Add back --append flag to save command (#4744)

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

@@ -24,6 +24,7 @@ impl Command for Save {
         Signature::build("save")
             .required("filename", SyntaxShape::Filepath, "the filename to use")
             .switch("raw", "save file as raw binary", Some('r'))
+            .switch("append", "append input to the end of the file", None)
             .category(Category::FileSystem)
     }
 
@@ -35,6 +36,7 @@ impl Command for Save {
         input: PipelineData,
     ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
         let raw = call.has_flag("raw");
+        let append = call.has_flag("append");
 
         let span = call.head;
 
@@ -42,7 +44,15 @@ impl Command for Save {
         let arg_span = path.span;
         let path = Path::new(&path.item);
 
-        let mut file = match std::fs::File::create(path) {
+        let file = match (append, path.exists()) {
+            (true, true) => std::fs::OpenOptions::new()
+                .write(true)
+                .append(true)
+                .open(path),
+            _ => std::fs::File::create(path),
+        };
+
+        let mut file = match file {
             Ok(file) => file,
             Err(err) => {
                 return Ok(PipelineData::Value(

crates/nu-command/tests/commands/save.rs

@@ -1,6 +1,7 @@
 use nu_test_support::fs::{file_contents, Stub::FileWithContent};
 use nu_test_support::nu;
 use nu_test_support::playground::Playground;
+use std::io::Write;
 
 #[test]
 fn figures_out_intelligently_where_to_write_out_with_metadata() {
@@ -48,8 +49,6 @@ fn writes_out_csv() {
     })
 }
 
-// FIXME: jt: needs more work
-#[ignore]
 #[test]
 fn save_append_will_create_file_if_not_exists() {
     Playground::setup("save_test_3", |dirs, sandbox| {
@@ -64,6 +63,31 @@ fn save_append_will_create_file_if_not_exists() {
 
         let actual = file_contents(expected_file);
         println!("{}", actual);
-        assert!(actual == "hello");
+        assert_eq!(actual, "hello");
+    })
+}
+
+#[test]
+fn save_append_will_not_overwrite_content() {
+    Playground::setup("save_test_4", |dirs, sandbox| {
+        sandbox.with_files(vec![]);
+
+        let expected_file = dirs.test().join("new-file.txt");
+
+        {
+            let mut file =
+                std::fs::File::create(&expected_file).expect("Failed to create test file");
+            file.write_all("hello ".as_bytes())
+                .expect("Failed to write to test file")
+        }
+
+        nu!(
+            cwd: dirs.root(),
+            r#"echo world | save --append save_test_4/new-file.txt"#,
+        );
+
+        let actual = file_contents(expected_file);
+        println!("{}", actual);
+        assert_eq!(actual, "hello world");
     })
 }