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001-make.7 2.4KB

MAKE(7)            FreeBSD Miscellaneous Information Manual            MAKE(7)

     Using Make – writing less Makefile

     Let's talk about make(1).  I think an important thing to know about
     make(1) is that you don't need to write a Makefile to use it.  There are
     default rules for C, C++ and probably Fortran.  To build foo from foo.c,
     just run:

           make foo

     The default rule for C files uses the CFLAGS variable, so you can set
     that in the environment to pass flags to the C compiler:

           CFLAGS=-Wall make foo

     It also uses LDLIBS for linking, so you can add libraries with:

           LDLIBS=-lcurses make foo

     Obviously writing this every time would become tedious, so it might be
     time to write a Makefile.  But it really doesn't need much:

           CFLAGS += -Wall -Wextra
           LDLIBS = -lcurses


     Assigning CFLAGS with ‘+=’ preserves the system default or anything
     passed in the environment.  Declaring foo as the first rule makes it the
     default when ‘make’ is run without a target.  Note that the rule doesn't
     need a definition; the default will still be used.

     If foo is built from serveral source files, unfortunately a rule
     definition is required:

           OBJS = foo.o bar.o baz.o

           foo: $(OBJS)
                   $(CC) $(LDFLAGS) $(OBJS) $(LDLIBS) -o $@

     This rule uses LDFLAGS for passing linker flags, which is what the
     default rule does.  The ‘$@’ variable here expands to ‘foo’, so this rule
     can be copied easily for other binary targets.

     If some sources depend on a header file, they can be automatically
     rebuilt when the header changes by declaring a dependency rule:

           foo.o bar.o: foo.h

     Note that several files can appear either side of the ‘:’.

     Lastly, it's always nice to add a clean target:

                   rm -f $(OBJS) foo

     I hope this helps getting started with make(1) without writing too much

     The example Makefile in its entirety:

           CFLAGS += -Wall -Wextra
           LDLIBS = -lcurses
           OBJS = foo.o bar.o baz.o

           foo: $(OBJS)
                   $(CC) $(LDFLAGS) $(OBJS) $(LDLIBS) -o $@

           foo.o bar.o: foo.h

                   rm -f $(OBJS) foo

     June <>

     This document is produced from mdoc(7) source available from Code Toilet:

Causal Agency                 September 17, 2018                 Causal Agency