How to write a Make rule for files of certain type in a directory tree?

问题

Imagine a directory tree (which might be more than one level deep) containing several Markdown files. A PDF version of each file exist in the same directory and must be updated each time the corresponding Markdown file is updated. What rule must be written in a single Makefile in the root directory of this tree to achieve this?

I am looking a for a solution where files can be added or removed from the directory tree without a need for updating the Makefile.

Assumptions:

• all markdown files follow a certain pattern in their name; for example they end with a .md postfix.
• GNU Make is being used.

回答1:

You can use $(shell find) to find files recursively. For example:

markdown := $(shell find . -name '*.md')

all: $(patsubst %.md, %.pdf, $(markdown))

%.pdf: %.md
    pandoc -o $@ $<

来源：https://stackoverflow.com/questions/36246713/how-to-write-a-make-rule-for-files-of-certain-type-in-a-directory-tree