Add PWD variable and pwd command

src/main.rs

@@ -5,8 +5,8 @@ use std::process::{Child, Command, Stdio};
 
 
 fn main(){
-    let mut STATUS=0;
-    
+    let mut status=0;
+    let mut pwd = env::current_dir().unwrap();
     loop {
         // use the `>` character as the prompt
         // need to explicitly flush this to ensure it prints before read_line
@@ -22,6 +22,7 @@ fn main(){
         let mut previous_command = None;
 
         while let Some(command) = commands.next()  {
+            // Other shell variables that can be changed
 
             // everything after the first whitespace character is interpreted as args to the command
             let mut parts = command.trim().split_whitespace();
@@ -30,15 +31,17 @@ fn main(){
 
             match command {
                 "true" | ":"  => {
-                    STATUS = 0;
+                    status = 0;
                 },
                 "false" => {
-                    STATUS = 1;
+                    status = 1;
                 },
                 "echo" => {
                     let args = args.peekable().peek().map_or("", |x| *x);
-                    if args.clone() == "$STATUS" {
-                        println!("{}", STATUS);
+                    if args.clone() == "$?" {
+                        println!("{}", status);
+                    } else if args.clone() == "$PWD" {
+                        println!("{}", pwd.display());
                     } else {
                         println!("{}", args);
                     }
@@ -48,12 +51,16 @@ fn main(){
                     let home_dir = env::var("HOME").unwrap();
                     let new_dir = args.peekable().peek().map_or(home_dir, |x| (*x).to_string());
                     let root = Path::new(&new_dir);
+                    pwd=root.clone().to_path_buf();
                     if let Err(e) = env::set_current_dir(&root) {
                         eprintln!("{}", e);
                     }
 
                     previous_command = None;
                 },
+                "pwd" => {
+                    println!("{}", pwd.display());
+                }
                 "exit" => return,
                 command => {
                     let stdin = previous_command