src/builtins.c

@@ -27,6 +27,10 @@ bool is_builtin(char *command) {
         return true;
     }
 
+    if (strcmp(command, "help") == 0) {
+        return true;
+    }
+
     if (strcmp(command, "cd") == 0) {
         return true;
     }
@@ -50,6 +54,9 @@ void run_builtin(StringArray *args) {
     if (strcmp(args->array[0], "exit") == 0) {
         exit_shell(args);
     }
+    else if (strcmp(args->array[0], "help") == 0) {
+        help(args);
+    }
     else if (strcmp(args->array[0], "cd") == 0) {
         change_directory(args);
     }
@@ -67,6 +74,21 @@ void run_builtin(StringArray *args) {
     }
 }
 
+void help(StringArray *args) {
+    if (args->size > 1) {
+        fprintf(stderr, "Too many arguments!\n");
+        return;
+    }
+    fprintf(stdout, "myshellin help\n");
+    fprintf(stdout, "These command are defined internally in myshellin.\n\n");
+    fprintf(stdout, "set $<variable> = <value>                  set an environment variable\n");
+    fprintf(stdout, "environ                                    show all enviornment variables\n");
+    fprintf(stdout, "echo [$<variable> ...] [comment ...]       print comments or variables to stdout\n");
+    fprintf(stdout, "help                                       show this help message\n");
+    fprintf(stdout, "cd [dir] [$<variable>]                     change directory\n");
+    fprintf(stdout, "exit                                       exit the shell\n");
+}
+
 void exit_shell(StringArray *args) {
     free_string_array(args);
     exit(EXIT_SUCCESS);

src/include/builtins.h

@@ -32,6 +32,12 @@ bool is_builtin(char *command);
  */
 void run_builtin(StringArray *args);
 
+/**
+ * Show help message for the shell.
+ * @param args The arguments passed to help.
+ */
+void help(StringArray *args);
+
 /**
  * Exit the shell.
  * @param args The arguments that were used to call exit. This is used to free the memory before exit.