Add better exit command (#369)

crates/nu-command/src/shells/exit.rs

@@ -0,0 +1,33 @@
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{Category, PipelineData, ShellError, Signature};
+
+/// Source a file for environment variables.
+#[derive(Clone)]
+pub struct Exit;
+
+impl Command for Exit {
+    fn name(&self) -> &str {
+        "exit"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("exit").category(Category::Shells)
+    }
+
+    fn usage(&self) -> &str {
+        "Runs a script file in the current context."
+    }
+
+    fn run(
+        &self,
+        _engine_state: &EngineState,
+        _stack: &mut Stack,
+        _call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        //TODO: add more shell support
+
+        std::process::exit(0);
+    }
+}

crates/nu-command/src/shells/mod.rs

@@ -0,0 +1,3 @@
+mod exit;
+
+pub use exit::Exit;