Added git ignore list.

os/extra/src/.gitignore

+input.lex.*
+input.yacc.*
+shell

os/extra/src/input.y

@@ -39,7 +39,7 @@ Start: /* empty */
     | Commands
     ;
 
-Commands: Command
+Commands: Command  /*{ printf("cmd: %s\n", $1); }*/
 /*    | Command EOS*/
     | Commands EOL { start_shell_entry(); } Command
     | Commands '|' { start_shell_pipe(); } Command

os/extra/src/main.c

@@ -5,11 +5,14 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <assert.h>
+#include <sys/stat.h>
 
 #include "input.yacc.h"
 #include "input.lex.h"
 #include "input.l.h"
 
+int is_interactive = 0;
+
 void start_shell_pipe() {
     printf("start pipe");
 }
@@ -19,13 +22,33 @@ void start_shell_entry() {
 }
 
 int main(void) {
-    yyset_debug(0);
+    // Detect if terminal is attached
+    struct stat stats;
+    fstat(0, &stats);
+
+    // Looks like a tty, so we're in interactive mode.
+    if (S_ISCHR(stats.st_mode)) {
+        is_interactive = 1;
+        start_shell_entry();
+    }
+    else if (S_ISFIFO(stats.st_mode))
+        // Looks like a pipe, so we're in non-interactive mode.
+        is_interactive = 1;
+    else {
+        is_interactive = 1;
+        start_shell_entry();
+    }
+
+    // Disable yacc debug mode
+    yyset_debug(1);
 
+    // Start the shell parser
     if( yyparse() ) {
         fprintf(stderr, "Error: Parsing failed\n");
         return EXIT_FAILURE;
     }
 
+    // EOF reached: clean up the mess
     yylex_destroy();
 
     if( yyin )