How do I properly comment a variable definition in GNU Make?

问题

So I want to comment variable definitions in Makefile in-line. The problem is that Make doesn't strip white spaces between the definition and its comment. Here is an example of what I mean:

OPTS += -DBLA       # Does bla
OPTS += -DBLUBB     # Does blubb
OPTS += -DEND

.PHONY test
test:
    @echo $(OPTS)

The output of this is

-DBLA       -DBLUBB     -DEND

with annoying extra white spaces between the options. What I want is this:

-DBLA -DBLUBB -DEND

How do I get around this Problem? The Make string function @echo $(strip $(OPTS)) would only strip whitespaces after -DEND or before -DBLA, not inbetween. My dirty hack so far is @echo $(shell $(OPTS)), which strips the unwanted spaces but uses a shell call to do so, that probably will introduce other problems, i.e. unwanted shell injection via the $(OPTS) variable. Is there a better way to do it? Simple @echo ($subst ...) doesn't work on mixed whitespaces unless one replaces all of them an then reinserts at the -.

回答1:

OPTS += -DBLA#     Does bla
OPTS += -DBLUBB#   Does blubb
OPTS += -DEND

Canonical make? Not a fan of alignment though.

OPTS += -DBLA# Does bla
OPTS += -DBLUBB# Does blubb
OPTS += -DEND

Looks better to my eyes.

Assuming it makes your eyes bleed, $(strip) does in fact do what you want.

OPTS := $(strip ${OPTS})

A simple $(error [${OPTS}]) will prove it.

回答2:

Of course, 'zZz' could be replaced with any "impossible" match...

来源：https://stackoverflow.com/questions/31586713/how-do-i-properly-comment-a-variable-definition-in-gnu-make