all: temp.txt

temp.txt: target
    @echo "temp.txt has been created."

target: dep3
    echo $(string)                       >> temp.txt
    @echo "That's all I can tell you right now." >> temp.txt

# and let's mix 'em up a bit...

dep1:
    @echo "My name is 'echo'" >> temp.txt

dep3:dep2
    @echo "if you don't mind my asking."  >> temp.txt
    @echo                                 >> temp.txt

dep2:dep1
    @printf "What are you doing? "  >> temp.txt

# this tag/target will run when we type 'make clean'
clean:
    @rm temp.txt

string = "I'm doing something!"

all: temp.txt
    @echo "temp.txt has been created."

temp.txt:
    @echo "My name is 'echo'" >> temp.txt
    @printf "What are you doing? "  >> temp.txt
    @echo "if you don't mind my asking."  >> temp.txt
    @echo                                 >> temp.txt
    @echo $(string)                       >> temp.txt
    @echo "That's all I can tell you right now." >> temp.txt

clean:
    @rm temp.txt

Why didn't the make file keep writing strings into the file this time?
  [Once the file existed there was nothing more that needed to be done for the 'rule' governing temp.txt.]

string = "I'm doing something!"

all: temp.txt

temp.txt:
    @echo "My name is 'echo'" >> temp.txt
    @printf "What are you doing? "  >> temp.txt
    @echo "if you don't mind my asking."  >> temp.txt
    @echo                                 >> temp.txt
    @echo $(string)                       >> temp.txt
    @echo "That's all I can tell you right now." >> temp.txt

clean:
    @rm temp.txt

make    #fine, temp.txt created
make    #Error, or warning:
make: Nothing to be done for 'all'.