Temporarily change contents of an existing Makevars file.
with_makevars(new, code, path = file.path("~", ".R", "Makevars"),
assignment = c("=", ":=", "?=", "+="))[named character] New variables and their values
[any] Code to execute in the temporary environment
[character(1)] location of existing Makevars file to modify.
[character(1)] assignment type to use.
[any] The results of the evaluation of the code
argument.
If no Makevars file exists or the fields in new do
not exist in the existing Makevars file then the fields are added to
the new file. Existing fields which are not included in new are
appended unchanged. Fields which exist in Makevars and in new
are modified to use the value in new.
withr for examples