| Explicit search targets | ||
|---|---|---|
 | Search patterns |  |
| Explicit search targets | ||
|---|---|---|
| | Search patterns | |
Some particularly complex searches can be expressed in aptitude using
explicit targets. In normal search expressions,
there is no way to refer to the package or version that is currently being
tested. For instance, suppose that you want to search for all packages
P that depend on a second package
Q such that Q
recommends P. Clearly you need to start out with
a ?depends(...)... needs to somehow select packages that are identical
to the one being matched against ?dependsP and Q;
terms with explicit targets do exactly the same thing. [17]
An explicit target is introduced by the ?for term:
This behaves exactly like pattern, but
variable can be used within
pattern to refer to the package or version that
pattern is being matched against. You can use
variable in two ways:
The term ?= will match exactly the package or version indicated by the
given variable. Specifically: if the corresponding ?for term is limited
to a particular version, then ?= will match either that version (if
?= is limited) or the whole package; otherwise it will match any
version of the package.
See 例2.2「
Use of the ?= term.
」 for an example of how to use
?=.
The term ?bind(variable,
pattern)variable matches against
pattern.
For ?-style terms, a shorthand form is available. The
expression ?bind(variable,
?term[(args)])?.
variable:term(args)
See 例2.3「Use of the ?bind term」 for an example of how to use
?bind.
[17]
Astute readers will note that this is essentially a way to explicitly name
the variable in the λ-terms corresponding to the term. A typical
term would have the form 「λ x
. name-equals(x,
pattern)」; giving this an explicit target
makes x visible in the search language.
| |  | |
| Searches and versions |  | Search term reference |