variable=@value@ in Makefiles

Question

I understand that @ suppresses printing of a command in a Makefile...

http://www.gnu.org/software/make/manual/make.html#Echoing

... and I understand that $@ is the target name...

http://www.gnu.org/software/make/manual/make.html#Automatic-Variables

... but I can't find any information on what a line like this might mean:

variable=@value@

I'm not trying to fix anything here, just trying to better understand Makefiles.

Update: The "Makefile Subsitutions" section of the GNU autoconf manual explains that it's a value that is substituted by autoconf.

Answer 1

Typically you find this in Makefile.in files, which are processed by configure (which are in turn generated by autoconf) scripts.

In that case @X@ will be replaced by the value of a shell variable $X, if configure is told so. If it's not, no occurrence in the input file will be touched by configure, hence leaving the replaceable string as it is. If you ask me these instances indicate slips in the build system.