mimesupport.html

mutt-1.5.12 源代码。linux 下邮件接受的工具。

</p><p>
Perhaps you wish to use lynx to view text/html files, and a pager on
all other text formats, then you would use the following:

</p><pre class="screen">
text/html; lynx %s
text/*; more
</pre><p>

This is the simplest form of a mailcap file.
</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2688432"></a>3.2.聽Secure use of mailcap</h3></div></div></div><p>
The interpretion of shell meta-characters embedded in MIME parameters
can lead to security problems in general.  Mutt tries to quote parameters
in expansion of %s syntaxes properly, and avoids risky characters by
substituting them, see the <a href="reference.html#mailcap-sanitize" title="3.101.聽mailcap_sanitize">$mailcap_sanitize</a> variable.
</p><p>
Although mutt's procedures to invoke programs with mailcap seem to be
safe, there are other applications parsing mailcap, maybe taking less care
of it.  Therefore you should pay attention to the following rules:
</p><p>
<span class="emphasis"><em>Keep the %-expandos away from shell quoting.</em></span>
Don't quote them with single or double quotes.  Mutt does this for
you, the right way, as should any other program which interprets
mailcap.  Don't put them into backtick expansions.  Be highly careful
with eval statements, and avoid them if possible at all.  Trying to fix
broken behaviour with quotes introduces new leaks - there is no
alternative to correct quoting in the first place.
</p><p>
If you have to use the %-expandos' values in context where you need
quoting or backtick expansions, put that value into a shell variable
and reference the shell variable where necessary, as in the following
example (using <code class="literal">$charset</code> inside the backtick expansion is safe,
since it is not itself subject to any further expansion):
</p><p>

</p><pre class="screen">
text/test-mailcap-bug; cat %s; copiousoutput; test=charset=%{charset} \
        &amp;&amp; test "`echo $charset | tr '[A-Z]' '[a-z]'`" != iso-8859-1
</pre><p>

</p></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2688503"></a>3.3.聽Advanced mailcap Usage</h3></div></div></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id2688509"></a>3.3.1.聽Optional Fields</h4></div></div></div><p>
In addition to the required content-type and view command fields, you
can add semi-colon ';' separated fields to set flags and other options.
Mutt recognizes the following optional fields:
</p><div class="variablelist"><dl><dt><span class="term">copiousoutput</span></dt><dd><p>
This flag tells Mutt that the command passes possibly large amounts of
text on stdout.  This causes Mutt to invoke a pager (either the internal
pager or the external pager defined by the pager variable) on the output
of the view command.  Without this flag, Mutt assumes that the command
is interactive.  One could use this to replace the pipe to <code class="literal">more</code>
in the <code class="literal">lynx -dump</code> example in the Basic section:

</p><pre class="screen">
text/html; lynx -dump %s ; copiousoutput
</pre><p>

This will cause lynx to format the text/html output as text/plain
and Mutt will use your standard pager to display the results.
</p></dd><dt><span class="term">needsterminal</span></dt><dd><p>
Mutt uses this flag when viewing attachments with <a href="mimesupport.html#auto-view" title="4.聽MIME Autoview">auto_view</a>, in order to decide whether it should honor the setting
of the <a href="reference.html#wait-key" title="3.286.聽wait_key">$wait_key</a> variable or
not.  When an attachment is viewed using an interactive program, and the
corresponding mailcap entry has a <span class="emphasis"><em>needsterminal</em></span> flag, Mutt will use
<a href="reference.html#wait-key" title="3.286.聽wait_key">$wait_key</a> and the exit status
of the program to decide if it will ask you to press a key after the
external program has exited.  In all other situations it will not prompt
you for a key.
</p></dd><dt><span class="term">compose=&lt;command&gt;</span></dt><dd><p>
This flag specifies the command to use to create a new attachment of a
specific MIME type.  Mutt supports this from the compose menu.
</p></dd><dt><span class="term">composetyped=&lt;command&gt;</span></dt><dd><p>
This flag specifies the command to use to create a new attachment of a
specific MIME type.  This command differs from the compose command in
that mutt will expect standard MIME headers on the data.  This can be
used to specify parameters, filename, description, etc. for a new
attachment.   Mutt supports this from the compose menu.
</p></dd><dt><span class="term">print=&lt;command&gt;</span></dt><dd><p>
This flag specifies the command to use to print a specific MIME type.
Mutt supports this from the attachment and compose menus.
</p></dd><dt><span class="term">edit=&lt;command&gt;</span></dt><dd><p>
This flag specifies the command to use to edit a specific MIME type.
Mutt supports this from the compose menu, and also uses it to compose
new attachments.  Mutt will default to the defined editor for text
attachments.
</p></dd><dt><span class="term">nametemplate=&lt;template&gt;</span></dt><dd><p>
This field specifies the format for the file denoted by %s in the
command fields.  Certain programs will require a certain file extension,
for instance, to correctly view a file.  For instance, lynx will only
interpret a file as <code class="literal">text/html</code> if the file ends in <code class="literal">.html</code>.
So, you would specify lynx as a <code class="literal">text/html</code> viewer with a line in
the mailcap file like:

</p><pre class="screen">
text/html; lynx %s; nametemplate=%s.html
</pre><p>

</p></dd><dt><span class="term">test=&lt;command&gt;</span></dt><dd><p>
This field specifies a command to run to test whether this mailcap
entry should be used.  The command is defined with the command expansion
rules defined in the next section.  If the command returns 0, then the
test passed, and Mutt uses this entry.  If the command returns non-zero,
then the test failed, and Mutt continues searching for the right entry.
<span class="bold"><strong>Note:</strong></span> <span class="emphasis"><em>the content-type must match before Mutt performs the test.</em></span>
For example:

</p><pre class="screen">
text/html; netscape -remote 'openURL(%s)' ; test=RunningX
text/html; lynx %s
</pre><p>

In this example, Mutt will run the program RunningX which will return 0
if the X Window manager is running, and non-zero if it isn't.  If
RunningX returns 0, then Mutt will call netscape to display the
text/html object.  If RunningX doesn't return 0, then Mutt will go on
to the next entry and use lynx to display the text/html object.
</p></dd></dl></div><p>
</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id2688764"></a>3.3.2.聽Search Order</h4></div></div></div><p>
When searching for an entry in the mailcap file, Mutt will search for
the most useful entry for its purpose.  For instance, if you are
attempting to print an <code class="literal">image/gif</code>, and you have the following
entries in your mailcap file, Mutt will search for an entry with the
print command:

</p><pre class="screen">
image/*;        xv %s
image/gif;      ; print= anytopnm %s | pnmtops | lpr; \
                nametemplate=%s.gif
</pre><p>

Mutt will skip the <code class="literal">image/*</code> entry and use the <code class="literal">image/gif</code>
entry with the print command.
</p><p>
In addition, you can use this with <a href="mimesupport.html#auto-view" title="4.聽MIME Autoview">auto_view</a> 
to denote two commands for viewing an attachment, one to be viewed
automatically, the other to be viewed interactively from the attachment
menu.  In addition, you can then use the test feature to determine which
viewer to use interactively depending on your environment.

</p><pre class="screen">
text/html;      netscape -remote 'openURL(%s)' ; test=RunningX
text/html;      lynx %s; nametemplate=%s.html
text/html;      lynx -dump %s; nametemplate=%s.html; copiousoutput
</pre><p>

For <a href="mimesupport.html#auto-view" title="4.聽MIME Autoview">auto_view</a>, Mutt will choose the third
entry because of the copiousoutput tag.  For interactive viewing, Mutt
will run the program RunningX to determine if it should use the first
entry.  If the program returns non-zero, Mutt will use the second entry
for interactive viewing.
</p></div><div class="sect3" lang="en" xml:lang="en"><div class="titlepage"><div><div><h4 class="title"><a id="id2688841"></a>3.3.3.聽Command Expansion</h4></div></div></div><p>
The various commands defined in the mailcap files are passed to the
<code class="literal">/bin/sh</code> shell using the system() function.  Before the
command is passed to <code class="literal">/bin/sh -c</code>, it is parsed to expand
various special parameters with information from Mutt.  The keywords
Mutt expands are:
</p><div class="variablelist"><dl><dt><span class="term">%s</span></dt><dd><p>
As seen in the basic mailcap section, this variable is expanded
to a filename specified by the calling program.  This file contains
the body of the message to view/print/edit or where the composing
program should place the results of composition.  In addition, the
use of this keyword causes Mutt to not pass the body of the message
to the view/print/edit program on stdin.
</p></dd><dt><span class="term">%t</span></dt><dd><p>
Mutt will expand %t to the text representation of the content
type of the message in the same form as the first parameter of the
mailcap definition line, ie <code class="literal">text/html</code> or
<code class="literal">image/gif</code>.
</p></dd><dt><span class="term">%{&lt;parameter&gt;}</span></dt><dd><p>
Mutt will expand this to the value of the specified parameter
from the Content-Type: line of the mail message.  For instance, if
Your mail message contains:

</p><pre class="screen">
Content-Type: text/plain; charset=iso-8859-1
</pre><p>

then Mutt will expand %{charset} to iso-8859-1.  The default metamail
mailcap file uses this feature to test the charset to spawn an xterm
using the right charset to view the message.
</p></dd><dt><span class="term">\%</span></dt><dd><p>
This will be replaced by a %
</p></dd></dl></div><p>
Mutt does not currently support the %F and %n keywords
specified in RFC 1524.  The main purpose of these parameters is for
multipart messages, which is handled internally by Mutt.
</p></div></div><div class="sect2" lang="en" xml:lang="en"><div class="titlepage"><div><div><h3 class="title"><a id="id2688963"></a>3.4.聽Example mailcap files</h3></div></div></div><p>
This mailcap file is fairly simple and standard:

</p><pre class="programlisting">
# I'm always running X :)
video/*;        xanim %s &gt; /dev/null
image/*;        xv %s &gt; /dev/null

# I'm always running netscape (if my computer had more memory, maybe)
text/html;      netscape -remote 'openURL(%s)'
</pre><p>

</p><p>
This mailcap file shows quite a number of examples:
</p><p>

</p><pre class="programlisting">
# Use xanim to view all videos   Xanim produces a header on startup,
# send that to /dev/null so I don't see it
video/*;        xanim %s &gt; /dev/null