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 |
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last |
the last message in the folder |
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cur |
the most recently accessed message |
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prev |
the message numerically preceding “cur” |
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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. |
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<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