Add pipeline redirection support (#4594)

* redirection

* Remove commented-out

* fix tests

* more fixes

crates/nu-command/src/env/let_env.rs

@@ -39,8 +39,9 @@ impl Command for LetEnv {
             .as_keyword()
             .expect("internal error: missing keyword");
 
-        let rhs = eval_expression_with_input(engine_state, stack, keyword_expr, input, false)?
-            .into_value(call.head);
+        let rhs =
+            eval_expression_with_input(engine_state, stack, keyword_expr, input, false, true)?
+                .into_value(call.head);
 
         if env_var == "PWD" {
             let cwd = current_dir(engine_state, stack)?;

crates/nu-command/src/env/with_env.rs

@@ -132,7 +132,14 @@ fn with_env(
         stack.add_env_var(k, v);
     }
 
-    eval_block(engine_state, &mut stack, block, input)
+    eval_block(
+        engine_state,
+        &mut stack,
+        block,
+        input,
+        call.redirect_stdout,
+        call.redirect_stderr,
+    )
 }
 
 #[cfg(test)]