Re: define variable in rule

[John Graham-Cumming]

On Wed, 2005-06-08 at 23:54 +0800, address@hidden wrote:
> Can the variable be defined in rule ? Like this:
> 
> 1 target :  $(OBJ_FILE)
> 2     TMP_LIB := $(shell cat $(OBJ_FILES))
> 3     $(LD) $(OPT_LD_STD) $(LDFLAGS) -o $@   $(TMP_LIB)
> $(EXTERNAL_LIBS) $(SYSTEM_LIBS) 
> 
> The OBJ_FILE is a text file with .o file list, and I want to translate
> it to .o list used as the argument of link, so the variable TMP_LIB is
> defined. 
> 
> But when do Make, syntax error found in line 3. So I doubt the variable
> can not be defined within a fule.

Not like that it can't, but you could do this:

target: TMP_LIB := $(shell cat $(OBJ_FILES))
target:
        $(LD) $(OPT_LD_STD) $(LDFLAGS) -o $@   $(TMP_LIB) \
        $(EXTERNAL_LIBS) $(SYSTEM_LIBS) 

(This has the side effect of defining TMP_LIB for any of target's
prerequisites.)

OTOH I don't see any real need for that TMP_LIB variable here (unless
it's being referenced in one of the other variables on the $(LD)
command-line) and so you could simplify your life greatly and just do:

target:
        $(LD) $(OPT_LD_STD) $(LDFLAGS) -o $@ $(shell cat $(OBJ_FILES)) \
        $(EXTERNAL_LIBS) $(SYSTEM_LIBS) 

If you do that then you don't even need to bother with the $(shell)
because you could just use backticks and do

target:
        $(LD) $(OPT_LD_STD) $(LDFLAGS) -o $@ `cat $(OBJ_FILES)` \
        $(EXTERNAL_LIBS) $(SYSTEM_LIBS) 

John.
-- 
John Graham-Cumming

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