Variables in GNU Make recipes, is that possible?

Thanks to https://stackoverflow.com/questions/6519234/cant-assign-variable-inside-recipe

This is the solution to change a variable in a recipe:

recipe: 
        $(eval variablename=whatever)

This doesn't work because the make tool starts a new shell process for each recipe line. And shell variables – even 'exported' environment variables – cannot possibly propagate "upwards"; they're gone as soon as the shell process exits.

• The traditional method is to join the recipe lines using \ in the Makefile:

  foo: bar baz
      line1; \
      line2; \
      line3
  

  (Note that the commands must be separated using ; or &&, because the backslashes are also passed to the shell which does the same line-joining.)

  See also info make "Splitting Lines" and info make "Splitting Recipe Lines" in the GNU Make manual.

• The other method is to tell make to always use one shell process for the entire recipe, using the .ONESHELL directive:

  .ONESHELL:
  
  foo: bar baz
      line1
      line2
      line3
  

  See info make "One Shell".

  (Note that while .ONESHELL is recommended by POSIX, not all make versions support it; e.g. BSD make only has a command-line flag for it. This shouldn't be a problem though.)