From 316d2d6af2bad041dafaf73172b2dfe8a9821fad Mon Sep 17 00:00:00 2001
From: 132ikl <132@ikl.sh>
Date: Mon, 14 Jul 2025 19:26:40 -0400
Subject: [PATCH] Add `extern` for `nu` command (#16119)

# Description
Adds an `extern` definition (`KnownExternal`) for the `nu` command. This
way you can do `help nu` and get tab completions for flags on the `nu`
executable

# User-Facing Changes
* You can now view the flags for Nushell itself with `help nu`, and tab
completion for flags on `nu` works
---
 .../tests/commands/bytes/ends_with.rs         | 18 ++--
 .../tests/commands/bytes/starts_with.rs       | 18 ++--
 .../nu-command/tests/commands/run_external.rs | 87 ++++++++++---------
 crates/nu-engine/src/compile/call.rs          |  3 +-
 crates/nu-protocol/src/signature.rs           |  8 ++
 src/command.rs                                | 26 +++++-
 src/main.rs                                   |  9 +-
 src/test_bins.rs                              | 34 +++++---
 tests/repl/test_known_external.rs             |  6 ++
 tests/repl/test_parser.rs                     |  8 +-
 tests/scope/mod.rs                            |  2 +-
 tests/shell/pipeline/commands/external.rs     | 12 +--
 12 files changed, 143 insertions(+), 88 deletions(-)

diff --git a/crates/nu-cmd-extra/tests/commands/bytes/ends_with.rs b/crates/nu-cmd-extra/tests/commands/bytes/ends_with.rs
index b90f936b96..f0971eb223 100644
--- a/crates/nu-cmd-extra/tests/commands/bytes/ends_with.rs
+++ b/crates/nu-cmd-extra/tests/commands/bytes/ends_with.rs
@@ -22,7 +22,7 @@ fn basic_string_fails() {
 #[test]
 fn short_stream_binary() {
     let actual = nu!(r#"
-            nu --testbin repeater (0x[01]) 5 | bytes ends-with 0x[010101]
+            ^nu --testbin repeater (0x[01]) 5 | bytes ends-with 0x[010101]
         "#);
 
     assert_eq!(actual.out, "true");
@@ -31,7 +31,7 @@ fn short_stream_binary() {
 #[test]
 fn short_stream_mismatch() {
     let actual = nu!(r#"
-            nu --testbin repeater (0x[010203]) 5 | bytes ends-with 0x[010204]
+            ^nu --testbin repeater (0x[010203]) 5 | bytes ends-with 0x[010204]
         "#);
 
     assert_eq!(actual.out, "false");
@@ -40,7 +40,7 @@ fn short_stream_mismatch() {
 #[test]
 fn short_stream_binary_overflow() {
     let actual = nu!(r#"
-            nu --testbin repeater (0x[01]) 5 | bytes ends-with 0x[010101010101]
+            ^nu --testbin repeater (0x[01]) 5 | bytes ends-with 0x[010101010101]
         "#);
 
     assert_eq!(actual.out, "false");
@@ -49,7 +49,7 @@ fn short_stream_binary_overflow() {
 #[test]
 fn long_stream_binary() {
     let actual = nu!(r#"
-            nu --testbin repeater (0x[01]) 32768 | bytes ends-with 0x[010101]
+            ^nu --testbin repeater (0x[01]) 32768 | bytes ends-with 0x[010101]
         "#);
 
     assert_eq!(actual.out, "true");
@@ -59,7 +59,7 @@ fn long_stream_binary() {
 fn long_stream_binary_overflow() {
     // .. ranges are inclusive..inclusive, so we don't need to +1 to check for an overflow
     let actual = nu!(r#"
-            nu --testbin repeater (0x[01]) 32768 | bytes ends-with (0..32768 | each {|| 0x[01] } | bytes collect)
+            ^nu --testbin repeater (0x[01]) 32768 | bytes ends-with (0..32768 | each {|| 0x[01] } | bytes collect)
         "#);
 
     assert_eq!(actual.out, "false");
@@ -69,7 +69,7 @@ fn long_stream_binary_overflow() {
 fn long_stream_binary_exact() {
     // ranges are inclusive..inclusive, so we don't need to +1 to check for an overflow
     let actual = nu!(r#"
-            nu --testbin repeater (0x[01020304]) 8192 | bytes ends-with (0..<8192 | each {|| 0x[01020304] } | bytes collect)
+            ^nu --testbin repeater (0x[01020304]) 8192 | bytes ends-with (0..<8192 | each {|| 0x[01020304] } | bytes collect)
         "#);
 
     assert_eq!(actual.out, "true");
@@ -79,7 +79,7 @@ fn long_stream_binary_exact() {
 fn long_stream_string_exact() {
     // ranges are inclusive..inclusive, so we don't need to +1 to check for an overflow
     let actual = nu!(r#"
-            nu --testbin repeater hell 8192 | bytes ends-with (0..<8192 | each {|| "hell" | into binary } | bytes collect)
+            ^nu --testbin repeater hell 8192 | bytes ends-with (0..<8192 | each {|| "hell" | into binary } | bytes collect)
         "#);
 
     assert_eq!(actual.out, "true");
@@ -92,7 +92,7 @@ fn long_stream_mixed_exact() {
             let binseg = (0..<2048 | each {|| 0x[003d9fbf] } | bytes collect)
             let strseg = (0..<2048 | each {|| "hell" | into binary } | bytes collect)
 
-            nu --testbin repeat_bytes 003d9fbf 2048 68656c6c 2048 | bytes ends-with (bytes build $binseg $strseg)
+            ^nu --testbin repeat_bytes 003d9fbf 2048 68656c6c 2048 | bytes ends-with (bytes build $binseg $strseg)
         "#);
 
     assert_eq!(
@@ -109,7 +109,7 @@ fn long_stream_mixed_overflow() {
             let binseg = (0..<2048 | each {|| 0x[003d9fbf] } | bytes collect)
             let strseg = (0..<2048 | each {|| "hell" | into binary } | bytes collect)
 
-            nu --testbin repeat_bytes 003d9fbf 2048 68656c6c 2048 | bytes ends-with (bytes build 0x[01] $binseg $strseg)
+            ^nu --testbin repeat_bytes 003d9fbf 2048 68656c6c 2048 | bytes ends-with (bytes build 0x[01] $binseg $strseg)
         "#);
 
     assert_eq!(
diff --git a/crates/nu-cmd-extra/tests/commands/bytes/starts_with.rs b/crates/nu-cmd-extra/tests/commands/bytes/starts_with.rs
index e7d57698b5..2cf5bc021a 100644
--- a/crates/nu-cmd-extra/tests/commands/bytes/starts_with.rs
+++ b/crates/nu-cmd-extra/tests/commands/bytes/starts_with.rs
@@ -22,7 +22,7 @@ fn basic_string_fails() {
 #[test]
 fn short_stream_binary() {
     let actual = nu!(r#"
-            nu --testbin repeater (0x[01]) 5 | bytes starts-with 0x[010101]
+            ^nu --testbin repeater (0x[01]) 5 | bytes starts-with 0x[010101]
         "#);
 
     assert_eq!(actual.out, "true");
@@ -31,7 +31,7 @@ fn short_stream_binary() {
 #[test]
 fn short_stream_mismatch() {
     let actual = nu!(r#"
-            nu --testbin repeater (0x[010203]) 5 | bytes starts-with 0x[010204]
+            ^nu --testbin repeater (0x[010203]) 5 | bytes starts-with 0x[010204]
         "#);
 
     assert_eq!(actual.out, "false");
@@ -40,7 +40,7 @@ fn short_stream_mismatch() {
 #[test]
 fn short_stream_binary_overflow() {
     let actual = nu!(r#"
-            nu --testbin repeater (0x[01]) 5 | bytes starts-with 0x[010101010101]
+            ^nu --testbin repeater (0x[01]) 5 | bytes starts-with 0x[010101010101]
         "#);
 
     assert_eq!(actual.out, "false");
@@ -49,7 +49,7 @@ fn short_stream_binary_overflow() {
 #[test]
 fn long_stream_binary() {
     let actual = nu!(r#"
-            nu --testbin repeater (0x[01]) 32768 | bytes starts-with 0x[010101]
+            ^nu --testbin repeater (0x[01]) 32768 | bytes starts-with 0x[010101]
         "#);
 
     assert_eq!(actual.out, "true");
@@ -59,7 +59,7 @@ fn long_stream_binary() {
 fn long_stream_binary_overflow() {
     // .. ranges are inclusive..inclusive, so we don't need to +1 to check for an overflow
     let actual = nu!(r#"
-            nu --testbin repeater (0x[01]) 32768 | bytes starts-with (0..32768 | each {|| 0x[01] } | bytes collect)
+            ^nu --testbin repeater (0x[01]) 32768 | bytes starts-with (0..32768 | each {|| 0x[01] } | bytes collect)
         "#);
 
     assert_eq!(actual.out, "false");
@@ -69,7 +69,7 @@ fn long_stream_binary_overflow() {
 fn long_stream_binary_exact() {
     // ranges are inclusive..inclusive, so we don't need to +1 to check for an overflow
     let actual = nu!(r#"
-            nu --testbin repeater (0x[01020304]) 8192 | bytes starts-with (0..<8192 | each {|| 0x[01020304] } | bytes collect)
+            ^nu --testbin repeater (0x[01020304]) 8192 | bytes starts-with (0..<8192 | each {|| 0x[01020304] } | bytes collect)
         "#);
 
     assert_eq!(actual.out, "true");
@@ -79,7 +79,7 @@ fn long_stream_binary_exact() {
 fn long_stream_string_exact() {
     // ranges are inclusive..inclusive, so we don't need to +1 to check for an overflow
     let actual = nu!(r#"
-            nu --testbin repeater hell 8192 | bytes starts-with (0..<8192 | each {|| "hell" | into binary } | bytes collect)
+            ^nu --testbin repeater hell 8192 | bytes starts-with (0..<8192 | each {|| "hell" | into binary } | bytes collect)
         "#);
 
     assert_eq!(actual.out, "true");
@@ -92,7 +92,7 @@ fn long_stream_mixed_exact() {
             let binseg = (0..<2048 | each {|| 0x[003d9fbf] } | bytes collect)
             let strseg = (0..<2048 | each {|| "hell" | into binary } | bytes collect)
 
-            nu --testbin repeat_bytes 003d9fbf 2048 68656c6c 2048 | bytes starts-with (bytes build $binseg $strseg)
+            ^nu --testbin repeat_bytes 003d9fbf 2048 68656c6c 2048 | bytes starts-with (bytes build $binseg $strseg)
         "#);
 
     assert_eq!(
@@ -109,7 +109,7 @@ fn long_stream_mixed_overflow() {
             let binseg = (0..<2048 | each {|| 0x[003d9fbf] } | bytes collect)
             let strseg = (0..<2048 | each {|| "hell" | into binary } | bytes collect)
 
-            nu --testbin repeat_bytes 003d9fbf 2048 68656c6c 2048 | bytes starts-with (bytes build $binseg $strseg 0x[01])
+            ^nu --testbin repeat_bytes 003d9fbf 2048 68656c6c 2048 | bytes starts-with (bytes build $binseg $strseg 0x[01])
         "#);
 
     assert_eq!(
diff --git a/crates/nu-command/tests/commands/run_external.rs b/crates/nu-command/tests/commands/run_external.rs
index 1c7bcc85a1..21fc8c7fa2 100644
--- a/crates/nu-command/tests/commands/run_external.rs
+++ b/crates/nu-command/tests/commands/run_external.rs
@@ -4,6 +4,14 @@ use nu_test_support::playground::Playground;
 use rstest::rstest;
 use rstest_reuse::*;
 
+// Get full path to nu, so we don't use the nu extern
+fn nu_path(prefix: &str) -> String {
+    let binary = nu_test_support::fs::executable_path()
+        .to_string_lossy()
+        .to_string();
+    format!("{prefix}{}", binary)
+}
+
 // Template for run-external test to ensure tests work when calling
 // the binary directly, using the caret operator, and when using
 // the run-external command
@@ -18,8 +26,8 @@ fn run_external_prefixes(#[case] prefix: &str) {}
 fn better_empty_redirection(prefix: &str) {
     let actual = nu!(
         cwd: "tests/fixtures/formats",
-        "ls | each {{ |it| {}nu `--testbin` cococo $it.name }} | ignore",
-        prefix
+        "ls | each {{ |it| {} `--testbin` cococo $it.name }} | ignore",
+        nu_path(prefix)
     );
 
     eprintln!("out: {}", actual.out);
@@ -39,9 +47,9 @@ fn explicit_glob(prefix: &str) {
         let actual = nu!(
             cwd: dirs.test(),
             r#"
-                {}nu `--testbin` cococo ('*.txt' | into glob)
+                {} `--testbin` cococo ('*.txt' | into glob)
             "#,
-            prefix
+            nu_path(prefix)
         );
 
         assert!(actual.out.contains("D&D_volume_1.txt"));
@@ -61,9 +69,9 @@ fn bare_word_expand_path_glob(prefix: &str) {
         let actual = nu!(
             cwd: dirs.test(),
             "
-                {}nu `--testbin` cococo *.txt
+                {} `--testbin` cococo *.txt
             ",
-            prefix
+            nu_path(prefix)
         );
 
         assert!(actual.out.contains("D&D_volume_1.txt"));
@@ -83,9 +91,9 @@ fn backtick_expand_path_glob(prefix: &str) {
         let actual = nu!(
             cwd: dirs.test(),
             r#"
-                {}nu `--testbin` cococo `*.txt`
+                {} `--testbin` cococo `*.txt`
             "#,
-            prefix
+            nu_path(prefix)
         );
 
         assert!(actual.out.contains("D&D_volume_1.txt"));
@@ -105,9 +113,9 @@ fn single_quote_does_not_expand_path_glob(prefix: &str) {
         let actual = nu!(
             cwd: dirs.test(),
             r#"
-                {}nu `--testbin` cococo '*.txt'
+                {} `--testbin` cococo '*.txt'
             "#,
-            prefix
+            nu_path(prefix)
         );
 
         assert_eq!(actual.out, "*.txt");
@@ -126,9 +134,9 @@ fn double_quote_does_not_expand_path_glob(prefix: &str) {
         let actual = nu!(
             cwd: dirs.test(),
             r#"
-                {}nu `--testbin` cococo "*.txt"
+                {} `--testbin` cococo "*.txt"
             "#,
-            prefix
+            nu_path(prefix)
         );
 
         assert_eq!(actual.out, "*.txt");
@@ -141,9 +149,9 @@ fn failed_command_with_semicolon_will_not_execute_following_cmds(prefix: &str) {
         let actual = nu!(
             cwd: dirs.test(),
             "
-                {}nu `--testbin` fail; echo done
+                {} `--testbin` fail; echo done
             ",
-            prefix
+            nu_path(prefix)
         );
 
         assert!(!actual.out.contains("done"));
@@ -156,9 +164,9 @@ fn external_args_with_quoted(prefix: &str) {
         let actual = nu!(
             cwd: dirs.test(),
             r#"
-                {}nu `--testbin` cococo "foo=bar 'hi'"
+                {} `--testbin` cococo "foo=bar 'hi'"
             "#,
-            prefix
+            nu_path(prefix)
         );
 
         assert_eq!(actual.out, "foo=bar 'hi'");
@@ -198,9 +206,9 @@ fn external_arg_with_non_option_like_embedded_quotes(#[case] prefix: &str) {
             let actual = nu!(
                 cwd: dirs.test(),
                 r#"
-                    {}nu `--testbin` cococo foo='bar' 'foo'=bar
+                    {} `--testbin` cococo foo='bar' 'foo'=bar
                 "#,
-                prefix
+                nu_path(prefix)
             );
 
             assert_eq!(actual.out, "foo=bar foo=bar");
@@ -217,9 +225,9 @@ fn external_arg_with_string_interpolation(#[case] prefix: &str) {
         let actual = nu!(
             cwd: dirs.test(),
             r#"
-                {}nu `--testbin` cococo foo=(2 + 2) $"foo=(2 + 2)" foo=$"(2 + 2)"
+                {} `--testbin` cococo foo=(2 + 2) $"foo=(2 + 2)" foo=$"(2 + 2)"
             "#,
-            prefix
+            nu_path(prefix)
         );
 
         assert_eq!(actual.out, "foo=4 foo=4 foo=4");
@@ -233,9 +241,9 @@ fn external_arg_with_variable_name(prefix: &str) {
             cwd: dirs.test(),
             r#"
                 let dump_command = "PGPASSWORD='db_secret' pg_dump -Fc -h 'db.host' -p '$db.port' -U postgres -d 'db_name' > '/tmp/dump_name'";
-                {}nu `--testbin` nonu $dump_command
+                {} `--testbin` nonu $dump_command
             "#,
-            prefix
+            nu_path(prefix)
         );
 
         assert_eq!(
@@ -251,9 +259,9 @@ fn external_command_escape_args(prefix: &str) {
         let actual = nu!(
             cwd: dirs.test(),
             r#"
-                {}nu `--testbin` cococo "\"abcd"
+                {} `--testbin` cococo "\"abcd"
             "#,
-            prefix
+            nu_path(prefix)
         );
 
         assert_eq!(actual.out, r#""abcd"#);
@@ -264,9 +272,9 @@ fn external_command_escape_args(prefix: &str) {
 fn external_command_ndots_args(prefix: &str) {
     let actual = nu!(
         r#"
-            {}nu `--testbin` cococo foo/. foo/.. foo/... foo/./bar foo/../bar foo/.../bar ./bar ../bar .../bar
+            {} `--testbin` cococo foo/. foo/.. foo/... foo/./bar foo/../bar foo/.../bar ./bar ../bar .../bar
         "#,
-        prefix
+        nu_path(prefix)
     );
 
     assert_eq!(
@@ -286,9 +294,9 @@ fn external_command_ndots_leading_dot_slash(prefix: &str) {
     // Don't expand ndots with a leading `./`
     let actual = nu!(
         r#"
-            {}nu `--testbin` cococo ./... ./....
+            {} `--testbin` cococo ./... ./....
         "#,
-        prefix
+        nu_path(prefix)
     );
 
     assert_eq!(actual.out, "./... ./....");
@@ -300,9 +308,9 @@ fn external_command_url_args(prefix: &str) {
     // here
     let actual = nu!(
         r#"
-            {}nu `--testbin` cococo http://example.com http://example.com/.../foo //foo
+            {} `--testbin` cococo http://example.com http://example.com/.../foo //foo
         "#,
-        prefix
+        nu_path(prefix)
     );
 
     assert_eq!(
@@ -359,9 +367,9 @@ fn external_arg_expand_tilde(#[case] prefix: &str) {
         let actual = nu!(
             cwd: dirs.test(),
             r#"
-                {}nu `--testbin` cococo ~/foo ~/(2 + 2)
+                {} `--testbin` cococo ~/foo ~/(2 + 2)
             "#,
-            prefix
+            nu_path(prefix)
         );
 
         let home = dirs::home_dir().expect("failed to find home dir");
@@ -382,7 +390,7 @@ fn external_command_not_expand_tilde_with_quotes(prefix: &str) {
     Playground::setup(
         "external command not expand tilde with quotes",
         |dirs, _| {
-            let actual = nu!(cwd: dirs.test(), r#"{}nu `--testbin` nonu "~""#, prefix);
+            let actual = nu!(cwd: dirs.test(), r#"{} `--testbin` nonu "~""#, nu_path(prefix));
             assert_eq!(actual.out, r#"~"#);
         },
     )
@@ -393,7 +401,7 @@ fn external_command_expand_tilde_with_back_quotes(prefix: &str) {
     Playground::setup(
         "external command not expand tilde with quotes",
         |dirs, _| {
-            let actual = nu!(cwd: dirs.test(), r#"{}nu `--testbin` nonu `~`"#, prefix);
+            let actual = nu!(cwd: dirs.test(), r#"{} `--testbin` nonu `~`"#, nu_path(prefix));
             assert!(!actual.out.contains('~'));
         },
     )
@@ -404,8 +412,8 @@ fn external_command_receives_raw_binary_data(prefix: &str) {
     Playground::setup("external command receives raw binary data", |dirs, _| {
         let actual = nu!(
             cwd: dirs.test(),
-            "0x[deadbeef] | {}nu `--testbin` input_bytes_length",
-            prefix
+            "0x[deadbeef] | {} `--testbin` input_bytes_length",
+            nu_path(prefix)
         );
         assert_eq!(actual.out, r#"4"#);
     })
@@ -494,9 +502,9 @@ fn quotes_trimmed_when_shelling_out(prefix: &str) {
     // regression test for a bug where we weren't trimming quotes around string args before shelling out to cmd.exe
     let actual = nu!(
         r#"
-            {}nu `--testbin` cococo "foo"
+            {} `--testbin` cococo "foo"
         "#,
-        prefix
+        nu_path(prefix)
     );
 
     assert_eq!(actual.out, "foo");
@@ -565,8 +573,9 @@ fn expand_command_if_list(#[case] prefix: &str) {
         let actual = nu!(
             cwd: dirs.test(),
             r#"
-                let cmd = [nu `--testbin`]; {}$cmd meow foo.txt
+                let cmd = ['{}' `--testbin`]; {}$cmd meow foo.txt
             "#,
+            nu_path(""),
             prefix
         );
 
diff --git a/crates/nu-engine/src/compile/call.rs b/crates/nu-engine/src/compile/call.rs
index 3729489dd2..0bdef3b664 100644
--- a/crates/nu-engine/src/compile/call.rs
+++ b/crates/nu-engine/src/compile/call.rs
@@ -19,7 +19,8 @@ pub(crate) fn compile_call(
     let decl = working_set.get_decl(call.decl_id);
 
     // Check if this call has --help - if so, just redirect to `help`
-    if call.named_iter().any(|(name, _, _)| name.item == "help") {
+    // Special case the `nu` extern: we want to forward --help to the script
+    if call.named_iter().any(|(name, _, _)| name.item == "help") && decl.name() != "nu" {
         let name = working_set
             .find_decl_name(call.decl_id) // check for name in scope
             .and_then(|name| std::str::from_utf8(name).ok())
diff --git a/crates/nu-protocol/src/signature.rs b/crates/nu-protocol/src/signature.rs
index 80bef3cc66..c774d66ba8 100644
--- a/crates/nu-protocol/src/signature.rs
+++ b/crates/nu-protocol/src/signature.rs
@@ -715,6 +715,14 @@ impl CustomExample {
             result: self.result.clone(),
         }
     }
+
+    pub fn from_example(example: Example<'_>) -> Self {
+        Self {
+            example: example.example.to_string(),
+            description: example.description.to_string(),
+            result: example.result,
+        }
+    }
 }
 
 #[derive(Clone)]
diff --git a/src/command.rs b/src/command.rs
index 85c7f8006c..0736a968a4 100644
--- a/src/command.rs
+++ b/src/command.rs
@@ -1,9 +1,10 @@
 use nu_engine::{command_prelude::*, get_full_help};
-use nu_parser::{escape_for_script_arg, parse};
+use nu_parser::{KnownExternal, escape_for_script_arg, parse};
 use nu_protocol::{
+    CustomExample,
     ast::{Expr, Expression},
     engine::StateWorkingSet,
-    report_parse_error,
+    report_parse_error, report_shell_error,
 };
 use nu_utils::{escape_quote_string, stdout_write_all_and_flush};
 
@@ -518,3 +519,24 @@ impl Command for Nu {
         ]
     }
 }
+
+/// Add the [`Nu`] command as an extern so we get help and flag completions
+pub(crate) fn add_nu_extern(engine_state: &mut EngineState) {
+    let nu_extern = KnownExternal {
+        signature: Box::new(Nu.signature()),
+        attributes: vec![],
+        examples: Nu
+            .examples()
+            .into_iter()
+            .map(CustomExample::from_example)
+            .collect(),
+    };
+
+    let mut working_set = nu_protocol::engine::StateWorkingSet::new(engine_state);
+    working_set.add_decl(Box::new(nu_extern));
+    let delta = working_set.render();
+
+    if let Err(err) = engine_state.merge_delta(delta) {
+        report_shell_error(engine_state, &err);
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index 520c0ba6af..3c17bb193c 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -15,7 +15,7 @@ use crate::{
     config_files::set_config_path,
     logger::{configure, logger},
 };
-use command::gather_commandline_args;
+use command::{add_nu_extern, gather_commandline_args};
 use log::{Level, trace};
 use miette::Result;
 use nu_cli::gather_parent_env_vars;
@@ -79,6 +79,7 @@ fn main() -> Result<()> {
         let mut working_set = nu_protocol::engine::StateWorkingSet::new(&engine_state);
         working_set.add_decl(Box::new(nu_cli::NuHighlight));
         working_set.add_decl(Box::new(nu_cli::Print));
+
         working_set.render()
     };
 
@@ -202,6 +203,9 @@ fn main() -> Result<()> {
             std::process::exit(1)
         });
 
+    // this has to happen after `parse_command_args` since that hides the `Nu` decl
+    add_nu_extern(&mut engine_state);
+
     experimental_options::load(&engine_state, &parsed_nu_cli_args, !script_name.is_empty());
 
     // keep this condition in sync with the branches at the end
@@ -383,9 +387,6 @@ fn main() -> Result<()> {
             "chop" => test_bins::chop(),
             "repeater" => test_bins::repeater(),
             "repeat_bytes" => test_bins::repeat_bytes(),
-            // Important: nu_repl must be called with `--testbin=nu_repl`
-            // `--testbin nu_repl` will not work due to argument count logic
-            // in test_bins.rs
             "nu_repl" => test_bins::nu_repl(),
             "input_bytes_length" => test_bins::input_bytes_length(),
             _ => std::process::exit(1),
diff --git a/src/test_bins.rs b/src/test_bins.rs
index e0587859f5..16d4ecf3dd 100644
--- a/src/test_bins.rs
+++ b/src/test_bins.rs
@@ -45,7 +45,6 @@ fn echo_one_env(arg: &str, to_stdout: bool) {
 /// If it's not present, panic instead
 pub fn echo_env_mixed() {
     let args = args();
-    let args = &args[1..];
 
     if args.len() != 3 {
         panic!(
@@ -75,11 +74,11 @@ pub fn echo_env_mixed() {
 pub fn cococo() {
     let args: Vec<String> = args();
 
-    if args.len() > 1 {
+    if !args.is_empty() {
         // Write back out all the arguments passed
         // if given at least 1 instead of chickens
         // speaking co co co.
-        println!("{}", &args[1..].join(" "));
+        println!("{}", args.join(" "));
     } else {
         println!("cococo");
     }
@@ -89,7 +88,7 @@ pub fn cococo() {
 pub fn meow() {
     let args: Vec<String> = args();
 
-    for arg in args.iter().skip(1) {
+    for arg in args.iter() {
         let contents = std::fs::read_to_string(arg).expect("Expected a filepath");
         println!("{contents}");
     }
@@ -102,7 +101,7 @@ pub fn meowb() {
     let stdout = io::stdout();
     let mut handle = stdout.lock();
 
-    for arg in args.iter().skip(1) {
+    for arg in args.iter() {
         let buf = std::fs::read(arg).expect("Expected a filepath");
         handle.write_all(&buf).expect("failed to write to stdout");
     }
@@ -118,7 +117,7 @@ pub fn relay() {
 /// nu --testbin nonu a b c
 /// abc
 pub fn nonu() {
-    args().iter().skip(1).for_each(|arg| print!("{arg}"));
+    args().iter().for_each(|arg| print!("{arg}"));
 }
 
 /// Repeat a string or char N times
@@ -128,8 +127,7 @@ pub fn nonu() {
 /// testtesttesttesttest
 pub fn repeater() {
     let mut stdout = io::stdout();
-    let args = args();
-    let mut args = args.iter().skip(1);
+    let mut args = args().into_iter();
     let letter = args.next().expect("needs a character to iterate");
     let count = args.next().expect("need the number of times to iterate");
 
@@ -144,8 +142,7 @@ pub fn repeater() {
 /// A version of repeater that can output binary data, even null bytes
 pub fn repeat_bytes() {
     let mut stdout = io::stdout();
-    let args = args();
-    let mut args = args.iter().skip(1);
+    let mut args = args().into_iter();
 
     while let (Some(binary), Some(count)) = (args.next(), args.next()) {
         let bytes: Vec<u8> = (0..binary.len())
@@ -173,7 +170,6 @@ pub fn iecho() {
     let mut stdout = io::stdout();
     let _ = args()
         .iter()
-        .skip(1)
         .cycle()
         .try_for_each(|v| writeln!(stdout, "{v}"));
 }
@@ -364,6 +360,18 @@ pub fn input_bytes_length() {
 }
 
 fn args() -> Vec<String> {
-    // skip (--testbin bin_name args)
-    std::env::args().skip(2).collect()
+    // skip `nu` path (first argument)
+    // then skip --testbin=foo OR --testbin foo
+    std::env::args().skip(1).fold(vec![], |mut acc, it| {
+        // if we have --testbin foo, skip the previous argument (--testbin) and this argument (foo)
+        if acc.last().is_some_and(|last| last == "--testbin") {
+            acc.pop();
+            return acc;
+        }
+        // if we have --testbin=foo, skip it
+        if !it.starts_with("--testbin=") {
+            acc.push(it);
+        }
+        acc
+    })
 }
diff --git a/tests/repl/test_known_external.rs b/tests/repl/test_known_external.rs
index 74bf8815b2..40d30efb7e 100644
--- a/tests/repl/test_known_external.rs
+++ b/tests/repl/test_known_external.rs
@@ -173,3 +173,9 @@ fn known_external_arg_internally_quoted_options() -> TestResult {
         "--option=test",
     )
 }
+
+// Verify that the KnownExternal for the `nu` binary exists
+#[test]
+fn known_external_nu() -> TestResult {
+    run_test_contains("help nu", "Usage")
+}
diff --git a/tests/repl/test_parser.rs b/tests/repl/test_parser.rs
index 45b890653c..92fb02520c 100644
--- a/tests/repl/test_parser.rs
+++ b/tests/repl/test_parser.rs
@@ -422,27 +422,27 @@ fn append_assign_takes_pipeline() -> TestResult {
 
 #[test]
 fn assign_bare_external_fails() {
-    let result = nu!("$env.FOO = nu --testbin cococo");
+    let result = nu!("$env.FOO = cargo --version");
     assert!(!result.status.success());
     assert!(result.err.contains("must be explicit"));
 }
 
 #[test]
 fn assign_bare_external_with_caret() {
-    let result = nu!("$env.FOO = ^nu --testbin cococo");
+    let result = nu!("$env.FOO = ^cargo --version");
     assert!(result.status.success());
 }
 
 #[test]
 fn assign_backtick_quoted_external_fails() {
-    let result = nu!("$env.FOO = `nu` --testbin cococo");
+    let result = nu!("$env.FOO = `cargo` --version");
     assert!(!result.status.success());
     assert!(result.err.contains("must be explicit"));
 }
 
 #[test]
 fn assign_backtick_quoted_external_with_caret() {
-    let result = nu!("$env.FOO = ^`nu` --testbin cococo");
+    let result = nu!("$env.FOO = ^`cargo` --version");
     assert!(result.status.success());
 }
 
diff --git a/tests/scope/mod.rs b/tests/scope/mod.rs
index ffcaa80bd7..026b4f4b38 100644
--- a/tests/scope/mod.rs
+++ b/tests/scope/mod.rs
@@ -290,7 +290,7 @@ fn scope_externs_sorted() {
     ];
 
     let actual = nu!(&inp.join("; "));
-    assert_eq!(actual.out, "abc");
+    assert!(actual.out.starts_with("abc"));
 }
 
 #[test]
diff --git a/tests/shell/pipeline/commands/external.rs b/tests/shell/pipeline/commands/external.rs
index 5b42798ba5..d5f50e5855 100644
--- a/tests/shell/pipeline/commands/external.rs
+++ b/tests/shell/pipeline/commands/external.rs
@@ -609,15 +609,15 @@ mod external_command_arguments {
 
     #[test]
     fn remove_quotes_in_shell_arguments() {
-        let actual = nu!("nu --testbin cococo expression='-r -w'");
+        let actual = nu!("^nu --testbin cococo expression='-r -w'");
         assert_eq!(actual.out, "expression=-r -w");
-        let actual = nu!(r#"nu --testbin cococo expression="-r -w""#);
+        let actual = nu!(r#"^nu --testbin cococo expression="-r -w""#);
         assert_eq!(actual.out, "expression=-r -w");
-        let actual = nu!("nu --testbin cococo expression='-r -w'");
+        let actual = nu!("^nu --testbin cococo expression='-r -w'");
         assert_eq!(actual.out, "expression=-r -w");
-        let actual = nu!(r#"nu --testbin cococo expression="-r\" -w""#);
+        let actual = nu!(r#"^nu --testbin cococo expression="-r\" -w""#);
         assert_eq!(actual.out, r#"expression=-r" -w"#);
-        let actual = nu!(r#"nu --testbin cococo expression='-r\" -w'"#);
+        let actual = nu!(r#"^nu --testbin cococo expression='-r\" -w'"#);
         assert_eq!(actual.out, r#"expression=-r\" -w"#);
     }
 }
@@ -722,7 +722,7 @@ fn external_error_with_backtrace() {
 
 #[test]
 fn sub_external_expression_with_and_op_should_raise_proper_error() {
-    let actual = nu!("(nu --testbin cococo false) and true");
+    let actual = nu!("(^nu --testbin cococo false) and true");
     assert!(
         actual
             .err