What about empty for loops in Makefiles?

What about empty for loops in Makefiles? 


It's fairly common to see constructs like this in automatically-generated

Makefiles:



SUBDIRS = @SUBDIRS@



	...



subdirs-clean:

	for d in ${SUBDIRS}; do \

		( cd $$d && ${MAKE} ${MFLAGS} clean ) \

	done



When SUBDIRS is empty, this results in a command like this being passed to

bash:



	for d in ; do

		( cd $d && ${MAKE} ${MFLAGS} clean )

	done



In versions of bash before bash-2.05a, this was a syntax error.  If the

reserved word `in' was present, a word must follow it before the semicolon

or newline.  The language in the manual page referring to the list of words

being empty referred to the list after it is expanded.  These versions of

bash required that there be at least one word following the `in' when the

construct was parsed.



The idiomatic Makefile solution is something like:



SUBDIRS = @SUBDIRS@



subdirs-clean:

	subdirs=$SUBDIRS ; for d in $$subdirs; do \

		( cd $$d && ${MAKE} ${MFLAGS} clean ) \

	done



The latest drafts of the updated POSIX standard have changed this:  the

word list is no longer required.  Bash versions 2.05a and later accept

the new syntax.

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