1.1.5 Debugging Make Variables

We’ve seen we can get information about GNU Remake’s targets. We can also get information about GNU Remake’s variables. That is done with the print command. (See Print.)

  remake<4> print MAKE
  (origin default) MAKE = $(MAKE_COMMAND)

The (origin default) means this is a built-in definition. There is another print which does full expansion of the variables. So if I run x (expand) instead I get:

  remake<5> expand MAKE
  (origin default) MAKE := /tmp/remake/src/./make

Note that in printing expanded values we use := while non-expanded values we use = This output matches the semantics of these assignment operators.

In fact, expand doesn’t need a variable name, it will work with a string. So I could type x This is $(MAKE) or x $(bin_PROGRAMS) $(noinst_PROGRAMS). For the latter, I get:

  remake<6> x $(bin_PROGRAMS) $(noinst_PROGRAMS)
  make remake

No location identification is given here since what I put in isn’t a variable.

But I can also change values too using either set or setq. (See set variable and setq.) Let’s see the difference between the two.

  remake<7> set MAKE $(MAKE_COMMAND)
  Variable MAKE now has value '/tmp/remake/src/./make'
  remake<8> setq MAKE $(MAKE_COMMAND)
  Variable MAKE now has value '$(MAKE_COMMAND)'

So with set, the value in the expression $(MAKE_COMMAND) is expanded before the variable definition is assigned. With setq the internal variables are kept unexpanded. Which you use or want is up to you.

Note the irregular syntax of set and setq. Don’t put an equal sign (=) between the variable and the expression. That is, set MAKE = $(MAKE_COMMAND) gives:

  Variable MAKE now has value '= /tmp/remake/src/./make'

which is probably not what you want. One may optionally put in the the word "variable" when using set, one must not supply it with setq. Down the line, someone (maybe you!) will probably put in a command parser.