.TH MH-SEQUENCE %manext5% 2013-10-17 "%nmhversion%"
.
.\" %nmhwarning%
.
.SH NAME
mh-sequence \- sequence specification for nmh message system
.SH DESCRIPTION
A sequence (or sequence set) is a symbolic name representing a
message or collection of messages.
.B nmh
has several internally defined sequences, as well as allowing
users to define their own sequences.
.SS "Message Specification and Pre-Defined Message Sequences"
Most
.B 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 \*(lqreserved\*(rq message names:
.PP
.RS 5
.PD 0
.TP
.B first
the first message in the folder
.TP
.B last
the last message in the folder
.TP
.B cur
the most recently accessed message
.TP
.B prev
the message numerically preceding \*(lqcur\*(rq
.TP
.B next
the message numerically following \*(lqcur\*(rq
.RE
.PD
.PP
In commands that take a `msg' argument, the default is \*(lqcur\*(rq.
As a shorthand, \*(lq.\*(rq is equivalent to \*(lqcur\*(rq.
.PP
For example: In a folder containing five messages numbered 5, 10, 94, 177
and 325, \*(lqfirst\*(rq is 5 and \*(lqlast\*(rq is 325.  If \*(lqcur\*(rq
is 94, then \*(lqprev\*(rq is 10 and \*(lqnext\*(rq is 177.
.PP
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.
.PP
A message range is specified as \*(lqname1\-name2\*(rq or
\*(lqname:n\*(rq, where `name', `name1' and `name2' are message names,
and `n' is an integer.
.PP
The specification \*(lqname1\-name2\*(rq designates all currently existing
messages from `name1' to `name2' inclusive.  The \*(lqreserved\*(rq
message name \*(lqall\*(rq is a shorthand for the message range
\*(lqfirst\-last\*(rq.
.PP
The specification \*(lqname:n\*(rq designates up to `n' messages.
These messages start with `name' if `name' is a message number or one of
the reserved names \*(lqfirst\*(rq \*(lqcur\*(rq, or \*(lqnext\*(rq, The
messages end with `name' if `name' is \*(lqprev\*(rq or \*(lqlast\*(rq.
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'.
.PP
Substituting `=' for `:' (i.e., \*(lqname=n\*(rq) 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 \*(lqname:-3\*(rq
selects the 3 messages ending with `name', \*(lqname=-3\*(rq 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).
.PP
In commands which accept a `msgs' argument, the default is either
\*(lqcur\*(rq or \*(lqall\*(rq, 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.
.PP
There is also a special \*(lqreserved\*(rq message name \*(lqnew\*(rq
which is used by the
.B mhpath
command.
.SS "User\-Defined Message Sequences"
In addition to the \*(lqreserved\*(rq (pre-defined) message names given
above,
.B nmh
supports user-defined sequence names.  User-defined sequences allow the
.B 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.
.PP
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 \*(lqreserved\*(rq message names above.  After defining a
sequence, it can be used wherever an
.B nmh
command expects a `msg' or
`msgs' argument.
.PP
Some forms of message ranges are allowed with user-defined sequences.
The specification \*(lqname:n\*(rq 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'.
.PP
The specifications \*(lqname:next\*(rq and \*(lqname:prev\*(rq 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 \*(lqname:first\*(rq and \*(lqname:last\*(rq are
equivalent to \*(lqname:1\*(rq and \*(lqname:\-1\*(rq, respectively.  The
specification \*(lqname:cur\*(rq is not allowed (use just \*(lqcur\*(rq
instead).  The syntax of these message range specifications is subject
to change in the future.
.PP
Single messages (as opposed to ranges) may also be selected by
substituting `=' for `:', as in \*(lqname=n\*(rq.  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 \*(lqseq:5\*(rq
selects the first 5 messages of sequence `seq', \*(lqseq=5\*(rq
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).
.PP
User-defined sequence names are specific to each folder.  They are
defined using the
.B pick
and
.B mark
commands.
.SS "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
.B nmh
user that can read that folder.  They are kept in each folder
in the file determined by the \*(lqmh\-sequences\*(rq profile entry
(default is
.IR \&.mh_sequences ).
Private sequences are accessible
only to the
.B nmh
user that defined those sequences and are kept in
the user's
.B nmh
context file.
.PP
In general, the commands that create sequences (such as
.B pick
and
.BR mark )
will create public sequences if the folder for which
the sequences are being defined is writable by the
.B nmh
user.
For most commands, this can be overridden by using the switches
.B \-public
and
.BR \-private .
But if the folder is read-only, or if
the \*(lqmh\-sequences\*(rq profile entry is defined but empty, then
\fIprivate\fR sequences will be created instead.
.SS "Sequence Negation"
.B Nmh
provides the ability to select all messages not elements of a
user-defined sequence.  To do this, the user should define the entry
\*(lqSequence\-Negation\*(rq in the
.B 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:
.PP
.RS 5
Sequence\-Negation: not
.RE
.PP
then any time an
.B nmh
command is given \*(lqnotfoo\*(rq as a `msg' or
`msgs' argument, it would substitute all messages that are not elements
of the sequence \*(lqfoo\*(rq.
.PP
Obviously, the user should beware of defining sequences with names that
begin with the value of the \*(lqSequence\-Negation\*(rq profile entry.
.SS "The Previous Sequence"
.B Nmh
provides the ability to remember the `msgs' or `msg' argument
last given to an
.B nmh
command.  The entry \*(lqPrevious\-Sequence\*(rq
should be defined in the
.B nmh
profile; its value should be a sequence
name or multiple sequence names, as separate arguments.  If this entry
is defined, when an
.B 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
.PP
.RS 5
Previous\-Sequence: pseq
.RE
.PP
directs any
.B nmh
command that accepts a `msg' or `msgs' argument to define the sequence
\*(lqpseq\*(rq as those messages when it finishes.
.PP
.BR Note :
there can be a performance penalty in using the
\*(lqPrevious\-Sequence\*(rq facility.  If it is used,
.B all
.B nmh
programs have to write the sequence information to the
.I \&.mh_sequences
file for the folder each time they run.  If the
\*(lqPrevious\-Sequence\*(rq profile entry is not included, only
.B pick
and
.B mark
will write to the
.B \&.mh_sequences
file.
.SS "The Unseen Sequence"
Finally, many users like to indicate which messages have not been
previously seen by them.  The commands
.BR flist ,
.BR inc ,
.BR mhshow ,
.BR rcvstore ,
and
.B show
honor the profile entry \*(lqUnseen\-Sequence\*(rq to support this
activity.  This entry in the
.I \&.mh_profile
should be defined as one or more sequence names, as separate arguments.
If there is a value for \*(lqUnseen\-Sequence\*(rq in the profile,
then whenever new messages are placed in a folder (using
.B inc
or
.BR rcvstore ),
the new messages will also be added to all the sequences named in this
profile entry.  For example, a profile entry of
.PP
.RS 5
Unseen\-Sequence: unseen
.RE
.PP
directs
.B inc
to add new messages to the sequence \*(lqunseen\*(rq.
Unlike the behavior of the \*(lqPrevious\-Sequence\*(rq entry in the
profile, however, the sequence(s) will
.I not
be zeroed by
.BR inc .
.PP
Similarly, whenever
.BR show ,
.BR mhshow ,
.BR next ,
or
.B prev
displays a message, that message will be removed from any sequences
named by the \*(lqUnseen\-Sequence\*(rq entry in the profile.
.SS 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 \*(lqlownum\-highnum\*(rq.
.PP
.B Sample sequence file
.PP
.RS 5
.nf
work: 3 6 8 22-33 46
unseen: 47 49-51 54
cur: 46
.fi
.RE
.PP
.B 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 \*(lqcur\*(rq sequence, which is allowed to point to a
nonexistent message.
.SS Sequence File Locking
The \*(lqdatalocking\*(rq profile entry controls the type of locking used
when reading and writing sequence files.  The locking mechanisms supported
are detailed in
.IR mh\-profile (5).
This protects sequence file integrity when multiple
.B nmh
commands are run simultaneously.
.B 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
.B nmh
commands, such as
.B inc
and
.BR 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.
.PP
Note:
Currently transactional locks are only supported for public sequences;
private sequences will not get corrupted, but the possibility exists that two
.B nmh
commands run simultaneously that add messages to a private sequence could result in
one command's messages not appearing on the requested sequence.
.SH FILES
.PD 0
.TP 20
$HOME/.mh\-profile
The user's profile.
.TP 20
<mh-dir>/context
The user's context.
.TP 20
<folder>/.mh\-sequences
File for public sequences.
.PD
.SH "PROFILE COMPONENTS"
.PD 0
.TP 20
mh-sequences:
Name of file to store public sequences.
.TP 20
Sequence\-Negation:
To designate messages not in a sequence.
.TP 20
Previous\-Sequence:
The last message specification given.
.TP 20
Unseen\-Sequence:
Those messages not yet seen by the user.
.PD
.SH "SEE ALSO"
.IR flist (1),
.IR mark (1),
.IR pick (1),
.IR mh-profile (5)
.SH DEFAULTS
None