Makefile, ${VARIABLE}= vs. ${VARIABLE}?=

[Helmut Schneider]

Hi,

[helmut at BSDHelmut ~]$ grep -ir latest /usr/ports/www/apache2?
/usr/ports/www/apache20/Makefile:LATEST_LINK=   apache20
/usr/ports/www/apache22/Makefile:LATEST_LINK?=  apache22
[helmut at BSDHelmut ~]$

So, what's the difference between e.g. "LATEST_LINK=" and
"LATEST_LINK?="?

Thanks, Helmut