Greetings.

I have a Makefile which needs to construct a command line for the program
curl.  Curl takes its filename arguments as a strictly comma-delimited list
(i.e., no spaces unless they're part of the filename).  In my case I need
to convert the contents of the $? variable from a space-delimited list into
such a comma-delimited list.  I can't figure out how to do this using
Make-internal string commands, though.

The $(subst) command is the obvious solution, but I can't figure out how to
escape the space and the comma so that they're recognized by Make.  That
is, $(subst \ ,\,,$?) (and variations thereof I've tried) don't work.

$(foreach f,$?,$f,) is not an option as it inserts extraneous space which
confuses curl.

Any solutions besides resorting to $(shell tr)?

Regards,
Tristan

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