Implements {fetch,configure,build,install}_clean.

build.sh:buildp_dispatch_fail_pkg(): print NL when writing to ${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}.
etc/{README.md,build.usage}: updated.
midipix.env: updated.
subr.rtl/rtl_complex.subr:rtl_sunset(): initial implementation.
subr.rtl/rtl_list.subr:rtl_l{filter[23],length2,lift[23]}(): initial implementation.
subr.rtl/rtl_state.subr:rtl_state_test(): take ${_build_steps} vs. ${_build_step}.
subr/{build_init,ex_pkg_restart}.subr: splits extended restart syntax processing logic.
subr/ex_pkg_exec.subr:ex_pkg_exec(): filter "start".
subr/pkg_{build,configure,fetch,install}_clean.subr: initial implementation.

14 files changed, 528 insertions, 231 deletions

diff --git a/build.sh b/build.sh
index aa4b4b5..a9db090 100755
--- a/build.sh
+++ b/build.sh
@@ -39,7 +39,7 @@ buildp_dispatch_fail_pkg() {
 		rtl_log_msg fatal "${BUILD_WORKDIR}/${_pkg_name}_stderrout.log:";
 		cat "${BUILD_WORKDIR}/${_pkg_name}_stderrout.log";
 		if [ -n "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}" ]; then
-			printf "%s" "${_pkg_name}" > "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}";
+			printf "%s\n" "${_pkg_name}" > "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}";
 		fi;
 		rtl_log_msg fatal "Build failed in \`%s', check \`%s' for details." "${_pkg_name}" "${BUILD_WORKDIR}/${_pkg_name}_stderrout.log";
 	else	rtl_log_msg warning "Build failed in \`%s', check \`%s' for details." "${_pkg_name}" "${BUILD_WORKDIR}/${_pkg_name}_stderrout.log";
diff --git a/etc/README.md b/etc/README.md
index 582a5da..be8c54f 100644
--- a/etc/README.md
+++ b/etc/README.md
@@ -248,7 +248,7 @@ Rebuild entire build groups including or excluding group dependencies, respectiv
 
 ```
 usage: ./build.sh [-a nt32|nt64]  [-b debug|release]   [-C dir[,..]]  [-D kind[,..]]
-                  [-F ipv4|ipv6|offline]   [-h]   [-p jobs]     [-P]   [-r ALL|LAST]
+                  [-F ipv4|ipv6|offline] [-h|--help|  [-p jobs]  [-P]  [-r ALL|LAST]
                   [-r [*[*[*]]]name[,..][:[^|<|<=|>|>=]step,..]]  [-R] [-v[v[v[v]]]]
                   [--as-needed] [--debug-minipix] [--dump-on-abort]  [--reset-state]
                   [--roar]     [[=]<group>|<variable name>=<variable override>[ ..]]
@@ -265,7 +265,7 @@ usage: ./build.sh [-a nt32|nt64]  [-b debug|release]   [-C dir[,..]]  [-D kind[,
                           Force IPv4 (ipv4) or IPv6 (ipv6) when downloading package
                           archives and/or Git repositories or don't download either at all
                           (offline.)
-        -h                Show this screen.
+        -h|--help         Show short/full help screen, respectively.
         -p jobs           Enables parallelisation at group-level, whenever applicable.
         -P                The maximum count of jobs defaults to the number of logical
                           processors on the host system divided by two (2.)
@@ -292,14 +292,14 @@ usage: ./build.sh [-a nt32|nt64]  [-b debug|release]   [-C dir[,..]]  [-D kind[,
                           with, resp.
 
                           Currently defined build steps are:
-                          fetch_download, fetch_extract, configure_patch_pre,
-                          configure_autotools, configure_patch, configure, build,
-                          install_subdirs, install_make, install_files, install_libs,
-                          install, install_rpm, and clean.
-
-                          Additionally, the following shorthand aliases and pseudo-steps are provided:
-                          @fetch, @configure, @build, @install, and @clean, and
-                          start and finish.
+                          fetch_clean, fetch_download, fetch_extract, configure_clean,
+                          configure_patch_pre, configure_autotools, configure_patch,
+                          configure, build_clean, build, install_clean, install_subdirs,
+                          install_make, install_files, install_libs, install, install_rpm,
+                          and clean.
+
+                          Additionally, the following virtual steps are provided:
+                          @fetch, @configure, @build, @install, @clean, and finish.
 
         -R                Ignore build failures, skip printing package logs, and continue
                           building (relaxed mode.)
diff --git a/etc/build.usage b/etc/build.usage
index aeb775b..8ba2445 100644
--- a/etc/build.usage
+++ b/etc/build.usage
@@ -43,14 +43,14 @@ usage: ./build.sh [-a nt32|nt64]  [-b debug|release]   [-C dir[,..]]  [-D kind[,
                           with, resp.
 
                           Currently defined build steps are:
-                          fetch_download, fetch_extract, configure_patch_pre,
-                          configure_autotools, configure_patch, configure, build,
-                          install_subdirs, install_make, install_files, install_libs,
-                          install, install_rpm, and clean.
+                          fetch_clean, fetch_download, fetch_extract, configure_clean,
+                          configure_patch_pre, configure_autotools, configure_patch,
+                          configure, build_clean, build, install_clean, install_subdirs,
+                          install_make, install_files, install_libs, install, install_rpm,
+                          and clean.
 
-                          Additionally, the following shorthand aliases and pseudo-steps are provided:
-                          @fetch, @configure, @build, @install, and @clean, and
-                          start and finish.
+                          Additionally, the following virtual steps are provided:
+                          @fetch, @configure, @build, @install, @clean, and finish.
 
         -R                Ignore build failures, skip printing package logs, and continue
                           building (relaxed mode.)
diff --git a/midipix.env b/midipix.env
index f023398..51f3d40 100644
--- a/midipix.env
+++ b/midipix.env
@@ -9,34 +9,42 @@
 #
 
 # Build {step,variable}s
-DEFAULT_BUILD_STEPS="										\
-	start											\
-	fetch_download fetch_extract 								\
-	configure_patch_pre configure_autotools configure_patch configure			\
-	build											\
-	install_subdirs install_make install_files install_libs install install_rpm		\
-	clean											\
+DEFAULT_BUILD_STEPS="											\
+	fetch_clean fetch_download fetch_extract 							\
+	configure_clean configure_patch_pre configure_autotools configure_patch configure		\
+	build_clean build										\
+	install_clean install_subdirs install_make install_files install_libs install install_rpm	\
+	clean												\
 	finish";
-DEFAULT_BUILD_VARS="										\
-	AR BASE_DIR BUILD_DIR BUILD_STEPS_DISABLE BUILD_TYPE					\
-	CC CFLAGS_BUILD CFLAGS_BUILD_EXTRA CFLAGS_CONFIGURE					\
-	CFLAGS_CONFIGURE_EXTRA CONFIG_CACHE CONFIG_CACHE_EXTRA					\
-	CONFIG_CACHE_LOCAL CONFIGURE CONFIGURE_ARGS CONFIGURE_ARGS_EXTRA			\
-	CXX CXXFLAGS_CONFIGURE CXXFLAGS_CONFIGURE_EXTRA						\
-	DEPENDS DESTDIR DESTDIR_HOST DISABLED ENV_VARS_EXTRA					\
-	FNAME FORCE_AUTORECONF GITROOT INHERIT_FROM INSTALL_FILES				\
-	INSTALL_FILES_DESTDIR INSTALL_FILES_DESTDIR_EXTRA INSTALL_TARGET			\
-	INSTALL_TARGET_EXTRA IN_TREE LDFLAGS_BUILD_EXTRA LDFLAGS_CONFIGURE			\
-	LDFLAGS_CONFIGURE_EXTRA LIBTOOL MAKE MAKE_INSTALL_VNAME					\
-	MAKE_SUBDIRS MAKEFLAGS_BUILD MAKEFLAGS_BUILD_EXTRA					\
-	MAKEFLAGS_INSTALL MAKEFLAGS_INSTALL_EXTRA MAKEFLAGS_VERBOSITY				\
-	MIRRORS MIRRORS_GIT SOFORT_FORCE SOFORT_NATIVE_CC SOFORT_NATIVE_CFLAGS			\
-	SOFORT_NATIVE_CFLAGS_EXTRA SOFORT_NATIVE_CXX SOFORT_NATIVE_CXXFLAGS			\
-	SOFORT_NATIVE_CXXFLAGS_EXTRA SOFORT_NATIVE_LD SOFORT_NATIVE_LDFLAGS			\
-	SOFORT_NATIVE_LDFLAGS_EXTRA NO_CLEAN NO_CLEAN_BASE_DIR NO_LOG_VARS			\
-	PYTHON PATCHES_EXTRA PKG_CONFIG PKG_CONFIG_LIBDIR PKGLIST_DISABLE PREFIX		\
+DEFAULT_BUILD_VARS="											\
+	AR BASE_DIR BUILD_DIR BUILD_STEPS_DISABLE BUILD_TYPE						\
+	CC CFLAGS_BUILD CFLAGS_BUILD_EXTRA CFLAGS_CONFIGURE						\
+	CFLAGS_CONFIGURE_EXTRA CONFIG_CACHE CONFIG_CACHE_EXTRA						\
+	CONFIG_CACHE_LOCAL CONFIGURE CONFIGURE_ARGS CONFIGURE_ARGS_EXTRA				\
+	CXX CXXFLAGS_CONFIGURE CXXFLAGS_CONFIGURE_EXTRA							\
+	DEPENDS DESTDIR DESTDIR_HOST DISABLED ENV_VARS_EXTRA						\
+	FNAME FORCE_AUTORECONF GITROOT INHERIT_FROM INSTALL_FILES					\
+	INSTALL_FILES_DESTDIR INSTALL_FILES_DESTDIR_EXTRA INSTALL_TARGET				\
+	INSTALL_TARGET_EXTRA IN_TREE LDFLAGS_BUILD_EXTRA LDFLAGS_CONFIGURE				\
+	LDFLAGS_CONFIGURE_EXTRA LIBTOOL MAKE MAKE_INSTALL_VNAME						\
+	MAKE_SUBDIRS MAKEFLAGS_BUILD MAKEFLAGS_BUILD_EXTRA						\
+	MAKEFLAGS_INSTALL MAKEFLAGS_INSTALL_EXTRA MAKEFLAGS_VERBOSITY					\
+	MIRRORS MIRRORS_GIT SOFORT_FORCE SOFORT_NATIVE_CC SOFORT_NATIVE_CFLAGS				\
+	SOFORT_NATIVE_CFLAGS_EXTRA SOFORT_NATIVE_CXX SOFORT_NATIVE_CXXFLAGS				\
+	SOFORT_NATIVE_CXXFLAGS_EXTRA SOFORT_NATIVE_LD SOFORT_NATIVE_LDFLAGS				\
+	SOFORT_NATIVE_LDFLAGS_EXTRA NO_CLEAN NO_CLEAN_BASE_DIR NO_LOG_VARS				\
+	PYTHON PATCHES_EXTRA PKG_CONFIG PKG_CONFIG_LIBDIR PKGLIST_DISABLE PREFIX			\
 	RANLIB RPM_DISABLE SHA256SUM SUBDIR TARGET URL URLS_GIT VERSION";
 
+#
+# Prerequisite commands
+DEFAULT_PREREQS="											\
+	awk bunzip2 bzip2 cat chmod cmake cp date find flock						\
+	g++ gcc git grep gunzip gzip hostname id install kill						\
+	ln lzip make mkdir mkfifo mktemp mv paste patch perl						\
+	pgrep pkill printf readlink rm sed sha256sum sort						\
+	stat tail tar test touch tr uniq wget xz zip";
+
 # Path names
 : ${PREFIX_ROOT:="${HOME}/midipix"};
 : ${PREFIX:="${PREFIX_ROOT}/${ARCH}/${BUILD_KIND}"};
@@ -48,36 +56,36 @@ DEFAULT_BUILD_VARS="										\
 : ${BUILD_DLCACHEDIR:="${PREFIX_ROOT}/dlcache"};
 : ${BUILD_WORKDIR:="${PREFIX}/tmp"};
 : ${DEFAULT_CHECK_PATH_VARS:="PREFIX PREFIX_NATIVE PREFIX_CROSS BUILD_DLCACHEDIR BUILD_WORKDIR"};
-: ${DEFAULT_CLEAR_ENV_VARS_EXCEPT:="								\
-	HOME PATH TERM USER									\
-	ARCH BUILD_KIND										\
-	BUILD_DLCACHEDIR BUILD_HNAME BUILD_WORKDIR						\
+: ${DEFAULT_CLEAR_ENV_VARS_EXCEPT:="									\
+	HOME PATH TERM USER										\
+	ARCH BUILD_KIND											\
+	BUILD_DLCACHEDIR BUILD_HNAME BUILD_WORKDIR							\
 	PREFIX PREFIX_CROSS PREFIX_MINGW32 PREFIX_MINIPIX PREFIX_NATIVE PREFIX_ROOT PREFIX_RPM"};
 : ${DEFAULT_CLEAR_PREFIX_PATHS:="
 	bin i686-nt32-midipix doc include info lib lib64 libexec man minipix minipix_dist native
 	rpm sbin share tmp usr x86_64-nt64-midipix x86_64-w64-mingw32 pkglist.cross pkglist.host
 	pkglist.native SHA256SUMS SHA256SUMS.last"};
-: ${DEFAULT_INSTALL_FILES_DESTDIR:="								\
-	/=bin /=include /=lib /=lib/pkgconfig /=sbin						\
-	/=share /=share/doc /=share/info /=share/man						\
-	/=share/man/man1 /=share/man/man2 /=share/man/man3 /=share/man/man4 /=share/man/man5	\
-	/=share/man/man6 /=share/man/man7 /=share/man/man8 /=share/man/man9			\
-	@share/doc=doc										\
-	@share/info=info									\
-	@lib=lib64										\
-	@share/man=man										\
-	@../lib/pkgconfig=share/pkgconfig							\
+: ${DEFAULT_INSTALL_FILES_DESTDIR:="									\
+	/=bin /=include /=lib /=lib/pkgconfig /=sbin							\
+	/=share /=share/doc /=share/info /=share/man							\
+	/=share/man/man1 /=share/man/man2 /=share/man/man3 /=share/man/man4 /=share/man/man5		\
+	/=share/man/man6 /=share/man/man7 /=share/man/man8 /=share/man/man9				\
+	@share/doc=doc											\
+	@share/info=info										\
+	@lib=lib64											\
+	@share/man=man											\
+	@../lib/pkgconfig=share/pkgconfig								\
 	@.=usr"};
-: ${DEFAULT_LOG_ENV_VARS:="									\
-	ARCH BUILD_KIND BUILD_DLCACHEDIR BUILD_WORKDIR DEFAULT_GITROOT				\
-	HOME PATH PREFIX PREFIX_CROSS PREFIX_MINGW32 PREFIX_MINIPIX				\
+: ${DEFAULT_LOG_ENV_VARS:="										\
+	ARCH BUILD_KIND BUILD_DLCACHEDIR BUILD_WORKDIR DEFAULT_GITROOT					\
+	HOME PATH PREFIX PREFIX_CROSS PREFIX_MINGW32 PREFIX_MINIPIX					\
 	PREFIX_NATIVE PREFIX_RPM USER"};
-: ${DEFAULT_MIRRORS:="										\
-https://midipix.org/mirror/									\
-https://midipix.lucioillanes.de/archives/							\
+: ${DEFAULT_MIRRORS:="											\
+https://midipix.org/mirror/										\
+https://midipix.lucioillanes.de/archives/								\
 "};
-: ${DEFAULT_MIRRORS_GIT:="									\
-https://midipix.lucioillanes.de/repos_git/							\
+: ${DEFAULT_MIRRORS_GIT:="										\
+https://midipix.lucioillanes.de/repos_git/								\
 "};
 
 # Default flags & variables
diff --git a/subr.rtl/rtl_complex.subr b/subr.rtl/rtl_complex.subr
index 8866484..61637f6 100644
--- a/subr.rtl/rtl_complex.subr
+++ b/subr.rtl/rtl_complex.subr
@@ -72,4 +72,12 @@ rtl_percentage() {
 	printf "%d\n" "${_perc}";
 };
 
+rtl_sunset() {
+	local _rs_rset="${1#\$}" _rs_kname="" IFS=" 	";
+	eval set -- '${'"${_rs_rset}"'}';
+	while [ "${#}" -gt 0 ]; do
+		unset "${_rs_rset}${_rs_kname}"; shift;
+	done; unset "${_rs_rset}";
+};
+
 # vim:filetype=sh
diff --git a/subr.rtl/rtl_list.subr b/subr.rtl/rtl_list.subr
index 29abef2..e24973e 100644
--- a/subr.rtl/rtl_list.subr
+++ b/subr.rtl/rtl_list.subr
@@ -46,6 +46,31 @@ rtl_lfilter() {
 	printf "%s" "${_lnew}";
 };
 
+rtl_lfilter2() {
+	local	_rlist="${1#\$}" _rlist_new="${2#\$}" _filter="${3}" _sep="${4:- }" IFS="${4:-${IFS:- }}"\
+		_filterfl="" _litem="" _litem_filter="" _lnew="";
+
+	if [ "${_filter:+1}" != 1 ]; then
+		eval ${_rlist_new}=; return 0;
+	else	eval set -- '${'"${_rlist}"'}'\; ${_rlist_new}=;
+		while [ "${#}" -gt 0 ]; do
+			_litem="${1}"; shift; _filterfl=0;
+			for _litem_filter in ${_filter}; do
+				if [ "${_litem_filter}" = "${_litem}" ]; then
+					_filterfl=1; break;
+				fi;
+			done;
+			if [ "${_filterfl:-0}" -eq 0 ]; then
+				eval ${_rlist_new}='${'"${_rlist_new}"':+${'"${_rlist_new}"'}${_sep}}${_litem}';
+			fi;
+		done;
+	fi;
+};
+
+rtl_lfilter3() {
+	rtl_lfilter2 "${1}" "${1}" "${2}" "${3:-}";
+};
+
 rtl_lfirst() {
 	local _list="${1}" _sep="${2}" IFS; IFS="${_sep}";
 	set -- ${_list}; RTL_LFIRST_HEAD="${1}";
@@ -64,12 +89,29 @@ rtl_llength() {
 	printf "%s" "${_llength}";
 };
 
+rtl_llength2() {
+	local _rlist="${1#\$}" _rlen="${2#\$}" _sep="${3:- }" IFS="${3:-${IFS:- }}";
+	eval set -- '${'"${_rlist}"'}'\; ${_rlen}='${#}';
+};
+
 rtl_llift() {
 	local _list="${1}" _sep="${2}" _sep_new="${3}" IFS; IFS="${_sep}";
 	set -- ${_list}; IFS="${_sep_new}";
 	printf "%s" "${*}";
 };
 
+rtl_llift2() {
+	local	_rlist="${1#\$}" _rlist_new="${2#\$}" _sep="${3}"	\
+		_sep_new="${4}" IFS; IFS="${_sep}";
+
+	eval set -- '${'"${_rlist}"'}'; IFS="${_sep_new}";
+	eval ${_rlist_new}='"${*}"';
+};
+
+rtl_llift3() {
+	rtl_llift2 "${1}" "${1}" "${2}" "${3}";
+};
+
 rtl_lmatch() {
 	local _list="${1}" _item="${2}" _sep="${3:- }";
 	[ -n "$(rtl_lsearch "${_list}" "${_item}" "${_sep}")" ];
diff --git a/subr.rtl/rtl_state.subr b/subr.rtl/rtl_state.subr
index 203ec52..da091e9 100644
--- a/subr.rtl/rtl_state.subr
+++ b/subr.rtl/rtl_state.subr
@@ -23,16 +23,22 @@ rtl_state_set() {
 };
 
 rtl_state_test() {
-	local _workdir="${1}" _pkg_name="${2}" _build_step="${3}" _restart_at="${4:-}" _done_fname="";
-	_done_fname="${_workdir}/.${_pkg_name}.${_build_step}";
-	if [ -z "${_restart_at}" ]\
-	|| [ "${_restart_at}" = "LAST" ]; then
-		rtl_fileop test "${_done_fname}";
-	elif [ "${_restart_at}" = "ALL" ]; then
-		return 1;
-	else
-		! rtl_lmatch "${_restart_at}" "${_build_step}" ",";
-	fi;
+	local	_workdir="${1}" _pkg_name="${2}" _build_steps="${3}"	\
+		_restart_at="${4:-}" _build_step="" _done_fname=""	\
+		IFS="," _rc=0;
+
+	for _build_step in ${_build_steps}; do
+		_done_fname="${_workdir}/.${_pkg_name}.${_build_step}";
+		if [ "${_restart_at:+1}" != 1 ]\
+		|| [ "${_restart_at}" = "LAST" ]; then
+			rtl_fileop test "${_done_fname}"; _rc="${?}";
+		elif [ "${_restart_at}" = "ALL" ]; then
+			_rc=1;
+		else
+			rtl_lmatch "${_restart_at}" "${_build_step}" ",";
+			_rc=$((${?} ? 0 : 1));
+		fi; [ "${_rc}" -eq 0 ] && break;
+	done; return "${_rc}";
 };
 
 # vim:filetype=sh
diff --git a/subr/build_init.subr b/subr/build_init.subr
index f5894e6..2d78da9 100644
--- a/subr/build_init.subr
+++ b/subr/build_init.subr
@@ -2,145 +2,8 @@
 # set +o errexit -o noglob -o nounset is assumed.
 #
 
-buildp_expand_restart_at() {
-	local _restart_at_spec="${1}" _restart_at="" _restart_at_spec_new="";
-
-	for _restart_at in $(rtl_llift "${_restart_at_spec}" "," " "); do
-		case "${_restart_at}" in
-		@fetch)	_restart_at="fetch_download,fetch_extract"; ;;
-		@configure)
-			_restart_at="configure_patch_pre,configure_autotools,configure_patch,configure"; ;;
-		@build)	_restart_at="build"; ;;
-		@install)
-			_restart_at="install_subdirs,install_make,install_files,install_libs,install,install_rpm"; ;;
-		@clean)
-			_restart_at="clean"; ;;
-		*)	;;
-		esac;
-		_restart_at_spec_new="$(rtl_lconcat "${_restart_at_spec_new}" "${_restart_at}" ",")"
-	done;
-	printf "%s" "${_restart_at_spec_new}";
-};
-
-buildp_expand_restart_recursive() {
-	local _restart_spec="${1}" _last_pkg="" _restart_spec_at="" _restart_spec_recursive=0;
-
-	case "${_restart_spec}" in
-	\*\*\*[a-zA-Z]*)
-			_restart_spec="${_restart_spec#\*\*\*}"; _restart_spec_recursive=3; ;;
-	\*\*[a-zA-Z]*)	_restart_spec="${_restart_spec#\*\*}"; _restart_spec_recursive=2; ;;
-	\*[a-zA-Z]*)	_restart_spec="${_restart_spec#\*}"; _restart_spec_recursive=1; ;;
-	ALL)		_restart_spec_at=ALL; _restart_spec_recursive=2; ;;
-	LAST)		_restart_spec_at=ALL; _restart_spec_recursive=0;
-			if [ -n "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}" ]\
-			&& [ -e "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}" ]; then
-				_last_pkg="$(cat "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}")";
-				rtl_fileop rm "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}";
-				rtl_state_clear "${BUILD_WORKDIR}" "${_last_pkg}";
-				_restart_spec="${_last_pkg}";
-			else
-				_status="cannot rebuild last failed package"; return 1;
-			fi; ;;
-	esac;
-	ARG_RESTART="${_restart_spec}";
-	ARG_RESTART_AT="${_restart_spec_at}";
-	ARG_RESTART_RECURSIVE="${_restart_spec_recursive}";
-	return 0;
-};
-
-buildp_process_restart_spec() {
-	local _restart_spec="${1}" _eqfl=0 _ltfl=0 _restart_spec_at0="" _restart_spec_at="" _step="" _step1=""; _status="";
-
-	buildp_expand_restart_recursive "${_restart_spec}" || return "${?}";
-	_restart_spec="${ARG_RESTART}"; _restart_spec_at="${ARG_RESTART_AT}";
-
-	case "${_restart_spec}" in
-	"")	return 0; ;;
-	*:*)
-		_restart_spec_at="${_restart_spec#*:}"; _restart_spec="${_restart_spec%%:*}";
-		_restart_spec_at0="${_restart_spec_at}"; _restart_spec_at="";
-		case "${_restart_spec_at0}" in
-		ALL|LAST)
-			_restart_spec_at="${_restart_spec_at0}"; ;;
-
-		^*)	_restart_spec_at0="${_restart_spec_at0#^}";
-			_restart_spec_at0="$(buildp_expand_restart_at "${_restart_spec_at0}")";
-			_restart_spec_at="$(rtl_llift "${DEFAULT_BUILD_STEPS}" " 	" ",")";
-			for _restart_at in $(rtl_llift "${_restart_spec_at0}" "," " "); do
-				_restart_spec_at="$(rtl_lfilter "${_restart_spec_at}" "${_restart_at}" ",")";
-			done; _restart_spec_at="$(rtl_lfilter "${_restart_spec_at}" "finish" ",")"; ;;
-
-		\<=*|\<*|\>=*|\>*)
-			[ "${_restart_spec_at0#<}" != "${_restart_spec_at0}" ] && _ltfl=1;
-			if [ "${_restart_spec_at0#[<>]=}" != "${_restart_spec_at0}" ]; then
-				_restart_spec_at0="${_restart_spec_at0#[<>]=}"; _eqfl=1;
-			else
-				_restart_spec_at0="${_restart_spec_at0#[<>]}"; _eqfl=0;
-			fi; _restart_spec_at="";
-			_restart_spec_at0="$(buildp_expand_restart_at "${_restart_spec_at0%%,*}")";
-			if [ \( "${_eqfl}" -eq 1 \) -a \( "${_ltfl}" -eq 1 \) ]\
-			|| [ \( "${_eqfl}" -eq 0 \) -a \( "${_ltfl}" -eq 0 \) ]; then
-				_restart_spec_at0="${_restart_spec_at0##*,}";
-			elif [ \( "${_eqfl}" -eq 1 \) -a \( "${_ltfl}" -eq 0 \) ]\
-			||   [ \( "${_eqfl}" -eq 0 \) -a \( "${_ltfl}" -eq 1 \) ]; then
-				_restart_spec_at0="${_restart_spec_at0%%,*}";
-			fi;
-			for _restart_at in ${DEFAULT_BUILD_STEPS}; do
-				if [ "${_ltfl}" -eq 1 ]; then
-					if [ "${_restart_at}" = "${_restart_spec_at0%%,*}" ]; then
-						if [ "${_eqfl}" -eq 1 ]; then
-							_restart_spec_at="$(rtl_lconcat "${_restart_spec_at}" "${_restart_at}" ",")";
-						fi; break;
-					fi;
-				else
-					if [ "${_restart_at}" = "${_restart_spec_at0%%,*}" ]; then
-						_foundfl=1; [ "${_eqfl}" -eq 0 ] && continue;
-					fi; [ "${_foundfl}" -eq 0 ] && continue;
-				fi;
-				_restart_spec_at="$(rtl_lconcat "${_restart_spec_at}" "${_restart_at}" ",")";
-			done; ;;
-
-		*)	_restart_spec_at="$(buildp_expand_restart_at "${_restart_spec_at0}")"; ;;
-		esac; ;;
-
-	*)	_restart_spec_at=ALL; ;;
-	esac;
-
-	ARG_RESTART="$(rtl_llift "${_restart_spec}" "," " ")";
-	ARG_RESTART_AT="${_restart_spec_at}";
-	if [ "${#ARG_RESTART_AT}" -eq 0 ]; then
-		_status="zero-length build step list"; return 1;
-	elif [ "${ARG_RESTART_AT}" != "ALL" ]\
-	&&   [ "${ARG_RESTART_AT}" != "LAST" ]; then
-		for _restart_at in $(rtl_lfilter "$(rtl_llift "${ARG_RESTART_AT}" "," " ")" "${DEFAULT_BUILD_STEPS}"); do
-			case "${_restart_at}" in
-			start)	;;
-			*)	_status="unknown build step \`${_restart_at}'"; return 1; ;;
-			esac;
-		done;
-	fi;
-	if [ "${#ARG_RESTART_AT}" -gt 0 ]\
-	&& [ "${ARG_RESTART_AT}" != "ALL" ]\
-	&& [ "${ARG_RESTART_AT}" != "LAST" ]; then
-		_restart_spec_at="${ARG_RESTART_AT}"; ARG_RESTART_AT="";
-		for _restart_at in ${DEFAULT_BUILD_STEPS}; do
-			if rtl_lmatch "${_restart_spec_at}" "${_restart_at}" ","; then
-				ARG_RESTART_AT="$(rtl_lconcat "${ARG_RESTART_AT}" "${_restart_at}" ",")";
-			fi;
-		done;
-		if [ "${ARG_RESTART_AT##*,}" != "finish" ]; then
-			_step="$(rtl_lfilter "${ARG_RESTART_AT}" "clean,finish" ",")"; _step="${_step##*,}";
-			_step1="$(rtl_lfilter "${DEFAULT_BUILD_STEPS}" "clean finish")"; _step1="${_step1##* }";
-			if [ "${_step}" = "${_step1}" ]; then
-				ARG_RESTART_AT="$(rtl_lconcat "${ARG_RESTART_AT}" "finish" ",")";
-			fi;
-		fi;
-	fi;
-	return 0;
-};
-
 buildp_init_args() {
-	local	_eqfl=0 _foundfl=0 _group="" _pkg_names_unknown="" _rc=0	\
+	local	_foundfl=0 _group="" _pkg_names_unknown="" _rc=0	\
 		EX_PKG_BUILD_GROUPS EX_PKG_BUILD_GROUPS_NOAUTO; _status="";
 
 	case "${ARG_FETCH_FORCE}" in
@@ -149,26 +12,26 @@ buildp_init_args() {
 	ipv6)	DEFAULT_GIT_ARGS="$(rtl_lconcat "-6" "${DEFAULT_GIT_ARGS}")";
 		DEFAULT_WGET_ARGS="$(rtl_lconcat "-6" "${DEFAULT_WGET_ARGS}")"; ;;
 	esac;
-	if [ -z "${BUILD_HNAME:-}" ]\
+	if [ "${BUILD_HNAME:+1}" != 1 ]\
 	&& ! BUILD_HNAME="$(hostname)"; then
 		_rc=1; _status="Error: failed to obtain hostname.";
 	elif [ "${ARG_DUMP_ON_ABORT:-0}" -eq 1 ]\
-	&& [ "${ARG_RELAXED:-0}" -eq 1 ]; then
+	&&   [ "${ARG_RELAXED:-0}" -eq 1 ]; then
 		_rc=1; _status="Error: --dump-on-abort excludes -R.";
 	elif [ "${ARG_AS_NEEDED:-0}" -eq 1 ]\
-	&& [ -e "${PREFIX}/build.gitref" ]\
-	&& [ "$(git rev-parse HEAD)" = "$(cat "${PREFIX}/build.gitref")" ]; then
+	&&   [ -e "${PREFIX}/build.gitref" ]\
+	&&   [ "$(git rev-parse HEAD)" = "$(cat "${PREFIX}/build.gitref")" ]; then
 		_rc=0; _status="Git repository has not changed since last build and --as-needed was specified.";
-	elif ! buildp_process_restart_spec "${ARG_RESTART:-}"; then
+	elif ! ex_pkg_process_restart_spec \$ARG_RESTART \$ARG_RESTART_AT \$ARG_RESTART_RECURSIVE; then
 		_rc=1; _status="Error: failed to process -r specification: ${_status}.";
 	elif ! ex_pkg_load_groups; then
 		_rc=1; _status="Error: failed to load build groups.";
 	else	if ! rtl_lmatch "${ARG_DIST:-}" "rpm" ","\
-		&& [ -z "${ARG_DUMP_IN:-}" ]\
+		&& [ "${ARG_DUMP_IN:+1}" != 1 ]\
 		&& [ "${ARG_DUMP_ON_ABORT:-0}" -eq 0 ]; then
 			EX_PKG_BUILD_GROUPS="$(rtl_lfilter "${EX_PKG_BUILD_GROUPS}" "host_deps_rpm")";
 		fi;
-		if [ -z "${BUILD_GROUPS}" ]; then
+		if [ "${BUILD_GROUPS:+1}" != 1 ]; then
 			BUILD_GROUPS="${EX_PKG_BUILD_GROUPS}";
 		else	_foundfl=0; for _group in ${BUILD_GROUPS}; do
 				if rtl_lmatch "${EX_PKG_BUILD_GROUPS}" "${_group}"; then
@@ -184,10 +47,11 @@ buildp_init_args() {
 			fi;
 		fi;
 		if [ "${_rc:-0}" -eq 0 ]; then
-			if [ -n "${ARG_DIST}" ]; then
+			if [ "${ARG_DIST:+1}" = 1 ]; then
 				BUILD_GROUPS="$(rtl_lconcat "$(rtl_lfilter "${BUILD_GROUPS}" "dist")" "dist")";
 			fi;
-			if [ -n "${ARG_RESTART}" ] && ! rtl_lmatch "${ARG_RESTART}" "ALL LAST"; then
+			if [ "${ARG_RESTART:+1}" = 1 ]\
+			&& ! rtl_lmatch "${ARG_RESTART}" "ALL LAST"; then
 				for _pkg_name in ${ARG_RESTART}; do
 					if ! ex_pkg_find_package "${BUILD_GROUPS}" "${_pkg_name}" >/dev/null; then
 						_pkg_names_unknown="$(rtl_lconcat "${_pkg_names_unknown}" "${_pkg_name}")";
@@ -205,6 +69,7 @@ buildp_init_args() {
 
 buildp_init_env() {
 	local _fname="" _rc=0; _status="";
+
 	if ! cd "${0%/*}"; then
 		printf "Error: failed to change working directory to \`${0%/*}'." >&2; exit 1;
 	elif ! umask 022; then
@@ -221,6 +86,7 @@ buildp_init_env() {
 
 buildp_init_files() {
 	local _log_last_fname="" _log_last_num=1 _rc=0; _status=""
+
 	if ! rtl_fileop mkdir "${BUILD_DLCACHEDIR}" "${BUILD_WORKDIR}"\
 	|| rtl_lmatch "${ARG_DIST}" "rpm" ","\
 	&& ! rtl_fileop mkdir "${PREFIX_RPM}"; then
@@ -359,16 +225,11 @@ buildp_init_getopts() {
 };
 
 buildp_init_prereqs() {
-	if ! rtl_check_prereqs \
-			awk bunzip2 bzip2 cat chmod cmake cp date find flock	\
-			g++ gcc git grep gunzip gzip hostname id install kill	\
-			ln lzip make mkdir mkfifo mktemp mv paste patch perl	\
-			pgrep pkill printf readlink rm sed sha256sum sort	\
-			stat tail tar test touch tr uniq wget xz zip; then
+	if ! rtl_check_prereqs ${DEFAULT_PREREQS}; then
 		printf "%s\n" "${_status}" >&2; exit 1;
 	elif ! awk -V 2>/dev/null | grep -q "^GNU Awk "; then
 		printf "Error: awk(1) in \$PATH must be GNU Awk." >&2; exit 1;
-	elif ! (FNAME="$(mktemp)" && { trap "rm -f \"\${FNAME}\"" EXIT;		\
+	elif ! (FNAME="$(mktemp)" && { trap "rm -f \"\${FNAME}\"" EXIT;	\
 			sed -i'' -e '' "${FNAME}" >/dev/null 2>&1; }); then
 		printf "Error: sed(1) in \${PATH} does not support the \`-i' option.\n" >&2; exit 1;
 	fi;
@@ -378,8 +239,8 @@ build_init() {
 	local _rc=0; _status="";
 	if ! buildp_init_env			\
 	|| ! buildp_init_getopts "${@}"		\
-	|| ! buildp_init_prereqs		\
 	|| ! ex_pkg_load_vars			\
+	|| ! buildp_init_prereqs		\
 	|| ! buildp_init_args			\
 	|| ! buildp_init_files; then
 		_rc=1; _status="${_status}";
diff --git a/subr/ex_pkg_exec.subr b/subr/ex_pkg_exec.subr
index ee49b87..f20c5c3 100644
--- a/subr/ex_pkg_exec.subr
+++ b/subr/ex_pkg_exec.subr
@@ -94,7 +94,7 @@ ex_pkg_exec() {
 		_rc=1;
 	elif rtl_test_cmd "pkg_${_pkg_name}_all"; then
 		"pkg_${_pkg_name}_all" "${_restart_at}"; _rc="${?}";
-	else	set -- $(rtl_lfilter "${PKG_BUILD_STEPS}" "start");
+	else	set -- ${PKG_BUILD_STEPS};
 		while [ ${#} -gt 0 ]; do
 			_step="${1}"; shift;
 			if [ "${#_restart_at}" -gt 0 ]\
diff --git a/subr/ex_pkg_restart.subr b/subr/ex_pkg_restart.subr
new file mode 100644
index 0000000..20e35b6
--- /dev/null
+++ b/subr/ex_pkg_restart.subr
@@ -0,0 +1,286 @@
+#
+# set +o errexit -o noglob -o nounset is assumed.
+#
+
+#
+# exp_pkg_check_restart_at() - XXX
+# @_rspec_at:		in reference to restart build step list
+#
+# Calling convention:	in ref. @_rspec_at
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_check_restart_at() {
+	local _epcra_rspec_at="${1#\$}" _epcra_len="" _epcra_rc=0 _epcra_spec_at=""; _status=""
+
+	if ! rtl_llift2 "${_epcra_rspec_at}" \$_epcra_spec_at "," " "\
+	|| ! rtl_lfilter3 \$_epcra_spec_at "${DEFAULT_BUILD_STEPS} ALL LAST"\
+	|| ! rtl_llength2 \$_epcra_spec_at \$_epcra_len; then
+		_epcra_rc=1;
+	elif [ "${_epcra_len}" -gt 0 ]; then
+		_status="unknown build step(s) \`${_epcra_spec_at}'"; _epcra_rc=1;
+	fi; return "${_epcra_rc}";
+};
+
+#
+# exp_pkg_expand_restart_at_spec() - XXX
+# @_rset:		in reference to restart virtual build step set
+# @_rspec_at:		inout reference to restart build step list
+#
+# Calling convention:	in ref. @_rset, inout ref. @_rspec_at
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_expand_restart_at_spec() {
+	local	_eperas_rset="${1#\$}" _eperas_rspec_at="${2#\$}" _eperas_at=""			\
+		_eperas_rc=0 _eperas_spec_at="" _eperas_spec_at_=""; _status="";
+	eval _eperas_spec_at='${'"${_eperas_rspec_at}"'}';
+
+	case "${_eperas_spec_at}" in
+	ALL|LAST|"")
+		;;
+
+	^*)
+		_eperas_spec_at="${_eperas_spec_at#^}";
+		if exp_pkg_expand_restart_at_virtual						\
+				"${_eperas_spec_at}" \$_eperas_spec_at				\
+				"${_eperas_rset}"						\
+		&& exp_pkg_check_restart_at \$_eperas_spec_at; then
+			rtl_llift2 \$DEFAULT_BUILD_STEPS "${_eperas_rspec_at}" " 	" ",";
+			rtl_llift2 \$_eperas_spec_at \$_eperas_spec_at_ "," " ";
+			for _eperas_at in ${_eperas_spec_at_}; do
+				rtl_lfilter3 "${_eperas_rspec_at}" "${_eperas_at}" ",";
+			done; rtl_lfilter3 "${_eperas_rspec_at}" "finish" ",";
+		else
+			_eperas_rc=1;
+		fi; ;;
+
+	\<=*|\<*|\>=*|\>*)
+		exp_pkg_expand_restart_at_spec_cmp						\
+			"${_eperas_rset}" "${_eperas_rspec_at}"; _eperas_rc="${?}"; ;;
+
+	*)
+		if ! exp_pkg_expand_restart_at_virtual						\
+				"${_eperas_spec_at}" "${_eperas_rspec_at}"			\
+				"${_eperas_rset}"; then
+			_eperas_rc=1;
+		fi; ;;
+	esac;
+
+	if [ "${_eperas_rc}" -eq 0 ]; then
+		if ! exp_pkg_check_restart_at "${_eperas_rspec_at}"; then
+			_epprs_rc=1;
+		elif eval [ '"${'"${_eperas_rspec_at}"':+1}"' != 1 ]; then
+			_status="zero-length build step list"; _epprs_rc=1;
+		fi;
+	fi;
+	return "${_eperas_rc}";
+};
+
+#
+# exp_pkg_expand_restart_at_spec_cmp() - XXX
+# @_rset:		in reference to restart virtual build step set
+# @_rspec_at:		inout reference to restart build step list
+#
+# Calling convention:	in ref. @_rset, inout ref. @_rspec_at
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_expand_restart_at_spec_cmp() {
+	local	_eperasc_rset="${1#\$}" _eperasc_rspec_at="${2#\$}" _eperasc_at=""		\
+		_eperasc_eqfl="" _eperasc_foundfl="" _eperasc_ltfl="" _eperasc_rc=0		\
+		_eperasc_spec_at="" _eperasc_spec_at0="";
+	eval _eperasc_spec_at0='${'"${_eperasc_rspec_at}"'}';
+
+	[ "${_eperasc_spec_at0#<}" = "${_eperasc_spec_at0}" ]; _eperasc_ltfl="${?}";
+	if [ "${_eperasc_spec_at0#[<>]=}" != "${_eperasc_spec_at0}" ]; then
+		_eperasc_spec_at0="${_eperasc_spec_at0#[<>]=}"; _eperasc_eqfl=1;
+	else
+		_eperasc_spec_at0="${_eperasc_spec_at0#[<>]}"; _eperasc_eqfl=0;
+	fi; _eperasc_spec_at="";
+
+	if exp_pkg_expand_restart_at_virtual							\
+			"${_eperasc_spec_at0%%,*}" \$_eperasc_spec_at0				\
+			"${_eperasc_rset}"							\
+	&& exp_pkg_check_restart_at \$_eperasc_spec_at0; then
+		if [ \( "${_eperasc_eqfl}" -eq 1 \) -a \( "${_eperasc_ltfl}" -eq 1 \) ]\
+		|| [ \( "${_eperasc_eqfl}" -eq 0 \) -a \( "${_eperasc_ltfl}" -eq 0 \) ]; then
+			_eperasc_spec_at0="${_eperasc_spec_at0##*,}";
+		elif [ \( "${_eperasc_eqfl}" -eq 1 \) -a \( "${_eperasc_ltfl}" -eq 0 \) ]\
+		||   [ \( "${_eperasc_eqfl}" -eq 0 \) -a \( "${_eperasc_ltfl}" -eq 1 \) ]; then
+			_eperasc_spec_at0="${_eperasc_spec_at0%%,*}";
+		fi;
+
+		_eperasc_foundfl=0; for _eperasc_at in ${DEFAULT_BUILD_STEPS}; do
+			if [ "${_eperasc_ltfl}" -eq 1 ]; then
+				if [ "${_eperasc_at}" = "${_eperasc_spec_at0%%,*}" ]; then
+					if [ "${_eperasc_eqfl}" -eq 1 ]; then
+						_eperasc_spec_at="${_eperasc_spec_at:+${_eperasc_spec_at},}${_eperasc_at}";
+					fi; break;
+				fi;
+			else
+				if [ "${_eperasc_at}" = "${_eperasc_spec_at0%%,*}" ]; then
+					_eperasc_foundfl=1; [ "${_eperasc_eqfl}" -eq 0 ] && continue;
+				fi; [ "${_eperasc_foundfl}" -eq 0 ] && continue;
+			fi;
+			_eperasc_spec_at="${_eperasc_spec_at:+${_eperasc_spec_at},}${_eperasc_at}";
+		done;
+	else
+		_eperasc_rc=1;
+	fi;
+
+	eval ${_eperasc_rspec_at}='${_eperasc_spec_at}';
+	return "${_eperasc_rc}";
+};
+
+#
+# exp_pkg_expand_restart_at_virtual() - XXX
+# @_spec_at:		restart build step list
+# @_rspec_at_new:	out reference to new restart build step list
+# @_rset:		inout reference to restart virtual build step set
+#
+# Calling convention:	inout ref. @_rspec_recursive
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_expand_restart_at_virtual() {
+	local	_epera_spec_at="${1}" _epera_rspec_at_new="${2#\$}" _epera_rset="${3#\$}"	\
+		_epera_at="" _epera_IFS0="${IFS:- 	}" _epera_rc=0 _epera_spec_at_new=""	\
+		IFS; _status="";
+
+	eval ${_epera_rspec_at_new}=;
+	IFS=","; set -- ${_epera_spec_at}; IFS="${_epera_IFS0}";
+	while [ "${#}" -gt 0 ]; do
+		_epera_at="${1}"; shift;
+		if [ "${_epera_at#@}" != "${_epera_at}" ]; then
+			_epera_at="${_epera_at#@}";
+			if [ "${_epera_at%[^0-9a-zA-Z_]*}" != "${_epera_at}" ]; then
+				_status="invalid virtual build step \`${_epera_at}'"; _epera_rc=1;
+			elif eval [ '"${'"${_epera_rset}${_epera_at}"':+1}"' = 1 ]; then
+				eval _epera_at='${'"${_epera_rset}${_epera_at}"'}';
+			else
+				_status="unknown virtual build step \`${_epera_at}'"; _epera_rc=1;
+			fi;
+		fi;
+		eval ${_epera_rspec_at_new}='${'"${_epera_rspec_at_new}"':+${'"${_epera_rspec_at_new}"'},}${_epera_at}';
+	done;
+	return "${_epera_rc}";
+};
+
+#
+# exp_pkg_expand_restart_recursive() - XXX
+# @_rspec:		inout reference to restart {specification,package name list}
+# @_rrecursive:		out reference to recursion flag
+#
+# Calling convention:	inout ref. @_rspec, out ref. @_rrecursive
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_expand_restart_recursive() {
+	local _eperr_rspec="${1#\$}" _eperr_rrecursive="${2#\$}" _eperr_spec=""; _status=""
+	eval _eperr_spec='${'"${_eperr_rspec}"'}';
+
+	case "${_eperr_spec}" in
+	\*\*\*[a-zA-Z]*)
+			eval ${_eperr_rspec}='${_eperr_spec#\*\*\*}' ${_eperr_rrecursive}=3; ;;
+	\*\*[a-zA-Z]*)	eval ${_eperr_rspec}='${_eperr_spec#\*\*}' ${_eperr_rrecursive}=2; ;;
+	\*[a-zA-Z]*)	eval ${_eperr_rspec}='${_eperr_spec#\*}' ${_eperr_rrecursive}=1; ;;
+	ALL)		eval ${_eperr_rrecursive}=2; ;;
+	LAST)		eval ${_eperr_rrecursive}=0; ;;
+	esac;
+	return 0;
+};
+
+#
+# exp_pkg_expand_restart_spec() - XXX
+# @_rspec:		inout reference to restart {specification,package name list}
+# @_rspec_at:		out reference to restart build step list
+#
+# Calling convention:	inout ref. @_rspec, out ref. @_rspec_at, out ref. @_rrecursive
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_expand_restart_spec() {
+	local	_epers_rspec="${1#\$}" _epers_rspec_at="${2#\$}" _epers_last_pkg=""	\
+		_epers_rc=0 _epers_spec="" _epers_spec_at="" _epers_spec_at0="";
+	eval _epers_spec='${'"${_epers_rspec}"'}';
+
+	case "${_epers_spec}" in
+	"")	eval ${_eppras_rspec_at}=; ;;
+	ALL)	eval ${_epers_rspec_at}=ALL; ;;
+	LAST|LAST:*)
+		case "${_epers_spec}" in
+		LAST)	eval ${_epers_rspec_at}=LAST; ;;
+		LAST:*)	eval ${_epers_rspec_at}='${_epers_spec#LAST:}'; ;;
+		esac;
+		if [ "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME:+1}" = 1 ]\
+		&& [ -e "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}" ]; then
+			if read -r _epers_last_pkg <"${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}"\
+			&& rtl_fileop rm "${DEFAULT_BUILD_LAST_FAILED_PKG_FNAME}"; then
+				eval ${_epers_rspec}='${_epers_last_pkg}';
+			else
+				_status="failed to read or clear status of last failed package \`${_epers_last_pkg}'"; _epers_rc=1;
+			fi;
+		else
+			_status="cannot rebuild last failed package"; _epers_rc=1;
+		fi; ;;
+
+	*:*)	eval ${_epers_rspec}='${_epers_spec%:*}' ${_epers_rspec_at}='${_epers_spec#*:}'; ;;
+	*)	eval ${_epers_rspec_at}= ${_epers_rspec_at}=ALL; ;;
+	esac;
+	return "${_epers_rc}";
+};
+
+#
+# exp_pkg_init_restart_at_virtual() - XXX
+# @_rset:		out reference to restart virtual build step set
+#
+# Calling convention:	out ref. @_rset
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+exp_pkg_init_restart_at_virtual() {
+	local _eperav_rset="${1#\$}" _eperav_step="" _eperav_step_virtual="" _epera_steps="";
+
+	rtl_lfilter2 \$DEFAULT_BUILD_STEPS \$_epera_steps "finish";
+	for _eperav_step in ${_epera_steps}; do
+		_eperav_step_virtual="${_eperav_step%%_*}";
+		if eval [ '"${'"${_eperav_rset}${_eperav_step_virtual}"':+1}"' != 1 ]; then
+			eval ${_eperav_rset}='"${'"${_eperav_rset}"':+${'"${_eperav_rset}"'},}${_eperav_step_virtual}"';
+		fi;
+		eval ${_eperav_rset}${_eperav_step_virtual}='"${'"${_eperav_rset}${_eperav_step_virtual}"':+${'"${_eperav_rset}${_eperav_step_virtual}"'},}${_eperav_step}"';
+	done; return 0;
+};
+
+#
+# ex_pkg_process_restart_spec() - XXX
+# @_rspec:		inout reference to restart {specification,package name list}
+# @_rspec_at:		out reference to restart build step list
+# @_rrecursive:		out reference to restart recursion flag
+#
+# Calling convention:	inout ref. @_rspec, out ref. @_rspec_at
+# Returns:		zero (0) on success, non-zero (>0) on failure
+#
+ex_pkg_process_restart_spec() {
+	local	_epprs_rspec="${1#\$}" _epprs_rspec_at="${2#\$}" _epprs_rrecursive="${3#\$}"	\
+		_epprs_at="" _epprs_rc=0 _epprs_spec_at_new="" _epprs_step="" _epprs_step1=""	\
+		_epprs_virtual_set=""; _status="";
+
+	if exp_pkg_init_restart_at_virtual \$_epprs_virtual_set					\
+	&& exp_pkg_expand_restart_spec "${_epprs_rspec}" \$_epprs_spec_at_new			\
+	&& exp_pkg_expand_restart_recursive "${_epprs_rspec}" "${_epprs_rrecursive}"		\
+	&& exp_pkg_expand_restart_at_spec \$_epprs_virtual_set \$_epprs_spec_at_new; then
+		eval ${_epprs_rspec_at}=;
+		for _epprs_at in ${DEFAULT_BUILD_STEPS}; do
+			if rtl_lmatch "${_epprs_at}" "${_epprs_spec_at_new}" ","; then
+				eval ${_epprs_rspec_at}='${'"${_epprs_rspec_at}"':+${'"${_epprs_rspec_at}"'},}${_epprs_at}';
+			fi;
+		done;
+		if eval [ '"${'"${_epprs_rspec_at}"'##*,}"' != "finish" ]; then
+			rtl_lfilter2 "${_epprs_rspec_at}" \$_epprs_step "clean,finish" ","; _epprs_step="${_epprs_step##*,}";
+			rtl_lfilter2 \$DEFAULT_BUILD_STEPS \$_epprs_step1 "clean finish"; _epprs_step1="${_epprs_step1##* }";
+			if [ "${_epprs_step}" = "${_epprs_step1}" ]; then
+				eval ${_epprs_rspec_at}='${'"${_epprs_rspec_at}"':+${'"${_epprs_rspec_at}"'},}finish';
+			fi;
+		fi;
+	else
+		_epprs_rc=1;
+	fi;
+	rtl_sunset \$_epprs_virtual_set;
+	return "${_epprs_rc}";
+};
+
+# vim:filetype=sh
diff --git a/subr/pkg_build_clean.subr b/subr/pkg_build_clean.subr
new file mode 100644
index 0000000..55dc19c
--- /dev/null
+++ b/subr/pkg_build_clean.subr
@@ -0,0 +1,33 @@
+#
+# set +o errexit -o noglob -o nounset is assumed.
+#
+
+pkg_build_clean() {
+	local	_libtool="" _makeflags_verbosity="${PKG_MAKEFLAGS_VERBOSITY:-}"			\
+		_no_autoconf="" _rc=0 _subdir="";
+
+	if ex_pkg_state_test "${_pkg_name}" "build" "${_restart_at}"; then
+		case "${PKG_LIBTOOL:-}" in
+		"")	_libtool=""; ;;
+		none)	_libtool=""; ;;
+		*)	_libtool="${PKG_LIBTOOL}"; ;;
+		esac;
+		[ ! -x "${PKG_CONFIGURE:-}" ] && _no_autoconf=1;
+
+		for _subdir in ${PKG_MAKE_SUBDIRS:-:}; do
+			[ "${_subdir}" = ":" ] && _subdir="";
+			[ "${#_libtool}" -gt 0 ] && export MAKE="make LIBTOOL=${_libtool}";
+			rtl_run_cmd_unsplit "${PKG_MAKE}"					\
+				${PKG_MAKEFLAGS_BUILD:-}					\
+				${PKG_MAKEFLAGS_BUILD_EXTRA:-}					\
+				${_libtool:+"LIBTOOL=${_libtool}"}				\
+				${_makeflags_verbosity}						\
+				${_subdir:+-C "${_subdir}"}					\
+				clean; _rc="${?}";
+			[ "${#_libtool}" -gt 0 ] && unset MAKE;
+			[ "${_rc}" -ne 0 ] && return 1;
+		done; return 0;
+	fi;
+};
+
+# vim:filetype=sh
diff --git a/subr/pkg_configure_clean.subr b/subr/pkg_configure_clean.subr
new file mode 100644
index 0000000..48549a9
--- /dev/null
+++ b/subr/pkg_configure_clean.subr
@@ -0,0 +1,20 @@
+#
+# set +o errexit -o noglob -o nounset is assumed.
+#
+
+pkg_configure_clean() {
+	local _group_name="${1}" _pkg_name="${2}" _restart_at="${3}";
+
+	if ex_pkg_state_test									\
+			"${_pkg_name}"								\
+			"configure_patch_pre,configure_autotools,configure_patch,configure"	\
+			"${_restart_at}"; then
+		if [ "${PKG_BUILD_DIR:-}" != "${PKG_SUBDIR:-}" ]; then
+			rtl_fileop rm "${PKG_BUILD_DIR}" || return 1;
+			rtl_fileop mkdir "${PKG_BUILD_DIR}" || return 1;
+			rtl_fileop cd "${PKG_BUILD_DIR}" || return 1;
+		fi;
+	fi;
+};
+
+# vim:filetype=sh
diff --git a/subr/pkg_fetch_clean.subr b/subr/pkg_fetch_clean.subr
new file mode 100644
index 0000000..a56196c
--- /dev/null
+++ b/subr/pkg_fetch_clean.subr
@@ -0,0 +1,21 @@
+#
+# set +o errexit -o noglob -o nounset is assumed.
+#
+
+pkg_fetch_clean() {
+	local _dname="";
+
+	if [ -n "${PKG_URLS_GIT:-}" ]; then
+		if [ -n "${PKG_SUBDIR:-}" ]\
+		&& [ "${PKG_SUBDIR}" != "${PKG_URLS_GIT%%=*}" ]; then
+			rtl_fileopm rm "${PKG_SUBDIR}";
+		fi;
+		for _dname in ${PKG_URLS_GIT}; do
+			_dname="${_dname%%=*}"; rtl_fileop rm "${_dname}";
+		done;
+	elif [ -n "${PKG_SUBDIR}" ]; then
+		rtl_fileop rm "${PKG_SUBDIR}";
+	fi; return 0;
+};
+
+# vim:filetype=sh
diff --git a/subr/pkg_install_clean.subr b/subr/pkg_install_clean.subr
new file mode 100644
index 0000000..3d99f32
--- /dev/null
+++ b/subr/pkg_install_clean.subr
@@ -0,0 +1,12 @@
+#
+# set +o errexit -o noglob -o nounset is assumed.
+#
+
+pkg_install_clean() {
+	if [ -n "${PKG_DESTDIR:-}" ]; then
+		rtl_fileop rm "${PKG_DESTDIR}" || return 1;
+		rtl_fileop mkdir "${PKG_DESTDIR}" || return 1;
+	fi; return 0;
+};
+
+# vim:filetype=sh