diff --git a/qse/Makefile.in b/qse/Makefile.in
index ac445d01..fd1fe0a1 100644
--- a/qse/Makefile.in
+++ b/qse/Makefile.in
@@ -34,7 +34,7 @@ POST_UNINSTALL = :
 build_triplet = @build@
 host_triplet = @host@
 subdir = .
-DIST_COMMON = README $(am__configure_deps) $(srcdir)/Makefile.am \
+DIST_COMMON = $(am__configure_deps) $(srcdir)/Makefile.am \
 	$(srcdir)/Makefile.in $(srcdir)/README.in \
 	$(top_srcdir)/configure ac/config.guess ac/config.sub \
 	ac/depcomp ac/install-sh ac/ltmain.sh ac/missing
diff --git a/qse/cmd/sed/sed.c b/qse/cmd/sed/sed.c
index 63e236be..f4306696 100644
--- a/qse/cmd/sed/sed.c
+++ b/qse/cmd/sed/sed.c
@@ -64,7 +64,9 @@ static qse_char_t* g_output_file = QSE_NULL;
 static int g_infile_pos = 0;
 static int g_option = 0;
 static int g_separate = 0;
+#if defined(QSE_ENABLE_SEDTRACER)
 static int g_trace = 0;
+#endif
 static qse_ulong_t g_memlimit = 0;
 static qse_sed_t* g_sed = QSE_NULL;
 
@@ -131,6 +133,9 @@ static void print_usage (QSE_FILE* out, int argc, qse_char_t* argv[])
 	qse_fprintf (out, QSE_T("           <start~step>,<start,+line>,<start,~line>,<0,/regex/>\n"));
 	qse_fprintf (out, QSE_T(" -x        allow text on the same line as c, a, i\n"));
 	qse_fprintf (out, QSE_T(" -y        ensure a newline at text end\n"));
+#if defined(QSE_ENABLE_SEDTRACER)
+	qse_fprintf (out, QSE_T(" -t        print command traces\n"));
+#endif
 	qse_fprintf (out, QSE_T(" -m number specify the maximum amount of memory to use in bytes\n"));
 #if defined(QSE_BUILD_DEBUG)
 	qse_fprintf (out, QSE_T(" -X number fail the number'th memory allocation\n"));
@@ -160,7 +165,9 @@ static int add_script (const qse_char_t* str, int mem)
 	if (mem)
 	{
 		g_script.io[g_script.size].type = QSE_SED_IOSTD_MEM;
-		g_script.io[g_script.size].u.mem.ptr = str;
+		/* though its type is not qualified to be const, 
+		 * u.mem.ptr is actually const when used for input */
+		g_script.io[g_script.size].u.mem.ptr = (qse_char_t*)str;
 		g_script.io[g_script.size].u.mem.len = qse_strlen(str);
 	}
 	else
@@ -270,8 +277,13 @@ static int handle_args (int argc, qse_char_t* argv[])
 				break;
 
 			case QSE_T('t'):
+#if defined(QSE_ENABLE_SEDTRACER)
 				g_trace = 1;
 				break;
+#else
+				print_usage (QSE_STDERR, argc, argv);
+				goto oops;
+#endif
  
 			case QSE_T('m'):
 				g_memlimit = qse_strtoulong (opt.arg);
@@ -450,33 +462,39 @@ static void unset_intr_run (void)
 #endif
 }
 
+#if defined(QSE_ENABLE_SEDTRACER)
 static void trace_exec (qse_sed_t* sed, qse_sed_exec_op_t op, const qse_sed_cmd_t* cmd)
 {
 	switch (op)
 	{
 #if 0
 		case QSE_SED_EXEC_READ:
-			qse_printf (QSE_T("reading...\n"));
+			qse_fprintf (QSE_STDERR, QSE_T("reading...\n"));
 			break;
 		case QSE_SED_EXEC_WRITE:
-			qse_printf (QSE_T("wrting...\n"));
+			qse_fprintf (QSE_STDERR, QSE_T("wrting...\n"));
 			break;
 #endif
+		/* TODO: use function to get hold space and pattern space and print them */
+
 		case QSE_SED_EXEC_MATCH:
-			qse_printf (QSE_T("matching address for [%c] in %s at line %lu\n"), 
-				cmd->type, 
-				(cmd->lid? cmd->lid: QSE_T("<<UNKNOWN>>")), 
-				(unsigned long)cmd->loc.line);
+			qse_fprintf (QSE_STDERR, QSE_T("%s:%lu [%c] MA\n"), 
+				((cmd->lid && cmd->lid[0])? cmd->lid: QSE_T("<<UNKNOWN>>")), 
+				(unsigned long)cmd->loc.line,
+				cmd->type
+			);
 			break;
 
 		case QSE_SED_EXEC_EXEC:
-			qse_printf (QSE_T("executing [%c] in %s at line %lu\n"), 
-				cmd->type, 
-				(cmd->lid? cmd->lid: QSE_T("<<UNKNOWN>>")), 
-				(unsigned long)cmd->loc.line);
+			qse_fprintf (QSE_STDERR, QSE_T("%s:%lu [%c] EC\n"), 
+				((cmd->lid && cmd->lid[0])? cmd->lid: QSE_T("<<UNKNOWN>>")), 
+				(unsigned long)cmd->loc.line,
+				cmd->type
+			);
 			break;
 	}
 }
+#endif
 
 int sed_main (int argc, qse_char_t* argv[])
 {
@@ -559,7 +577,9 @@ int sed_main (int argc, qse_char_t* argv[])
 		goto oops;
 	}
 
+#if defined(QSE_ENABLE_SEDTRACER)
 	if (g_trace) qse_sed_setexectracer (sed, trace_exec);
+#endif
 
 	if (g_separate && g_infile_pos > 0)
 	{
diff --git a/qse/configure b/qse/configure
index dc3402d4..a653a5dc 100755
--- a/qse/configure
+++ b/qse/configure
@@ -902,6 +902,7 @@ enable_syscall
 enable_debug
 enable_cxx
 enable_reentrant
+enable_sedtracer
 '
       ac_precious_vars='build_alias
 host_alias
@@ -1551,6 +1552,7 @@ Optional Features:
   --enable-cxx            build the library for C++ if a C++ compiler is
                           available (default. yes)
   --enable-reentrant      define _REENTRANT (default. yes)
+  --enable-sedtracer      enable qse_sed_setexectracer() (default. yes)
 
 Optional Packages:
   --with-PACKAGE[=ARG]    use PACKAGE [ARG=yes]
@@ -5696,13 +5698,13 @@ if test "${lt_cv_nm_interface+set}" = set; then :
 else
   lt_cv_nm_interface="BSD nm"
   echo "int some_variable = 0;" > conftest.$ac_ext
-  (eval echo "\"\$as_me:5699: $ac_compile\"" >&5)
+  (eval echo "\"\$as_me:5701: $ac_compile\"" >&5)
   (eval "$ac_compile" 2>conftest.err)
   cat conftest.err >&5
-  (eval echo "\"\$as_me:5702: $NM \\\"conftest.$ac_objext\\\"\"" >&5)
+  (eval echo "\"\$as_me:5704: $NM \\\"conftest.$ac_objext\\\"\"" >&5)
   (eval "$NM \"conftest.$ac_objext\"" 2>conftest.err > conftest.out)
   cat conftest.err >&5
-  (eval echo "\"\$as_me:5705: output\"" >&5)
+  (eval echo "\"\$as_me:5707: output\"" >&5)
   cat conftest.out >&5
   if $GREP 'External.*some_variable' conftest.out > /dev/null; then
     lt_cv_nm_interface="MS dumpbin"
@@ -6897,7 +6899,7 @@ ia64-*-hpux*)
   ;;
 *-*-irix6*)
   # Find out which ABI we are using.
-  echo '#line 6900 "configure"' > conftest.$ac_ext
+  echo '#line 6902 "configure"' > conftest.$ac_ext
   if { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_compile\""; } >&5
   (eval $ac_compile) 2>&5
   ac_status=$?
@@ -8953,11 +8955,11 @@ else
    -e 's:.*FLAGS}\{0,1\} :&$lt_compiler_flag :; t' \
    -e 's: [^ ]*conftest\.: $lt_compiler_flag&:; t' \
    -e 's:$: $lt_compiler_flag:'`
-   (eval echo "\"\$as_me:8956: $lt_compile\"" >&5)
+   (eval echo "\"\$as_me:8958: $lt_compile\"" >&5)
    (eval "$lt_compile" 2>conftest.err)
    ac_status=$?
    cat conftest.err >&5
-   echo "$as_me:8960: \$? = $ac_status" >&5
+   echo "$as_me:8962: \$? = $ac_status" >&5
    if (exit $ac_status) && test -s "$ac_outfile"; then
      # The compiler can only warn and ignore the option if not recognized
      # So say no if there are warnings other than the usual output.
@@ -9292,11 +9294,11 @@ else
    -e 's:.*FLAGS}\{0,1\} :&$lt_compiler_flag :; t' \
    -e 's: [^ ]*conftest\.: $lt_compiler_flag&:; t' \
    -e 's:$: $lt_compiler_flag:'`
-   (eval echo "\"\$as_me:9295: $lt_compile\"" >&5)
+   (eval echo "\"\$as_me:9297: $lt_compile\"" >&5)
    (eval "$lt_compile" 2>conftest.err)
    ac_status=$?
    cat conftest.err >&5
-   echo "$as_me:9299: \$? = $ac_status" >&5
+   echo "$as_me:9301: \$? = $ac_status" >&5
    if (exit $ac_status) && test -s "$ac_outfile"; then
      # The compiler can only warn and ignore the option if not recognized
      # So say no if there are warnings other than the usual output.
@@ -9397,11 +9399,11 @@ else
    -e 's:.*FLAGS}\{0,1\} :&$lt_compiler_flag :; t' \
    -e 's: [^ ]*conftest\.: $lt_compiler_flag&:; t' \
    -e 's:$: $lt_compiler_flag:'`
-   (eval echo "\"\$as_me:9400: $lt_compile\"" >&5)
+   (eval echo "\"\$as_me:9402: $lt_compile\"" >&5)
    (eval "$lt_compile" 2>out/conftest.err)
    ac_status=$?
    cat out/conftest.err >&5
-   echo "$as_me:9404: \$? = $ac_status" >&5
+   echo "$as_me:9406: \$? = $ac_status" >&5
    if (exit $ac_status) && test -s out/conftest2.$ac_objext
    then
      # The compiler can only warn and ignore the option if not recognized
@@ -9452,11 +9454,11 @@ else
    -e 's:.*FLAGS}\{0,1\} :&$lt_compiler_flag :; t' \
    -e 's: [^ ]*conftest\.: $lt_compiler_flag&:; t' \
    -e 's:$: $lt_compiler_flag:'`
-   (eval echo "\"\$as_me:9455: $lt_compile\"" >&5)
+   (eval echo "\"\$as_me:9457: $lt_compile\"" >&5)
    (eval "$lt_compile" 2>out/conftest.err)
    ac_status=$?
    cat out/conftest.err >&5
-   echo "$as_me:9459: \$? = $ac_status" >&5
+   echo "$as_me:9461: \$? = $ac_status" >&5
    if (exit $ac_status) && test -s out/conftest2.$ac_objext
    then
      # The compiler can only warn and ignore the option if not recognized
@@ -11836,7 +11838,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 11839 "configure"
+#line 11841 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -11932,7 +11934,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 11935 "configure"
+#line 11937 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -13888,11 +13890,11 @@ else
    -e 's:.*FLAGS}\{0,1\} :&$lt_compiler_flag :; t' \
    -e 's: [^ ]*conftest\.: $lt_compiler_flag&:; t' \
    -e 's:$: $lt_compiler_flag:'`
-   (eval echo "\"\$as_me:13891: $lt_compile\"" >&5)
+   (eval echo "\"\$as_me:13893: $lt_compile\"" >&5)
    (eval "$lt_compile" 2>conftest.err)
    ac_status=$?
    cat conftest.err >&5
-   echo "$as_me:13895: \$? = $ac_status" >&5
+   echo "$as_me:13897: \$? = $ac_status" >&5
    if (exit $ac_status) && test -s "$ac_outfile"; then
      # The compiler can only warn and ignore the option if not recognized
      # So say no if there are warnings other than the usual output.
@@ -13987,11 +13989,11 @@ else
    -e 's:.*FLAGS}\{0,1\} :&$lt_compiler_flag :; t' \
    -e 's: [^ ]*conftest\.: $lt_compiler_flag&:; t' \
    -e 's:$: $lt_compiler_flag:'`
-   (eval echo "\"\$as_me:13990: $lt_compile\"" >&5)
+   (eval echo "\"\$as_me:13992: $lt_compile\"" >&5)
    (eval "$lt_compile" 2>out/conftest.err)
    ac_status=$?
    cat out/conftest.err >&5
-   echo "$as_me:13994: \$? = $ac_status" >&5
+   echo "$as_me:13996: \$? = $ac_status" >&5
    if (exit $ac_status) && test -s out/conftest2.$ac_objext
    then
      # The compiler can only warn and ignore the option if not recognized
@@ -14039,11 +14041,11 @@ else
    -e 's:.*FLAGS}\{0,1\} :&$lt_compiler_flag :; t' \
    -e 's: [^ ]*conftest\.: $lt_compiler_flag&:; t' \
    -e 's:$: $lt_compiler_flag:'`
-   (eval echo "\"\$as_me:14042: $lt_compile\"" >&5)
+   (eval echo "\"\$as_me:14044: $lt_compile\"" >&5)
    (eval "$lt_compile" 2>out/conftest.err)
    ac_status=$?
    cat out/conftest.err >&5
-   echo "$as_me:14046: \$? = $ac_status" >&5
+   echo "$as_me:14048: \$? = $ac_status" >&5
    if (exit $ac_status) && test -s out/conftest2.$ac_objext
    then
      # The compiler can only warn and ignore the option if not recognized
@@ -17236,6 +17238,20 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 	CXXFLAGS="$CXXFLAGS $PTHREAD_CFLAGS"
 fi
 
+# Check whether --enable-sedtracer was given.
+if test "${enable_sedtracer+set}" = set; then :
+  enableval=$enable_sedtracer; enable_sedtracer_is=$enableval
+else
+  enable_sedtracer_is=yes
+fi
+
+if test "${enable_sedtracer_is}" = "yes"
+then
+
+$as_echo "#define QSE_ENABLE_SEDTRACER /**/" >>confdefs.h
+
+fi
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for socklen_t in sys/socket.h" >&5
 $as_echo_n "checking for socklen_t in sys/socket.h... " >&6; }
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
diff --git a/qse/configure.ac b/qse/configure.ac
index b056434e..d0f7e398 100644
--- a/qse/configure.ac
+++ b/qse/configure.ac
@@ -228,6 +228,13 @@ then
 	[CXXFLAGS="$CXXFLAGS $PTHREAD_CFLAGS"]
 fi
 
+AC_ARG_ENABLE([sedtracer], [AS_HELP_STRING([--enable-sedtracer],[enable qse_sed_setexectracer() (default. yes)])],
+	enable_sedtracer_is=$enableval,enable_sedtracer_is=yes)
+if test "${enable_sedtracer_is}" = "yes"
+then
+	AC_DEFINE([QSE_ENABLE_SEDTRACER],[],[enable qse_sed_setexectracer()])
+fi
+
 AC_MSG_CHECKING([for socklen_t in sys/socket.h])
 AC_TRY_COMPILE([#define _POSIX_PII_SOCKET
 #include <sys/types.h>
diff --git a/qse/include/qse/config.h.in b/qse/include/qse/config.h.in
index 8d8d9555..812506d4 100644
--- a/qse/include/qse/config.h.in
+++ b/qse/include/qse/config.h.in
@@ -284,6 +284,9 @@
 /* char is wchar */
 #undef QSE_CHAR_IS_WCHAR
 
+/* enable qse_sed_setexectracer() */
+#undef QSE_ENABLE_SEDTRACER
+
 /* Big Endian */
 #undef QSE_ENDIAN_BIG
 
diff --git a/qse/include/qse/sed/sed.h b/qse/include/qse/sed/sed.h
index 45cdc8d8..86a81d18 100644
--- a/qse/include/qse/sed/sed.h
+++ b/qse/include/qse/sed/sed.h
@@ -303,6 +303,7 @@ typedef int (*qse_sed_lformatter_t) (
 	int (*cwriter) (qse_sed_t*, qse_char_t)
 );
 
+#ifdef QSE_ENABLE_SEDTRACER
 enum qse_sed_exec_op_t
 {
 	QSE_SED_EXEC_READ,
@@ -317,6 +318,7 @@ typedef void (*qse_sed_exec_tracer_t) (
 	qse_sed_exec_op_t    op,
 	const qse_sed_cmd_t* cmd
 );
+#endif
 
 #ifdef __cplusplus
 extern "C" {
@@ -561,14 +563,24 @@ void qse_sed_setlinenum (
 	qse_size_t num    /**< a line number */
 );
 
+#ifdef QSE_ENABLE_SEDTRACER
+/**
+ * The qse_sed_getexectracer() function returns the execution tracer 
+ * function.
+ */
 qse_sed_exec_tracer_t qse_sed_getexectracer (
 	qse_sed_t* sed
 );
 
+/**
+ * The qse_sed_getexectracer() function sets a hook function via which 
+ * you can trace commands being executed.
+ */
 void qse_sed_setexectracer (
 	qse_sed_t*            sed,
 	qse_sed_exec_tracer_t tracer
 );
+#endif
 
 #ifdef __cplusplus
 }
diff --git a/qse/lib/sed/sed.c b/qse/lib/sed/sed.c
index 8e7609f9..cb0b6cec 100644
--- a/qse/lib/sed/sed.c
+++ b/qse/lib/sed/sed.c
@@ -586,6 +586,9 @@ static void free_command (qse_sed_t* sed, qse_sed_cmd_t* cmd)
 
 static void free_all_cids (qse_sed_t* sed)
 {
+	if (sed->src.cid == (qse_sed_cid_t*)&sed->src.unknown_cid) 
+		sed->src.cid = sed->src.cid->next;
+
 	while (sed->src.cid)
 	{
 		qse_sed_cid_t* next = sed->src.cid->next;
@@ -3542,7 +3545,9 @@ int qse_sed_exec (qse_sed_t* sed, qse_sed_io_fun_t inf, qse_sed_io_fun_t outf)
 
 	while (!sed->e.stopreq)
 	{
+#ifdef QSE_ENABLE_SEDTRACER
 		if (sed->e.tracer) sed->e.tracer (sed, QSE_SED_EXEC_READ, QSE_NULL);
+#endif
 
 		n = read_line (sed, 0);
 		if (n <= -1) { ret = -1; goto done; }
@@ -3561,7 +3566,9 @@ int qse_sed_exec (qse_sed_t* sed, qse_sed_io_fun_t inf, qse_sed_io_fun_t outf)
 
 			while (c != &sed->cmd.over)
 			{
+#ifdef QSE_ENABLE_SEDTRACER
 				if (sed->e.tracer) sed->e.tracer (sed, QSE_SED_EXEC_MATCH, c);
+#endif
 
 				n = match_address (sed, c);
 				if (n <= -1) { ret = -1; goto done; }
@@ -3573,7 +3580,9 @@ int qse_sed_exec (qse_sed_t* sed, qse_sed_io_fun_t inf, qse_sed_io_fun_t outf)
 					continue;
 				}
 
+#ifdef QSE_ENABLE_SEDTRACER
 				if (sed->e.tracer) sed->e.tracer (sed, QSE_SED_EXEC_EXEC, c);
+#endif
 				j = exec_cmd (sed, c);
 				if (j == QSE_NULL) { ret = -1; goto done; }
 				if (j == &sed->cmd.quit_quiet) goto done;
@@ -3590,7 +3599,9 @@ int qse_sed_exec (qse_sed_t* sed, qse_sed_io_fun_t inf, qse_sed_io_fun_t outf)
 			}
 		}
 
+#ifdef QSE_ENABLE_SEDTRACER
 		if (sed->e.tracer) sed->e.tracer (sed, QSE_SED_EXEC_WRITE, QSE_NULL);
+#endif
 		if (emit_output (sed, 0) <= -1) { ret = -1; goto done; }
 	}
 
@@ -3635,14 +3646,29 @@ const qse_char_t* qse_sed_setcompid (qse_sed_t* sed, const qse_char_t* id)
 	qse_sed_cid_t* cid;
 	qse_size_t len;
 	
+	if (sed->src.cid == (qse_sed_cid_t*)&sed->src.unknown_cid) 
+	{
+		/* if an error has occurred in a previously, you can't set it
+		 * any more */
+		return (const qse_char_t*)(sed->src.cid + 1);
+	}
+
 	len = qse_strlen (id);
-	cid = QSE_MMGR_ALLOC (sed->mmgr, QSE_SIZEOF(*cid) + ((len + 1) * QSE_SIZEOF(*id)));
-	if (cid == QSE_NULL) return QSE_NULL;
-	
+	cid = QSE_MMGR_ALLOC (sed->mmgr, 
+		QSE_SIZEOF(*cid) + ((len + 1) * QSE_SIZEOF(*id)));
+	if (cid == QSE_NULL) 
+	{
+		/* mark that an error has occurred */ 
+		sed->src.unknown_cid.buf[0] = QSE_T('\0');
+		cid = (qse_sed_cid_t*)&sed->src.unknown_cid;
+	}
+	else
+	{
+		qse_strcpy ((qse_char_t*)(cid + 1), id);
+	}
+
 	cid->next = sed->src.cid;
 	sed->src.cid = cid;
-	qse_strcpy ((qse_char_t*)(cid + 1), id);
-
 	return (const qse_char_t*)(cid + 1);
 }
 
@@ -3656,6 +3682,7 @@ void qse_sed_setlinenum (qse_sed_t* sed, qse_size_t num)
 	sed->e.in.num = num;
 }
 
+#ifdef QSE_ENABLE_SEDTRACER
 qse_sed_exec_tracer_t qse_sed_getexectracer (qse_sed_t* sed)
 {
 	return sed->e.tracer;
@@ -3665,4 +3692,5 @@ void qse_sed_setexectracer (qse_sed_t* sed, qse_sed_exec_tracer_t tracer)
 {
 	sed->e.tracer = tracer;
 }
+#endif
 
diff --git a/qse/lib/sed/sed.h b/qse/lib/sed/sed.h
index 8227b0fa..75e71100 100644
--- a/qse/lib/sed/sed.h
+++ b/qse/lib/sed/sed.h
@@ -61,6 +61,13 @@ struct qse_sed_cid_t
 	qse_sed_cid_t* next;		
 };
 
+typedef struct qse_sed_unknown_cid_t qse_sed_unknown_cid_t;
+struct qse_sed_unknown_cid_t
+{
+	qse_sed_cid_t* next;		
+	qse_char_t buf[1];
+};
+
 /** 
  * The qse_sed_t type defines a stream editor 
  */
@@ -94,7 +101,9 @@ struct qse_sed_t
 		qse_char_t        buf[1024];
 		int               eof;
 
-		qse_sed_cid_t*    cid;
+		qse_sed_cid_t*         cid;
+		qse_sed_unknown_cid_t  unknown_cid;
+
 		qse_sed_loc_t     loc; /**< location */
 		qse_cint_t        cc;  /**< last character read */
 		const qse_char_t* ptr; /**< beginning of the source text */
@@ -197,8 +206,10 @@ struct qse_sed_t
 		/** stop requested */
 		int stopreq;
 
+#ifdef QSE_ENABLE_SEDTRACER
 		/** trace function */
 		qse_sed_exec_tracer_t tracer;
+#endif
 	} e;
 };