diff --git a/src/CommandLine.cc b/src/CommandLine.cc
index 0f7b24d..c2b28a2 100644
--- a/src/CommandLine.cc
+++ b/src/CommandLine.cc
@@ -28,7 +28,7 @@ using namespace std;
 
 /// strict weak ordering by flag (lexicographic).
 bool Option::operator<(const _Option &b) const {
-  return std::strcmp(flag, b.flag) < 0;
+  return (flag && b.flag) ? std::strcmp(flag, b.flag) < 0 : (flag < b.flag);
 }
 
 ostream &operator<<(ostream &a, const Option &b) {
@@ -50,8 +50,12 @@ ostream &operator<<(ostream &a, const Option &b) {
 
 CommandLine::CommandLine(const set<Option> &a) : logger(LogConfig()), option_s(a) {
   for (auto option : a) {
-    flag_m.insert(make_pair(option.flag, option));
-    longname_m.insert(make_pair(option.longname, option));
+    if (option.flag) {
+      flag_m.insert(make_pair(option.flag, option));
+    }
+    if (option.longname) {
+      longname_m.insert(make_pair(option.longname, option));
+    }
   }
 }
 
@@ -131,11 +135,11 @@ bool CommandLine::is_set_option(const Option &a) const {
 }
 
 bool CommandLine::is_set_flag(const char *a) const {
-  return flag_m.find(a) != flag_m.end() && is_set_option(flag_m.find(a)->second);
+  return a && flag_m.find(a) != flag_m.end() && is_set_option(flag_m.find(a)->second);
 }
 
 bool CommandLine::is_set_longname(const char *a) const {
-  return longname_m.find(a) != longname_m.end() && is_set_option(longname_m.find(a)->second);
+  return a && longname_m.find(a) != longname_m.end() && is_set_option(longname_m.find(a)->second);
 }
 
 vector<vector<const char*> > CommandLine::get_values_for_option(const Option &a) const {
@@ -146,11 +150,11 @@ vector<vector<const char*> > CommandLine::get_values_for_option(const Option &a)
 }
 
 vector<vector<const char*> > CommandLine::get_values_for_flag(const char *a) const {
-  return flag_m.find(a) != flag_m.end() ? get_values_for_option(flag_m.find(a)->second) : vector<vector<const char*> >();
+  return (a && flag_m.find(a) != flag_m.end()) ? get_values_for_option(flag_m.find(a)->second) : vector<vector<const char*> >();
 }
 
 vector<vector<const char*> > CommandLine::get_values_for_longname(const char *a) const {
-  return longname_m.find(a) != longname_m.end() ? get_values_for_option(longname_m.find(a)->second) : vector<vector<const char*> >();
+  return (a && longname_m.find(a) != longname_m.end()) ? get_values_for_option(longname_m.find(a)->second) : vector<vector<const char*> >();
 }
 
 const char* CommandLine::get_arg_for_option(const Option &a, int i) const {
diff --git a/src/csvjoin.cc b/src/csvjoin.cc
index 3302110..2a1a1c3 100644
--- a/src/csvjoin.cc
+++ b/src/csvjoin.cc
@@ -50,9 +50,9 @@ const int join_option_n = sizeof(join_option_a)/sizeof(Option);
 
 /// Extension to DefaultCommandLine: JoinCommandLine can derive join parameters from options.
 class JoinCommandLine : public DefaultCommandLine {
- pair<ColIvalV,ColIvalV> join_columns=make_pair(false,false);
- const char *right_fname = NULL;
- JoinType join_type=JOIN_INNER;
+ pair<ColIvalV,ColIvalV> join_columns;
+ const char *right_fname;
+ JoinType join_type;
 
  int set_join_columns() {
   if (!is_set_flag("jc")){
@@ -80,7 +80,8 @@ class JoinCommandLine : public DefaultCommandLine {
  };
 public:
  JoinCommandLine(const string &desc, const string &usage) :
-  DefaultCommandLine(desc, usage,set<Option>(join_option_a,join_option_a+join_option_n)){};
+  DefaultCommandLine(desc, usage,set<Option>(join_option_a,join_option_a+join_option_n)),
+  join_columns(make_pair(false,false)),right_fname(nullptr),join_type(JoinType::JOIN_INNER){};
 
  int process() {
 // join type
diff --git a/tests/CommandLine_test.cc b/tests/CommandLine_test.cc
new file mode 100644
index 0000000..c59a879
--- /dev/null
+++ b/tests/CommandLine_test.cc
@@ -0,0 +1,166 @@
+#include "CommandLine.h"
+#include <sstream>
+#include <string>
+#include <cassert>
+#include "stl_out.h"
+
+using namespace std;
+
+bool test_Option_print(const Option &obj, const string &expected) {
+ bool retv = true;
+
+ stringstream ss;
+ ss << obj;
+ string actual = ss.str();
+
+ retv = (actual == expected);
+ if (!retv) {
+  cerr << "actual: " << actual << endl;
+  cerr << "expected: " << expected << endl;
+ }
+ return retv;
+}
+
+bool vvchrptr_eq(const vector<vector<const char*>> &a, const vector<vector<const char*>> &b) {
+ bool retv = true;
+ if (a.size()!=b.size()) return false;
+ for (unsigned int i = 0; i<a.size(); ++i) {
+  if (a[i].size()!=b[i].size()) return false;
+  for (unsigned int j =0; j< a[i].size(); ++j) {
+   if (strcmp(a[i][j],b[i][j])) return false;
+  }
+ }
+ return retv;
+}
+
+bool test_CommandLine_getopt(CommandLine *obj, const Option &check_option, bool expected_found, const vector<vector<const char*> > &expected_values) {
+ bool retv = true;
+
+ bool actual_found_flag = obj->is_set_flag(check_option.flag);
+ bool actual_found_longname = obj->is_set_longname(check_option.longname);
+ bool actual_found_option = obj->is_set_option(check_option);
+
+ auto actual_val_flag = obj->get_values_for_flag(check_option.flag);
+ auto actual_val_longname = obj->get_values_for_longname(check_option.longname);
+ auto actual_val_option = obj->get_values_for_option(check_option);
+
+ if (actual_found_flag != expected_found) {
+  cerr << "is_set_flag mismatch\tflag: " << check_option.flag << "\tactual: " << actual_found_flag << "\texpected: " << expected_found << endl;
+  retv = false;
+ }
+ if (actual_found_longname != expected_found) {
+  cerr << "is_set_longname mismatch\tlongname: " << check_option.longname << "\tactual: " << actual_found_longname << "\texpected: " << expected_found << endl;
+  retv = false;
+ }
+ if (actual_found_option != expected_found) {
+  cerr << "is_set_option mismatch\toption: " << check_option << "\tactual: " << actual_found_option << "\texpected: " << expected_found << endl;
+  retv = false;
+ }
+ if (!vvchrptr_eq(actual_val_flag,expected_values)) {
+  cerr<<"get_values_for_flag mismatch\tflag: "<<check_option.flag<<endl;
+  cerr<<"actual: "<<actual_val_flag<<" vs. expected: "<<expected_values<<endl;
+  retv = false;
+ }
+ if (!vvchrptr_eq(actual_val_longname,expected_values)) {
+  cerr<<"get_values_for_longname mismatch\tlongname: "<<check_option.longname<<endl;
+  retv = false;
+ }
+ if (!vvchrptr_eq(actual_val_option,expected_values)) {
+  cerr<<"get_values_for_option mismatch\toption: "<<check_option<<endl;
+  retv = false;
+ }
+ if (retv) {
+  for (unsigned int i = 0; i<check_option.arg_num; ++i) {
+   auto actual_flag_val_i = obj->get_arg_for_flag(check_option.flag,i);
+   auto actual_longname_val_i = obj->get_arg_for_longname(check_option.longname,i);
+   auto actual_option_val_i = obj->get_arg_for_option(check_option,i);
+   if (expected_values.empty() || (expected_values[0].size() <= i)) {
+    if (actual_flag_val_i!=nullptr) {
+     cerr<<"get_arg_for_flag should have return nullptr\tflag"<<check_option.flag<<" arg #"<<i<<"actual: "<<actual_flag_val_i<<endl;
+     retv = false;
+    }
+    if (actual_longname_val_i!=nullptr) {
+     cerr<<"get_arg_for_longname should have return nullptr\tlongname"<<check_option.longname<<" arg #"<<i<<"actual: "<<actual_longname_val_i<<endl;
+     retv = false;
+    }
+    if (actual_option_val_i!=nullptr) {
+     cerr<<"get_arg_for_option should have return nullptr\toption"<<check_option<<" arg #"<<i<<"actual: "<<actual_option_val_i<<endl;
+     retv = false;
+    }
+   } else {
+    if (strcmp(actual_flag_val_i, expected_values[0][i])) {
+     cerr<<"get_arg_for_flag mismatch\tflag "<<check_option.flag<<" arg #"<<i<<"\t actual: "<<actual_flag_val_i<<" vs. expected: "<<expected_values[0][i]<<endl;
+     retv = false;
+    }
+    if (strcmp(actual_longname_val_i, expected_values[0][i])) {
+     cerr<<"get_arg_for_longname mismatch\tlongname "<<check_option.longname<<" arg #"<<i<<"\t actual: "<<actual_longname_val_i<<" vs. expected: "<<expected_values[0][i]<<endl;
+     retv = false;
+    }
+    if (strcmp(actual_option_val_i, expected_values[0][i])) {
+     cerr<<"get_arg_for_option mismatch\toption "<<check_option<<" arg #"<<i<<"\t actual: "<<actual_option_val_i<<" vs. expected: "<<expected_values[0][i]<<endl;
+     retv = false;
+    }
+   }
+  }
+ }
+ return retv;
+}
+
+class TestCommandLine : public CommandLine {
+
+ int process() {
+  return 0;
+ }
+public:
+
+ TestCommandLine(const set<Option> &_opts) : CommandLine(_opts) {
+ }
+
+ CommandLineExecuteResponse execute(int argc, const char *a[]) {
+  parse(argc, a);
+  return CommandLineExecuteResponse::CMDLINE_OK;
+ }
+};
+
+int main(int argc, const char *argv[]) {
+ Option opt1 = {"a", "append", 2, MultipleDefinition::APPEND, "This is opt1.\n"};
+ Option opt1_noflag = {nullptr, "append", 2, MultipleDefinition::APPEND, "This is opt1.\n"};
+ Option opt1_nolongname = {"a", nullptr, 2, MultipleDefinition::APPEND, "This is opt1.\n"};
+ Option opt1_nohelp = {"a", "append", 2, MultipleDefinition::APPEND, nullptr};
+ Option opt1_nothing = {nullptr, nullptr, 2, MultipleDefinition::APPEND, nullptr};
+
+ assert(test_Option_print(opt1, "-a\t--append=<arg1> <arg2>\tThis is opt1.\n"));
+ assert(test_Option_print(opt1_noflag, "\t--append=<arg1> <arg2>\tThis is opt1.\n"));
+ assert(test_Option_print(opt1_nolongname, "-a\tThis is opt1.\n"));
+ assert(test_Option_print(opt1_nohelp, "-a\t--append=<arg1> <arg2>"));
+ assert(test_Option_print(opt1_nothing, ""));
+
+ Option opts[] = {
+  {"a", "alpha", 0, MultipleDefinition::IGNORE, "This is option alpha."},
+  {"b", "bravo", 1, MultipleDefinition::IGNORE, "This is option bravo."},
+  {"c", "charlie", 2, MultipleDefinition::OVERRIDE, "This is option charlie."},
+  {"d", "delta", 1, MultipleDefinition::OVERRIDE, "This is option delta."}
+ };
+ TestCommandLine cmdline0(set<Option>(opts, opts + sizeof (opts) / sizeof (opts[0])));
+ TestCommandLine cmdline1=cmdline0;
+ const char *cmdline0args[] = {"progname", "-a", "-b", "1"};
+ cmdline0.execute(4, cmdline0args);
+ const char *cmdline1args[] = {"progname", "-b", "1", "-b", "2", "--charlie=a", "b", "--charlie=c", "d"};
+ cmdline1.execute(9, cmdline1args);
+
+ assert(test_CommandLine_getopt(&cmdline0, opts[0], true, {{}}));
+ assert(test_CommandLine_getopt(&cmdline0, opts[1], true, {{"1"}}));
+ assert(test_CommandLine_getopt(&cmdline0, opts[2], false, {}));
+ assert(test_CommandLine_getopt(&cmdline0, opts[3], false, {}));
+
+ assert(test_CommandLine_getopt(&cmdline0, opt1_noflag, false, {}));
+ assert(test_CommandLine_getopt(&cmdline0, opt1_nothing, false, {}));
+
+
+ assert(test_CommandLine_getopt(&cmdline1, opts[0], false, {}));
+ assert(test_CommandLine_getopt(&cmdline1, opts[1], true, {{"1"}}));
+ assert(test_CommandLine_getopt(&cmdline1, opts[2], true, {{"c","d"}}));
+ assert(test_CommandLine_getopt(&cmdline1, opts[3], false, {}));
+
+ return 0;
+}
diff --git a/tests/Makefile.am b/tests/Makefile.am
index b63e207..b061d93 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -4,6 +4,7 @@ TESTS = \
 	ColIval_ctor_test \
 	ColIvalV_ctor_test \
 	ColIvalV_extract_ival_test \
+	CommandLine_test \
 	CsvCell_ctor_test \
 	CsvCell_decimal_test \
 	CsvCell_less_test \
@@ -19,6 +20,7 @@ check_PROGRAMS = \
 	ColIval_ctor_test \
 	ColIvalV_ctor_test \
 	ColIvalV_extract_ival_test \
+	CommandLine_test \
 	CsvCell_ctor_test \
 	CsvCell_decimal_test \
 	CsvCell_less_test \
@@ -37,9 +39,7 @@ BUILT_SOURCES =
 AM_CXXFLAGS = -I${top_srcdir}/src
 LDADD = ../src/libcsvtools.a
 
-#strsplit_test_SOURCES=strsplit_test.cc ../src/CommandLine.cc
-#stdrowfuncs_test_SOURCES=stdrowfuncs_test.cc ../src/Numeric.cc ../src/RowFunc.cc
-#stdrowfuncs_test_OBJS=stdrowfuncs_test.cc src/Numeric.o src/RowFunc.o
+CommandLine_test_LDADD=../src/CommandLine.o ../src/libcsvtools.a
 strsplit_test_LDADD=../src/CommandLine.o ../src/libcsvtools.a
 stdrowfuncs_test_LDADD= ../src/Numeric.o ../src/RowFunc.o
 
diff --git a/tests/app/Makefile.am b/tests/app/Makefile.am
index 6545218..2c1f01e 100644
--- a/tests/app/Makefile.am
+++ b/tests/app/Makefile.am
@@ -21,6 +21,7 @@ dist_check_DATA= \
 	t1_filt01.csv t1_filt02.csv t1_filt1a.csv t1_filtne.csv \
 	t1_sort1e0d.csv t1_esc0.csv \
 	t1t2_natural.csv t1t2_outer.csv \
+	t1t4_natural.csv \
 	t2.csv t2esc.csv t2esch.csv t3.csv t2t3_cross.csv \
 	t3_rsx.csv t3_rstab.csv \
 	t4.csv \
diff --git a/tests/app/csvjoin_jtx_test.sh b/tests/app/csvjoin_jtx_test.sh
index b571228..6ca7b19 100755
--- a/tests/app/csvjoin_jtx_test.sh
+++ b/tests/app/csvjoin_jtx_test.sh
@@ -8,6 +8,7 @@ CSVCONV="../../src/csvconv"
 < "$WDIR/t1.csv" "$CSVJOIN" -jt natural -jf "$WDIR/t2.csv" | diff - "$WDIR/t1t2_natural.csv" || exit 1
 < "$WDIR/t1.csv" "$CSVJOIN" -jt natural -jf "$WDIR/t2esc.csv" | "$CSVCONV" -esc remove | diff - "$WDIR/t1t2_natural.csv" || exit 1
 < "$WDIR/t1.csv" "$CSVJOIN" -jt natural -jf "$WDIR/t2esch.csv" | "$CSVCONV" -esc remove | diff - "$WDIR/t1t2_natural.csv" || exit 1
+< "$WDIR/t1.csv" "$CSVJOIN" -jt natural -jf "$WDIR/t4.csv" | "$CSVCONV" -esc remove | diff - "$WDIR/t1t4_natural.csv" || exit 1
 < "$WDIR/t1.csv" "$CSVJOIN" -jt inner -jc 1:0 -jf "$WDIR/t2.csv" | diff - "$WDIR/t1t2_natural.csv" || exit 1
 < "$WDIR/t1.csv" "$CSVJOIN" -jt outer -jc 1:0 -jf "$WDIR/t2.csv" | diff - "$WDIR/t1t2_outer.csv" || exit 1
 < "$WDIR/t2.csv" "$CSVJOIN" -jt cross -jf "$WDIR/t3.csv" | diff - "$WDIR/t2t3_cross.csv" || exit 1
diff --git a/tests/app/t1t4_natural.csv b/tests/app/t1t4_natural.csv
new file mode 100644
index 0000000..a449ee8
--- /dev/null
+++ b/tests/app/t1t4_natural.csv
@@ -0,0 +1 @@
+foo,bar,name,test_string