env: require a command when --argv0 is given

src/uu/env/locales/en-US.ftl

@@ -33,6 +33,7 @@ env-error-use-s-shebang = use -[v]S to pass options in shebang lines
 env-error-cannot-unset = cannot unset '{ $name }': Invalid argument
 env-error-cannot-unset-invalid = cannot unset { $name }: Invalid argument
 env-error-must-specify-command-with-chdir = must specify command with --chdir (-C)
+env-error-must-specify-command-with-argv0 = must specify command with --argv0 (-a)
 env-error-cannot-change-directory = cannot change directory to { $directory }: { $error }
 env-error-argv0-not-supported = --argv0 is currently not supported on this platform
 env-error-failed-set-signal-action = failed to set signal action for signal { $signal }: { $error }

src/uu/env/src/env.rs

@@ -814,6 +814,15 @@ impl EnvAppData {
             }
         }
 
+        // GNU env requires a command when --argv0 is given. Validate before
+        // apply_change_directory performs its side effect.
+        if opts.program.is_empty() && opts.argv0.is_some() {
+            return Err(UUsageError::new(
+                125,
+                translate!("env-error-must-specify-command-with-argv0"),
+            ));
+        }
+
         apply_change_directory(&opts)?;
         if opts.program.is_empty() {
             // no program provided, so just dump all env vars to stdout

tests/by-util/test_env.rs

@@ -477,6 +477,17 @@ fn test_fail_change_directory() {
     assert!(out.contains("env: cannot change directory to "));
 }
 
+#[test]
+fn test_argv0_without_command_fails() {
+    for arg in ["-a", "--argv0"] {
+        let out = new_ucmd!()
+            .args(&[arg, "foo"])
+            .fails_with_code(125)
+            .stderr_move_str();
+        assert!(out.contains("must specify command with --argv0 (-a)"));
+    }
+}
+
 #[cfg(not(windows))] // windows has no executable "echo", its only supported as part of a batch-file
 #[test]
 fn test_split_string_into_args_one_argument_no_quotes() {