Port over the clear command from nushell (#373)

* Port over the clear command from nushell

* cargo fmt

crates/nu-command/src/default_context.rs

@@ -26,6 +26,7 @@ pub fn create_default_context() -> EngineState {
             Benchmark,
             BuildString,
             Cd,
+            Clear,
             Collect,
             Cp,
             Date,

crates/nu-command/src/lib.rs

@@ -9,6 +9,7 @@ mod filesystem;
 mod filters;
 mod formats;
 mod math;
+mod platform;
 mod shells;
 mod strings;
 mod system;
@@ -28,6 +29,7 @@ pub use filesystem::*;
 pub use filters::*;
 pub use formats::*;
 pub use math::*;
+pub use platform::*;
 pub use shells::*;
 pub use strings::*;
 pub use system::*;

crates/nu-command/src/platform/clear.rs

@@ -0,0 +1,53 @@
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{
+    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Value,
+};
+use std::process::Command as CommandSys;
+
+#[derive(Clone)]
+pub struct Clear;
+
+impl Command for Clear {
+    fn name(&self) -> &str {
+        "clear"
+    }
+
+    fn usage(&self) -> &str {
+        "Clear the terminal."
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("clear").category(Category::Platform)
+    }
+
+    fn run(
+        &self,
+        _engine_state: &EngineState,
+        _stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        if cfg!(windows) {
+            CommandSys::new("cmd")
+                .args(["/C", "cls"])
+                .status()
+                .expect("failed to execute process");
+        } else if cfg!(unix) {
+            CommandSys::new("/bin/sh")
+                .args(["-c", "clear"])
+                .status()
+                .expect("failed to execute process");
+        }
+
+        Ok(Value::Nothing { span: call.head }.into_pipeline_data())
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Clear the terminal",
+            example: "clear",
+            result: None,
+        }]
+    }
+}

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

@@ -0,0 +1,3 @@
+mod clear;
+
+pub use clear::Clear;

crates/nu-protocol/src/signature.rs

@@ -42,6 +42,7 @@ pub enum Category {
     Filters,
     Formats,
     Math,
+    Platform,
     Shells,
     Strings,
     System,
@@ -62,6 +63,7 @@ impl std::fmt::Display for Category {
             Category::Filters => "filters",
             Category::Formats => "formats",
             Category::Math => "math",
+            Category::Platform => "platform",
             Category::Shells => "shells",
             Category::Strings => "strings",
             Category::System => "system",