Do not skip over the null terminator

sys/shell/shell.c

@@ -94,13 +94,12 @@ static void handle_input_line(shell_t *shell, char *line)
 
     /* first we need to calculate the number of arguments */
     unsigned argc = 0;
-    char *pos;
-    for (pos = line; *pos; ++pos) {
-        if (*pos <= ' ') {
-            *pos = 0;
-            continue;
-        }
-        else if (*pos == '"') {
+    char *pos = line;
+    while (1) {
+        if (*pos > ' ') {
+            /* found an argument */
+            if (*pos == '"') {
+                /* it's an quoted argument */
                 do {
                     ++pos;
                     if (!*pos) {
@@ -114,6 +113,7 @@ static void handle_input_line(shell_t *shell, char *line)
                 }
             }
             else {
+                /* it's an unquoted argument */
                 do {
                     ++pos;
                     if (*pos == '"') {
@@ -122,10 +122,20 @@ static void handle_input_line(shell_t *shell, char *line)
                     }
                 } while (*pos > ' ');
             }
+
+            /* count the number of arguments we got */
             ++argc;
-        *pos = 0;
         }
 
+        /* zero out the current position (space or quotation mark) and advance */
+        if (*pos > 0) {
+            *pos = 0;
+            ++pos;
+        }
+        else {
+            break;
+        }
+    }
     if (!argc) {
         return;
     }