Minimal example:
$ cat makefile
$(shell rm -rf /tmp/blah)
$(shell mkdir -p /tmp/blah)
ASDF = $(info $1 $(wildcard /tmp/blah/*)
$(if ${BLAH},$(info before $(wildcard /tmp/blah/*)))
$(shell touch /tmp/blah/{a,b,c}.txt)
$(info after $(wildcard /tmp/blah/*.txt))
$ make --version
GNU Make 4.1
I usually instruct my co-workers to avoid making recipes along those lines
as I consider it to be a form of painting yourself into a corner, though
there are times where it's unavoidable.
In the build I maintain it used to have something like this:
blah.o : blah.xyz
> some command | sed 'some
