Is it possible to create a multi-line string variable in a Makefile

Question

I want to create a makefile variable that is a multi-line string (e.g. the body of an email release announcement). something like

ANNOUNCE_BODY=\"
Version $         


        

Answer 1

Use string substitution:

VERSION := 1.1.1
PACKAGE_NAME := Foo Bar
DOWNLOAD_URL := https://go.get/some/thing.tar.gz

ANNOUNCE_BODY := Version $(VERSION) of $(PACKAGE_NAME) has been released. \
    | \
    | It can be downloaded from $(DOWNLOAD_URL) \
    | \
    | etc, etc

Then in your recipe, put

    @echo $(subst | ,$$'\n',$(ANNOUNCE_BODY))

This works because Make is substituting all occurrences of |  (note the space) and swapping it with a newline character ($$'\n'). You can think of the equivalent shell-script invocations as being something like this:

Before:

$ echo "Version 1.1.1 of Foo Bar has been released. | | It can be downloaded from https://go.get/some/thing.tar.gz | | etc, etc"

After:

$ echo "Version 1.1.1 of Foo Bar has been released.
>
> It can be downloaded from https://go.get/some/thing.tar.gz
> 
> etc, etc"

I'm not sure if $'\n' is available on non-POSIX systems, but if you can gain access to a single newline character (even by reading a string from an external file), the underlying principle is the same.

If you have many messages like this, you can reduce noise by using a macro:

print = $(subst | ,$$'\n',$(1))

Where you'd invoke it like this:

@$(call print,$(ANNOUNCE_BODY))

Hope this helps somebody. =)