1MAILCAP(4) Kernel Interfaces Manual MAILCAP(4)
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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 % character. (In
57 fact, the backslash can be used to quote any character, including
58 itself.)
59 If no "%s" appears in the command field, then instead of placing the
61 message body in a temporary file, metamail will pass the body to the
62 command on the standard input. This is helpful in saving /tmp file
63 space, but can be problematic for window-oriented applications under
64 some window systems such as MGR.
65 Two special codes can appear in the viewing command for objects of type
67 multipart (any subtype). These are "%n" and "%F". %n will be replaced
68 by the number of parts within the multipart object. %F will be
69 replaced by a series of arguments, two for each part, giving first the
70 content-type and then the name of the temporary file where the decoded
71 part has been stored. In addition, for each file created by %F, a sec‐
72 ond file is created, with the same name followed by "H", which contains
73 the header information for that body part. This will not be needed by
74 most multipart handlers, but it is there if you ever need it.
75 The "notes=xxx" field is an uninterpreted string that is used to spec‐
77 ify the name of the person who installed this entry in the mailcap
78 file. (The "xxx" may be replaced by any text string.)
79 The "test=xxx" field is a command that is executed to determine whether
81 or not the mailcap line actually applies. That is, if the content-type
82 field matches the content-type on the message, but a "test=" field is
83 present, then the test must succeed before the mailcap line is consid‐
84 ered to "match" the message being viewed. The command may be any UNIX
85 command, using the same syntax and the same %-escapes as for the view‐
86 ing command, as described above. A command is considered to succeed if
87 it exits with a zero exit status, and to fail otherwise.
88 The "print=xxx" field is a command that is executed to print the data
90 instead of display it interactively. This behavior is usually a conse‐
91 quence of invoking metamail with the "-h" switch.
92 The "textualnewlines" field can be used in the rather obscure case
94 where metamail's default rules for treating newlines in base64-encoded
95 data are unsatisfactory. By default, metamail will translate CRLF to
96 the local newline character in decoded base64 output if the content-
97 type is "text" (any subtype), but will not do so otherwise. A mailcap
98 entry with a field of "textualnewlines=1" will force such translation
99 for the specified content-type, while "textualnewlines=0" will guaran‐
100 tee that the translation does not take place even for textual content-
101 types.
102 The "compose" field may be used to specify a program that can be used
104 to compose a new body or body part in the given format. Its intended
105 use is to support mail composing agents that support the composition of
106 multiple types of mail using external composing agents. As with the
107 view-command, the compose command will be executed after replacing cer‐
108 tain escape sequences starting with "%". In particular, %s should be
109 replaced by the name of a file to which the composed data is to be
110 written by the specified composing program, thus allowing the calling
111 program (e.g. metamail) to tell the called program where to store the
112 composed data. If %s does not appear, then the composed data will be
113 assumed to be written by the composing programs to standard output.
114 The result of the composing program may be data that is NOT yet suit‐
115 able for mail transport -- that is, a Content-Transfer-Encoding may
116 still need to be applied to the data.
117 The "composetyped" field is similar to the "compose" field, but is to
119 be used when the composing program needs to specify the Content-type
120 header field to be applied to the composed data. The "compose" field
121 is simpler, and is preferred for use with existing (non-mail-oriented)
122 programs for composing data in a given format. The "composetyped"
123 field is necessary when the Content-type information must include aux‐
124 iliary parameters, and the composition program must then know enough
125 about mail formats to produce output that includes the mail type infor‐
126 mation, and to apply any necessary Content-Transfer-Encoding. Concep‐
127 tually, "compose" specifies a program that simply outputs the specified
128 type of data in its raw form, while "composetyped" specifies a program
129 that outputs the data as a MIME object, with all necessary Content-*
130 headers already in place.
131 needsterminal
134 If this flag is given, the named interpreter needs to interact
135 with the user on a terminal. In some environments (e.g. a win‐
136 dow-oriented mail reader under X11) this will require the cre‐
137 ation of a new terminal emulation window, while in most envi‐
138 ronments it will not. If the mailcap entry specifies "need‐
139 sterminal" and metamail is not running on a terminal (as deter‐
140 mined by isatty(3), the -x option, and the MM_NOTTTY environ‐
141 ment variable) then metamail will try to run the command in a
142 new terminal emulation window. Currently, metamail knows how
143 to create new windows under the X11, SunTools, and WM window
144 systems.
145 copiousoutput
147 This flag should be given whenever the interpreter is capable
148 of producing more than a few lines of output on stdout, and
149 does no interaction with the user. If the mailcap entry speci‐
150 fies copiousoutput, and pagination has been requested via the
151 "-p" command, then the output of the command being executed
152 will be piped through a pagination program ("more" by default,
153 but this can be overridden with the METAMAIL_PAGER environment
154 variable).
155
157 The metamail program has built-in support for a few key content-types.
158 In particular, it supports the text type, the multipart and multi‐
159 part/alternative type, and the message/rfc822 types. This support is
160 incomplete for many subtypes -- for example, it only supports US-ASCII
161 text in general. This kind of built-in support can be OVERRIDDEN by an
162 entry in any mailcap file on the user's search path. Metamail also has
163 rudimentary built-in support for types that are totally unrecognized --
164 i.e. for which no mailcap entry or built-in handler exists. For such
165 unrecognized types, metamail will write a file with a "clean" copy of
166 the data -- i.e. a copy in which all mail headers have been removed,
167 and in which any 7-bit transport encoding has been decoded.
168
170 $HOME/.mailcap:/etc/mailcap:/usr/etc/mailcap:/usr/local/etc/mailcap --
171 default path for mailcap files.
172
174 metamail(1)
175
177 Copyright (c) 1991 Bell Communications Research, Inc. (Bellcore)
178 Permission to use, copy, modify, and distribute this material for any
180 purpose and without fee is hereby granted, provided that the above
181 copyright notice and this permission notice appear in all copies, and
182 that the name of Bellcore not be used in advertising or publicity per‐
183 taining to this material without the specific, prior written permission
184 of an authorized representative of Bellcore. BELLCORE MAKES NO REPRE‐
185 SENTATIONS ABOUT THE ACCURACY OR SUITABILITY OF THIS MATERIAL FOR ANY
186 PURPOSE. IT IS PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED WAR‐
187 RANTIES.
188
190 Nathaniel S. Borenstein
191Bellcore Prototype Release 2 MAILCAP(4)