{ "mode": "man", "parameter": "MAILCAP", "section": "5", "url": "https://www.chedong.com/phpMan.php/man/MAILCAP/5/json", "generated": "2026-10-04T13:22:00Z", "sections": { "NAME": { "content": "mailcap - metamail capabilities file\n", "subsections": [] }, "DESCRIPTION": { "content": "The mailcap file is read by the metamail program to determine how to display non-text at the\nlocal site.\n\nThe syntax of a mailcap file is quite simple, at least compared to termcap files. Any line\nthat starts with \"#\" is a comment. Blank lines are ignored. Otherwise, each line defines a\nsingle mailcap entry for a single content type. Long lines may be continued by ending them\nwith a backslash character, \\.\n\nEach individual mailcap entry consists of a content-type specification, a command to execute,\nand (possibly) a set of optional \"flag\" values. For example, a very simple mailcap entry\n(which is actually a built-in default behavior for metamail) would look like this:\n\ntext/plain; cat %s\n\nThe optional flags can be used to specify additional information about the mail-handling com‐\nmand. For example:\n\ntext/plain; cat %s; copiousoutput\n\ncan be used to indicate that the output of the 'cat' command may be voluminous, requiring ei‐\nther a scrolling window, a pager, or some other appropriate coping mechanism.\n\nThe \"type\" field (text/plain, in the above example) is simply any legal content type name, as\ndefined by informational RFC 1524. In practice, this is almost any string. It is the string\nthat will be matched against the \"Content-type\" header (or the value passed in with -c) to\ndecide if this is the mailcap entry that matches the current message. Additionally, the type\nfield may specify a subtype (e.g. \"text/ISO-8859-1\") or a wildcard to match all subtypes\n(e.g. \"image/*\").\n\nThe \"command\" field is any UNIX command (\"cat %s\" in the above example), and is used to spec‐\nify the interpreter for the given type of message. It will be passed to the shell via the\nsystem(3) facility. Semicolons and backslashes within the command must be quoted with back‐\nslashes. If the command contains \"%s\", those two characters will be replaced by the name of\na file that contains the body of the message. If it contains \"%t\", those two characters will\nbe replaced by the content-type field, including the subtype, if any. (That is, if the con‐\ntent-type was \"image/pbm; opt1=something-else\", then \"%t\" would be replaced by \"image/pbm\".)\nIf the command field contains \"%{\" followed by a parameter name and a closing \"}\", then all\nthose characters will be replaced by the value of the named parameter, if any, from the Con‐\ntent-type header. Thus, in the previous example, \"%{opt1}\" will be replaced by \"something-\nelse\". Finally, if the command contains \"\\%\", those two characters will be replaced by a\nsingle % character. (In fact, the backslash can be used to quote any character, including\nitself.)\n\nIf no \"%s\" appears in the command field, then instead of placing the message body in a tempo‐\nrary file, metamail will pass the body to the command on the standard input. This is helpful\nin saving /tmp file space, but can be problematic for window-oriented applications under some\nwindow systems such as MGR.\n\nTwo special codes can appear in the viewing command for objects of type multipart (any sub‐\ntype). These are \"%n\" and \"%F\". %n will be replaced by the number of parts within the mul‐\ntipart object. %F will be replaced by a series of arguments, two for each part, giving first\nthe content-type and then the name of the temporary file where the decoded part has been\nstored. In addition, for each file created by %F, a second file is created, with the same\nname followed by \"H\", which contains the header information for that body part. This will\nnot be needed by most multipart handlers, but it is there if you ever need it.\n\nThe \"notes=xxx\" field is an uninterpreted string that is used to specify the name of the per‐\nson who installed this entry in the mailcap file. (The \"xxx\" may be replaced by any text\nstring.)\n\nThe \"test=xxx\" field is a command that is executed to determine whether or not the mailcap\nline actually applies. That is, if the content-type field matches the content-type on the\nmessage, but a \"test=\" field is present, then the test must succeed before the mailcap line\nis considered to \"match\" the message being viewed. The command may be any UNIX command, us‐\ning the same syntax and the same %-escapes as for the viewing command, as described above. A\ncommand is considered to succeed if it exits with a zero exit status, and to fail otherwise.\n\nThe \"print=xxx\" field is a command that is executed to print the data instead of display it\ninteractively. This behavior is usually a consequence of invoking metamail with the \"-h\"\nswitch.\n\nThe \"textualnewlines\" field can be used in the rather obscure case where metamail's default\nrules for treating newlines in base64-encoded data are unsatisfactory. By default, metamail\nwill translate CRLF to the local newline character in decoded base64 output if the content-\ntype is \"text\" (any subtype), but will not do so otherwise. A mailcap entry with a field of\n\"textualnewlines=1\" will force such translation for the specified content-type, while \"textu‐\nalnewlines=0\" will guarantee that the translation does not take place even for textual con‐\ntent-types.\n\nThe \"compose\" field may be used to specify a program that can be used to compose a new body\nor body part in the given format. Its intended use is to support mail composing agents that\nsupport the composition of multiple types of mail using external composing agents. As with\nthe view-command, the compose command will be executed after replacing certain escape se‐\nquences starting with \"%\". In particular, %s should be replaced by the name of a file to\nwhich the composed data is to be written by the specified composing program, thus allowing\nthe calling program (e.g. metamail) to tell the called program where to store the composed\ndata. If %s does not appear, then the composed data will be assumed to be written by the\ncomposing programs to standard output. The result of the composing program may be data that\nis NOT yet suitable for mail transport -- that is, a Content-Transfer-Encoding may still need\nto be applied to the data.\n\nThe \"composetyped\" field is similar to the \"compose\" field, but is to be used when the com‐\nposing program needs to specify the Content-type header field to be applied to the composed\ndata. The \"compose\" field is simpler, and is preferred for use with existing (non-mail-ori‐\nented) programs for composing data in a given format. The \"composetyped\" field is necessary\nwhen the Content-type information must include auxiliary parameters, and the composition pro‐\ngram must then know enough about mail formats to produce output that includes the mail type\ninformation, and to apply any necessary Content-Transfer-Encoding. Conceptually, \"compose\"\nspecifies a program that simply outputs the specified type of data in its raw form, while\n\"composetyped\" specifies a program that outputs the data as a MIME object, with all necessary\nContent-* headers already in place.\n\n", "subsections": [ { "name": "needsterminal", "content": "If this flag is given, the named interpreter needs to interact with the user on a\nterminal. In some environments (e.g. a window-oriented mail reader under X11) this\nwill require the creation of a new terminal emulation window, while in most environ‐\nments it will not. If the mailcap entry specifies \"needsterminal\" and metamail is\nnot running on a terminal (as determined by isatty(3), the -x option, and the\nMMNOTTTY environment variable) then metamail will try to run the command in a new\nterminal emulation window. Currently, metamail knows how to create new windows under\nthe X11, SunTools, and WM window systems.\n" }, { "name": "copiousoutput", "content": "This flag should be given whenever the interpreter is capable of producing more than\na few lines of output on stdout, and does no interaction with the user. If the mail‐\ncap entry specifies copiousoutput, and pagination has been requested via the \"-p\"\ncommand, then the output of the command being executed will be piped through a pagi‐\nnation program (\"more\" by default, but this can be overridden with the METAMAILPAGER\nenvironment variable).\n" } ] }, "BUILT-IN CONTENT-TYPE SUPPORT": { "content": "The metamail program has built-in support for a few key content-types. In particular, it\nsupports the text type, the multipart and multipart/alternative type, and the message/rfc822\ntypes. This support is incomplete for many subtypes -- for example, it only supports US-\nASCII text in general. This kind of built-in support can be OVERRIDDEN by an entry in any\nmailcap file on the user's search path. Metamail also has rudimentary built-in support for\ntypes that are totally unrecognized -- i.e. for which no mailcap entry or built-in handler\nexists. For such unrecognized types, metamail will write a file with a \"clean\" copy of the\ndata -- i.e. a copy in which all mail headers have been removed, and in which any 7-bit\ntransport encoding has been decoded.\n", "subsections": [] }, "FILES": { "content": "$HOME/.mailcap:/etc/mailcap:/usr/share/etc/mailcap:/usr/local/etc/mailcap -- default path for\nmailcap files.\n", "subsections": [] }, "SEE ALSO": { "content": "run-mailcap(1), mailcap.order(5), update-mime(8)\n\nRFC 1524 ()\n\n", "subsections": [] }, "COPYRIGHT": { "content": "Copyright (c) 1991 Bell Communications Research, Inc. (Bellcore)\n\nPermission to use, copy, modify, and distribute this material for any purpose and without fee\nis hereby granted, provided that the above copyright notice and this permission notice appear\nin all copies, and that the name of Bellcore not be used in advertising or publicity pertain‐\ning to this material without the specific, prior written permission of an authorized repre‐\nsentative of Bellcore. BELLCORE MAKES NO REPRESENTATIONS ABOUT THE ACCURACY OR SUITABILITY\nOF THIS MATERIAL FOR ANY PURPOSE. IT IS PROVIDED \"AS IS\", WITHOUT ANY EXPRESS OR IMPLIED\nWARRANTIES.\n", "subsections": [] }, "AUTHOR": { "content": "Nathaniel S. Borenstein\n\nBellcore Prototype Release 2 MAILCAP(5)", "subsections": [] } }, "summary": "mailcap - metamail capabilities file", "flags": [], "examples": [], "see_also": [ { "name": "run-mailcap", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/run-mailcap/1/json" }, { "name": "mailcap.order", "section": "5", "url": "https://www.chedong.com/phpMan.php/man/mailcap.order/5/json" }, { "name": "update-mime", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/update-mime/8/json" } ] }