Makefile filter-out 是什么

在 Makefile 中，`filter-out` 是一个函数，用于从一个字符串列表中过滤掉特定的字符串。它的语法如下：

$(filter-out pattern...,text)

其中，`pattern...` 是需要被过滤掉的字符串模式，可以使用通配符 `%`，`text` 是要进行过滤的原始字符串列表。

`filter-out` 函数会返回一个新的字符串列表，其中过滤掉了所有匹配 `pattern...` 的字符串。

下面是一个示例，演示如何使用 `filter-out` 从 Makefile 的文件列表中过滤掉所有以 `.pdf` 结尾的文件：

# 定义文件列表
FILES := file1.txt file2.pdf file3.dat file4.pdf

# 过滤掉所有以 .pdf 结尾的文件
PDF_FILES := $(filter-out %.pdf, $(FILES))

# 打印过滤后的文件列表
all:
    @echo $(PDF_FILES)

在上面的示例中，`PDF_FILES` 变量将只包含文件 `file1.txt` 和 `file3.dat`，因为 `file2.pdf` 和 `file4.pdf` 已经被过滤掉了。

希望这个解释能够帮助您理解 Makefile 中的 `filter-out` 函数。

相关问题

makefile filter-out

Sure, I can help with that!

The `filter-out` function in a Makefile is used to remove certain strings from a list of strings.

Here's an example of how to use `filter-out` in a Makefile:

# Define a list of files
FILES := file1.txt file2.txt file3.dat file4.pdf

# Remove all files with a .pdf extension
PDF_FILES := $(filter-out %.pdf,$(FILES))

# Print the filtered list of files
all:
    @echo $(PDF_FILES)

In the above example, the `filter-out` function removes all files with a `.pdf` extension from the `FILES` list and stores the resulting list in the `PDF_FILES` variable.

The resulting output when running `make` would be:

file1.txt file2.txt file3.dat

Let me know if you have any further questions!

@MAKE -C dir1 dir2 -f Makefile1 $(filter-out _all sub-make,$(MAKECMDGOALS)) explain the grammar in this snippet

Sure, here is an explanation of the grammar in this snippet:

- `@MAKE`: This tells Make to run the command `MAKE` silently, without displaying the command itself.
- `-C dir1 dir2`: This tells Make to change to the directory `dir1/dir2` before running the rest of the command.
- `-f Makefile1`: This tells Make to use the file `Makefile1` instead of the default `Makefile` for this command.
- `$(filter-out _all sub-make,$(MAKECMDGOALS))`: This is a Make function that filters out any targets that match `_all` or `sub-make` from the list of goals specified on the command line (`$(MAKECMDGOALS)`). The resulting list of targets is used as the goals for this Make command.

Put together, this command runs Make silently, changes to the directory `dir1/dir2`, uses `Makefile1` as the Makefile, and filters out any targets that match `_all` or `sub-make` from the list of goals specified on the command line. The resulting list of targets is then used as the goals for this Make command.