how to prevent “directory already exists error” in a makefile when using mkdir

Question

I need to generate a directory in my makefile and I would like to not get the \"directory already exists error\" over and over even though I can easily ignore it.

I

Answer 1

If having the directory already exist is not a problem for you, you could just redirect stderr for that command, getting rid of the error message:

-mkdir $(OBJDIR) 2>/dev/null

Answer 2

Inside your makefile:

target:
    if test -d dir; then echo "hello world!"; else mkdir dir; fi

Answer 3

Here is a trick I use with GNU make for creating compiler-output directories. First define this rule:

  %/.d:
          mkdir -p $(@D)
          touch $@

Then make all files that go into the directory dependent on the .d file in that directory:

 obj/%.o: %.c obj/.d
    $(CC) $(CFLAGS) -c -o $@ $<

Note use of $< instead of $^.

Finally prevent the .d files from being removed automatically:

 .PRECIOUS: %/.d

Skipping the .d file, and depending directly on the directory, will not work, as the directory modification time is updated every time a file is written in that directory, which would force rebuild at every invocation of make.

Answer 4

If you explicitly ignore the return code and dump the error stream then your make will ignore the error if it occurs:

mkdir 2>/dev/null || true

This should not cause a race hazard in a parallel make - but I haven't tested it to be sure.

Answer 5

$(OBJDIR):
    mkdir $@

Which also works for multiple directories, e.g..

OBJDIRS := $(sort $(dir $(OBJECTS)))

$(OBJDIRS):
    mkdir $@

Adding $(OBJDIR) as the first target works well.

Answer 6

You can use the test command:

test -d $(OBJDIR) || mkdir $(OBJDIR)