a few basic doubts

[Payal]

Hi,
Please excuse for these basic doubts. 

1) $ cat Makefile 
a.tar: data
        tar -cvf $@ $^

d.tar: sharu
        @echo hi

$ make
make: `a.tar' is up to date.
$ make d.tar 
hi
$ make d.tar 
hi

My doubt it why did it print "hi" the last time too. I expected,
make: `d.tar' is up to date.

2) What is the difference in wildcard "%" & "*"?


3) How do I define a variable whose value are files abc, "cde xyz" & lmn?

4) How do I define a variable-name with a space in between like 'my
tar'?  (I understand tht it is a bad habit to do so.

With warm regards,
-Payal
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