Joining elements of a list in GNU Make

Question

In my makefile I have a variable with a list of directories, like this:

DIRS = /usr /usr/share/ /lib 

Now, I need to create PATH variable from it, which is basically the same, but uses semicolon as a separator:

PATH = /usr:/usr/share/:/lib 

How do I do that? I mean, how do I join elements of DIRS list with semicolons, instead of spaces?

Answer 1

You can use the $(subst) command, combined with a little trick to get a variable that has a value of a single space:

p = /usr /usr/share /lib noop= space = $(noop) $(noop)  all:         @echo $(subst $(space),:,$(p)) 

Answer 2

Cleanest Form (that I can find):

classpathify = $(subst $(eval) ,:,$(wildcard $1)) cp = a b c d/*.jar  target:     echo $(call classpathify,$(cp)) # prints a:b:c:d/1.jar:d/2.jar 

Notes:

• Turning it into a pseudo-function makes the intention clearer than doing a bunch of arcane string manipulation inline.
• I included the $(wildcard) function because you almost always use these two together when specifying a classpath
• Make sure not to put any extra spaces in after the commas or you will get something like "::a:b:c:d:e".