By default, configure sets the prefix for files it installs to /usr/local. The user of configure can select a different prefix using the -prefix and -exec-prefix options. There are two ways to change the default: when creating configure, and when running it.
Some software packages might want to install in a directory besides /usr/local by default. To accomplish that, use the AC_PREFIX_DEFAULT macro.
function>AC_PREFIX_DEFAULT/function> (prefix) Set the default installation prefix to prefix instead of /usr/local.
It may be convenient for users to have configure guess the installation prefix from the location of a related program that they have already installed. If you wish to do that, you can call AC_PREFIX_PROGRAM.
function>AC_PREFIX_PROGRAM/function> (program) If the user did not specify an installation prefix (using the -prefix option), guess a value for it by looking for program in PATH, the way the shell does. If program is found, set the prefix to the parent of the directory containing program; otherwise leave the prefix specified in Makefile.in unchanged. For example, if program is gcc and the PATH contains /usr/local/gnu/bin/gcc, set the prefix to /usr/local/gnu.