-[ "$PREFIX" = "" ] && PREFIX=/usr/local/citadel
-[ "$BINDIR" = "" ] && BINDIR=${PREFIX}
-[ "$CTDLDIR" = "" ] && CTDLDIR=${PREFIX}
+# Accept PREFIX as a substitute for CTDLDIR, but only if CTDLDIR is not already set
+[ "$CTDLDIR" = "" ] && [ "$PREFIX" != "" ] && CTDLDIR=$PREFIX
+
+# Configure the directory into which Citadel Server will be installed.
+[ "$CTDLDIR" = "" ] && CTDLDIR=/usr/local/citadel
+
+# Permit override of CFLAGS and LDFLAGS using environment variables