Makefile string variable

Lazy Set

VARIABLE = value

Normal setting of a variable, but any other variables mentioned with the value field are recursively expanded with their value at the point at which the variable is used, not the one it had when it was declared

Immediate Set

VARIABLE := value

Setting of a variable with simple expansion of the values inside - values within it are expanded at declaration time.

Lazy Set If Absent

VARIABLE ?= value

Setting of a variable only if it doesn't have a value. value is always evaluated when VARIABLE is accessed. It is equivalent to

ifeq ($(origin VARIABLE), undefined)
  VARIABLE = value
endif

See the documentation for more details.

Append

VARIABLE += value

Appending the supplied value to the existing value (or setting to that value if the variable didn't exist)

Yes, you can use the define keyword to declare a multi-line variable, like this:

define ANNOUNCE_BODY
Version $(VERSION) of $(PACKAGE_NAME) has been released.

It can be downloaded from $(DOWNLOAD_URL).

etc, etc.
endef

The tricky part is getting your multi-line variable back out of the makefile. If you just do the obvious thing of using "echo $(ANNOUNCE_BODY)", you'll see the result that others have posted here -- the shell tries to handle the second and subsequent lines of the variable as commands themselves.

However, you can export the variable value as-is to the shell as an environment variable, and then reference it from the shell as an environment variable (NOT a make variable). For example:

export ANNOUNCE_BODY
all:
    @echo "$$ANNOUNCE_BODY"

Note the use of $$ANNOUNCE_BODY, indicating a shell environment variable reference, rather than $(ANNOUNCE_BODY), which would be a regular make variable reference. Also be sure to use quotes around your variable reference, to make sure that the newlines aren't interpreted by the shell itself.

Of course, this particular trick may be platform and shell sensitive. I tested it on Ubuntu Linux with GNU bash 3.2.13; YMMV.