Create directories using make file

Solution 1:

In my opinion, directories should not be considered targets of your makefile, either in technical or in design sense. You should create files and if a file creation needs a new directory then quietly create the directory within the rule for the relevant file.

If you're targeting a usual or "patterned" file, just use make's internal variable $(@D), that means "the directory the current target resides in" (cmp. with $@ for the target). For example,

$(OUT_O_DIR)/%.o: %.cpp
        @mkdir -p $(@D)
        @$(CC) -c $< -o $@

title: $(OBJS)

Then, you're effectively doing the same: create directories for all $(OBJS), but you'll do it in a less complicated way.

The same policy (files are targets, directories never are) is used in various applications. For example, git revision control system doesn't store directories.

Note: If you're going to use it, it might be useful to introduce a convenience variable and utilize make's expansion rules.

dir_guard=@mkdir -p $(@D)

$(OUT_O_DIR)/%.o: %.cpp
        $(dir_guard)
        @$(CC) -c $< -o $@

$(OUT_O_DIR_DEBUG)/%.o: %.cpp
        $(dir_guard)
        @$(CC) -g -c $< -o $@

title: $(OBJS)

Solution 2:

This would do it - assuming a Unix-like environment.

MKDIR_P = mkdir -p

.PHONY: directories

all: directories program

directories: ${OUT_DIR}

${OUT_DIR}:
        ${MKDIR_P} ${OUT_DIR}

This would have to be run in the top-level directory - or the definition of ${OUT_DIR} would have to be correct relative to where it is run. Of course, if you follow the edicts of Peter Miller's "Recursive Make Considered Harmful" paper, then you'll be running make in the top-level directory anyway.

I'm playing with this (RMCH) at the moment. It needed a bit of adaptation to the suite of software that I am using as a test ground. The suite has a dozen separate programs built with source spread across 15 directories, some of it shared. But with a bit of care, it can be done. OTOH, it might not be appropriate for a newbie.

As noted in the comments, listing the 'mkdir' command as the action for 'directories' is wrong. As also noted in the comments, there are other ways to fix the 'do not know how to make output/debug' error that results. One is to remove the dependency on the the 'directories' line. This works because 'mkdir -p' does not generate errors if all the directories it is asked to create already exist. The other is the mechanism shown, which will only attempt to create the directory if it does not exist. The 'as amended' version is what I had in mind last night - but both techniques work (and both have problems if output/debug exists but is a file rather than a directory).

Solution 3:

Or, KISS.

DIRS=build build/bins

... 

$(shell mkdir -p $(DIRS))

This will create all the directories after the Makefile is parsed.

Solution 4:

make in, and off itself, handles directory targets just the same as file targets. So, it's easy to write rules like this:

outDir/someTarget: Makefile outDir
    touch outDir/someTarget

outDir:
    mkdir -p outDir

The only problem with that is, that the directories timestamp depends on what is done to the files inside. For the rules above, this leads to the following result:

$ make
mkdir -p outDir
touch outDir/someTarget
$ make
touch outDir/someTarget
$ make
touch outDir/someTarget
$ make
touch outDir/someTarget

This is most definitely not what you want. Whenever you touch the file, you also touch the directory. And since the file depends on the directory, the file consequently appears to be out of date, forcing it to be rebuilt.

However, you can easily break this loop by telling make to ignore the timestamp of the directory. This is done by declaring the directory as an order-only prerequsite:

# The pipe symbol tells make that the following prerequisites are order-only
#                           |
#                           v
outDir/someTarget: Makefile | outDir
    touch outDir/someTarget

outDir:
    mkdir -p outDir

This correctly yields:

$ make
mkdir -p outDir
touch outDir/someTarget
$ make
make: 'outDir/someTarget' is up to date.

TL;DR:

Write a rule to create the directory:

$(OUT_DIR):
    mkdir -p $(OUT_DIR)

And have the targets for the stuff inside depend on the directory order-only:

$(OUT_DIR)/someTarget: ... | $(OUT_DIR)

Solution 5:

All solutions including the accepted one have some issues as stated in their respective comments. The accepted answer by @jonathan-leffler is already quite good but does not take into effect that prerequisites are not necessarily to be built in order (during make -j for example). However simply moving the directories prerequisite from all to program provokes rebuilds on every run AFAICT. The following solution does not have that problem and AFAICS works as intended.

MKDIR_P := mkdir -p
OUT_DIR := build

.PHONY: directories all clean

all: $(OUT_DIR)/program

directories: $(OUT_DIR)

$(OUT_DIR):
    ${MKDIR_P} $(OUT_DIR)

$(OUT_DIR)/program: | directories
    touch $(OUT_DIR)/program

clean:
    rm -rf $(OUT_DIR)