CODEWITHSUNDEEP
makefilewildcard
user267298
user267298

Reputation: 139

Loop through files in make file

Right now I have the following in my make file to create a symbolic link to a file in my current directory:

MY_FILE := "$(SOME_PATH)/file.txt"

ln -s $(MY_FILE)

What I would like is to do some sort of glob operation to link a bunch of files (or none).

MY_FILES :=  "$(SOME_PATH)/*.txt"
for file in files:
   ln -s $(MY_FILE)

Could anyone point me in the right direction to do this? Thanks!

Upvotes: 1

Views: 697

Answers (2)

Renaud Pacalet
Renaud Pacalet

Reputation: 29040

The following should do what you want:

MY_FILES := $(wildcard $(SOME_PATH)/*.txt)
LINKS    := $(notdir $(MY_FILES))

.PHONY: links clean-links
links: $(LINKS)

$(LINKS): %: $(SOME_PATH)/%
    ln -s $<

clean-links:
    rm -f $(LINKS)

Explanation:

  1. Make functions. wildcard and notdir are two make functions. Knowing the make functions (at least the most frequently used) really helps writing nice, elegant and efficient make files. Of course, if you have spaces or special characters in your file names you will encounter some problems because most make functions consider spaces as separators. But if you have such files and directory names you should probably use something else than make.

  2. Static pattern rules:

    $(LINKS): %: $(SOME_PATH)/%

    is a static pattern rule. For each word foo.txt in $(LINKS) it instantiates one single make rule:

    foo.txt: $(SOME_PATH)/foo.txt
    ln -s $(SOME_PATH)/foo.txt

    Knowing how to use pattern rules (static or not) is essential if you want to write compact and generic make files.

  3. Automatic variables. $< is a make automatic variable. In recipes (the commands part of rules) it expands as the first listed pre-requisite. There are many other automatic variables and they are quite handy to write generic rules.

  4. Phony targets. links and clean-links are phony targets because they do not correspond to real files that we want make to create or update. They are kind of short-hands for actions. make links creates all missing links and make clean-links removes them all. As make has no way to guess that these targets are not regular file names we tell it with the .PHONY special target.

Upvotes: 2

Andreas
Andreas

Reputation: 5301

Make creates "targets" from "prerequisites". In your case MY_FILES holds prerequisites to create the (link) targets. The rule for a single file might look like this:

file.txt: $(SOME_PATH)/file.txt
    ln -s $<

You want multiple files, and in this case we can use this pattern rule:

%.txt: $(SOME_PATH)/%.txt
    ln -s $<

You can now create links with the make commands:

make file.txt
make otherfile.txt

Finally we will look into the wildcard function to get all files, and the function notdir function to get the link names from the file names. Following rule will print all text files, and depends on all files in SOME_PATH linked to current working directory:

MY_FILES := $(notdir $(wildcard $(SOME_PATH)/*.txt))
cat: $(MY_FILES)
    cat $^

%.txt: $(SOME_PATH)/%.txt
    ln -s $<

Upvotes: 0

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