MH-SEQUENCE(5)MH-SEQUENCE(5)NAMEmh-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:
Name Description
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 mes‐
sages 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 mes‐
sages 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 over‐
ridden 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 alpha‐
betic 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 substi‐
tuting `=' 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
seqence `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). Pri‐
vate 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 anytime 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 mul‐
tiple sequence names, as separate arguments. If this entry is defined,
when 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 “Previ‐
ous-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 pre‐
viously seen by them. The commands inc, rcvstore, show, mhshow, and
flist honor the profile entry “Unseen-Sequence” to support this activ‐
ity. 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-sep‐
arated list of message numbers that correspond to messages that are
part of the named sequence. A contiguous range of messages can be rep‐
resented 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 nonexistant messages when the sequence file is updated.
The exception to this is the “cur” sequence, which is allowed to point
to a nonexistant 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 possibil‐
ity 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 profile
<mh-dir>/context The user 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 ALSOflist(1), mark(1), pick(1), mh-profile(5)DEFAULTS
None
nmh-1.6 June 11, 2013 MH-SEQUENCE(5)
