# simple Makefile that shows which files in 
# directory tree have changed since they've 
# last been displayed
# call: make -f Makefile-delta <rule>

# 1st rule: target 'changes' depends on all the files 
# that contain a dot in the current directory
# 	
# 1. command: display all the prerequisites that changed since 
#    last display, internal variable $? contains this list, 
#    display each on separate line using BASH-shell for-loop
# 2. command: touch (i.e. update) empty file 'changes', so that make
#    knows about the last time this rule has been carried 
#    out
# the '@' says that the command should not be echoed in the shell

changes: *.*
	@for i in $?; do echo $$i; done
	@touch changes


# 2nd rule: remove file 'changes', Implicit understanding of this rule:
# Reset everything to the state before make was executed the first time
# no '@' - see the difference
clean:
	rm changes
