1MAILCAP(4) Kernel Interfaces Manual MAILCAP(4)
2
6 mailcap - metamail capabilities file
7
9 The mailcap file is read by the metamail program to determine how to
10 display non-text at the local site.
11 The syntax of a mailcap file is quite simple, at least compared to
13 termcap files. Any line that starts with "#" is a comment. Blank
14 lines are ignored. Otherwise, each line defines a single mailcap entry
15 for a single content type. Long lines may be continued by ending them
16 with a backslash character, \.
17 Each individual mailcap entry consists of a content-type specification,
19 a command to execute, and (possibly) a set of optional "flag" values.
20 For example, a very simple mailcap entry (which is actually a built-in
21 default behavior for metamail) would look like this:
22 text/plain; cat %s
24 The optional flags can be used to specify additional information about
26 the mail-handling command. For example:
27 text/plain; cat %s; copiousoutput
29 can be used to indicate that the output of the 'cat' command may be
31 voluminous, requiring either a scrolling window, a pager, or some other
32 appropriate coping mechanism.
33 The "type" field (text/plain, in the above example) is simply any legal
35 content type name, as defined by RFC 822. In practice, this is almost
36 any string. It is the string that will be matched against the "Con‐
37 tent-type" header (or the value passed in with -c) to decide if this is
38 the mailcap entry that matches the current message. Additionally, the
39 type field may specify a subtype (e.g. "text/ISO-8859-1") or a wildcard
40 to match all subtypes (e.g. "image/*").
41 The "command" field is any UNIX command ("cat %s" in the above exam‐
43 ple), and is used to specify the interpreter for the given type of mes‐
44 sage. It will be passed to the shell via the system(3) facility.
45 Semicolons and backslashes within the command must be quoted with back‐
46 slashes. If the command contains "%s", those two characters will be
47 replaced by the name of a file that contains the body of the message.
48 If it contains "%t', those two characters will be replaced by the con‐
49 tent-type field, including the subtype, if any. (That is, if the con‐
50 tent-type was "image/pbm; opt1=something-else", then "%t" would be
51 replaced by "image/pbm".) If the command field contains "%{" fol‐
52 lowed by a parameter name and a closing "}", then all those characters
53 will be replaced by the value of the named parameter, if any, from the
54 Content-type header. Thus, in the previous example, "%{opt1}" will be
55 replaced by "something-else". Finally, if the command contains "",
56 those two characters will be replaced by a single % ch
57 aracter. (In fact, the backslash can be used to quote any character,
61 including itself.)
62 If no "%s" appears in the command field, then instead of placing the
64 message body in a temporary file, metamail will pass the body to the
65 command on the standard input. This is helpful in saving /tmp file
66 space, but can be problematic for window-oriented applications under
67 some window systems such as MGR.
68 Two special codes can appear in the viewing command for objects of type
70 multipart (any subtype). These are "%n" and "%F". %n will be replaced
71 by the number of parts within the multipart object. %F will be
72 replaced by a series of arguments, two for each part, giving first the
73 content-type and then the name of the temporary file where the decoded
74 part has been stored. In addition, for each file created by %F, a sec‐
75 ond file is created, with the same name followed by "H", which contains
76 the header information for that body part. This will not be needed by
77 most multipart handlers, but it is there if you ever need it.
78 The "notes=xxx" field is an uninterpreted string that is used to spec‐
80 ify the name of the person who installed this entry in the mailcap
81 file. (The "xxx" may be replaced by any text string.)
82 The "test=xxx" field is a command that is executed to determine whether
84 or not the mailcap line actually applies. That is, if the content-type
85 field matches the content-type on the message, but a "test=" field is
86 present, then the test must succeed before the mailcap line is consid‐
87 ered to "match" the message being viewed. The command may be any UNIX
88 command, using the same syntax and the same %-escapes as for the view‐
89 ing command, as described above. A command is considered to succeed if
90 it exits with a zero exit status, and to fail otherwise.
91 The "print=xxx" field is a command that is executed to print the data
93 instead of display it interactively. This behavior is usually a conse‐
94 quence of invoking metamail with the "-h" switch.
95 The "textualnewlines" field can be used in the rather obscure case
97 where metamail's default rules for treating newlines in base64-encoded
98 data are unsatisfactory. By default, metamail will translate CRLF to
99 the local newline character in decoded base64 output if the content-
100 type is "text" (any subtype), but will not do so otherwise. A mailcap
101 entry with a field of "textualnewlines=1" will force such translation
102 for the specified content-type, while "textualnewlines=0" will guaran‐
103 tee that the translation does not take place even for textual content-
104 types.
105 The "compose" field may be used to specify a program that can be used
107 to compose a new body or body part in the given format. Its intended
108 use is to support mail composing agents that support the composition of
109 multiple types of mail using external composing agents. As with the
110 view-command, the compose command will be executed after replacing cer‐
111 tain escape sequences starting with "%". In particular, %s should be
112 replaced by the name of a file to which the composed data is to be
113 written by the specified composing program, thus allowing th3e calling
114 program (e.g. metamail) to tell the called program where to store the
115 composed data. If %s does not appear, then the composed data will be
116 assumed to be written by the composing programs to standard output.
117 The result of the composing program may be data that is NOT yet suit‐
118 able for mail transport -- that is, a Content-Transfer-Encoding may
119 still need to be applied to the data.
120 The "composetyped" field is similar to the "compose" field, but is to
122 be used when the composing program needs to specify the Content-type
123 header field to be applied to the composed data. The "compose" field
124 is simpler, and is preferred for use with existing (non-mail-oriented)
125 programs for composing data in a given format. The "composetyped"
126 field is necessary when the Content-type information must include aux‐
127 illiary parameters, and the composition program must then know enough
128 about mail formats to produce output that includes the mail type infor‐
129 mation, and to apply any necessary Content-Transfer-Encoding. Concep‐
130 tually, "compose" specifies a program that simply outputs the specified
131 type of data in its raw form, while "composetyped" specifies a program
132 that outputs the data as a MIME object, with all necessary Content-*
133 headers already in place.
134 needsterminal
137 If this flag is given, the named interpreter needs to interact
138 with the user on a terminal. In some environments (e.g. a win‐
139 dow-oriented mail reader under X11) this will require the cre‐
140 ation of a new terminal emulation window, while in most envi‐
141 ronments it will not. If the mailcap entry specifies "need‐
142 sterminal" and metamail is not running on a terminal (as deter‐
143 mined by isatty(3), the -x option, and the MM_NOTTTY environ‐
144 ment variable) then metamail will try to run the command in a
145 new terminal emulation window. Currently, metamail knows how
146 to create new windows under the X11, SunTools, and WM window
147 systems.
148 copiousoutput
150 This flag should be given whenever the interpreter is capable
151 of producing more than a few lines of output on stdout, and
152 does no interaction with the user. If the mailcap entry speci‐
153 fies copiousoutput, and pagination has been requested via the
154 "-p" command, then the output of the command being executed
155 will be piped through a pagination program ("more" by default,
156 but this can be overridden with the METAMAIL_PAGER environment
157 variable).
158
160 The metamail program has built-in support for a few key content-types.
161 In particular, it supports the text type, the multipart and multi‐
162 part/alternative type, and the message/rfc822 types. This support is
163 incomplete for many subtypes -- for example, it only supports US-ASCII
164 text in general. This kind of built-in support can be OVERRIDDEN by an
165 entry in any mailcap file on the user's search path. Metamail also has
166 rudimentary built-in support for types that are totally unrecognized --
167 i.e. for which no mailcap entry or built-in handler exists. For such
168 unrecognized types, metamail will write a file with a "clean" copy of
169 the data -- i.e. a copy in which all mail headers have been removed,
170 and in which any 7-bit transport encoding has been decoded.
171
173 $HOME/.mailcap:/etc/mailcap:/usr/etc/mailcap:/usr/local/etc/mailcap --
174 default path for mailcap files.
175
177 metamail(1)
178
180 Copyright (c) 1991 Bell Communications Research, Inc. (Bellcore)
181 Permission to use, copy, modify, and distribute this material for any
183 purpose and without fee is hereby granted, provided that the above
184 copyright notice and this permission notice appear in all copies, and
185 that the name of Bellcore not be used in advertising or publicity per‐
186 taining to this material without the specific, prior written permission
187 of an authorized representative of Bellcore. BELLCORE MAKES NO REPRE‐
188 SENTATIONS ABOUT THE ACCURACY OR SUITABILITY OF THIS MATERIAL FOR ANY
189 PURPOSE. IT IS PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED WAR‐
190 RANTIES.
191
193 Nathaniel S. Borenstein
194Bellcore Prototype Release 2 MAILCAP(4)