如何在Makefile规则之外检查文件是否存在？

Question

这是一个伪代码：

if .gitignore exists 
    GITIGNORE_PATH := .gitignore
else
    GITIGNORE_PATH := ../.gitignore
fi

all: 
    do_build...

我试图搜索这个，但他们总是在规则中显示如何执行此操作，如：

$(UBIN)/%:
    @if [ -f '$@' ]; then \
        $(CC) $(CFLAGS) -o '$@' $(OBJS) -L $(ORAHOME) $(ORALIBS) \
        $(LNKPATH) $(DSTN_LIBS); \
        echo ""; \
    fi

1. Testing if a file exists in a make file
2. Testing if a file exists in makefile target, and quitting if not present
3. How to check if a file exists in a makefile

Answer 1

单行：

GITIGNORE_PATH := $(if $(wildcard .gitignore),,../).gitignore

Answer 2

这有效：

# Read it as `if .gitignore file exists`
ifneq (,$(wildcard .gitignore))
    GITIGNORE_PATH := .gitignore
else
    GITIGNORE_PATH := ../.gitignore
endif

all:
    echo GITIGNORE_PATH ${GITIGNORE_PATH}

从这个回答：https://stackoverflow.com/a/17712774/4934640