mailcap(5) - man - phpMan

Che Dong

MAILCAP(5) File Formats Manual MAILCAP(5)

NAME
mailcap - metamail capabilities file

DESCRIPTION
The mailcap file is read by the metamail program to determine 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 behavior for metamail) would look like this:

text/plain; cat %s

The optional flags can be used to specify additional information about the mail-handling com‐
mand. For example:

text/plain; cat %s; copiousoutput

can be used to indicate that the output of the 'cat' command may be voluminous, requiring ei‐
ther a scrolling window, 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 informational RFC 1524. In practice, this is almost any string. It is the string
that will be matched against the "Content-type" header (or the value passed in with -c) to
decide if this is the mailcap entry that matches the current 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 spec‐
ify 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 back‐
slashes. 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 con‐
tent-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 all
those characters will be replaced by the value of the named parameter, if any, from the Con‐
tent-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 % character. (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 tempo‐
rary 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 sub‐
type). These are "%n" and "%F". %n will be replaced by the number of parts within the mul‐
tipart 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 per‐
son 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 present, then the test must succeed before the mailcap line
is considered to "match" the message being viewed. The command may be any UNIX command, us‐
ing 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 "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 "textu‐
alnewlines=0" will guarantee that the translation does not take place even for textual con‐
tent-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 composing 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 se‐
quences 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
the calling program (e.g. metamail) to tell the called program where to store the composed
data. If %s does not appear, then the composed 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 com‐
posing 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-ori‐
ented) programs for composing data in a given format. The "composetyped" field is necessary
when the Content-type information must include auxiliary parameters, and the composition pro‐
gram 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 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 mail‐
cap entry specifies copiousoutput, and pagination has been requested via the "-p"
command, then the output of the command being executed will be piped through a pagi‐
nation program ("more" by default, but this can be overridden 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 message/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/share/etc/mailcap:/usr/local/etc/mailcap -- default path for
mailcap files.

SEE ALSO
run-mailcap(1), mailcap.order(5), update-mime(8)

RFC 1524 (<http://tools.ietf.org/html/rfc1524>)

Permission to use, copy, modify, and distribute this material for any purpose and without fee
is hereby granted, provided that the above copyright notice and this permission 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 repre‐
sentative of Bellcore. BELLCORE MAKES NO REPRESENTATIONS ABOUT THE ACCURACY OR SUITABILITY
OF THIS MATERIAL FOR ANY PURPOSE. IT IS PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
WARRANTIES.

AUTHOR
Nathaniel S. Borenstein

Bellcore Prototype Release 2 MAILCAP(5)