add some basic inbuilt commands

src/inbuilt.rs

@@ -0,0 +1,15 @@
+use std::env;
+
+pub fn cd(args: Vec<&str>) {
+    let path = args[0].to_string();
+    assert!(env::set_current_dir(&path).is_ok());
+}
+
+pub fn help() {
+    println!("This is an example help message")
+}
+
+pub fn exit() {
+    std::process::exit(0x0100)
+}
+

src/main.rs

@@ -21,7 +21,12 @@ fn main() {
         let cmd = core::get_command(tokens.clone());
         let args = core::get_args(tokens);
 
-        // Execute command and argument.
-        core::execute(cmd, args);
+        // Execute inbuilt commands if supplied, otherwise execute command and argument.
+        match cmd {
+            "cd" => inbuilt::cd(args),
+            "help" => inbuilt::help(),
+            "exit" => inbuilt::exit(),
+            _ => core::execute(cmd, args),
+        }
     }
 }