Makefile stdout redirection

gistfile1.txt

# In relation to the discussion taking place at
# http://stackoverflow.com/questions/44097324/timing-of-makefile-include-statements-for-auto-generated-files/44103228

# OK, since I can't use PHONY to force the rebuild of piped.mk
# without losing the re-inclusion itself, I will just delete the file
# directly after using it (and thus force it to be re-created each
# time, as intended, without using .PHONY).

$ cat Makefile
all:    piped.mk
ifeq ($(PIPED),1)
        @echo Output of make is piped because PIPED is ${PIPED}
else
        @echo Output of make is NOT piped because PIPED is ${PIPED}
endif
        @rm -f piped.mk

piped.mk:
        [ -t 1 ] && PIPED=0 || PIPED=1 ; echo "PIPED=$${PIPED}" > piped.mk

-include piped.mk

$ # And this seems to work...

$ make
[ -t 1 ] && PIPED=0 || PIPED=1 ; echo "PIPED=${PIPED}" > piped.mk
Output of make is NOT piped becaused PIPED is 0

$ # Until I saw this amazing result:
$ # The action reports that indeed PIPED is set to 1...
$ # ...but the action that is executed is wrong! 
$ # It's the one that is surrounded with ifeq NOT set to 1!

$ make | more
[ -t 1 ] && PIPED=0 || PIPED=1 ; echo "PIPED=${PIPED}" > piped.mk
Output of make is NOT piped becaused PIPED is 1

$ # Looks like make has "cached" the decision somehow?