diff --git a/src/main.zig b/src/main.zig
index 317746f..92827cc 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -11,24 +11,36 @@ pub fn main() !void {
 
     var prng = Random.DefaultPrng.init(blk: {
         var seed: u64 = undefined;
-        try std.posix.getrandom(std.mem.asBytes(&seed));
+        try posix.getrandom(mem.asBytes(&seed));
         break :blk seed;
     });
     const rand = prng.random();
 
-    const p = try getPrompt(allocator);
-    defer allocator.free(p);
+    const uname_cmd = try tokenizeCommand("uname -a", allocator);
+    defer allocator.free(uname_cmd);
 
-    var shell_state: ShellState = .{};
+    var shell_state: ShellState = .{
+        .env_map = try process.getEnvMap(allocator),
+    };
+    defer shell_state.env_map.deinit();
+
+    _ = try runCommand(uname_cmd, &shell_state, allocator);
+    var p = try getPrompt(allocator);
+
+    var limit: i32 = 100;
 
     while (try ln.linenoise(p)) |input| {
+        allocator.free(p);
         defer allocator.free(input);
+
         if (input.len > 0) {
-            shell_state.iteration += 1;
             try ln.history.add(input);
             const command = try tokenizeCommand(input, allocator);
             defer allocator.free(command);
-            if (!shell_state.should_test or try mathTest(rand, 100, shell_state.iteration)) {
+            if (!shell_state.should_test or
+                eql(u8, command[0], "nomorenumbers") or
+                try mathTest(rand, limit, shell_state.iteration))
+            {
                 _ = execCommand(command, &shell_state, allocator) catch |err| switch (err) {
                     error.FileNotFound => print("mash: {s}: command not found\n", .{command[0]}),
                     error.AccessDenied => print("mash: {s}: Permission denied\n", .{command[0]}),
@@ -41,15 +53,22 @@ pub fn main() !void {
                     \\
                 , .{});
             }
+
+            shell_state.iteration += 1;
+            if (shell_state.iteration % 3 == 0) {
+                limit *= 10;
+            }
         }
         if (shell_state.should_exit) break;
-    }
+        p = try getPrompt(allocator);
+    } else allocator.free(p); // free on crtl+d
 }
 
 const ShellState = struct {
     iteration: u32 = 0,
     should_test: bool = true,
     should_exit: bool = false,
+    env_map: process.EnvMap,
 };
 
 const Operator = enum(u8) {
@@ -96,11 +115,22 @@ fn mathTest(rand: Random, limit: i32, iteration: u32) !bool {
     const num2 = rand.intRangeAtMost(i32, 1, limit);
     const answer = op.apply(num1, num2);
 
-    if (builtin.mode == .Debug) {
+    if (comptime builtin.mode == .Debug) {
         print("Answer: {d}\n", .{answer});
     }
     print("{d} {s} {d} = ", .{ num1, op.toString(), num2 });
 
+    defer {
+        print("Calculating", .{});
+        for (0..3) |_| {
+            print(".", .{});
+            if (comptime builtin.mode != .Debug) {
+                sleep(2 * 1000 * 1000 * 1000);
+            }
+        }
+        print("\n", .{});
+    }
+
     return answer == while (true) {
         break readInt(stdin) catch |err| switch (err) {
             error.InvalidCharacter, error.EndOfStream => continue,
@@ -109,7 +139,7 @@ fn mathTest(rand: Random, limit: i32, iteration: u32) !bool {
     };
 }
 
-const BuiltinCommand = *const fn (*ShellState, [][]const u8, Allocator) anyerror!void;
+const BuiltinFunc = *const fn (*ShellState, [][]const u8, Allocator) anyerror!void;
 
 fn exitFn(shell_state: *ShellState, command: [][]const u8, allocator: Allocator) !void {
     _ = command;
@@ -120,26 +150,88 @@ fn exitFn(shell_state: *ShellState, command: [][]const u8, allocator: Allocator)
 fn nomorenumbersFn(shell_state: *ShellState, command: [][]const u8, allocator: Allocator) !void {
     shell_state.*.should_test = false;
     if (command.len > 1) {
-        _ = runCommand(command[1..], allocator) catch |err| {
+        _ = execCommand(command[1..], shell_state, allocator) catch |err| {
             return err;
         };
     }
 }
 
+fn cdFn(shell_state: *ShellState, command: [][]const u8, allocator: Allocator) !void {
+    const cwd = fs.cwd();
+    var env_map = shell_state.*.env_map;
+    const pwd = try cwd.realpathAlloc(allocator, ".");
+    const old_pwd = env_map.get("OLDPWD");
+    const home = env_map.get("HOME");
+    defer allocator.free(pwd);
+    var err: ?anyerror = null;
+
+    var target: ?[]const u8 = null;
+    if (command.len == 1) {
+        if (home) |h| {
+            target = h;
+        }
+    } else if (eql(u8, command[1], "-")) {
+        if (old_pwd) |old| {
+            target = old;
+        } else {
+            print("mash: cd: OLDPWD not set\n", .{});
+            return;
+        }
+    } else {
+        var buf: [fs.max_path_bytes]u8 = undefined;
+        target = cwd.realpath(command[1], &buf) catch |e| blk: {
+            err = e;
+            break :blk null;
+        };
+    }
+
+    if (target) |t| {
+        if (posix.chdir(t)) {
+            try env_map.put("OLDPWD", pwd);
+            try env_map.put("PWD", t);
+        } else |e| {
+            err = e;
+        }
+    }
+
+    if (err) |e| {
+        switch (e) {
+            error.FileNotFound => {
+                print("mash: cd: {s}: No such file or directory\n", .{target orelse command[1]});
+                return;
+            },
+            error.AccessDenied => {
+                print("mash: cd: {s}: Permission denied\n", .{target orelse command[1]});
+                return;
+            },
+            error.NameTooLong => {
+                print("mash: cd: {s}: File name too long\n", .{target orelse command[1]});
+                return;
+            },
+            else => return e,
+        }
+    }
+}
+
 fn execCommand(command: [][]const u8, shell_state: *ShellState, allocator: Allocator) !u8 {
-    const builtins = comptime .{ .{ "exit", exitFn }, .{ "nomorenumbers", nomorenumbersFn } };
-    const builtinMap = StaticStringMap(BuiltinCommand).initComptime(builtins);
+    const builtins = comptime .{
+        .{ "exit", exitFn },
+        .{ "nomorenumbers", nomorenumbersFn },
+        .{ "cd", cdFn },
+    };
+    const builtinMap = StaticStringMap(BuiltinFunc).initComptime(builtins);
 
     if (builtinMap.has(command[0])) {
         try builtinMap.get(command[0]).?(shell_state, command, allocator);
         return 0;
     } else {
-        return runCommand(command, allocator);
+        return runCommand(command, shell_state, allocator);
     }
 }
 
-fn runCommand(command: [][]const u8, allocator: Allocator) !u8 {
+fn runCommand(command: [][]const u8, shell_state: *ShellState, allocator: Allocator) !u8 {
     var child = process.Child.init(command, allocator);
+    child.env_map = &shell_state.env_map;
     const result = try child.spawnAndWait();
     return result.Exited;
 }
@@ -158,7 +250,7 @@ fn tokenizeCommand(command: []const u8, allocator: Allocator) ![][]const u8 {
     var argv_array_list = ArrayList([]const u8).init(allocator);
     defer argv_array_list.deinit();
 
-    var tokens = tokenizeAny(u8, command, " ");
+    var tokens = tokenizeAny(u8, command, "\t\r\n ");
     while (tokens.next()) |token| {
         try argv_array_list.append(token);
     }
@@ -180,15 +272,28 @@ fn readInt(reader: anytype) !i32 {
 }
 
 const std = @import("std");
+const posix = std.posix;
+
+const fs = std.fs;
+const path = std.fs.path;
+
+const mem = std.mem;
+const Allocator = mem.Allocator;
+const eql = mem.eql;
+
+const Reader = std.io.Reader;
 const stdout = std.io.getStdOut().writer();
 const stdin = std.io.getStdIn().reader();
-const tokenizeAny = std.mem.tokenizeAny;
+const tokenizeAny = mem.tokenizeAny;
+
 const process = std.process;
-const Allocator = std.mem.Allocator;
+
+const sleep = std.Thread.sleep;
+
+const Random = std.Random;
 const ArrayList = std.ArrayList;
 const StaticStringMap = std.static_string_map.StaticStringMap;
-const Random = std.Random;
-const Reader = std.io.Reader;
+
 const Linenoise = @import("linenoise").Linenoise;
 
 const builtin = @import("builtin");