4.12.2 Static Pattern Rules versus Implicit Rules
A static pattern rule has much in common with an implicit rule defined as a
pattern rule (see section Defining and Redefining Pattern Rules).
Both have a pattern for the target and patterns for constructing the
names of prerequisites. The difference is in how make decides
when the rule applies.
An implicit rule can apply to any target that matches its pattern,
but it does apply only when the target has no commands otherwise
specified, and only when the prerequisites can be found. If more than one
implicit rule appears applicable, only one applies; the choice depends on
the order of rules.
By contrast, a static pattern rule applies to the precise list of targets
that you specify in the rule. It cannot apply to any other target and it
invariably does apply to each of the targets specified. If two conflicting
rules apply, and both have commands, that's an error.
The static pattern rule can be better than an implicit rule for these
reasons:
-
You may wish to override the usual implicit rule for a few
files whose names cannot be categorized syntactically but
can be given in an explicit list.
-
If you cannot be sure of the precise contents of the directories
you are using, you may not be sure which other irrelevant files
might lead
make to use the wrong implicit rule. The choice
might depend on the order in which the implicit rule search is done.
With static pattern rules, there is no uncertainty: each rule applies
to precisely the targets specified.
