The Autotools are always being updated—on average, a significant update of each of the three tools, Autoconf, Automake, and Libtool, is released every year and a half, and minor updates are released every three to six months. The Autotools designers attempt to maintain a reasonable level of backward compatibility with each new release, but occasionally something significant is broken, and older documentation simply becomes out of date.
While I describe new significant features of recent releases of the Autotools, in my efforts to make this a more timeless work, I've tried to stick to descriptions of Autoconf features (macros for instance) that have been in widespread use for several years. Minor details change occasionally, but the general use has stayed the same through many releases.
At appropriate places in the text, I mention the versions of the Autotools that I've used for this book, but I'll summarize here. I've used version 2.64 of Autoconf, version 1.11 of Automake, and version 2.2.6 of Libtool. These were the latest versions as of this writing, and even through the publication process, I was able to make minor corrections and update to new releases as they became available.