What do these variables with 'at symbols' in Makefiles mean?

Question

I couldn't find any documentation on this. What exactly are these variables with 'at' symbols found in Makefiles? Example:

temp = @temp@
srcdir = @srcdir@

Answer 1

They are placeholders that are put in makefiles for autoconf or related tools. The post-processing from the configuration stage replaces them with values determined during the configuration process.

Usually, you'd see them in Makefile.in or similar names; the values should not be present in the final generated makefile. It suggests that the configuration process did not complete correctly.