Add magic $in variable (#309)

* Add magic in variable

* Oops, missing file

crates/nu-command/src/default_context.rs

@@ -27,6 +27,7 @@ pub fn create_default_context() -> EngineState {
             BuildString,
             CamelCase,
             Cd,
+            Collect,
             Cp,
             Date,
             DateFormat,

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

@@ -0,0 +1,75 @@
+use nu_engine::eval_block;
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{Example, PipelineData, Signature, SyntaxShape, Value};
+
+#[derive(Clone)]
+pub struct Collect;
+
+impl Command for Collect {
+    fn name(&self) -> &str {
+        "collect"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("collect").required(
+            "block",
+            SyntaxShape::Block(Some(vec![SyntaxShape::Any])),
+            "the block to run once the stream is collected",
+        )
+    }
+
+    fn usage(&self) -> &str {
+        "Collect the stream and pass it to a block."
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        input: PipelineData,
+    ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
+        let block_id = call.positional[0]
+            .as_block()
+            .expect("internal error: expected block");
+
+        let block = engine_state.get_block(block_id).clone();
+        let mut stack = stack.collect_captures(&block.captures);
+
+        let input: Value = input.into_value(call.head);
+
+        if let Some(var) = block.signature.get_positional(0) {
+            if let Some(var_id) = &var.var_id {
+                stack.add_var(*var_id, input);
+            }
+        }
+
+        eval_block(
+            engine_state,
+            &mut stack,
+            &block,
+            PipelineData::new(call.head),
+        )
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Use the second value in the stream",
+            example: "echo 1 2 3 | collect { |x| echo $x.1 }",
+            result: Some(Value::test_int(2)),
+        }]
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(Collect {})
+    }
+}

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

@@ -1,3 +1,4 @@
+mod collect;
 mod each;
 mod first;
 mod get;
@@ -13,6 +14,7 @@ mod where_;
 mod wrap;
 mod zip;
 
+pub use collect::Collect;
 pub use each::Each;
 pub use first::First;
 pub use get::Get;