4 files changed, 29 insertions, 4 deletions
diff --git a/include/eval.h b/include/eval.h
index 00f466a..c93d346 100644
--- a/include/eval.h
+++ b/include/eval.h
@@ -5,9 +5,22 @@
 
 namespace ov4
 {
+
+struct T_pipe
+{
+    enum class T_pipe_type
+    {
+        NOT_PIPE,
+        WRITE_PIPE,
+        READ_PIPE,
+    };
+    T_pipe_type pipe_type = NOT_PIPE;
+    int fd = -1; 
+} T_pipe_not_pipe;
+
 int eval_exe(const std::string &s, bool is_async);
-int eval_exe(const std::string &s, bool is_async, const T_lexer *lexer_instance, size_t i);
-int eval_tree_cd(size_t i, const T_lexer &lexer_instance, bool inside_subshell);
+int eval_exe(const std::string &s, bool is_async, const T_lexer *lexer_instance, size_t i, const T_pipe &pi = T_pipe_not_pipe);
+int eval_tree_cd(size_t i, const T_lexer &lexer_instance, bool inside_subshell, T_pipe pi = T_pipe_not_pipe);
 void eval(char *cmdline);
 void eval_err(int err);
 
diff --git a/src/eval/eval_err.cc b/src/eval/eval_err.cc
index 3d90262..6a7c4e0 100644
--- a/src/eval/eval_err.cc
+++ b/src/eval/eval_err.cc
@@ -8,6 +8,9 @@ using namespace std;
 namespace ov4
 {
 
+/*
+ * print exec error message
+ */
 void eval_err(int err)
 {
     switch (err)
diff --git a/src/eval/eval_exe.cc b/src/eval/eval_exe.cc
index 4e893f3..9a2a592 100644
--- a/src/eval/eval_exe.cc
+++ b/src/eval/eval_exe.cc
@@ -23,7 +23,10 @@ int eval_exe(const string &s, bool is_async)
     return eval_exe(s, is_async, nullptr, string::npos);
 }
 
-int eval_exe(const string &s, bool is_async, const T_lexer *lexer_instance, size_t i)
+/*
+ * receive a single command, and execute
+ */
+int eval_exe(const string &s, bool is_async, const T_lexer *lexer_instance, size_t i, const T_pipe &pi)
 {
     loggerln("eval_exe: receive {}", s);
 
diff --git a/src/eval/eval_tree_cd.cc b/src/eval/eval_tree_cd.cc
index 7d7c1af..0e5b8f4 100644
--- a/src/eval/eval_tree_cd.cc
+++ b/src/eval/eval_tree_cd.cc
@@ -1,6 +1,7 @@
 #include "eval.h"
 
 #include <string>
+#include <unistd.h>
 
 #include "error.h"
 #include "lang_analysis/lexer_class.h"
@@ -15,11 +16,16 @@ using namespace std;
 namespace ov4
 {
 
-int eval_tree_cd(size_t i, const T_lexer &lexer_instance, bool inside_subshell)
+/*
+ * browse AST
+ * and recurse or set up a subshell
+ */
+int eval_tree_cd(size_t i, const T_lexer &lexer_instance, bool inside_subshell, T_pipe pi)
 {
     // TODO: async
 
     int ret = -1;
+    int fd[2];
 
     println("eval_tree_cd: processing {} subshell {}", i, (lexer_instance.ast[i].subshell ? "TRUE" : "FALSE"));