Question

我想用libswscale.so.2替换字符串libswscale.so（分别称为$(SLIBNAME_WITH_MAJOR)和$(SLIBNAME)的变量）。这是我在Makefile中尝试的：

$(SUBDIR)$(SLIBNAME_WITH_MAJOR): $(OBJS) $(SUBDIR)lib$(NAME).ver
    [...]
    @echo SHFLAGS=$(SHFLAGS)
    @echo SLIBNAME_WITH_MAJOR=$(SLIBNAME_WITH_MAJOR)
    @echo SLIBNAME=$(SLIBNAME)
    @echo A $(patsubst $(SLIBNAME_WITH_MAJOR),$(SLIBNAME),$(SHFLAGS))
    @echo B $(SHFLAGS:$(SLIBNAME_WITH_MAJOR)=$(SLIBNAME))
    @echo C $($(SHFLAGS):$(SLIBNAME_WITH_MAJOR)=$(SLIBNAME))
    @echo D $(SHFLAGS:$(SLIBNAME_WITH_MAJOR)=$(SLIBNAME))
    @echo E $(subst $(SLIBNAME_WITH_MAJOR),$(SLIBNAME),$(SHFLAGS))
    @echo F $(subst l,L,$(SHFLAGS))

输出

SHFLAGS=-shared -Wl,-soname,libswscale.so.2 -Wl,-Bsymbolic -Wl,--version-script,libswscale/libswscale.ver
SLIBNAME_WITH_MAJOR=libswscale.so.2
SLIBNAME=libswscale.so
A -shared -Wl,-soname,libswscale.so.2 -Wl,-Bsymbolic -Wl,--version-script,libswscale/libswscale.ver
B -shared -Wl,-soname,libswscale.so.2 -Wl,-Bsymbolic -Wl,--version-script,libswscale/libswscale.ver
C
D -shared -Wl,-soname,libswscale.so.2 -Wl,-Bsymbolic -Wl,--version-script,libswscale/libswscale.ver
E -shared -Wl,-soname,libswscale.so.2 -Wl,-Bsymbolic -Wl,--version-script,libswscale/libswscale.ver
F -shared -WL,-soname,libswscale.so.2 -WL,-BsymboLic -WL,--version-script,LibswscaLe/LibswscaLe.ver

最后一个（F）特别荒谬。这有什么不对？是因为$(SHFLAGS)也是由变量组成的吗？

Answer 1

找到它：$(SHFLAGS)被定义为

SHFLAGS=-shared -Wl,-soname,$$(@F) blablafoo

并在其上使用任何替换在$$(@F)实际评估之前无效（在我的情况下为libswscale.so.2）。

我通过替换变量引用来解决它：

@echo $(subst $$(@F),$(SLIBNAME),$(SHFLAGS))

分配的小提示：VAR = $(OTHERVAR)在使用时进行评估，立即评估VAR := $(OTHERVAR)。

Makefile中的简单字符串替换

1 个答案: