makemime - Online in the Cloud

PROGRAM:

NAME

makemime - Create MIME-formatted messages

SYNOPSIS

makemime [options...]

makemime [@filename]

DESCRIPTION

makemime creates MIME-formatted messages of arbitrary complexity. makemime reads one or
more individual files, MIME-encodes them, adds basic MIME headers, and adds any additional
headers specified bye command line options. The result is saved to another file or
standard output. Complex MIME-formatted messages are created by piping together multiple
instances of makemime. Advanced options direct makemime to fork() itself, and handle the
details of setting up all the pipelines.

In most cases, options for makemime come directly from the command line. @filename reads
the options from a file. "@&n" reads options from a pipe on file descriptor #n. "@-" is a
shortcut for "@&0", which reads options from standard input.

When options are read from a file or a pipe, each option must be on a line by itself. If
an option requires an argument, the argument must follow on the next line.

For readability, leading whitespace is deleted when options are read from a file or a
pipe. Empty lines are also ignored, as well as lines that begin with the '#' character.

Options and their arguments may contain characters that are special characters to the
shell, such as '(' and ')'. These characters must be backslashed when specified on the
command line, to avoid their special meaning to the shell. These characters MUST NOT be
backslashed when options are read from a file or a pipe. Similarly, the contents of most
headers nearly always include spaces. Therefore they must be quoted when specified on the
command line. Header contents MUST NOT be quoted when options come from a file or a pipe.

makemime reads the content to be formatted as a MIME message from some other file. The
files can also be a pipe. It is possible to supply both the options and a file from the
same pipe, by terminating the options list with a line containing the single character
"-". The remainder of the pipe will be available to be used as an input file (which must
be explicitly specified by one of the options). Of course, only one input file can come
from a single pipe.

MIME overview
A MIME-formatted message contains one or several MIME sections. MIME headers specify how
multiple MIME sections are to be interpreted as a whole (whether they are attached
together; whether they are alternative representations of the same content; or something
even more esoteric). This manual page gives a very brief, terse, overview of basic MIME
concepts. The description is biased towards describing the functionality of the makemime
utility. See RFC 2045[1], RFC 2046[2], RFC 2047[3], RFC 2048[4], and RFC 2049[4] for a
formal definition of MIME-formatted messages.

Each file in a MIME message is encoded as a single MIME section. A MIME section consists
of at least one header line, "Content-Type:". The "Content-Type:" header gives the type of
the data ontained in the file. Other header lines may also be present. Their relative
order does not matter. MIME headers are followed by a blank line, then the contents of the
file, encoded appropriately. All MIME sections generated by makemime will always contain
another header, "Content-Transfer-Encoding:". This header gives the encoding method used
for the file; it is an optional header, but makemime always creates it.

The MIME encoding method defaults to "7bit" if this header is absent. 7bit encoding is
only suitable for plain text messages in the US-ASCII character set. The "8bit" encoding
method is used by plain text messages in other character sets that use octets with the
high bit set. An alternative to 8bit encoding is "quoted-printable". The "base64" encoding
method is used for files containing binary data (anything other than plain text).

MIME sections that contain text messages have their "Content-Type:" header set to
"text/plain"; or "text/html" for HTML messages. There are also several other, rare,
content types that can be used. MIME sections that contain other kinds of data will use
some other, appropriate "Content-Type:" header, such as "image/gif", or "audio/x-wav".

MIME sections that contain textual content may also use the base64 encoding method, they
are not required to use 7bit, 8bit, or quoted-printable. "text/pdf" sections, that contain
PDF files, typically contain binary data and must use the base64 encoding. Consequently,
MIME sections that typically contain binary data, such as image/gif and audio/x-wav, are
free to use encodings other than base64, as long as all the data can be represented by
printable characters (but, in practice, that never happens).

MIME sections may also contain other, optional, headers such as "Content-Disposition:",
"Content-ID:", and "Content-Name:". Consult the appropriate RFCs for the specific usage of
these headers. These headers can be added by makemime by using the -a option, as described
below. These headers play no part in creating the overall structure of a MIME-encoded
message, and makemime does not care much about these headers. It simply includes them, and
their content, upon request.

Multiple files are formatted as a single message MIME message in two steps: first, by
creating a MIME section for each file; and then creating a single MIME section that
contains other MIME sections. A "multipart/mixed" MIME section contains a collection of
MIME sections that represent different objects, attached together. A
"multipart/alternative" MIME section contains a collection of MIME sections which are
alternative representations of the same object, such as an HTML and a plain text version
of the same message. Other "multipart" MIME sections also exist, and their usage is
defined by their respective RFCs.

Creating a single MIME section
makemime {-c "type"} [-e "encoding"] [-o outputfile] [-C "charset"] [-N "name"]
[-a "header: value"...] {filename}

The -c option reads filename, encodes it appropriately, adds the "Content-Type: type" and
"Content-Transfer-Encoding:" MIME headers, then writes the result to standard output.
type can be any valid MIME type, except for multipart. Setting filename to "-" reads from
standard input. Setting filename to "&n" reads from file descriptor #n.

The -C option sets the MIME charset attribute for text/plain content. The -N option sets
the name attribute for Content-Type:.

encoding argument should be specified. It's more efficient to do so. encoding must be one
of the following: 7bit, 8bit, quoted-printable, or base64.

If encoding is not specified, makemime reads the filename twice - once to figure out the
best encoding method, and the second time to encode filename. If filename is a pipe
makemime creates a temporary file, which is not very efficient if filename is large.
However letting makemime pick the encoding method is more convenient if filename is
relatively small.

Another possibility is to omit encoding and set type to auto. This combination sets
"Content-Type:" to either text/plain, or application/octet-stream, based on the selected
encoding.

By default the encoded MIME section is written to standard output. The -o option writes
the MIME section to outputfile. outputfile may be "&n", which writes the MIME section to
a pipe on file descriptor #n.

makemime does not generate any other headers. Particularly, the "Mime-Version:" header is
required for MIME-formatted E-mail messages. Additional headers are specified by the -a
option, which may be used multiple times to insert multiple headers. makemime doesn't do
anything with them except to insert the headers into the generated MIME section.

Note that "Mime-Version:" is only required for the top level MIME section. This header is
not required for individual MIME sections that are later combined into a multipart MIME
collection.

Note
The -c option must occur listed first, the remaining options must follow the -c
option.

Creating a multipart MIME collection
makemime {-m "multipart/type"} [-e "encoding"] [-o outputfile] [-a "header: value"...]
{filename}

The -m option is identical to the -c option, except for three differences.

type must be either "multipart/mixed", "multipart/alternative", or some other MIME
multipart content type. Additionally, "encoding" can only be "7bit" or "8bit", and will
default to "8bit" if not specified. Finally, filename must be a MIME-formatted section,
NOT a regular file. Usually filename is created by a previous invocation of makemime (it
can also be a pipe, like the -c option), but it can be created via any other means.

The -m option creates an initial multipart MIME collection, that contains only one MIME
section, taken from filename. The collection is written to standard output, or the pipe or
to outputfile.

Creating a multipart MIME section
makemime {-j file1"} [-o outputfile] {file2}

This option adds a MIME section to an existing MIME collection. file1 must be a MIME
collection that was previously created by the -m option. file2 must be a MIME section
that was previously created by the -c option. The -j options adds the MIME section in
file2 to the MIME collection in file1. The result is written to standard output or to
outputfile.

file1 and/or file2 may be "@&n" which reads from file descriptor #n. The outputfile may
also specify a file descriptor.

file1 and file2 should ideally be created by makemime as well. It's also possible to use
MIME-formatted files created by other software, but with some degree of care. makemime is
not intended to be a MIME parser, but a MIME generator. However some amount of MIME
parsing is necessary to append a MIME section to an existing MIME collection. makemime's
parsing is sufficient for appending a new section to a MIME collection, as long as the
MIME headers in the MIME collections are straightforward. Very convoluted MIME headers may
confuse makemime, and it may not be able to handle them.

Recursive MIME collections
MIME collection may contain other MIME collections as well as MIME sections. The -m and
the -j options may use a multipart MIME collection in place of a MIME section
automatically because a multipart MIME collection is just a special type of a MIME
section. The following example encodes a text message that can be alternatively
represented as HTML or plain text, with some additional attachments:

1. Create a MIME collection that has a text/plain and a text/html MIME section.

2. Create a MIME collection consisting of the MIME section generated in step one, plus
additional MIME sections containing other attachments.

For example:

# Take two files containing the text and the html version of a message, and
# add MIME headers to them.

makemime -c "text/plain; charset=iso-8859-1" -o tmp1.txt msg.txt
makemime -c "text/html; charset=iso-8859-1" -o tmp1.html msg.html

# Combine the result into a multipart/alternative collection

makemime -m "multipart/alternative" -a "Content-Disposition: inline" \
-o tmp.ma1 tmp1.txt
makemime -j tmp.ma1 -o tmp.ma2 tmp1.html

# Add MIME headers to an image attachment.

makemime -c "image/gif" -a "Content-Disposition: attachment" \
-o tmp2.gif attachment.gif

# Create the final multipart/mixed collection

makemime -m "multipart/mixed" -a "Mime-Version: 1.0" \
-o tmp.mm1 tmp.ma2
makemime -j tmp.mm1 -o output.msg tmp2.gif

output.msg now contains the complete MIME collection. Just add the Subject:, From:, and
To: headers (can also be done by additional -a options, of course), and send it on its
way.

Building complex MIME encodings
There are several different ways to build complete MIME encodings from multiple MIME
sections. One way is to use temporary files to create MIME sections, then combine them
together into a single MIME collection. A slightly more complicated approach involves
setting up pipes between multiple makemime processes, in order to avoid using temporary
files.

This can be done manually, by hand. It is also possible to have makemime do this
automatically. makemime will set up these pipes and run multiple instances of itself to
create a single MIME collection, with multiple attachments of complexity limited only by
your system's limit on the maximum number of open files and pipes.

Any file that's read by the -c, -m, and -j options ( -o specifies a file to create, and
doesn't count) may be replaced by a single argument containing a left parenthesis,
additional options, then a single argument containing a right parenthesis. A single
invocation of makemime can only use one -c, -m, or -j option. However, another -c, -m, or
-j option may be specified inside the left and the right parenthesis, and its output is
used in place of the file it replaced. In the previous example the third and the fourth
invocation of makemime can be replaced with the following command:

makemime -j \( \
-m "multipart/alternative" \
-a "Content-Disposition: inline" tmp1.txt \
\) -o tmp.ma2 \
tmp1.html

Note that the parenthesis must be backslashed, to avoid their special meaning to the
shell. An equivalent argument file would have the following contents:

-j
(
-m
multipart/alternative
-a
Content-Disposition: inline
tmp1.txt
)
-o
tmp.ma2
tmp1.html

These constructs can be arbitrarily nested, and are limited by the amount of available
memory and resources. The entire sequence in the previous section is equivalent to the
following command:

makemime -j \
\( \
-m "multipart/mixed" \
-a "Mime-Version: 1.0" \
\( \
-j \
\( \
-m "multipart/alternative" \
-a "Content-Disposition: inline" \
\( \
-c "text/plain; charset=iso-8859-1" \
msg.txt \
\) \
\) \
\( \
-c "text/html; charset=iso-8859-1" \
msg.html \
\) \
\) \
\) \
-o output.msg \
\( \
-c "image/gif" \
-a "Content-Disposition: attachment" \
attachment.gif \
\)

An equivalent argument file would be:

-j
(
-m
multipart/mixed
-a
Mime-Version: 1.0
(
-j
(
-m
multipart/alternative
-a
Content-Disposition: inline
(
-c
text/plain; charset=iso-8859-1
msg.txt
)
)
(
-c
text/html; charset=iso-8859-1
msg.html
)
)
)
-o
output.msg
(
-c
image/gif
-a
Content-Disposition: attachment
attachment.gif
)

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