谁能帮我解释configre.in部分片段中的语句吗?

devel

configre.in部分片段:

dnl support old-style
AC_ARG_WITH(dbdir,
[ --with-dbdir=DIR Berkeley DB files are in prefix DIR],
with_bdb_lib="$withval/lib"; with_bdb_inc="$withval/include",
with_bdb_lib=none; with_bdb_inc=none)

CYRUS_BERKELEY_DB_CHK()

if test "$dblib" = "no"; then
AC_ERROR([this version requires Berkeley DB 3.x or later.
(Get it from http://www.sleepycat.com/). You may need to suppply the
--with-bdb-libdir or --with-bdb-incdir configure options.])
fi

if test "$with_bdb_lib" != "none"; then
CMU_ADD_LIBPATH($with_bdb_lib)
fi
LIBS="${LIBS} ${BDB_LIBADD}"
CPPFLAGS="${BDB_INCADD} ${CPPFLAGS}"

dnl End Berkeley DB Detection
谁能帮我逐句解释一下,这个问题困扰我很久了