Merge pull request #259 from stormasm/last2

working on implementing the filters/last command

crates/nu-command/src/default_context.rs

@@ -43,6 +43,7 @@ pub fn create_default_context() -> EngineState {
             IntoBinary,
             IntoFilesize,
             IntoInt,
+            Last,
             Length,
             Let,
             LetEnv,

crates/nu-command/src/filters/last.rs

@@ -0,0 +1,85 @@
+use nu_engine::CallExt;
+
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{
+    Example, IntoPipelineData, PipelineData, ShellError, Signature, Span, SyntaxShape, Value,
+};
+use std::convert::TryInto;
+
+#[derive(Clone)]
+pub struct Last;
+
+impl Command for Last {
+    fn name(&self) -> &str {
+        "last"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("last").optional(
+            "rows",
+            SyntaxShape::Int,
+            "starting from the back, the number of rows to return",
+        )
+    }
+
+    fn usage(&self) -> &str {
+        "Show only the last number of rows."
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            example: "[1,2,3] | last 2",
+            description: "Get the last 2 items",
+            result: Some(Value::List {
+                vals: vec![Value::test_int(2), Value::test_int(3)],
+                span: Span::unknown(),
+            }),
+        }]
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let rows: Option<i64> = call.opt(engine_state, stack, 0)?;
+        let v: Vec<_> = input.into_iter().collect();
+        let vlen: i64 = v.len() as i64;
+        let beginning_rows_to_skip = rows_to_skip(vlen, rows);
+
+        let iter = v
+            .into_iter()
+            .skip(beginning_rows_to_skip.try_into().unwrap());
+
+        Ok(iter.into_pipeline_data())
+    }
+}
+
+fn rows_to_skip(count: i64, rows: Option<i64>) -> i64 {
+    let end_rows_desired = if let Some(quantity) = rows {
+        quantity
+    } else {
+        1
+    };
+
+    if end_rows_desired < count {
+        count - end_rows_desired
+    } else {
+        0
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(Last {})
+    }
+}

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

@@ -1,5 +1,6 @@
 mod each;
 mod get;
+mod last;
 mod length;
 mod lines;
 mod par_each;
@@ -9,6 +10,7 @@ mod wrap;
 
 pub use each::Each;
 pub use get::Get;
+pub use last::Last;
 pub use length::Length;
 pub use lines::Lines;
 pub use par_each::ParEach;