What does this part mean in Makefile?

Question

What does this part mean in Makefile?

    1 CC=gcc
    2 CXX=g++
    3 RM=rm
    4 PROTOC=protoc
    5 ODB=odb

Sorry, I'm a beginner

Answer 1

They're setting up substitutions so that you can later have a command like:

$(RM) x.o

and it will magically become, when executing:

rm x.o

It allows you to (for example) change it later to be rm -rf and you only change it in one place.

Typically you'll see things like:

$(CC) $(CFLAGS) -c -o object_file.o source_file.c

If you compile a compile of hundred C source files, and you suddenly discover they all needed a new -I directive, you probably want that in one single place :-)

See the "variables" section of the GNU Make manual for (much) more detail, if you wish.

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We also use it in our shop for making our builds somewhat more "readable", things like:

PERM_FOR_EXE=chmod 700
PERM_FOR_CFG=chmod 400
PERM_FOR_DATA=chmod 500

RM=rm
FORCE_RM=rm -f
RM_DIR_AND_BELOW=rm -rf

PROTO_FOR_PY=protoc --output=betterproto
PROTO_FOR_CPP=protoc --output=cpp
PROTO_FOR_BCPL=echo FAT CHANCE