Message Specification and Pre-Defined Message Sequences

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

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

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

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

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

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

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

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.