don't understand $$ in this Makefile

[IAMTubby]

Hello,
I have a small question regarding a Makefile. I was able to understand most of the important aspects, but still haven't been able to figure out the meaning of -o $$a $$a.o below.



SRCS = sourceOne.c sourceTwo.c
SOBJ = $(patsubst %.c,%.o,$(SRCS)) #I understand this will translate to sourceOne.o and sourceTwo.o
APP = $(patsubst %.c,%,$(SRCS)) #I understand this will translate to sourceOne and sourceTwo, which will be the names of the eventual executables


$(APP): $(SOBJ) $(LIBSHARED)
@set -e ; \
for a in $(APP) ; do \
$(CC) $(CFLAGS) $(CPPFLAGS) -o $$a $$a.o $(PRJLIB) $(LINKMAP) $(DEPLIBS) ; \
done
#Again, here I understand that basically it generates executables called sourceOne and sourceTwo from sourceOne.o and sourceTwo.o, but what I don't understand is the $$ part.

What exactly does -o $$a $$a.o mean ?


I read that "If you need a literal dollar sign, put in a double dollar sign ($$)". But hmm, still can't relate to this.

Please advise.
Thanks.

[MG&TL]

for a in $(APP) ; do \
$(CC) $(CFLAGS) $(CPPFLAGS) -o $$a $$a.o $(PRJLIB) $(LINKMAP) $(DEPLIBS) ; \
done

What exactly does -o $$a $$a.o mean ?


I read that "If you need a literal dollar sign, put in a double dollar sign ($$)". But hmm, still can't relate to this.


You probably know that make uses a '$' character to reference variables. Unfortunately, so do most system shells. In the for-loop I hightlighted, it builds a binary for every entry in the $(APP) variable.
To do this, it uses a shell variable, 'a' in order to keep track. However, you can't just use '$a' to use the variable, as make would try and find a make variable called 'a', when in fact it is a shell variable. So in order to get '$a' passed to the shell, rather than a blank, a double-dollar '$$a' is used. Make evaluates this as '$a', so everyone is happy.

[IAMTubby]

So in order to get '$a' passed to the shell, rather than a blank, a double-dollar '$$a' is used. Make evaluates this as '$a', so everyone is happy.
Thanks a lot for the reply MG&TL. Your explanation is very clear :)