Why does AWK not work correctly in a makefile? [du

问题:

This question already has answers here:

Escaping in makefile (2 answers)

Closed 4 years ago.

NOTICE: Escaping not problem, sample from shell is only sample, in Makefile $$.

GNU Makefile man says why it's doesn't work:

Note that expansion using ‘%’ in pattern rules occurs after any variable or function expansions, which take place when the makefile is read.

--Orig. question:
In pure shell, the next script works correctly:

echo "test2.cpp src2/test2.cpp src1/test1.cpp src1/test.cpp" | \
awk 'BEGIN{RS=" "}{if(NR == 1) f=$0; else if(match($0, f)) print $0;}'

Filter is first: test1.cpp
And it returns: src1/test1.cpp

But in Makefile it does not work correctly (error compared to awk):

OBJ_DIR:=obj    
SOURCES:=$(wildcard */*.cpp *.cpp)
OBJECTS_LOCAL:= $(addprefix $(OBJ_DIR)/, $(notdir $(SOURCES:.cpp=.o)))
LOCAL_PATHS_HEADERS:=$(sort $(dir $(wildcard *.h */*.h)))

TARGET:=libcommon.a

all:$(TARGET)

$(TARGET): $(OBJECTS_LOCAL)
        ar -rcs $@ $^

$(OBJECTS_LOCAL): $(OBJ_DIR)/%.o : $(shell echo %.cpp $(SOURCES) | awk 'BEGIN{RS=" "}{if(NR == 1) f=$$0; else if($$0 ~ f) print $$0;}' )
        @mkdir -p $(OBJ_DIR)
        @$(CC) -c $< -o $@ $(addprefix -I,$(LOCAL_PATHS_HEADERS))

So I take simple in Makefile and check value f, and found some strange length of f

...%.cpp $(SOURCES)  | awk '{print ("file1.cpp" ~ $$1)"."$$1"."length($$1)}' )

awk return fail in compared; print returns "0.file1.cpp.5" to fail with length, because it has forgotten .cppvalue of %, info bellow. I attempted to correct it:

...%.cpp $(SOURCES) | awk 'BEGIN{RS=" "}{if(NR == 1) f=$$0".cpp"; print ("file1.cpp.cpp" ~ f)"."("file1.cpp" ~ f)"."f"."length(f)}' )

but awk return fail in all compared; print returns "0.0.file1.cpp.cpp.9".

I check awk in manual mode, like this:

...%.cpp $(SOURCES) : $(shell echo %.cpp $(SOURCES) | awk '{print "src/"$$1}' )

It works fine, but it isn't variant, because it will kill automatic mode.

--Add
Information about lost length from parameter % to AWK

...%.cppppppp $(SOURCES) | awk '{print ("file1.cpp" ~ $$1)"."$$1"."length($$1)}' )

print returns "0.test2.cppppppp.10"

--Upd, some problem
Above, I was printing return value from $<
But file redirect show that value % does not work in prerequisites(file redirect: "0.%.cpp.5").

Can I use any automatic variable with value in prerequisites?

回答1:

Almost invariably, when a question is asked about awk in a Makefile, the solution is to properly escape the $ symbols. It's not entirely clear what your question is, but there are some substantial misunderstandings that need to be resolved. In particular, the following "works", but hardly for the reasons you think:

echo "test2.cpp src2/test2.cpp src1/test1.cpp src1/test.cpp" | \
awk 'BEGIN{RS=" "}{if(NR == 1) f=$$0; else if(match($$0, f)) print $$0;}'

You almost certainly do not want $$ in any of the cases they appear here. awk is generally looking for single dollar signs, and when they appear in a Makefile, they are doubled because Make parses the $$ and invoked awk with a single $. In the quoted sample, $$0 on the first record is equivalent to $test2.cpp, but the variable test2.cpp is uninitialized and so has value 0, so on the first pass f is set to the value of $0 (the string "test2.cpp").

In short, if you are invoking awk from the shell, use single $. In the Makefile, use $$ and awk will only see $.