template

GIT

git clone http://sethub.club/sethub/XML_Data_Parsing.git
git checkout -b dev_xxx origin/dev

git pull origin dev

git push origin dev_xxx -u

Makefile.in: A template for Makefile. It is filled with placeholder variables such as @srcdir@, @CC@, @prefix@, etc. Configure replaces these variables with actual values, outputting a directly usable Makefile.
config.h.in: A header file template. The configure script will generate config.h based on the detection results, which defines macros such as #define HAVE_STDLIB_H 1 for use in the source code.
Why is it called .in? It stands for input template, waiting to be filled by configure.

m4 is an ancient macro processing language used by Autoconf to extend configure.ac.
aclocal.m4: Generated by aclocal, it contains macros written by the project itself and macros installed by the system (such as macros for detecting a specific library), intended for use by autoconf.
pkg.m4: This is a macro file provided by the pkg-config tool, which defines macros such as PKG_CHECK_MODULES, intended for conveniently detecting dependent libraries in configure.ac. Your script checks for its existence to ensure that the project can correctly detect dependencies.
Other .m4 files: They are usually stored in /usr/share/aclocal and are detection macros provided by various third-party libraries.

Handwritten files: configure.ac (configuration requirements) Makefile.am (prototype of build rules) ... source code .. ↓ Run autogen.sh (i.e., the script you analyzed) Generated files: configure (executable configuration script), Makefile.in (Makefile template), aclocal.m4 (macro package), config.h.in (header file template) ↓ Run ./configure Generated files: Makefile (final usable Makefile), config.h (final header file), config.status (configuration status script)