4.4.3 The Function wildcard
Wildcard expansion happens automatically in rules. But wildcard expansion does not normally take place when a variable is set, or inside the arguments of a function. If you want to do wildcard expansion in such places, you need to use the wildcard function, like this:
$(wildcard pattern…)
This string, used anywhere in a makefile, is replaced by a space-separated list of names of existing files that match one of the given file name patterns.
If no existing file name matches a pattern, then that pattern is omitted from the output of the wildcard function. Note that this is different from how unmatched
wildcards behave in rules, where they are used verbatim rather than ignored (see Wildcard Pitfall).
One use of the wildcard function is to get a list of all the C source files in a directory, like this:
$(wildcard *.c)
We can change the list of C source files into a list of object files by replacing the ‘.c’ suffix with ‘.o’ in the result, like this:
$(patsubst %.c,%.o,$(wildcard *.c))
(Here we have used another function, patsubst. See Functions for String Substitution and Analysis.)
Thus, a makefile to compile all C source files in the directory and then link them together could be written as follows:
objects := $(patsubst %.c,%.o,$(wildcard *.c))
foo : $(objects)
cc -o foo $(objects)
(This takes advantage of the implicit rule for compiling C programs, so there is no need to write explicit rules for compiling the files. See The Two Flavors of Variables, for an explanation of ‘:=’, which is a variant of ‘=’.)
https://www.gnu.org/software/make/manual/html_node/Wildcard-Function.html
补充一段在网上看到的博客：
patsubst函数用于将文件模式进行替换。
一、作用
替换文件后缀。
二、格式
$(patsubst 原模式， 目标模式， 文件列表)