mh-sequence - sequence specification for nmh message system
A sequence (or sequence set) is a symbolic name representing a message or
collection of messages. nmh
has several internally defined sequences,
as well as allowing users to define their own sequences.
commands accept a `msg' or `msgs' specification, where `msg'
indicates one message and `msgs' indicates one or more messages. To designate
a message, you may use either its number (e.g., 1, 10, 234) or one of these
“reserved” message names:
- the first message in the folder
- the last message in the folder
- the most recently accessed message
- the message numerically preceding “cur”
- the message numerically following “cur”
In commands that take a `msg' argument, the default is “cur”. As a
shorthand, “.” is equivalent to “cur”.
For example: In a folder containing five messages numbered 5, 10, 94, 177 and
325, “first” is 5 and “last” is 325. If
“cur” is 94, then “prev” is 10 and
“next” is 177.
The word `msgs' indicates that one or more messages may be specified. Such a
specification consists of one message designation or of several message
designations, as separate arguments. A message designation consists either of
a message name as defined above, or a message range.
A message range is specified as “name1-name2” or
“name:n”, where `name', `name1' and `name2' are message names,
and `n' is an integer.
The specification “name1-name2” designates all currently existing
messages from `name1' to `name2' inclusive. The “reserved”
message name “all” is a shorthand for the message range
The specification “name:n” designates up to `n' messages. These
messages start with `name' if `name' is a message number or one of the
reserved names “first” “cur”, or
“next”, The messages end with `name' if `name' is
“prev” or “last”. The interpretation of `n' may be
overridden by preceding `n' with a plus or minus sign; `+n' always means up to
`n' messages starting with `name', and `-n' always means up to `n' messages
ending with `name'.
Substituting `=' for `:' (i.e., “name=n”) will reduce the
selection from a range of up to `n' messages, to a selection of just the `n'th
message. So for example, while “name:-3” selects the 3 messages
ending with `name', “name=-3” selects just the 2nd previous
message. It is an error if the requested message does not exist (i.e., there
aren't enough messages in the folder).
In commands which accept a `msgs' argument, the default is either
“cur” or “all”, depending on which makes more
sense for each command (see the individual man pages for details). Repeated
specifications of the same message have the same effect as a single
specification of the message.
There is also a special “reserved” message name
“new” which is used by the mhpath
In addition to the “reserved” (pre-defined) message names given
supports user-defined sequence names. User-defined sequences
allow the nmh
user a tremendous amount of power in dealing with groups
of messages in the same folder by allowing the user to bind a group of
messages to a meaningful symbolic name.
The name used to denote a message sequence must consist of an alphabetic
character followed by zero or more alphanumeric characters, and can not be one
of the “reserved” message names above. After defining a
sequence, it can be used wherever an nmh
command expects a `msg' or
Some forms of message ranges are allowed with user-defined sequences. The
specification “name:n” may be used, and it designates up to the
first `n' messages (or last `n' messages for `-n') which are elements of the
user-defined sequence `name'.
The specifications “name:next” and “name:prev” may
also be used, and they designate the next or previous message (relative to the
current message) which is an element of the user-defined sequence `name'. The
specifications “name:first” and “name:last” are
equivalent to “name:1” and “name:-1”,
respectively. The specification “name:cur” is not allowed (use
just “cur” instead). The syntax of these message range
specifications is subject to change in the future.
Single messages (as opposed to ranges) may also be selected by substituting `='
for `:', as in “name=n”. This will reduce the selection from
being a range of up to `n' messages, to being a selection of just the `n'th
message. So while “seq:5” selects the first 5 messages of
sequence `seq', “seq=5” selects just the 5th message of the
sequence. It is an error if the requested message does not exist (i.e., there
aren't at least `n' messages in the sequence).
User-defined sequence names are specific to each folder. They are defined using
There are two varieties of user-defined sequences: public and private. Public
sequences of a folder are accessible to any nmh
user that can read that
folder. They are kept in each folder in the file determined by the
“mh-sequences” profile entry (default is .mh_sequences
Private sequences are accessible only to the nmh
user that defined
those sequences and are kept in the user's nmh
In general, the commands that create sequences (such as pick
) will create public sequences if the folder for which the
sequences are being defined is writable by the nmh
user. For most
commands, this can be overridden by using the switches -public
. But if the folder is read-only, or if the
“mh-sequences” profile entry is defined but empty, then
sequences will be created instead.
provides the ability to select all messages not elements of a
user-defined sequence. To do this, the user should define the entry
“Sequence-Negation” in the nmh
profile file; its value
may be any string. This string is then used to preface an existing
user-defined sequence name. This specification then refers to those messages
not elements of the specified sequence name. For example, if the profile entry
then any time an nmh
command is given “notfoo” as a `msg'
or `msgs' argument, it would substitute all messages that are not elements of
the sequence “foo”.
Obviously, the user should beware of defining sequences with names that begin
with the value of the “Sequence-Negation” profile entry.
provides the ability to remember the `msgs' or `msg' argument last
given to an nmh
command. The entry “Previous-Sequence”
should be defined in the nmh
profile; its value should be a sequence
name or multiple sequence names, as separate arguments. If this entry is
defined, when an nmh
command finishes, it will define the sequence(s)
named in the value of this entry to be those messages that were specified to
the command. Hence, a profile entry of
directs any nmh
command that accepts a `msg' or `msgs' argument to define
the sequence “pseq” as those messages when it finishes.
: there can be a performance penalty in using the
“Previous-Sequence” facility. If it is used, all
programs have to write the sequence information to the
file for the folder each time they run. If the
“Previous-Sequence” profile entry is not included, only
will write to the .mh_sequences
Finally, many users like to indicate which messages have not been previously
seen by them. The commands flist
, and show
honor the profile entry
“Unseen-Sequence” to support this activity. This entry in the
should be defined as one or more sequence names, as
separate arguments. If there is a value for “Unseen-Sequence” in
the profile, then whenever new messages are placed in a folder (using
), the new messages will also be added to all the
sequences named in this profile entry. For example, a profile entry of
to add new messages to the sequence “unseen”.
Unlike the behavior of the “Previous-Sequence” entry in the
profile, however, the sequence(s) will not
be zeroed by inc
Similarly, whenever show
, or prev
displays a message, that message will be removed from any sequences named by
the “Unseen-Sequence” entry in the profile.
The sequence file format is based on the RFC 5322 message format. Each line of
the sequence file corresponds to one sequence. The line starts with the
sequence name followed by a `:', then followed by a space-separated list of
message numbers that correspond to messages that are part of the named
sequence. A contiguous range of messages can be represented as
Sample sequence file
work: 3 6 8 22-33 46
unseen: 47 49-51 54
commands that modify the sequence file will silently remove sequences
for nonexistent messages when the sequence file is updated. The exception to
this is the “cur” sequence, which is allowed to point to a
The “datalocking” profile entry controls the type of locking used
when reading and writing sequence files. The locking mechanisms supported are
detailed in mh-profile
(5). This protects sequence file integrity when
commands are run simultaneously. Nmh
modify the sequence file use transactional locks; the lock is held from the
time the sequence file is read until it it written out. This ensures that
modifications to the sequence file will not be lost if multiple commands are
run simultaneously. Long-running nmh
commands, such as inc
, will release the sequence lock during the bulk of their runtime
and reread the sequence file after their processing is complete to reduce lock
Note: Currently transactional locks are only supported for public sequences;
private sequences will not get corrupted, but the possibility exists that two
commands run simultaneously that add messages to a private sequence
could result in one command's messages not appearing on the requested
- The user's profile.
- The user's context.
- File for public sequences.
- Name of file to store public sequences.
- To designate messages not in a sequence.
- The last message specification given.
- Those messages not yet seen by the user.