Makefile rule to create several files, that each depend on different targets -

i trying write makefile file aggregation. following: have data several days ate breakfast lunch , dinner. files named like:

monday_breakfast.meal monday_lunch.meal monday_dinner.meal tuesday_breakfast.meal ... 

or if working numbers makes simpler:

00_00.meal 00_11.meal 00_22.meal 11_00.meal ... 

the objective aggregate 3 files each day single file each day, days. possible write rule this? tricky part don't know how many days worth of files there when run make, want generic.

i thinking like:

days= $(sort $(patsubst _*,,*.meal)) day: %.day: $(days): 

but stuck. using sort of exercise learn more makefiles---it seemed easy @ first can not think through.

make's ability manipulate strings not 1 might desire. here goes.

suppose have:

monday_breakfast.meal monday_lunch.meal monday_dinner.meal tuesday_breakfast.meal tuesday_lunch.meal tuesday_dinner.meal wednesday_breakfast.meal 

first, names of meal files:

meals := $(wildcard *.meal) 

then somehow want reduce list names of days. if take one filename:

firstmeal := monday_breakfast.meal 

we can split turning underscore space, grab first fragment:

frags := $(subst _, , $(firstmeal))  #  monday breakfast.meal firstday := $(word 1, $(frags))      #  monday 

so can meals:

days := $(sort $(foreach x,$(meals), $(word 1,$(subst _, ,$(x))))) 

(the sort removes repetitions in list.)

now have days ("monday tuesday wednesday"), want write rule or rules aggregation. how easy depends on kind of aggregation mean, tool you'll use, , whether accepts wildcards.