Change a make variable, and call another rule, fro

问题:

I have already seen How to manually call another target from a make target?, but my question is a bit different; consider this example (note, stackoverflow.com changes the tabs to spaces in display; but tabs are preserved in source, if you try to edit):

TEXENGINE=pdflatex

pdflatex:
    echo the engine is $(TEXENGINE)

lualatex:
    TEXENGINE=lualatex
    echo Here I want to call the pdflatex rule, to check $(TEXENGINE) there!

Here, if I run the default target (pdflatex), I get the expected output:

$ make pdflatex 
echo the engine is pdflatex
the engine is pdflatex

But, with the target lualatex, I want to:

• change the make variable TEXENGINE to lualatex, and then
• call the same code as in pdflatex (which uses it).

How could I do that?

Clearly, in my lualatex rule I don't even manage to change the TEXENGINE variable, because I get this when I try it:

$ make lualatex 
TEXENGINE=lualatex
echo Here I want to call the pdflatex rule, to check pdflatex there!
Here I want to call the pdflatex rule, to check pdflatex there!

... so I would really like to know if something like this is possible in Makefiles.

回答1:

Use a target-specific variable

There is one more special feature of target-specific variables: when you define a target-specific variable that variable value is also in effect for all prerequisites of this target, and all their prerequisites, etc. (unless those prerequisites override that variable with their own target-specific variable value).

TEXENGINE=pdflatex

pdflatex:
    echo the engine is $(TEXENGINE)

lualatex: TEXENGINE=lualatex
lualatex: pdflatex
    echo Here I want to call the pdflatex rule, to check $(TEXENGINE) there!

The output is:

$ make pdflatex
echo the engine is pdflatex
the engine is pdflatex
$ make lualatex
echo the engine is lualatex
the engine is lualatex
echo Here I want to call the pdflatex rule, to check lualatex there!
Here I want to call the pdflatex rule, to check lualatex there!

回答2:

Well, I managed to get to a sort of a workaround, but I don't exactly understand it much - so a more learned answer will be appreciated. For me here, these links helped:

• Set a variable from within a rule
• make : rule call rule
• Passing additional variables from command line to make

So here is the example modified - apparently, to call a rule from a rule afterwards (not as a prerequisite, rather, as a postrequisite), I can only recursively call make, while having the new variable value specified on its command line:

TEXENGINE=pdflatex

pdflatex:
    echo the engine is $(TEXENGINE)

lualatex:
    echo Here I want to call the pdflatex rule, to check $(TEXENGINE) there!
    $(MAKE) TEXENGINE=lualatex pdflatex

The output is somewhat more verbose than I'd like it, but it works:

$ make lualatex 
echo Here I want to call the pdflatex rule, to check pdflatex there!
Here I want to call the pdflatex rule, to check pdflatex there!
make TEXENGINE=lualatex pdflatex
make[1]: Entering directory `/tmp'
echo the engine is lualatex
the engine is lualatex
make[1]: Leaving directory `/tmp'

... which is what I wanted purely command-line interaction-wise, but I know is not the best solution (see @JonathanWakely's comment below)