A category consists of a name, the list of groups belonging to the category, and a number of optional parameters that override the customizable variables. The complete list of agent parameters are listed below.
agent-groupsThe list of groups that are in this category.
agent-predicateA predicate which (generally) gives a rough outline of which articles are eligible for downloading; and
agent-scorea score rule which (generally) gives you a finer granularity when deciding what articles to download. (Note that this download score is not necessarily related to normal scores.)
agent-enable-expirationa boolean indicating whether the agent should expire old articles in this group. Most groups should be expired to conserve disk space. In fact, its probably safe to say that the gnus.* hierarchy contains the only groups that should not be expired.
agent-days-until-oldan integer indicating the number of days that the agent should wait before deciding that a read article is safe to expire.
agent-low-scorean integer that overrides the value of gnus-agent-low-score.
agent-high-scorean integer that overrides the value of gnus-agent-high-score.
agent-short-articlean integer that overrides the value of
gnus-agent-short-article.
agent-long-articlean integer that overrides the value of gnus-agent-long-article.
agent-enable-undownloaded-facesa symbol indicating whether the summary buffer should display
undownloaded articles using the gnus-summary-*-undownloaded-face
faces. Any symbol other than nil will enable the use of
undownloaded faces.
The name of a category can not be changed once the category has been created.
Each category maintains a list of groups that are exclusive members of that category. The exclusivity rule is automatically enforced, add a group to a new category and it is automatically removed from its old category.
A predicate in its simplest form can be a single predicate such as
true or false. These two will download every available
article or nothing respectively. In the case of these two special
predicates an additional score rule is superfluous.
Predicates of high or low download articles in respect of
their scores in relationship to gnus-agent-high-score and
gnus-agent-low-score as described below.
To gain even finer control of what is to be regarded eligible for download a predicate can consist of a number of predicates with logical operators sprinkled in between.
Perhaps some examples are in order.
Here’s a simple predicate. (It’s the default predicate, in fact, used for all groups that don’t belong to any other category.)
short
Quite simple, eh? This predicate is true if and only if the article is short (for some value of “short”).
Here’s a more complex predicate:
(or high
(and
(not low)
(not long)))
This means that an article should be downloaded if it has a high score, or if the score is not low and the article is not long. You get the drift.
The available logical operators are or, and and
not. (If you prefer, you can use the more “C”-ish operators
‘|’, & and ! instead.)
The following predicates are pre-defined, but if none of these fit what you want to do, you can write your own.
When evaluating each of these predicates, the named constant will be
bound to the value determined by calling
gnus-agent-find-parameter on the appropriate parameter. For
example, gnus-agent-short-article will be bound to
(gnus-agent-find-parameter group 'agent-short-article). This
means that you can specify a predicate in your category then tune that
predicate to individual groups.
shortTrue if the article is shorter than gnus-agent-short-article
lines; default 100.
longTrue if the article is longer than gnus-agent-long-article
lines; default 200.
lowTrue if the article has a download score less than
gnus-agent-low-score; default 0.
highTrue if the article has a download score greater than
gnus-agent-high-score; default 0.
spamTrue if the Gnus Agent guesses that the article is spam. The heuristics may change over time, but at present it just computes a checksum and sees whether articles match.
trueAlways true.
falseAlways false.
If you want to create your own predicate function, here’s what you have
to know: The functions are called with no parameters, but the
gnus-headers and gnus-score dynamic variables are bound to
useful values.
For example, you could decide that you don’t want to download articles
that were posted more than a certain number of days ago (e.g., posted
more than gnus-agent-expire-days ago) you might write a function
something along the lines of the following:
(defun my-article-old-p ()
"Say whether an article is old."
(< (time-to-days (date-to-time (mail-header-date gnus-headers)))
(- (time-to-days nil) gnus-agent-expire-days)))
with the predicate then defined as:
(not my-article-old-p)
or you could append your predicate to the predefined
gnus-category-predicate-alist in your ~/.gnus.el or
wherever.
(require 'gnus-agent)
(setq gnus-category-predicate-alist
(append gnus-category-predicate-alist
'((old . my-article-old-p))))
and simply specify your predicate as:
(not old)
If/when using something like the above, be aware that there are many misconfigured systems/mailers out there and so an article’s date is not always a reliable indication of when it was posted. Hell, some people just don’t give a damn.
The above predicates apply to all the groups which belong to the category. However, if you wish to have a specific predicate for an individual group within a category, or you’re just too lazy to set up a new category, you can enter a group’s individual predicate in its group parameters like so:
(agent-predicate . short)
This is the group/topic parameter equivalent of the agent category default.
Note that when specifying a single word predicate like this, the
agent-predicate specification must be in dotted pair notation.
The equivalent of the longer example from above would be:
(agent-predicate or high (and (not low) (not long)))
The outer parenthesis required in the category specification are not entered here as, not being in dotted pair notation, the value of the predicate is assumed to be a list.
Now, the syntax of the download score is the same as the syntax of
normal score files, except that all elements that require actually
seeing the article itself are verboten. This means that only the
following headers can be scored on: Subject, From,
Date, Message-ID, References, Chars,
Lines, and Xref.
As with predicates, the specification of the download score rule
to use in respect of a group can be in either the category definition if
it’s to be applicable to all groups in therein, or a group’s parameters
if it’s to be specific to that group.
In both of these places the download score rule can take one of
three forms:
This has the same syntax as a normal Gnus score file except only a subset of scoring keywords are available as mentioned above.
example:
(("from"
("Lars Ingebrigtsen" 1000000 nil s))
("lines"
(500 -100 nil <)))
(agent-score ("from"
("Lars Ingebrigtsen" 1000000 nil s))
("lines"
(500 -100 nil <)))
Again, note the omission of the outermost parenthesis here.
These score files must only contain the permitted scoring keywords stated above.
example:
("~/News/agent.SCORE")
or perhaps
("~/News/agent.SCORE" "~/News/agent.group.SCORE")
(agent-score "~/News/agent.SCORE")
Additional score files can be specified as above. Need I say anything about parenthesis?
normal score files
If you don’t want to maintain two sets of scoring rules for a group, and
your desired downloading criteria for a group are the same as your
reading criteria then you can tell the agent to refer to your
normal score files when deciding what to download.
These directives in either the category definition or a group’s parameters will cause the agent to read in all the applicable score files for a group, filtering out those sections that do not relate to one of the permitted subset of scoring keywords.
file
(agent-score . file)