如何爲gmake變量加上前綴

Question

我有一個包含另一個makefile的Makefile，比如CommonMakefile。有一個變量，我想用一個值作爲前綴（參見附加使用+=）保持值的其餘值不變。

V = value1 # set in CommonMakefile that is included 

V = value0 $(V) # I want to prefix value0 to V 

# rule defined in CommonMakefile that is included 
whatsV: 
    echo $V # first char is a <TAB> here 

我該怎麼做？

期待：

$ gmake whatsV 
value0 value1 

實際：

$ gmake whatsV 
Makefile:3: *** Recursive variable `V' references itself (eventually). Stop. 

PS：我而不是/拒收要換CommonMakefile。

Answer 1

這是行不通的：

V = value0 $(V) 

因爲這裏V是recursively expanded variable，它不能在其本身來定義。但是，將其更改爲簡單擴展型變量：

V := value0 $(V) # <-- Note the colon 

，並如預期它會奏效。