Use external exceptions in path strings (#4636)

src/utils.rs

@@ -301,6 +301,13 @@ pub fn external_exceptions(engine_state: &EngineState, stack: &Stack) -> Vec<Vec
                                         executables.push(name);
                                     }
                                 }
+                                if let Some(name) = item.path().file_stem() {
+                                    let name = name.to_string_lossy();
+                                    let name = name.as_bytes().to_vec();
+                                    if nu_parser::is_math_expression_like(&name) {
+                                        executables.push(name);
+                                    }
+                                }
                             }
                         }
                     }