detecting OS

[Helder Correia]

Hello

How can I write a configure.in file in a way I can make something like this:

if linux
    do this
else if freebsd
    do that
else if solaris
    do this;
    do that;


Do I have to work out with automake too?
(note: if solaris then I have to do something like app_LDADD in Makefile.am)

Thanks in advance...