makefile - How to run Linux shell commands from GNU make file to setup preconditions for a build target -

my issue in make file want create directory object code before building , cannot find way whithout having impact output of make. also, want in 1 place , not each , every object file.

i have tried this:

build: setup exe.i686  setup:     mkdir -p obj  exe.i686: $(objs)     @echo 'building target: $@'     @echo 'invoking: gcc c++ linker'     ${gcc_location}/linux/i686/bin/i686-pc-linux-gnu-g++ $(objs) -o "exe.i686" -l...     @echo 'finished building target: $@'     @echo ' ' 

where objs object code. if don't run setup first , there no ./obj directory present build fail because of missing directory when trying build object code.

just clear, here example of how 1 object file built:

./obj/cell.o: ${cell_root}/main/cell/cell/src/cell.cc     @echo 'building file: $<'     @echo 'invoking: gcc c++ compiler'     $(gcc_c++_build) -mf"$(@:%.o=%.d)" -mt"$(@:%.o=%.d)" -o "$@" "$<"     @echo 'finished building: $<'     @echo ' ' 

i don't want build object code in same directory have make file.

now actual problem. when build tarket "build" first time works fine:

make build 

but if build again , there no updates in source code (object code up-to-date) behaves this:

[7:37] [user1] [/local/repo/user1/project_x/test/bin] $ make build mkdir -p obj [7:37] [user1] [/local/repo/user1/project_x/test/bin] $  

in situation have liked make return nothing-to-be-done string this:

[7:37] [user1] [/local/repo/user1/project_x/test/bin] $ make build make: nothing done `build'. [7:41] [user1] [/local/repo/user1/project_x/test/bin] $  

this have been case if didn't have depend on setup target (which added .phony). alternative each object code file? possible suppose wanted avoid if possible clutters make file quite bit. @ least in opinion.

thanks

your target setup executed because has no dependency.

you have 2 choices:

(1) make stamp or use other mechanism there actual dependency. directory can target may incur wrinkles: see http://www.gnu.org/software/make/manual/html_node/prerequisite-types.html example.

modified relevant extract linked article:

$(objs): | obj  obj:     mkdir $(objdir) 

(2) suppress output testing existence:

setup:     test -d obj || mkdir -p obj