for bibliographic protocol
 (BibP). BibP links are links to published works such as books or
 journal articles, without a predefined server. BibP links are
 intended for resolution by a local bibhost server
 (http://bibhost/) if it exists. Otherwise, resolution is
 performed by a document-specified server or a known global
 server.

<h2><a name="exec_url">The lynxexec and
 lynxprog URLs:</a></h2>

If execution of spawned commands has been enabled in your Lynx
 image, the lynxexec and lynxprog URLs can be used to execute
 arbitrary system commands or invoke system utilities. Any system
 command and associated switches or qualifiers can be used, with
 the syntax appropriate for a shell running Lynx on Unix, or for
 DCL on VMS, e.g.:
 <pre>
 lynxexec:dir/date/size foo:[blah] (VMS)
 lynxexec:ls -l /foo/blah (Unix)
 lynxprog:news
</pre>(Note, however, that restrictions on acceptable commands or
utilities may be imposed by the system administrator.)

You optionally can include //localhost/ in the URL,
 between the scheme field and the command, but that is always
 implied. The lynxexec and lynxprog URLs differ only in that with
 lynxexec you are prompted to enter RETURN before Lynx
 clears the screen and restores the previously displayed document,
 so that you can read any screen output generated by the spawned
 command, whereas no such pause is imposed upon exit from the
 utility invoked via lynxprog.

These are Lynxisms and should be used only in local documents
 intended solely for Lynx.
 <hr>

<h2><a name="cgi_url">The lynxcgi URL:</a></h2>

The lynxcgi URL is implemented only on Unix, can be used as
 the ACTION for a FORM, and if enabled in your Lynx image has the
 format:
 <pre>
 lynxcgi://localhost/path_to_CGI_script
</pre>where //localhost is optional and always implied;
the full path should be specified, as `~' is not recognized; if the
script is in the directory Lynx was started from, the simple file
name is adequate. The output of the script should be text/html and
is rendered and displayed by Lynx. Restrictions on use of lynxcgi
and on acceptable paths can be imposed in userdefs.h and
lynx.cfg, qv.

This is a Lynxism and should be used only in local documents
 intended solely for Lynx, or for limited local testing of CGI
 scripts without an http server.
 <hr>

<h2><a name="ncftp_url">The NcFTP URL:</a></h2>

Lynx recognizes the NcFTP-style ftp URL, e.g.,
 <pre>
 <cite>ftpHost</cite>:<cite>fileSpecification</cite>
</pre>for example
 <pre>
<code>
 ftp.gnu.org:/pub/gnu
</code>
</pre>
 <hr>

<h2><a name="internal_url">The LYNXfoo internal
 URLs:</a></h2>

Lynx uses a variety of private URL schemes for communication
 among its internal modules. They start with uppercase letters
 <code>LYNX</code> by convention, although, as input, URL schemes
 are recognized in a case-insensitive manner.

As you discover what they are, and are tempted to use them
 externally in documents, you should resist that
 temptation:

<ul>
 <li>There already is too much browser-specific markup
 around...</li>

<li>The schemes, or their meanings, may change between Lynx
 versions.</li>

<li>Even if a scheme stays the same, some aspect of its
 behavior may be modified without notice, or the context in
 which it is allowed may change.</li>

<li>If it doesn't work as expected when used outside of the
 intended purpose, don't expect anyone to "fix" it.</li>
 </ul>

For example, tempting though it might be, do not use
 these:
 <pre>
 Return to your &lt;A HREF="LYNXHIST:0"&gt;Startfile&lt;/A&gt;
 Review your &lt;A HREF="LYNXKEYMAP:"&gt;Keymap&lt;/A&gt;
</pre>(No, they won't do any harm. Yes, they work. But don't rely
on it.)

If you must try one, the second is OK from the command
 line: 
 <pre>
 lynx LYNXKEYMAP:
</pre>But within Lynx, use the 'K' keystroke command.
Sometimes it may be convenient to use a private scheme with
'g'oto, as in:
 <pre>
 g LYNXMESSAGES:
 g LYNXCOMPILEOPTS:
 g LYNXCFG:
</pre>But again, there usually is a way in which those special
pages are meant to be reached that is more convenient.
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