[darnir]

That's a very nice summary. But you're missing one crucial point. These are GNU tools and if you use them within that ecosystem, you also often use gnulib.

Gnulib is effectively the GNU Portability Library. Your fancy, new, auto generated configure script can find all the differences, but someone still needs to account for them and write alternative code to support the various platforms. This is where gnulib comes into play. It reads all the configure checks and plugs in replacements / stubs for whatever is different. This allows you, the developer to simply target GNU/Linux in your code while gnulib handles everything else (and pretty automatically) making is portable across all the unices and even non UNIX systems.

[db48x]

Yea, I completely forgot to mention gnulib.

[fanf2]

Yeah, there’s a lot of software that uses autoconf without gnulib. It’s common to include a load of default platform tests in the configure script that are used by gnulib, but without gnulib the software never uses the results of the tests. All these futile tests are an appalling waste of time and energy.