Provided by: nmh_1.8-1build4_amd64 
NAME
mh-sequence - sequence specification for nmh message system
DESCRIPTION
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.
Message Specification and Pre-Defined Message Sequences
Most nmh 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:
first the first message in the folder
last the last message in the folder
cur the most recently accessed message
prev the message numerically preceding “cur”
next 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 “first-last”.
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 command.
User-Defined Message Sequences
In addition to the “reserved” (pre-defined) message names given above, nmh 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 `msgs' argument.
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 the pick and mark
commands.
Public and Private User-Defined Sequences
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 context file.
In general, the commands that create sequences (such as pick and mark) 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 and -private. But if the folder is read-only, or if
the “mh-sequences” profile entry is defined but empty, then private sequences will be created instead.
Sequence Negation
Nmh 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
is:
Sequence-Negation: not
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.
The Previous Sequence
Nmh 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
Previous-Sequence: pseq
directs any nmh command that accepts a `msg' or `msgs' argument to define the sequence “pseq” as those
messages when it finishes.
Note: there can be a performance penalty in using the “Previous-Sequence” facility. If it is used, all
nmh programs have to write the sequence information to the .mh_sequences file for the folder each time
they run. If the “Previous-Sequence” profile entry is not included, only pick and mark will write to the
.mh_sequences file.
The Unseen Sequence
Finally, many users like to indicate which messages have not been previously seen by them. The commands
flist, inc, mhshow, rcvstore, and show honor the profile entry “Unseen-Sequence” to support this
activity. This entry in the .mh_profile 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 inc or rcvstore), the new messages will also be added to all the sequences
named in this profile entry. For example, a profile entry of
Unseen-Sequence: unseen
directs inc 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, mhshow, next, or prev displays a message, that message will be removed from any
sequences named by the “Unseen-Sequence” entry in the profile.
Sequence File Format
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 “lownum-highnum”.
Sample sequence file
work: 3 6 8 22-33 46
unseen: 47 49-51 54
cur: 46
Nmh 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 nonexistent message.
Sequence File Locking
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 multiple nmh commands are run simultaneously. Nmh commands that 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 and pick, will release the sequence lock during
the bulk of their runtime and reread the sequence file after their processing is complete to reduce lock
contention time.
Note: Currently transactional locks are only supported for public sequences; private sequences will not
get corrupted, but the possibility exists that two nmh commands run simultaneously that add messages to a
private sequence could result in one command's messages not appearing on the requested sequence.
FILES
$HOME/.mh-profile The user's profile.
<mh-dir>/context The user's context.
<folder>/.mh-sequences
File for public sequences.
PROFILE COMPONENTS
mh-sequences: Name of file to store public sequences.
Sequence-Negation: To designate messages not in a sequence.
Previous-Sequence: The last message specification given.
Unseen-Sequence: Those messages not yet seen by the user.
SEE ALSO
flist(1), mark(1), pick(1), mh-profile(5)
DEFAULTS
None
nmh-1.8 2013-10-17 MH-SEQUENCE(5mh)