MAILCAP(5)MAILCAP(5)NAMEmailcap ‐ metamail capabilities file
DESCRIPTION
The mailcap file is read by the metamail program to deter‐
mine how to display non‐text at the local site.
The syntax of a mailcap file is quite simple, at least
compared to termcap files. Any line that starts with "#"
is a comment. Blank lines are ignored. Otherwise, each
line defines a single mailcap entry for a single content
type. Long lines may be continued by ending them with a
backslash character, .
Each individual mailcap entry consists of a content‐type
specification, a command to execute, and (possibly) a set
of optional "flag" values. For example, a very simple
mailcap entry (which is actually a built‐in default behav‐
ior for metamail) would look like this:
text/plain; cat %s
The optional flags can be used to specify additional
information about the mail‐handling command. For example:
text/plain; cat %s; copiousoutput
can be used to indicate that the output of the ’cat’ com‐
mand may be voluminous, requiring either a scrolling win‐
dow, a pager, or some other appropriate coping mechanism.
The "type" field (text/plain, in the above example) is
simply any legal content type name, as defined by informa‐
tional RFC 1524. In practice, this is almost any string.
It is the string that will be matched against the "Con‐
tent‐type" header (or the value passed in with ‐c) to
decide if this is the mailcap entry that matches the cur‐
rent message. Additionally, the type field may specify a
subtype (e.g. "text/ISO‐8859‐1") or a wildcard to match
all subtypes (e.g. "image/*").
The "command" field is any UNIX command ("cat %s" in the
above example), and is used to specify the interpreter for
the given type of message. It will be passed to the shell
via the system(3) facility. Semicolons and backslashes
within the command must be quoted with backslashes. If
the command contains "%s", those two characters will be
replaced by the name of a file that contains the body of
the message. If it contains "%t’, those two characters
will be replaced by the content‐type field, including the
subtype, if any. (That is, if the content‐type was
"image/pbm; opt1=something‐else", then "%t" would be
replaced by "image/pbm".) If the command field contains
"%{" followed by a parameter name and a closing "}", then
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all those characters will be replaced by the value of the
named parameter, if any, from the Content‐type header.
Thus, in the previous example, "%{opt1}" will be replaced
by "something‐else". Finally, if the command contains "",
those two characters will be replaced by a single % char‐
acter. (In fact, the backslash can be used to quote any
character, including itself.)
If no "%s" appears in the command field, then instead of
placing the message body in a temporary file, metamail
will pass the body to the command on the standard input.
This is helpful in saving /tmp file space, but can be
problematic for window‐oriented applications under some
window systems such as MGR.
Two special codes can appear in the viewing command for
objects of type multipart (any subtype). These are "%n"
and "%F". %n will be replaced by the number of parts
within the multipart object. %F will be replaced by a
series of arguments, two for each part, giving first the
content‐type and then the name of the temporary file where
the decoded part has been stored. In addition, for each
file created by %F, a second file is created, with the
same name followed by "H", which contains the header
information for that body part. This will not be needed
by most multipart handlers, but it is there if you ever
need it.
The "notes=xxx" field is an uninterpreted string that is
used to specify the name of the person who installed this
entry in the mailcap file. (The "xxx" may be replaced by
any text string.)
The "test=xxx" field is a command that is executed to
determine whether or not the mailcap line actually
applies. That is, if the content‐type field matches the
content‐type on the message, but a "test=" field is pre‐
sent, then the test must succeed before the mailcap line
is considered to "match" the message being viewed. The
command may be any UNIX command, using the same syntax and
the same %‐escapes as for the viewing command, as
described above. A command is considered to succeed if it
exits with a zero exit status, and to fail otherwise.
The "print=xxx" field is a command that is executed to
print the data instead of display it interactively. This
behavior is usually a consequence of invoking metamail
with the "‐h" switch.
The "textualnewlines" field can be used in the rather
obscure case where metamail’s default rules for treating
newlines in base64‐encoded data are unsatisfactory. By
default, metamail will translate CRLF to the local newline
character in decoded base64 output if the content‐type is
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"text" (any subtype), but will not do so otherwise. A
mailcap entry with a field of "textualnewlines=1" will
force such translation for the specified content‐type,
while "textualnewlines=0" will guarantee that the transla‐
tion does not take place even for textual content‐types.
The "compose" field may be used to specify a program that
can be used to compose a new body or body part in the
given format. Its intended use is to support mail compos‐
ing agents that support the composition of multiple types
of mail using external composing agents. As with the view‐
command, the compose command will be executed after
replacing certain escape sequences starting with "%". In
particular, %s should be replaced by the name of a file to
which the composed data is to be written by the specified
composing program, thus allowing th3e calling program
(e.g. metamail) to tell the called program where to store
the composed data. If %s does not appear, then the com‐
posed data will be assumed to be written by the composing
programs to standard output. The result of the composing
program may be data that is NOT yet suitable for mail
transport ‐‐ that is, a Content‐Transfer‐Encoding may
still need to be applied to the data.
The "composetyped" field is similar to the "compose"
field, but is to be used when the composing program needs
to specify the Content‐type header field to be applied to
the composed data. The "compose" field is simpler, and is
preferred for use with existing (non‐mail‐oriented) pro‐
grams for composing data in a given format. The "compose‐
typed" field is necessary when the Content‐type informa‐
tion must include auxilliary parameters, and the composi‐
tion program must then know enough about mail formats to
produce output that includes the mail type information,
and to apply any necessary Content‐Transfer‐Encoding.
Conceptually, "compose" specifies a program that simply
outputs the specified type of data in its raw form, while
"composetyped" specifies a program that outputs the data
as a MIME object, with all necessary Content‐* headers
already in place.
needsterminal
If this flag is given, the named interpreter needs
to interact with the user on a terminal. In some
environments (e.g. a window‐oriented mail reader
under X11) this will require the creation of a new
terminal emulation window, while in most environ‐
ments it will not. If the mailcap entry specifies
"needsterminal" and metamail is not running on a
terminal (as determined by isatty(3), the ‐x
option, and the MM_NOTTTY environment variable)
then metamail will try to run the command in a new
terminal emulation window. Currently, metamail
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knows how to create new windows under the X11,
SunTools, and WM window systems.
copiousoutput
This flag should be given whenever the interpreter
is capable of producing more than a few lines of
output on stdout, and does no interaction with the
user. If the mailcap entry specifies copiousout‐
put, and pagination has been requested via the
"‐p" command, then the output of the command being
executed will be piped through a pagination pro‐
gram ("more" by default, but this can be overrid‐
den with the METAMAIL_PAGER environment variable).
BUILT‐IN CONTENT‐TYPE SUPPORT
The metamail program has built‐in support for a few key
content‐types. In particular, it supports the text type,
the multipart and multipart/alternative type, and the mes‐
sage/rfc822 types. This support is incomplete for many
subtypes ‐‐ for example, it only supports US‐ASCII text in
general. This kind of built‐in support can be OVERRIDDEN
by an entry in any mailcap file on the user’s search path.
Metamail also has rudimentary built‐in support for types
that are totally unrecognized ‐‐ i.e. for which no mailcap
entry or built‐in handler exists. For such unrecognized
types, metamail will write a file with a "clean" copy of
the data ‐‐ i.e. a copy in which all mail headers have
been removed, and in which any 7‐bit transport encoding
has been decoded.
FILES
$HOME/.mailcap:/etc/mailcap:/usr/etc/mail‐
cap:/usr/local/etc/mailcap ‐‐ default path for mailcap
files.
SEE ALSOmetamail(1)COPYRIGHT
Copyright (c) 1991 Bell Communications Research, Inc.
(Bellcore)
Permission to use, copy, modify, and distribute this mate‐
rial for any purpose and without fee is hereby granted,
provided that the above copyright notice and this permis‐
sion notice appear in all copies, and that the name of
Bellcore not be used in advertising or publicity pertain‐
ing to this material without the specific, prior written
permission of an authorized representative of Bellcore.
BELLCORE MAKES NO REPRESENTATIONS ABOUT THE ACCURACY OR
SUITABILITY OF THIS MATERIAL FOR ANY PURPOSE. IT IS PRO‐
VIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES.
Bellcore Prototype Release 2 4
MAILCAP(5)MAILCAP(5)AUTHOR
Nathaniel S. Borenstein
Bellcore Prototype Release 2 5
