— Variable: CFLAGS

Debugging and optimization options for the C compiler. If it is not set in the environment when configure runs, the default value is set when you call AC_PROG_CC (or empty if you don't). configure uses this variable when compiling programs to test for C features.

— Variable: configure_input

A comment saying that the file was generated automatically by configure and giving the name of the input file. AC_OUTPUT adds a comment line containing this variable to the top of every makefile it creates. For other files, you should reference this variable in a comment at the top of each input file. For example, an input shell script should begin like this:

          #!/bin/sh
          # @configure_input@
     

The presence of that line also reminds people editing the file that it needs to be processed by configure in order to be used.

— Variable: CPPFLAGS

Header file search directory (-Idir) and any other miscellaneous options for the C and C++ preprocessors and compilers. If it is not set in the environment when configure runs, the default value is empty. configure uses this variable when compiling or preprocessing programs to test for C and C++ features. See Special Chars in Variables, for limitations that CPPFLAGS might run into.

— Variable: CXXFLAGS

Debugging and optimization options for the C++ compiler. If it is not set in the environment when configure runs, the default value is set when you call AC_PROG_CXX (or empty if you don't). configure uses this variable when compiling programs to test for C++ features.

— Variable: DEFS

-D options to pass to the C compiler. If AC_CONFIG_HEADERS is called, configure replaces ‘@DEFS@’ with -DHAVE_CONFIG_H instead (see Configuration Headers). This variable is not defined while configure is performing its tests, only when creating the output files. See Setting Output Variables, for how to check the results of previous tests.

— Variable: ECHO_C
— Variable: ECHO_N
— Variable: ECHO_T

How does one suppress the trailing newline from echo for question-answer message pairs? These variables provide a way:

          echo $ECHO_N "And the winner is... $ECHO_C"
          sleep 100000000000
          echo "${ECHO_T}dead."
     

Some old and uncommon echo implementations offer no means to achieve this, in which case ECHO_T is set to tab. You might not want to use it.

— Variable: ERLCFLAGS

Debugging and optimization options for the Erlang compiler. If it is not set in the environment when configure runs, the default value is empty. configure uses this variable when compiling programs to test for Erlang features.

— Variable: FCFLAGS

Debugging and optimization options for the Fortran compiler. If it is not set in the environment when configure runs, the default value is set when you call AC_PROG_FC (or empty if you don't). configure uses this variable when compiling programs to test for Fortran features.

— Variable: FFLAGS

Debugging and optimization options for the Fortran 77 compiler. If it is not set in the environment when configure runs, the default value is set when you call AC_PROG_F77 (or empty if you don't). configure uses this variable when compiling programs to test for Fortran 77 features.

— Variable: LDFLAGS

Stripping (-s), path (-L), and any other miscellaneous options for the linker. Don't use this variable to pass library names (-l) to the linker, use LIBS instead. If it is not set in the environment when configure runs, the default value is empty. configure uses this variable when linking programs to test for C, C++, and Fortran features.

— Variable: LIBS

-l options to pass to the linker. The default value is empty, but some Autoconf macros may prepend extra libraries to this variable if those libraries are found and provide necessary functions, see Libraries. configure uses this variable when linking programs to test for C, C++, and Fortran features.

— Variable: OBJCFLAGS

Debugging and optimization options for the Objective C compiler. If it is not set in the environment when configure runs, the default value is set when you call AC_PROG_OBJC (or empty if you don't). configure uses this variable when compiling programs to test for Objective C features.

— Variable: builddir

Rigorously equal to ‘.’. Added for symmetry only.

— Variable: abs_builddir

Absolute name of builddir.

— Variable: top_builddir

The relative name of the top level of the current build tree. In the top-level directory, this is the same as builddir.

— Variable: abs_top_builddir

Absolute name of top_builddir.

— Variable: srcdir

The relative name of the directory that contains the source code for that makefile.

— Variable: abs_srcdir

Absolute name of srcdir.

— Variable: top_srcdir

The relative name of the top-level source code directory for the package. In the top-level directory, this is the same as srcdir.

— Variable: abs_top_srcdir

Absolute name of top_srcdir.