diff --git a/src/builtins.rs b/src/builtins.rs
index 8381458..b80efb3 100644
--- a/src/builtins.rs
+++ b/src/builtins.rs
@@ -1,17 +1,20 @@
 //! builtins to sesh
 #![allow(clippy::type_complexity)]
 
+use std::sync::{Arc, Mutex};
+
 /// List of builtins
 pub const BUILTINS: [(
     &str,
     fn(args: Vec<String>, unsplit_args: String, state: &mut super::State) -> i32,
     &str,
-); 5] = [
+); 6] = [
     ("cd", cd, "[dir]"),
     ("exit", exit, ""),
     ("echo", echo, "[-e] [text ...]"),
     ("alias", alias, "[name] [value]"),
     ("help", help, ""),
+    ("source", eval, "filename [arguments]"),
 ];
 
 /// Change the directory
@@ -86,8 +89,51 @@ pub fn help(_: Vec<String>, _: String, _: &mut super::State) -> i32 {
     println!("Use `man sesh` to find out more about the shell in general.");
     println!("Use `man -k' or `info' to find out more about commands not in this list.");
     println!();
-    for builtin in BUILTINS {
+    let mut builtins = BUILTINS.clone();
+    builtins.sort_by(|v1, v2| v1.0.cmp(v2.0));
+
+    for builtin in builtins {
         println!("{} {}", builtin.0, builtin.2);
     }
     0
 }
+
+/// Run a file.
+pub fn eval(args: Vec<String>, _: String, state: &mut super::State) -> i32 {
+    if args.len() < 2 {
+        println!("sesh: {}: filename argument required", args[0]);
+        println!("sesh: {0}: usage: {0} filename [arguments]", args[0]);
+        return 1;
+    }
+
+    let file = std::fs::read(args[1].clone());
+    if file.is_err() {
+        println!(
+            "sesh: {}: error opening file: {}",
+            args[0],
+            file.unwrap_err()
+        );
+        return 2;
+    }
+    let file = String::from_utf8(file.unwrap());
+    if file.is_err() {
+        println!("sesh: {}: invalid UTF-8: {}", args[0], file.unwrap_err());
+        return 3;
+    }
+    let file = file.unwrap();
+
+    let mut state2 = state.clone();
+
+    let mut i = 0usize;
+    for arg in &args[1..] {
+        state2.shell_env.push(super::ShellVar {
+            name: format!("{}", i),
+            value: arg.clone(),
+        });
+        i += 1;
+    }
+
+    super::eval(&file, &mut state2);
+
+    0
+}
diff --git a/src/main.rs b/src/main.rs
index 8116e74..1abccb4 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -38,14 +38,6 @@ struct ShellVar {
 /// A lot of [ShellVar]s.
 type ShellVars = Vec<ShellVar>;
 
-/// Whether a variable is local or not.
-#[derive(Clone, Debug, PartialEq, Eq)]
-enum VariableLocality {
-    /// A local variable.
-    Local,
-    /// A nonlocal variable.
-    Nonlocal,
-}
 /// A reference to a variable.
 #[derive(Clone, Debug, PartialEq, Eq)]
 enum Variable {
@@ -66,8 +58,6 @@ struct Alias {
 /// The state of the shell
 #[derive(Clone, Debug)]
 struct State {
-    /// Environment variables
-    env: Arc<Mutex<std::env::VarsOs>>,
     /// Shell-local variables only accessible via builtins.
     shell_env: ShellVars,
     /// The focused variable.
@@ -170,11 +160,20 @@ fn split_statements(statement: &str) -> Vec<String> {
         .concat()
 }
 
+/// Substitute in shell variables
+fn substitute_vars(statement: &str, state: State) -> String {
+    let mut out = statement.to_string();
+    for ShellVar { name, value } in state.shell_env {
+        out = out.replace(&("$".to_owned()+&name), &value);
+    }
+    out
+}
+
 #[allow(clippy::arc_with_non_send_sync)]
 /// Evaluate a statement. May include multiple.
 fn eval(statement: &str, state: &mut State) {
     let statement = remove_comments(statement);
-    let statements = split_statements(&statement);
+    let statements = split_statements(&substitute_vars(&statement, state.clone()));
 
     for statement in statements {
         let mut statement_split = split_statement(&statement);
@@ -236,7 +235,6 @@ fn eval(statement: &str, state: &mut State) {
         }
     }
 
-    state.env = Arc::new(Mutex::new(std::env::vars_os()));
     let s = state.clone();
     state.history.push(s);
 }
@@ -284,7 +282,6 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     let options = Args::parse();
 
     let mut state = State {
-        env: Arc::new(Mutex::new(std::env::vars_os())),
         shell_env: Vec::new(),
         focus: Variable::Local(String::new()),
         history: Vec::new(),
diff --git a/test.sesh b/test.sesh
new file mode 100644
index 0000000..728e625
--- /dev/null
+++ b/test.sesh
@@ -0,0 +1 @@
+echo test $0 $1
\ No newline at end of file