Test whether a directory exists inside a makefile

In his answer @Grundlefleck explains how to check whether a directory exists or not. I tried some to use this inside a makefile as follow:

foo.bak: foo.bar
    echo "foo"
    if [ -d "~/Dropbox" ]; then
        echo "Dir exists"
    fi

Running make foo.bak (given that foo.bar exists) yields the following error:

echo "foo"
foo
if [ -d "~/Dropbox" ]; then
/bin/sh: -c: line 1: syntax error: unexpected end of file
make: *** [foo.bak] Error 2

The workaround I made was to have a standalone bash script where the test is implemented and I called the script from the makefile . This, however, sounds very cumbersome. Is there a nicer way to check whether a directory exists from within a makefile ?

---

Make commands, if a shell command, must be in one line, or be on multiple lines using a backslash for line extension. So, this approach will work:

foo.bak: foo.bar
    echo "foo"
    if [ -d "~/Dropbox" ]; then echo "Dir exists"; fi

Or

foo.bak: foo.bar
    echo "foo"
    if [ -d "~/Dropbox" ]; then 
        echo "Dir exists"; 
    fi

---

这种方法具有最小的回声功能：

.PHONY: all
all:
ifneq ($(wildcard ~/Dropbox/.*),)
        @echo "Found ~/Dropbox."
else
        @echo "Did not find ~/Dropbox."
endif

---

Act upon the absence of a directory

If you only need to know if a directory does not exist and want to act upon that by for example creating it, you can use ordinary Makefile targets:

directory = ~/Dropbox

all: | $(directory)
    @echo "Continuation regardless of existence of ~/Dropbox"

$(directory):
    @echo "Folder $(directory) does not exist"
    mkdir -p $@

.PHONY: all

Remarks:

The | indicates that make shouldn't care about the timestamp (it's an order-only-prerequisite).

Rather than write mkdir -p $@ , you can write false to exit, or solve your case differently.

If you also need to run a particular series of instructions upon the existence of a directory, you cannot use the above. In other words, it is equivalent to:

if [ ! -d "~/Dropbox" ]; then
    echo "The ~/Dropbox folder does not exist"
fi

There is no else statement.

Act upon the presence of a directory

If you want the opposite if-statement this is also possible:

directory = $(wildcard ~/Dropbox)

all: | $(directory)
    @echo "Continuation regardless of existence of ~/Dropbox"

$(directory):
    @echo "Folder $(directory) exists"

.PHONY: all $(directory)

This is equivalent to:

if [ -d "~/Dropbox" ]; then
    echo "The ~/Dropbox folder does exist"
fi

Again, there is no else statement.

Act upon both the presence and the absence of a directory

This becomes a bit more cumbersome, but in the end gives you nice targets for both cases:

directory = ~/Dropbox
dir_target = $(directory)-$(wildcard $(directory))
dir_present = $(directory)-$(directory)
dir_absent = $(directory)-

all: | $(dir_target)
    @echo "Continuation regardless of existence of ~/Dropbox"

$(dir_present):
    @echo "Folder $(directory) exists"

$(dir_absent):
    @echo "Folder $(directory) does not exist"

.PHONY: all

This is equivalent to:

if [ -d "~/Dropbox" ]; then
    echo "The ~/Dropbox folder does exist"
else
    echo "The ~/Dropbox folder does not exist"
fi

Naturally, the wildcard expansion might be slower than an if-else-statement. However, the third case is probably quite rare and is just added for completeness.

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