diff --git a/cmdlang/ast.go b/cmdlang/ast.go
index 5fe41be..a305692 100644
--- a/cmdlang/ast.go
+++ b/cmdlang/ast.go
@@ -12,6 +12,7 @@ type astLiteral struct {
 
 type astCmdArg struct {
 	Literal *astLiteral  `parser:"@@"`
+	Var     *string      `parser:"| '$' @Ident"`
 	Sub     *astPipeline `parser:"| '(' @@ ')'"`
 }
 
diff --git a/cmdlang/builtins.go b/cmdlang/builtins.go
index f98dc4c..404622a 100644
--- a/cmdlang/builtins.go
+++ b/cmdlang/builtins.go
@@ -25,6 +25,23 @@ func echoBuiltin(ctx context.Context, args invocationArgs) (object, error) {
 	return asStream(line.String()), nil
 }
 
+func setBuiltin(ctx context.Context, args invocationArgs) (object, error) {
+	if err := args.expectArgn(2); err != nil {
+		return nil, err
+	}
+
+	name, err := args.stringArg(0)
+	if err != nil {
+		return nil, err
+	}
+
+	newVal := args.args[1]
+
+	// TODO: if the value is a stream, consume the stream and save it as a list
+	args.ec.setVar(name, newVal)
+	return newVal, nil
+}
+
 func toUpperBuiltin(ctx context.Context, inStream stream, args invocationArgs) (object, error) {
 	// Handle args
 	return mapFilterStream{
diff --git a/cmdlang/env.go b/cmdlang/env.go
index 3e78f9a..9861e0a 100644
--- a/cmdlang/env.go
+++ b/cmdlang/env.go
@@ -8,6 +8,7 @@ type evalCtx struct {
 	parent        *evalCtx
 	currentStream stream
 	commands      map[string]invokable
+	vars          map[string]object
 }
 
 func (ec *evalCtx) withCurrentStream(s stream) *evalCtx {
@@ -25,6 +26,27 @@ func (ec *evalCtx) addCmd(name string, inv invokable) {
 	ec.commands[name] = inv
 }
 
+func (ec *evalCtx) setVar(name string, val object) {
+	if ec.vars == nil {
+		ec.vars = make(map[string]object)
+	}
+	ec.vars[name] = val
+}
+
+func (ec *evalCtx) getVar(name string) (object, bool) {
+	if ec.vars == nil {
+		return nil, false
+	}
+
+	if v, ok := ec.vars[name]; ok {
+		return v, true
+	} else if ec.parent != nil {
+		return ec.parent.getVar(name)
+	}
+
+	return nil, false
+}
+
 func (ec *evalCtx) lookupCmd(name string) (invokable, error) {
 	for e := ec; e != nil; e = e.parent {
 		if e.commands == nil {
diff --git a/cmdlang/eval.go b/cmdlang/eval.go
index b00026e..9658508 100644
--- a/cmdlang/eval.go
+++ b/cmdlang/eval.go
@@ -45,9 +45,11 @@ func (e evaluator) evalCmd(ctx context.Context, ec *evalCtx, ast *astCmd) (objec
 		return nil, err
 	}
 
+	invArgs := invocationArgs{ec: ec, args: args}
+
 	if ec.currentStream != nil {
 		if si, ok := cmd.(streamInvokable); ok {
-			return si.invokeWithStream(ctx, ec.currentStream, invocationArgs{args: args})
+			return si.invokeWithStream(ctx, ec.currentStream, invArgs)
 		} else {
 			if err := ec.currentStream.close(); err != nil {
 				return nil, err
@@ -55,13 +57,19 @@ func (e evaluator) evalCmd(ctx context.Context, ec *evalCtx, ast *astCmd) (objec
 		}
 	}
 
-	return cmd.invoke(ctx, invocationArgs{args: args})
+	return cmd.invoke(ctx, invArgs)
 }
 
 func (e evaluator) evalArg(ctx context.Context, ec *evalCtx, n astCmdArg) (object, error) {
 	switch {
 	case n.Literal != nil:
 		return e.evalLiteral(ctx, ec, n.Literal)
+	case n.Var != nil:
+		v, ok := ec.getVar(*n.Var)
+		if !ok {
+			return nil, fmt.Errorf("unknown variable %s", *n.Var)
+		}
+		return v, nil
 	case n.Sub != nil:
 		return e.evalSub(ctx, ec, n.Sub)
 	}
diff --git a/cmdlang/inst.go b/cmdlang/inst.go
index 88c9d1f..3d15844 100644
--- a/cmdlang/inst.go
+++ b/cmdlang/inst.go
@@ -13,11 +13,14 @@ type Inst struct {
 func New() *Inst {
 	rootEC := evalCtx{}
 	rootEC.addCmd("echo", invokableFunc(echoBuiltin))
+	rootEC.addCmd("set", invokableFunc(setBuiltin))
 	rootEC.addCmd("toUpper", invokableStreamFunc(toUpperBuiltin))
 	rootEC.addCmd("cat", invokableFunc(catBuiltin))
 
 	rootEC.addCmd("testTimebomb", invokableStreamFunc(errorTestBuiltin))
 
+	rootEC.setVar("hello", strObject("world"))
+
 	return &Inst{
 		rootEC: &rootEC,
 	}
diff --git a/cmdlang/objs.go b/cmdlang/objs.go
index 8f372e7..1faa5a1 100644
--- a/cmdlang/objs.go
+++ b/cmdlang/objs.go
@@ -17,6 +17,7 @@ func (s strObject) String() string {
 }
 
 type invocationArgs struct {
+	ec   *evalCtx
 	args []object
 }