An IN file is an input file that GNU Autoconf uses when building an application. When the configure process is run, an Autoconf script (.AC file) may refer to one or more “.in” or “.h.in” files. IN files define variables that are referenced during programme installation, such as an app’s version number and release date. IN files can also be used to determine the presence or absence of features in a particular installation. Applications such as Notepad and Notepad++ can be used to open and edit IN files.
IN File Format - More Information
Autoconf is a component of the GNU build system that generates custom builds of applications for various platforms. It’s one of several GNU build tools. Other tools include Automake, Gnulib, and Libtool. Without the need for manual user intervention, these scripts can adapt the packages to a wide range of UNIX-like systems. Autoconf generates a package configuration script from a template file that lists the operating system features that the package can use in the form of M4 macro calls