{ "mode": "man", "parameter": "URI", "section": "7", "url": "https://www.chedong.com/phpMan.php/man/URI/7/json", "generated": "2026-05-30T06:05:20Z", "synopsis": "URI = [ absoluteURI | relativeURI ] [ \"#\" fragment ]\nabsoluteURI = scheme \":\" ( hierarchicalpart | opaquepart )\nrelativeURI = ( netpath | absolutepath | relativepath ) [ \"?\" query ]\nscheme = \"http\" | \"ftp\" | \"gopher\" | \"mailto\" | \"news\" | \"telnet\" |\n\"file\" | \"man\" | \"info\" | \"whatis\" | \"ldap\" | \"wais\" | ...\nhierarchicalpart = ( netpath | absolutepath ) [ \"?\" query ]\nnetpath = \"//\" authority [ absolutepath ]\nabsolutepath = \"/\" pathsegments\nrelativepath = relativesegment [ absolutepath ]", "sections": { "NAME": { "content": "uri, url, urn - uniform resource identifier (URI), including a URL or URN\n", "subsections": [] }, "SYNOPSIS": { "content": "URI = [ absoluteURI | relativeURI ] [ \"#\" fragment ]\n\nabsoluteURI = scheme \":\" ( hierarchicalpart | opaquepart )\n\nrelativeURI = ( netpath | absolutepath | relativepath ) [ \"?\" query ]\n\nscheme = \"http\" | \"ftp\" | \"gopher\" | \"mailto\" | \"news\" | \"telnet\" |\n\"file\" | \"man\" | \"info\" | \"whatis\" | \"ldap\" | \"wais\" | ...\n\nhierarchicalpart = ( netpath | absolutepath ) [ \"?\" query ]\n\nnetpath = \"//\" authority [ absolutepath ]\n\nabsolutepath = \"/\" pathsegments\n\nrelativepath = relativesegment [ absolutepath ]\n", "subsections": [] }, "DESCRIPTION": { "content": "A Uniform Resource Identifier (URI) is a short string of characters identifying an abstract\nor physical resource (for example, a web page). A Uniform Resource Locator (URL) is a URI\nthat identifies a resource through its primary access mechanism (e.g., its network \"loca‐\ntion\"), rather than by name or some other attribute of that resource. A Uniform Resource\nName (URN) is a URI that must remain globally unique and persistent even when the resource\nceases to exist or becomes unavailable.\n\nURIs are the standard way to name hypertext link destinations for tools such as web browsers.\nThe string \"http://www.kernel.org\" is a URL (and thus it is also a URI). Many people use the\nterm URL loosely as a synonym for URI (though technically URLs are a subset of URIs).\n\nURIs can be absolute or relative. An absolute identifier refers to a resource independent of\ncontext, while a relative identifier refers to a resource by describing the difference from\nthe current context. Within a relative path reference, the complete path segments \".\" and\n\"..\" have special meanings: \"the current hierarchy level\" and \"the level above this hierarchy\nlevel\", respectively, just like they do in UNIX-like systems. A path segment which contains\na colon character can't be used as the first segment of a relative URI path (e.g.,\n\"this:that\"), because it would be mistaken for a scheme name; precede such segments with ./\n(e.g., \"./this:that\"). Note that descendants of MS-DOS (e.g., Microsoft Windows) replace de‐\nvicename colons with the vertical bar (\"|\") in URIs, so \"C:\" becomes \"C|\".\n\nA fragment identifier, if included, refers to a particular named portion (fragment) of a re‐\nsource; text after a '#' identifies the fragment. A URI beginning with '#' refers to that\nfragment in the current resource.\n", "subsections": [ { "name": "Usage", "content": "There are many different URI schemes, each with specific additional rules and meanings, but\nthey are intentionally made to be as similar as possible. For example, many URL schemes per‐\nmit the authority to be the following format, called here an ipserver (square brackets show\nwhat's optional):\n\nipserver = [user [ : password ] @ ] host [ : port]\n\nThis format allows you to optionally insert a username, a user plus password, and/or a port\nnumber. The host is the name of the host computer, either its name as determined by DNS or\nan IP address (numbers separated by periods). Thus the URI logs into a web server on host example.com as fred (using fredpassword) using\nport 8080. Avoid including a password in a URI if possible because of the many security\nrisks of having a password written down. If the URL supplies a username but no password, and\nthe remote server requests a password, the program interpreting the URL should request one\nfrom the user.\n\nHere are some of the most common schemes in use on UNIX-like systems that are understood by\nmany tools. Note that many tools using URIs also have internal schemes or specialized\nschemes; see those tools' documentation for information on those schemes.\n" }, { "name": "http - Web (HTTP) server", "content": "http://ipserver/path\nhttp://ipserver/path?query\n\nThis is a URL accessing a web (HTTP) server. The default port is 80. If the path refers to\na directory, the web server will choose what to return; usually if there is a file named \"in‐\ndex.html\" or \"index.htm\" its content is returned, otherwise, a list of the files in the cur‐\nrent directory (with appropriate links) is generated and returned. An example is\n.\n\nA query can be given in the archaic \"isindex\" format, consisting of a word or phrase and not\nincluding an equal sign (=). A query can also be in the longer \"GET\" format, which has one\nor more query entries of the form key=value separated by the ampersand character (&). Note\nthat key can be repeated more than once, though it's up to the web server and its application\nprograms to determine if there's any meaning to that. There is an unfortunate interaction\nwith HTML/XML/SGML and the GET query format; when such URIs with more than one key are embed‐\nded in SGML/XML documents (including HTML), the ampersand (&) has to be rewritten as &.\nNote that not all queries use this format; larger forms may be too long to store as a URI, so\nthey use a different interaction mechanism (called POST) which does not include the data in\nthe URI. See the Common Gateway Interface specification at ⟨http://www.w3.org/CGI⟩ for more\ninformation.\n" }, { "name": "ftp - File Transfer Protocol (FTP)", "content": "ftp://ipserver/path\n\nThis is a URL accessing a file through the file transfer protocol (FTP). The default port\n(for control) is 21. If no username is included, the username \"anonymous\" is supplied, and\nin that case many clients provide as the password the requestor's Internet email address. An\nexample is .\n" }, { "name": "gopher - Gopher server", "content": "gopher://ipserver/gophertype selector\ngopher://ipserver/gophertype selector%09search\ngopher://ipserver/gophertype selector%09search%09gopher+string\n\nThe default gopher port is 70. gophertype is a single-character field to denote the Gopher\ntype of the resource to which the URL refers. The entire path may also be empty, in which\ncase the delimiting \"/\" is also optional and the gophertype defaults to \"1\".\n\nselector is the Gopher selector string. In the Gopher protocol, Gopher selector strings are\na sequence of octets which may contain any octets except 09 hexadecimal (US-ASCII HT or tab),\n0A hexadecimal (US-ASCII character LF), and 0D (US-ASCII character CR).\n" }, { "name": "mailto - Email address", "content": "mailto:email-address\n\nThis is an email address, usually of the form name@hostname. See mailaddr(7) for more infor‐\nmation on the correct format of an email address. Note that any % character must be rewrit‐\nten as %25. An example is .\n" }, { "name": "news - Newsgroup or News message", "content": "news:newsgroup-name\nnews:message-id\n\nA newsgroup-name is a period-delimited hierarchical name, such as \"comp.infosys‐\ntems.www.misc\". If is \"*\" (as in ), it is used to refer to \"all\navailable news groups\". An example is .\n\nA message-id corresponds to the Message-ID of IETF RFC 1036, ⟨http://www.ietf.org/rfc\n/rfc1036.txt⟩ without the enclosing \"<\" and \">\"; it takes the form unique@fulldomainname.\nA message identifier may be distinguished from a news group name by the presence of the \"@\"\ncharacter.\n" }, { "name": "telnet - Telnet login", "content": "telnet://ipserver/\n\nThe Telnet URL scheme is used to designate interactive text services that may be accessed by\nthe Telnet protocol. The final \"/\" character may be omitted. The default port is 23. An\nexample is .\n" }, { "name": "file - Normal file", "content": "file://ipserver/pathsegments\nfile:pathsegments\n\nThis represents a file or directory accessible locally. As a special case, ipserver can be\nthe string \"localhost\" or the empty string; this is interpreted as \"the machine from which\nthe URL is being interpreted\". If the path is to a directory, the viewer should display the\ndirectory's contents with links to each containee; not all viewers currently do this. KDE\nsupports generated files through the URL . If the given file isn't found,\nbrowser writers may want to try to expand the filename via filename globbing (see glob(7) and\nglob(3)).\n\nThe second format (e.g., ) is a correct format for referring to a local\nfile. However, older standards did not permit this format, and some programs don't recognize\nthis as a URI. A more portable syntax is to use an empty string as the server name, for ex‐\nample, ; this form does the same thing and is easily recognized by pat‐\ntern matchers and older programs as a URI. Note that if you really mean to say \"start from\nthe current location,\" don't specify the scheme at all; use a relative address like\n<../test.txt>, which has the side-effect of being scheme-independent. An example of this\nscheme is .\n" }, { "name": "man - Man page documentation", "content": "man:command-name\nman:command-name(section)\n\nThis refers to local online manual (man) reference pages. The command name can optionally be\nfollowed by a parenthesis and section number; see man(7) for more information on the meaning\nof the section numbers. This URI scheme is unique to UNIX-like systems (such as Linux) and\nis not currently registered by the IETF. An example is .\n" }, { "name": "info - Info page documentation", "content": "info:virtual-filename\ninfo:virtual-filename#nodename\ninfo:(virtual-filename)\ninfo:(virtual-filename)nodename\n\nThis scheme refers to online info reference pages (generated from texinfo files), a documen‐\ntation format used by programs such as the GNU tools. This URI scheme is unique to UNIX-like\nsystems (such as Linux) and is not currently registered by the IETF. As of this writing,\nGNOME and KDE differ in their URI syntax and do not accept the other's syntax. The first two\nformats are the GNOME format; in nodenames all spaces are written as underscores. The second\ntwo formats are the KDE format; spaces in nodenames must be written as spaces, even though\nthis is forbidden by the URI standards. It's hoped that in the future most tools will under‐\nstand all of these formats and will always accept underscores for spaces in nodenames. In\nboth GNOME and KDE, if the form without the nodename is used the nodename is assumed to be\n\"Top\". Examples of the GNOME format are and . Examples of\nthe KDE format are and .\n" }, { "name": "whatis - Documentation search", "content": "whatis:string\n\nThis scheme searches the database of short (one-line) descriptions of commands and returns a\nlist of descriptions containing that string. Only complete word matches are returned. See\nwhatis(1). This URI scheme is unique to UNIX-like systems (such as Linux) and is not cur‐\nrently registered by the IETF.\n" }, { "name": "ghelp - GNOME help documentation", "content": "ghelp:name-of-application\n\nThis loads GNOME help for the given application. Note that not much documentation currently\nexists in this format.\n" }, { "name": "ldap - Lightweight Directory Access Protocol", "content": "ldap://hostport\nldap://hostport/\nldap://hostport/dn\nldap://hostport/dn?attributes\nldap://hostport/dn?attributes?scope\nldap://hostport/dn?attributes?scope?filter\nldap://hostport/dn?attributes?scope?filter?extensions\n\nThis scheme supports queries to the Lightweight Directory Access Protocol (LDAP), a protocol\nfor querying a set of servers for hierarchically organized information (such as people and\ncomputing resources). See RFC 2255 ⟨http://www.ietf.org/rfc/rfc2255.txt⟩ for more informa‐\ntion on the LDAP URL scheme. The components of this URL are:\n\nhostport the LDAP server to query, written as a hostname optionally followed by a colon\nand the port number. The default LDAP port is TCP port 389. If empty, the\nclient determines which the LDAP server to use.\n\ndn the LDAP Distinguished Name, which identifies the base object of the LDAP search\n(see RFC 2253 ⟨http://www.ietf.org/rfc/rfc2253.txt⟩ section 3).\n\nattributes a comma-separated list of attributes to be returned; see RFC 2251 section 4.1.5.\nIf omitted, all attributes should be returned.\n\nscope specifies the scope of the search, which can be one of \"base\" (for a base object\nsearch), \"one\" (for a one-level search), or \"sub\" (for a subtree search). If\nscope is omitted, \"base\" is assumed.\n\nfilter specifies the search filter (subset of entries to return). If omitted, all en‐\ntries should be returned. See RFC 2254 ⟨http://www.ietf.org/rfc/rfc2254.txt⟩\nsection 4.\n\nextensions a comma-separated list of type=value pairs, where the =value portion may be omit‐\nted for options not requiring it. An extension prefixed with a '!' is critical\n(must be supported to be valid), otherwise it is noncritical (optional).\n\nLDAP queries are easiest to explain by example. Here's a query that asks ldap.itd.umich.edu\nfor information about the University of Michigan in the U.S.:\n\nldap://ldap.itd.umich.edu/o=University%20of%20Michigan,c=US\n\nTo just get its postal address attribute, request:\n\nldap://ldap.itd.umich.edu/o=University%20of%20Michigan,c=US?postalAddress\n\nTo ask a host.com at port 6666 for information about the person with common name (cn) \"Babs\nJensen\" at University of Michigan, request:\n\nldap://host.com:6666/o=University%20of%20Michigan,c=US??sub?(cn=Babs%20Jensen)\n" }, { "name": "wais - Wide Area Information Servers", "content": "wais://hostport/database\nwais://hostport/database?search\nwais://hostport/database/wtype/wpath\n\nThis scheme designates a WAIS database, search, or document (see IETF RFC 1625\n⟨http://www.ietf.org/rfc/rfc1625.txt⟩ for more information on WAIS). Hostport is the host‐\nname, optionally followed by a colon and port number (the default port number is 210).\n\nThe first form designates a WAIS database for searching. The second form designates a par‐\nticular search of the WAIS database database. The third form designates a particular docu‐\nment within a WAIS database to be retrieved. wtype is the WAIS designation of the type of\nthe object and wpath is the WAIS document-id.\n" }, { "name": "other schemes", "content": "There are many other URI schemes. Most tools that accept URIs support a set of internal URIs\n(e.g., Mozilla has the about: scheme for internal information, and the GNOME help browser has\nthe toc: scheme for various starting locations). There are many schemes that have been de‐\nfined but are not as widely used at the current time (e.g., prospero). The nntp: scheme is\ndeprecated in favor of the news: scheme. URNs are to be supported by the urn: scheme, with a\nhierarchical name space (e.g., urn:ietf:... would identify IETF documents); at this time URNs\nare not widely implemented. Not all tools support all schemes.\n" }, { "name": "Character encoding", "content": "URIs use a limited number of characters so that they can be typed in and used in a variety of\nsituations.\n\nThe following characters are reserved, that is, they may appear in a URI but their use is\nlimited to their reserved purpose (conflicting data must be escaped before forming the URI):\n\n; / ? : @ & = + $ ,\n\nUnreserved characters may be included in a URI. Unreserved characters include uppercase and\nlowercase English letters, decimal digits, and the following limited set of punctuation marks\nand symbols:\n\n- . ! ~ * ' ( )\n\nAll other characters must be escaped. An escaped octet is encoded as a character triplet,\nconsisting of the percent character \"%\" followed by the two hexadecimal digits representing\nthe octet code (you can use uppercase or lowercase letters for the hexadecimal digits). For\nexample, a blank space must be escaped as \"%20\", a tab character as \"%09\", and the \"&\" as\n\"%26\". Because the percent \"%\" character always has the reserved purpose of being the escape\nindicator, it must be escaped as \"%25\". It is common practice to escape space characters as\nthe plus symbol (+) in query text; this practice isn't uniformly defined in the relevant RFCs\n(which recommend %20 instead) but any tool accepting URIs with query text should be prepared\nfor them. A URI is always shown in its \"escaped\" form.\n\nUnreserved characters can be escaped without changing the semantics of the URI, but this\nshould not be done unless the URI is being used in a context that does not allow the un‐\nescaped character to appear. For example, \"%7e\" is sometimes used instead of \"~\" in an HTTP\nURL path, but the two are equivalent for an HTTP URL.\n\nFor URIs which must handle characters outside the US ASCII character set, the HTML 4.01 spec‐\nification (section B.2) and IETF RFC 2718 (section 2.2.5) recommend the following approach:\n\n1. translate the character sequences into UTF-8 (IETF RFC 2279)—see utf-8(7)—and then\n\n2. use the URI escaping mechanism, that is, use the %HH encoding for unsafe octets.\n" }, { "name": "Writing a URI", "content": "When written, URIs should be placed inside double quotes (e.g., \"http://www.kernel.org\"), en‐\nclosed in angle brackets (e.g., ), or placed on a line by themselves. A\nwarning for those who use double-quotes: never move extraneous punctuation (such as the pe‐\nriod ending a sentence or the comma in a list) inside a URI, since this will change the value\nof the URI. Instead, use angle brackets instead, or switch to a quoting system that never\nincludes extraneous characters inside quotation marks. This latter system, called the 'new'\nor 'logical' quoting system by \"Hart's Rules\" and the \"Oxford Dictionary for Writers and Edi‐\ntors\", is preferred practice in Great Britain and hackers worldwide (see the Jargon File's\nsection on Hacker Writing Style, ⟨http://www.fwi.uva.nl/~mes/jargon/h\n/HackerWritingStyle.html⟩, for more information). Older documents suggested inserting the\nprefix \"URL:\" just before the URI, but this form has never caught on.\n\nThe URI syntax was designed to be unambiguous. However, as URIs have become commonplace,\ntraditional media (television, radio, newspapers, billboards, etc.) have increasingly used\nabbreviated URI references consisting of only the authority and path portions of the identi‐\nfied resource (e.g., ). Such references are primarily intended for\nhuman interpretation rather than machine, with the assumption that context-based heuristics\nare sufficient to complete the URI (e.g., hostnames beginning with \"www\" are likely to have a\nURI prefix of \"http://\" and hostnames beginning with \"ftp\" likely to have a prefix of\n\"ftp://\"). Many client implementations heuristically resolve these references. Such heuris‐\ntics may change over time, particularly when new schemes are introduced. Since an abbrevi‐\nated URI has the same syntax as a relative URL path, abbreviated URI references cannot be\nused where relative URIs are permitted, and can be used only when there is no defined base\n(such as in dialog boxes). Don't use abbreviated URIs as hypertext links inside a document;\nuse the standard format as described here.\n" } ] }, "CONFORMING TO": { "content": "(IETF RFC 2396) ⟨http://www.ietf.org/rfc/rfc2396.txt⟩, (HTML 4.0) ⟨http://www.w3.org/TR\n/REC-html40⟩.\n", "subsections": [] }, "NOTES": { "content": "Any tool accepting URIs (e.g., a web browser) on a Linux system should be able to handle (di‐\nrectly or indirectly) all of the schemes described here, including the man: and info:\nschemes. Handling them by invoking some other program is fine and in fact encouraged.\n\nTechnically the fragment isn't part of the URI.\n\nFor information on how to embed URIs (including URLs) in a data format, see documentation on\nthat format. HTML uses the format text . Texinfo files use the format\n@uref{uri}. Man and mdoc have the recently added UR macro, or just include the URI in the\ntext (viewers should be able to detect :// as part of a URI).\n\nThe GNOME and KDE desktop environments currently vary in the URIs they accept, in particular\nin their respective help browsers. To list man pages, GNOME uses while KDE uses\n, and to list info pages, GNOME uses while KDE uses (the\nauthor of this man page prefers the KDE approach here, though a more regular format would be\neven better). In general, KDE uses as a prefix to a set of generated files.\nKDE prefers documentation in HTML, accessed via the . GNOME prefers\nthe ghelp scheme to store and find documentation. Neither browser handles file: references\nto directories at the time of this writing, making it difficult to refer to an entire direc‐\ntory with a browsable URI. As noted above, these environments differ in how they handle the\ninfo: scheme, probably the most important variation. It is expected that GNOME and KDE will\nconverge to common URI formats, and a future version of this man page will describe the con‐\nverged result. Efforts to aid this convergence are encouraged.\n", "subsections": [ { "name": "Security", "content": "A URI does not in itself pose a security threat. There is no general guarantee that a URL,\nwhich at one time located a given resource, will continue to do so. Nor is there any guaran‐\ntee that a URL will not locate a different resource at some later point in time; such a guar‐\nantee can be obtained only from the person(s) controlling that namespace and the resource in\nquestion.\n\nIt is sometimes possible to construct a URL such that an attempt to perform a seemingly harm‐\nless operation, such as the retrieval of an entity associated with the resource, will in fact\ncause a possibly damaging remote operation to occur. The unsafe URL is typically constructed\nby specifying a port number other than that reserved for the network protocol in question.\nThe client unwittingly contacts a site that is in fact running a different protocol. The\ncontent of the URL contains instructions that, when interpreted according to this other pro‐\ntocol, cause an unexpected operation. An example has been the use of a gopher URL to cause\nan unintended or impersonating message to be sent via a SMTP server.\n\nCaution should be used when using any URL that specifies a port number other than the default\nfor the protocol, especially when it is a number within the reserved space.\n\nCare should be taken when a URI contains escaped delimiters for a given protocol (for exam‐\nple, CR and LF characters for telnet protocols) that these are not unescaped before transmis‐\nsion. This might violate the protocol, but avoids the potential for such characters to be\nused to simulate an extra operation or parameter in that protocol, which might lead to an un‐\nexpected and possibly harmful remote operation to be performed.\n\nIt is clearly unwise to use a URI that contains a password which is intended to be secret.\nIn particular, the use of a password within the \"userinfo\" component of a URI is strongly\nrecommended against except in those rare cases where the \"password\" parameter is intended to\nbe public.\n" } ] }, "BUGS": { "content": "Documentation may be placed in a variety of locations, so there currently isn't a good URI\nscheme for general online documentation in arbitrary formats. References of the form\n don't work because different distributions and local installation re‐\nquirements may place the files in different directories (it may be in /usr/doc, or /usr/lo‐\ncal/doc, or /usr/share, or somewhere else). Also, the directory ZZZ usually changes when a\nversion changes (though filename globbing could partially overcome this). Finally, using the\nfile: scheme doesn't easily support people who dynamically load documentation from the Inter‐\nnet (instead of loading the files onto a local filesystem). A future URI scheme may be added\n(e.g., \"userdoc:\") to permit programs to include cross-references to more detailed documenta‐\ntion without having to know the exact location of that documentation. Alternatively, a fu‐\nture version of the filesystem specification may specify file locations sufficiently so that\nthe file: scheme will be able to locate documentation.\n\nMany programs and file formats don't include a way to incorporate or implement links using\nURIs.\n\nMany programs can't handle all of these different URI formats; there should be a standard\nmechanism to load an arbitrary URI that automatically detects the users' environment (e.g.,\ntext or graphics, desktop environment, local user preferences, and currently executing tools)\nand invokes the right tool for any URI.\n", "subsections": [] }, "SEE ALSO": { "content": "lynx(1), man2html(1), mailaddr(7), utf-8(7)\n\nIETF RFC 2255 ⟨http://www.ietf.org/rfc/rfc2255.txt⟩\n", "subsections": [] }, "COLOPHON": { "content": "This page is part of release 5.10 of the Linux man-pages project. A description of the\nproject, information about reporting bugs, and the latest version of this page, can be found\nat https://www.kernel.org/doc/man-pages/.\n\n\n\nLinux 2020-08-13 URI(7)", "subsections": [] } }, "summary": "uri, url, urn - uniform resource identifier (URI), including a URL or URN", "flags": [], "examples": [], "see_also": [ { "name": "lynx", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/lynx/1/json" }, { "name": "man2html", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/man2html/1/json" }, { "name": "mailaddr", "section": "7", "url": "https://www.chedong.com/phpMan.php/man/mailaddr/7/json" }, { "name": "utf-8", "section": "7", "url": "https://www.chedong.com/phpMan.php/man/utf-8/7/json" } ] }