Make external command substitution works friendly(like fish shell, trailing ending newlines) (#7156)

# Description

As title, when execute external sub command, auto-trimming end
new-lines, like how fish shell does.

And if the command is executed directly like: `cat tmp`, the result
won't change.

Fixes: #6816
Fixes: #3980


Note that although nushell works correctly by directly replace output of
external command to variable(or other places like string interpolation),
it's not friendly to user, and users almost want to use `str trim` to
trim trailing newline, I think that's why fish shell do this
automatically.

If the pr is ok, as a result, no more `str trim -r` is required when
user is writing scripts which using external commands.

# User-Facing Changes
Before:
<img width="523" alt="img"
src="https://user-images.githubusercontent.com/22256154/202468810-86b04dbb-c147-459a-96a5-e0095eeaab3d.png">

After:
<img width="505" alt="img"
src="https://user-images.githubusercontent.com/22256154/202468599-7b537488-3d6b-458e-9d75-d85780826db0.png">


# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace --features=extra -- -D warnings -D
clippy::unwrap_used -A clippy::needless_collect` to check that you're
using the standard code style
- `cargo test --workspace --features=extra` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/src/core_commands/do_.rs

@@ -116,6 +116,7 @@ impl Command for Do {
                 exit_code,
                 span,
                 metadata,
+                trim_end_newline,
             }) if capture_errors => {
                 let mut exit_code_ctrlc = None;
                 let exit_code: Vec<Value> = match exit_code {
@@ -149,6 +150,7 @@ impl Command for Do {
                     )),
                     span,
                     metadata,
+                    trim_end_newline,
                 })
             }
             Ok(PipelineData::ExternalStream {
@@ -157,12 +159,14 @@ impl Command for Do {
                 exit_code: _,
                 span,
                 metadata,
+                trim_end_newline,
             }) if ignore_program_errors => Ok(PipelineData::ExternalStream {
                 stdout,
                 stderr,
                 exit_code: None,
                 span,
                 metadata,
+                trim_end_newline,
             }),
             Err(_) if ignore_shell_errors => Ok(PipelineData::new(call.head)),
             r => r,

crates/nu-command/src/env/config/config_env.rs

@@ -74,6 +74,7 @@ impl Command for ConfigEnv {
             redirect_stdout: false,
             redirect_stderr: false,
             env_vars: env_vars_str,
+            trim_end_newline: false,
         };
 
         command.run_with_input(engine_state, stack, input, true)

crates/nu-command/src/env/config/config_nu.rs

@@ -74,6 +74,7 @@ impl Command for ConfigNu {
             redirect_stdout: false,
             redirect_stderr: false,
             env_vars: env_vars_str,
+            trim_end_newline: false,
         };
 
         command.run_with_input(engine_state, stack, input, true)

crates/nu-command/src/filesystem/open.rs

@@ -142,6 +142,7 @@ impl Command for Open {
                 exit_code: None,
                 span: call_span,
                 metadata: None,
+                trim_end_newline: false,
             };
 
             let ext = if raw {

crates/nu-command/src/network/fetch.rs

@@ -582,6 +582,7 @@ fn response_to_buffer(
         exit_code: None,
         span,
         metadata: None,
+        trim_end_newline: false,
     }
 }
 

crates/nu-command/src/network/post.rs

@@ -430,6 +430,7 @@ fn response_to_buffer(
         exit_code: None,
         span,
         metadata: None,
+        trim_end_newline: false,
     }
 }
 // Only panics if the user agent is invalid but we define it statically so either

crates/nu-command/src/strings/format/command.rs

@@ -273,7 +273,7 @@ fn format_record(
                 }
             }
             FormatOperation::ValueNeedEval(_col_name, span) => {
-                let (exp, may_parse_err) = parse_expression(working_set, &[*span], &[]);
+                let (exp, may_parse_err) = parse_expression(working_set, &[*span], &[], false);
                 match may_parse_err {
                     None => {
                         let parsed_result = eval_expression(engine_state, stack, &exp);

crates/nu-command/src/system/exec.rs

@@ -93,6 +93,7 @@ fn exec(
         env_vars,
         redirect_stdout: true,
         redirect_stderr: false,
+        trim_end_newline: false,
     };
 
     let mut command = external_command.spawn_simple_command(&cwd.to_string_lossy())?;

crates/nu-command/src/system/run_external.rs

@@ -36,6 +36,7 @@ impl Command for External {
         Signature::build(self.name())
             .switch("redirect-stdout", "redirect stdout to the pipeline", None)
             .switch("redirect-stderr", "redirect stderr to the pipeline", None)
+            .switch("trim-end-newline", "trimming end newlines", None)
             .required("command", SyntaxShape::Any, "external command to run")
             .rest("args", SyntaxShape::Any, "arguments for external command")
             .category(Category::System)
@@ -52,6 +53,7 @@ impl Command for External {
         let args: Vec<Value> = call.rest(engine_state, stack, 1)?;
         let redirect_stdout = call.has_flag("redirect-stdout");
         let redirect_stderr = call.has_flag("redirect-stderr");
+        let trim_end_newline = call.has_flag("trim-end-newline");
 
         // Translate environment variables from Values to Strings
         let env_vars_str = env_to_strings(engine_state, stack)?;
@@ -109,6 +111,7 @@ impl Command for External {
             redirect_stdout,
             redirect_stderr,
             env_vars: env_vars_str,
+            trim_end_newline,
         };
         command.run_with_input(engine_state, stack, input, false)
     }
@@ -137,6 +140,7 @@ pub struct ExternalCommand {
     pub redirect_stdout: bool,
     pub redirect_stderr: bool,
     pub env_vars: HashMap<String, String>,
+    pub trim_end_newline: bool,
 }
 
 impl ExternalCommand {
@@ -466,6 +470,7 @@ impl ExternalCommand {
                     )),
                     span: head,
                     metadata: None,
+                    trim_end_newline: self.trim_end_newline,
                 })
             }
         }

crates/nu-command/src/viewers/table.rs

@@ -256,6 +256,7 @@ fn handle_table_command(
             exit_code: None,
             span: call.head,
             metadata: None,
+            trim_end_newline: false,
         }),
         PipelineData::Value(Value::List { vals, .. }, metadata) => handle_row_stream(
             engine_state,
@@ -709,6 +710,7 @@ fn handle_row_stream(
         exit_code: None,
         span: head,
         metadata: None,
+        trim_end_newline: false,
     })
 }
 

crates/nu-engine/src/eval.rs

@@ -200,6 +200,7 @@ pub fn redirect_env(engine_state: &EngineState, caller_stack: &mut Stack, callee
 /// Eval extarnal expression
 ///
 /// It returns PipelineData with a boolean flag, indicate that if the external runs to failed.
+#[allow(clippy::too_many_arguments)]
 fn eval_external(
     engine_state: &EngineState,
     stack: &mut Stack,
@@ -208,6 +209,7 @@ fn eval_external(
     input: PipelineData,
     redirect_stdout: bool,
     redirect_stderr: bool,
+    is_subexpression: bool,
 ) -> Result<PipelineData, ShellError> {
     let decl_id = engine_state
         .find_decl("run-external".as_bytes(), &[])
@@ -245,6 +247,17 @@ fn eval_external(
         ))
     }
 
+    if is_subexpression {
+        call.add_named((
+            Spanned {
+                item: "trim-end-newline".into(),
+                span: head.span,
+            },
+            None,
+            None,
+        ))
+    }
+
     command.run(engine_state, stack, &call, input)
 }
 
@@ -331,7 +344,7 @@ pub fn eval_expression(
                     .into_value(call.head),
             )
         }
-        Expr::ExternalCall(head, args) => {
+        Expr::ExternalCall(head, args, is_subexpression) => {
             let span = head.span;
             // FIXME: protect this collect with ctrl-c
             Ok(eval_external(
@@ -342,6 +355,7 @@ pub fn eval_expression(
                 PipelineData::new(span),
                 false,
                 false,
+                *is_subexpression,
             )?
             .into_value(span))
         }
@@ -681,7 +695,7 @@ pub fn eval_expression_with_input(
             }
         }
         Expression {
-            expr: Expr::ExternalCall(head, args),
+            expr: Expr::ExternalCall(head, args, is_subexpression),
             ..
         } => {
             input = eval_external(
@@ -692,6 +706,7 @@ pub fn eval_expression_with_input(
                 input,
                 redirect_stdout,
                 redirect_stderr,
+                *is_subexpression,
             )?;
         }
 
@@ -727,6 +742,7 @@ fn might_consume_external_result(input: PipelineData) -> (PipelineData, bool) {
         mut exit_code,
         span,
         metadata,
+        trim_end_newline,
     } = input
     {
         let exit_code = exit_code.take();
@@ -772,6 +788,7 @@ fn might_consume_external_result(input: PipelineData) -> (PipelineData, bool) {
                         exit_code: Some(ListStream::from_stream(exit_code.into_iter(), ctrlc)),
                         span,
                         metadata,
+                        trim_end_newline,
                     },
                     runs_to_failed,
                 )
@@ -783,6 +800,7 @@ fn might_consume_external_result(input: PipelineData) -> (PipelineData, bool) {
                     exit_code: None,
                     span,
                     metadata,
+                    trim_end_newline,
                 },
                 runs_to_failed,
             ),
@@ -819,6 +837,7 @@ pub fn eval_element_with_input(
                             exit_code,
                             span,
                             metadata,
+                            trim_end_newline,
                             ..
                         },
                     ) => PipelineData::ExternalStream {
@@ -827,6 +846,7 @@ pub fn eval_element_with_input(
                         exit_code,
                         span,
                         metadata,
+                        trim_end_newline,
                     },
                     (
                         Redirection::StdoutAndStderr,
@@ -836,6 +856,7 @@ pub fn eval_element_with_input(
                             exit_code,
                             span,
                             metadata,
+                            trim_end_newline,
                         },
                     ) => match (stdout, stderr) {
                         (Some(stdout), Some(stderr)) => PipelineData::ExternalStream {
@@ -844,6 +865,7 @@ pub fn eval_element_with_input(
                             exit_code,
                             span,
                             metadata,
+                            trim_end_newline,
                         },
                         (None, Some(stderr)) => PipelineData::ExternalStream {
                             stdout: Some(stderr),
@@ -851,6 +873,7 @@ pub fn eval_element_with_input(
                             exit_code,
                             span,
                             metadata,
+                            trim_end_newline,
                         },
                         (Some(stdout), None) => PipelineData::ExternalStream {
                             stdout: Some(stdout),
@@ -858,6 +881,7 @@ pub fn eval_element_with_input(
                             exit_code,
                             span,
                             metadata,
+                            trim_end_newline,
                         },
                         (None, None) => PipelineData::ExternalStream {
                             stdout: None,
@@ -865,6 +889,7 @@ pub fn eval_element_with_input(
                             exit_code,
                             span,
                             metadata,
+                            trim_end_newline,
                         },
                     },
                     (_, input) => input,

crates/nu-parser/src/flatten.rs

@@ -175,7 +175,7 @@ pub fn flatten_expression(
             output.extend(args);
             output
         }
-        Expr::ExternalCall(head, args) => {
+        Expr::ExternalCall(head, args, _) => {
             let mut output = vec![];
 
             match **head {

crates/nu-parser/src/parser.rs

@@ -276,6 +276,7 @@ pub fn parse_external_call(
     working_set: &mut StateWorkingSet,
     spans: &[Span],
     expand_aliases_denylist: &[usize],
+    is_subexpression: bool,
 ) -> (Expression, Option<ParseError>) {
     trace!("parse external");
 
@@ -297,7 +298,8 @@ pub fn parse_external_call(
     let mut error = None;
 
     let head = if head_contents.starts_with(b"$") || head_contents.starts_with(b"(") {
-        let (arg, err) = parse_expression(working_set, &[head_span], expand_aliases_denylist);
+        // the expression is inside external_call, so it's a subexpression
+        let (arg, err) = parse_expression(working_set, &[head_span], expand_aliases_denylist, true);
         error = error.or(err);
         Box::new(arg)
     } else {
@@ -348,7 +350,7 @@ pub fn parse_external_call(
     }
     (
         Expression {
-            expr: Expr::ExternalCall(head, args),
+            expr: Expr::ExternalCall(head, args, is_subexpression),
             span: span(spans),
             ty: Type::Any,
             custom_completion: None,
@@ -663,8 +665,14 @@ pub fn parse_multispan_value(
         SyntaxShape::Expression => {
             trace!("parsing: expression");
 
-            let (arg, err) =
+            // is it subexpression?
-                parse_expression(working_set, &spans[*spans_idx..], expand_aliases_denylist);
+            // Not sure, but let's make it not, so the behavior is the same as previous version of nushell.
+            let (arg, err) = parse_expression(
+                working_set,
+                &spans[*spans_idx..],
+                expand_aliases_denylist,
+                false,
+            );
             error = error.or(err);
             *spans_idx = spans.len() - 1;
 
@@ -986,6 +994,7 @@ pub fn parse_call(
     spans: &[Span],
     head: Span,
     expand_aliases_denylist: &[usize],
+    is_subexpression: bool,
 ) -> (Expression, Option<ParseError>) {
     trace!("parsing: call");
 
@@ -1050,8 +1059,12 @@ pub fn parse_call(
                     parts: new_spans.clone(),
                 };
 
-                let (mut result, err) =
+                let (mut result, err) = parse_builtin_commands(
-                    parse_builtin_commands(working_set, &lite_command, &expand_aliases_denylist);
+                    working_set,
+                    &lite_command,
+                    &expand_aliases_denylist,
+                    is_subexpression,
+                );
 
                 let result = result.elements.remove(0);
 
@@ -1150,7 +1163,12 @@ pub fn parse_call(
         trace!("parsing: external call");
 
         // Otherwise, try external command
-        parse_external_call(working_set, spans, expand_aliases_denylist)
+        parse_external_call(
+            working_set,
+            spans,
+            expand_aliases_denylist,
+            is_subexpression,
+        )
     }
 }
 
@@ -4692,6 +4710,7 @@ pub fn parse_expression(
     working_set: &mut StateWorkingSet,
     spans: &[Span],
     expand_aliases_denylist: &[usize],
+    is_subexpression: bool,
 ) -> (Expression, Option<ParseError>) {
     let mut pos = 0;
     let mut shorthand = vec![];
@@ -4767,6 +4786,7 @@ pub fn parse_expression(
                     &spans[pos..],
                     spans[0],
                     expand_aliases_denylist,
+                    is_subexpression,
                 )
                 .0,
                 Some(ParseError::BuiltinCommandInPipeline("def".into(), spans[0])),
@@ -4777,6 +4797,7 @@ pub fn parse_expression(
                     &spans[pos..],
                     spans[0],
                     expand_aliases_denylist,
+                    is_subexpression,
                 )
                 .0,
                 Some(ParseError::BuiltinCommandInPipeline(
@@ -4790,6 +4811,7 @@ pub fn parse_expression(
                     &spans[pos..],
                     spans[0],
                     expand_aliases_denylist,
+                    is_subexpression,
                 )
                 .0,
                 Some(ParseError::BuiltinCommandInPipeline("for".into(), spans[0])),
@@ -4800,6 +4822,7 @@ pub fn parse_expression(
                     &spans[pos..],
                     spans[0],
                     expand_aliases_denylist,
+                    is_subexpression,
                 )
                 .0,
                 Some(ParseError::LetInPipeline(
@@ -4822,6 +4845,7 @@ pub fn parse_expression(
                     &spans[pos..],
                     spans[0],
                     expand_aliases_denylist,
+                    is_subexpression,
                 )
                 .0,
                 Some(ParseError::MutInPipeline(
@@ -4844,6 +4868,7 @@ pub fn parse_expression(
                     &spans[pos..],
                     spans[0],
                     expand_aliases_denylist,
+                    is_subexpression,
                 )
                 .0,
                 Some(ParseError::BuiltinCommandInPipeline(
@@ -4857,6 +4882,7 @@ pub fn parse_expression(
                     &spans[pos..],
                     spans[0],
                     expand_aliases_denylist,
+                    is_subexpression,
                 )
                 .0,
                 Some(ParseError::BuiltinCommandInPipeline(
@@ -4870,6 +4896,7 @@ pub fn parse_expression(
                     &spans[pos..],
                     spans[0],
                     expand_aliases_denylist,
+                    is_subexpression,
                 )
                 .0,
                 Some(ParseError::BuiltinCommandInPipeline("use".into(), spans[0])),
@@ -4882,6 +4909,7 @@ pub fn parse_expression(
                         &spans[pos..],
                         spans[0],
                         expand_aliases_denylist,
+                        is_subexpression,
                     )
                 } else {
                     (
@@ -4890,6 +4918,7 @@ pub fn parse_expression(
                             &spans[pos..],
                             spans[0],
                             expand_aliases_denylist,
+                            is_subexpression,
                         )
                         .0,
                         Some(ParseError::BuiltinCommandInPipeline(
@@ -4905,6 +4934,7 @@ pub fn parse_expression(
                     &spans[pos..],
                     spans[0],
                     expand_aliases_denylist,
+                    is_subexpression,
                 )
                 .0,
                 Some(ParseError::BuiltinCommandInPipeline(
@@ -4918,6 +4948,7 @@ pub fn parse_expression(
                     &spans[pos..],
                     spans[0],
                     expand_aliases_denylist,
+                    is_subexpression,
                 )
                 .0,
                 Some(ParseError::UnexpectedKeyword("export".into(), spans[0])),
@@ -4928,6 +4959,7 @@ pub fn parse_expression(
                     &spans[pos..],
                     spans[0],
                     expand_aliases_denylist,
+                    is_subexpression,
                 )
                 .0,
                 Some(ParseError::BuiltinCommandInPipeline(
@@ -4942,6 +4974,7 @@ pub fn parse_expression(
                     &spans[pos..],
                     spans[0],
                     expand_aliases_denylist,
+                    is_subexpression,
                 )
                 .0,
                 Some(ParseError::BuiltinCommandInPipeline(
@@ -4955,6 +4988,7 @@ pub fn parse_expression(
                 &spans[pos..],
                 spans[0],
                 expand_aliases_denylist,
+                is_subexpression,
             ),
         }
     };
@@ -5042,6 +5076,7 @@ pub fn parse_builtin_commands(
     working_set: &mut StateWorkingSet,
     lite_command: &LiteCommand,
     expand_aliases_denylist: &[usize],
+    is_subexpression: bool,
 ) -> (Pipeline, Option<ParseError>) {
     let name = working_set.get_span_contents(lite_command.parts[0]);
 
@@ -5070,8 +5105,12 @@ pub fn parse_builtin_commands(
         #[cfg(feature = "plugin")]
         b"register" => parse_register(working_set, &lite_command.parts, expand_aliases_denylist),
         _ => {
-            let (expr, err) =
+            let (expr, err) = parse_expression(
-                parse_expression(working_set, &lite_command.parts, expand_aliases_denylist);
+                working_set,
+                &lite_command.parts,
+                expand_aliases_denylist,
+                is_subexpression,
+            );
             (Pipeline::from_vec(vec![expr]), err)
         }
     }
@@ -5218,8 +5257,8 @@ pub fn parse_block(
                                 working_set,
                                 &command.parts,
                                 expand_aliases_denylist,
+                                is_subexpression,
                             );
-
                             working_set.type_scope.add_type(expr.ty.clone());
 
                             if error.is_none() {
@@ -5248,6 +5287,7 @@ pub fn parse_block(
                                 working_set,
                                 &command.parts,
                                 expand_aliases_denylist,
+                                is_subexpression,
                             );
 
                             working_set.type_scope.add_type(expr.ty.clone());
@@ -5263,6 +5303,7 @@ pub fn parse_block(
                                 working_set,
                                 &command.parts,
                                 expand_aliases_denylist,
+                                is_subexpression,
                             );
 
                             working_set.type_scope.add_type(expr.ty.clone());
@@ -5297,8 +5338,12 @@ pub fn parse_block(
                     | LiteElement::Redirection(_, _, command)
                     | LiteElement::And(_, command)
                     | LiteElement::Or(_, command) => {
-                        let (mut pipeline, err) =
+                        let (mut pipeline, err) = parse_builtin_commands(
-                            parse_builtin_commands(working_set, command, expand_aliases_denylist);
+                            working_set,
+                            command,
+                            expand_aliases_denylist,
+                            is_subexpression,
+                        );
 
                         if idx == 0 {
                             if let Some(let_decl_id) = working_set.find_decl(b"let", &Type::Any) {
@@ -5542,7 +5587,7 @@ pub fn discover_captures_in_expr(
         }
         Expr::CellPath(_) => {}
         Expr::DateTime(_) => {}
-        Expr::ExternalCall(head, exprs) => {
+        Expr::ExternalCall(head, exprs, _) => {
             let result = discover_captures_in_expr(working_set, head, seen, seen_blocks)?;
             output.extend(&result);
 

crates/nu-protocol/src/ast/expr.rs

@@ -19,7 +19,7 @@ pub enum Expr {
     Var(VarId),
     VarDecl(VarId),
     Call(Box<Call>),
-    ExternalCall(Box<Expression>, Vec<Expression>),
+    ExternalCall(Box<Expression>, Vec<Expression>, bool), // head, args, is_subexpression
     Operator(Operator),
     RowCondition(BlockId),
     UnaryNot(Box<Expression>),

crates/nu-protocol/src/ast/expression.rs

@@ -177,7 +177,7 @@ impl Expression {
             }
             Expr::CellPath(_) => false,
             Expr::DateTime(_) => false,
-            Expr::ExternalCall(head, args) => {
+            Expr::ExternalCall(head, args, _) => {
                 if head.has_in_variable(working_set) {
                     return true;
                 }
@@ -374,7 +374,7 @@ impl Expression {
             }
             Expr::CellPath(_) => {}
             Expr::DateTime(_) => {}
-            Expr::ExternalCall(head, args) => {
+            Expr::ExternalCall(head, args, _) => {
                 head.replace_in_variable(working_set, new_var_id);
                 for arg in args {
                     arg.replace_in_variable(working_set, new_var_id)
@@ -534,7 +534,7 @@ impl Expression {
             }
             Expr::CellPath(_) => {}
             Expr::DateTime(_) => {}
-            Expr::ExternalCall(head, args) => {
+            Expr::ExternalCall(head, args, _) => {
                 head.replace_span(working_set, replaced, new_span);
                 for arg in args {
                     arg.replace_span(working_set, replaced, new_span)

crates/nu-protocol/src/pipeline_data.rs

@@ -6,6 +6,12 @@ use crate::{
 use nu_utils::{stderr_write_all_and_flush, stdout_write_all_and_flush};
 use std::sync::{atomic::AtomicBool, Arc};
 
+const LINE_ENDING: &str = if cfg!(target_os = "windows") {
+    "\r\n"
+} else {
+    "\n"
+};
+
 /// The foundational abstraction for input and output to commands
 ///
 /// This represents either a single Value or a stream of values coming into the command or leaving a command.
@@ -45,6 +51,7 @@ pub enum PipelineData {
         exit_code: Option<ListStream>,
         span: Span,
         metadata: Option<PipelineMetadata>,
+        trim_end_newline: bool,
     },
 }
 
@@ -121,6 +128,7 @@ impl PipelineData {
             PipelineData::ExternalStream {
                 stdout: Some(mut s),
                 exit_code,
+                trim_end_newline,
                 ..
             } => {
                 let mut items = vec![];
@@ -141,6 +149,8 @@ impl PipelineData {
                     let _: Vec<_> = exit_code.into_iter().collect();
                 }
 
+                // NOTE: currently trim-end-newline only handles for string output.
+                // For binary, user might need origin data.
                 if s.is_binary {
                     let mut output = vec![];
                     for item in items {
@@ -168,6 +178,9 @@ impl PipelineData {
                             }
                         }
                     }
+                    if trim_end_newline {
+                        output.truncate(output.trim_end_matches(LINE_ENDING).len())
+                    }
                     Value::String {
                         val: output,
                         span, // FIXME?
@@ -193,7 +206,9 @@ impl PipelineData {
             PipelineData::ListStream(s, ..) => Ok(s.into_string(separator, config)),
             PipelineData::ExternalStream { stdout: None, .. } => Ok(String::new()),
             PipelineData::ExternalStream {
-                stdout: Some(s), ..
+                stdout: Some(s),
+                trim_end_newline,
+                ..
             } => {
                 let mut output = String::new();
 
@@ -206,6 +221,9 @@ impl PipelineData {
                         Err(e) => return Err(e),
                     }
                 }
+                if trim_end_newline {
+                    output.truncate(output.trim_end_matches(LINE_ENDING).len());
+                }
                 Ok(output)
             }
         }
@@ -294,11 +312,15 @@ impl PipelineData {
             }
             PipelineData::ExternalStream {
                 stdout: Some(stream),
+                trim_end_newline,
                 ..
             } => {
                 let collected = stream.into_bytes()?;
 
-                if let Ok(st) = String::from_utf8(collected.clone().item) {
+                if let Ok(mut st) = String::from_utf8(collected.clone().item) {
+                    if trim_end_newline {
+                        st.truncate(st.trim_end_matches(LINE_ENDING).len());
+                    }
                     Ok(f(Value::String {
                         val: st,
                         span: collected.span,
@@ -348,11 +370,15 @@ impl PipelineData {
             }
             PipelineData::ExternalStream {
                 stdout: Some(stream),
+                trim_end_newline,
                 ..
             } => {
                 let collected = stream.into_bytes()?;
 
-                if let Ok(st) = String::from_utf8(collected.clone().item) {
+                if let Ok(mut st) = String::from_utf8(collected.clone().item) {
+                    if trim_end_newline {
+                        st.truncate(st.trim_end_matches(LINE_ENDING).len())
+                    }
                     Ok(f(Value::String {
                         val: st,
                         span: collected.span,
@@ -397,11 +423,15 @@ impl PipelineData {
             }
             PipelineData::ExternalStream {
                 stdout: Some(stream),
+                trim_end_newline,
                 ..
             } => {
                 let collected = stream.into_bytes()?;
 
-                if let Ok(st) = String::from_utf8(collected.clone().item) {
+                if let Ok(mut st) = String::from_utf8(collected.clone().item) {
+                    if trim_end_newline {
+                        st.truncate(st.trim_end_matches(LINE_ENDING).len())
+                    }
                     let v = Value::String {
                         val: st,
                         span: collected.span,

src/main.rs

@@ -320,6 +320,7 @@ fn main() -> Result<()> {
                     exit_code: None,
                     span: redirect_stdin.span,
                     metadata: None,
+                    trim_end_newline: false,
                 }
             } else {
                 PipelineData::new(Span::new(0, 0))

tests/shell/pipeline/commands/external.rs

@@ -120,6 +120,25 @@ fn command_not_found_error_suggests_typo_fix() {
     assert!(actual.err.contains("benchmark"));
 }
 
+#[test]
+fn command_substitution_wont_output_extra_newline() {
+    let actual = nu!(
+        cwd: ".",
+        r#"
+        with-env [FOO "bar"] { echo $"prefix (nu --testbin echo_env FOO) suffix" }
+        "#
+    );
+    assert_eq!(actual.out, "prefix bar suffix");
+
+    let actual = nu!(
+        cwd: ".",
+        r#"
+        with-env [FOO "bar"] { (nu --testbin echo_env FOO) }
+        "#
+    );
+    assert_eq!(actual.out, "bar");
+}
+
 mod it_evaluation {
     use super::nu;
     use nu_test_support::fs::Stub::{EmptyFile, FileWithContent, FileWithContentToBeTrimmed};