add -u flag to cp, mv command (#9214)

# Description
Closes: #7853

I found that I want this feature too...

So I take over it, sorry for that @VincenzoCarlino 

# User-Facing Changes

# Tests + Formatting
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crates/nu-command/src/filesystem/cp.rs

@@ -57,6 +57,10 @@ impl Command for Cp {
                 "show successful copies in addition to failed copies (default:false)",
                 Some('v'),
             )
+            .switch("update",
+                "copy only when the SOURCE file is newer than the destination file or when the destination file is missing",
+                Some('u')
+            )
             // TODO: add back in additional features
             // .switch("force", "suppress error when no file", Some('f'))
             .switch("interactive", "ask user to confirm action", Some('i'))
@@ -88,6 +92,7 @@ impl Command for Cp {
         let verbose = call.has_flag("verbose");
         let interactive = call.has_flag("interactive");
         let progress = call.has_flag("progress");
+        let update_mode = call.has_flag("update");
 
         let current_dir_path = current_dir(engine_state, stack)?;
         let source = current_dir_path.join(src.item.as_str());
@@ -177,6 +182,12 @@ impl Command for Cp {
                     if src.is_file() {
                         let dst =
                             canonicalize_with(dst.as_path(), &current_dir_path).unwrap_or(dst);
+
+                        // ignore when source file is not newer than target file
+                        if update_mode && super::util::is_older(&src, &dst) {
+                            continue;
+                        }
+
                         let res = if src == dst {
                             let message = format!(
                                 "src {source:?} and dst {destination:?} are identical(not copied)"
@@ -361,6 +372,11 @@ impl Command for Cp {
                 example: "cp *.txt dir_a",
                 result: None,
             },
+            Example {
+                description: "Copy only if source file is newer than target file",
+                example: "cp -u a b",
+                result: None,
+            },
         ]
     }
 }

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

@@ -53,6 +53,11 @@ impl Command for Mv {
             )
             .switch("force", "overwrite the destination.", Some('f'))
             .switch("interactive", "ask user to confirm action", Some('i'))
+            .switch("update", 
+                "move only when the SOURCE file is newer than the destination file(with -f) or when the destination file is missing",
+                Some('u')
+            )
+            // TODO: add back in additional features
             .category(Category::FileSystem)
     }
 
@@ -75,6 +80,7 @@ impl Command for Mv {
         let verbose = call.has_flag("verbose");
         let interactive = call.has_flag("interactive");
         let force = call.has_flag("force");
+        let update_mode = call.has_flag("update");
 
         let ctrlc = engine_state.ctrlc.clone();
 
@@ -191,6 +197,7 @@ impl Command for Mv {
                         span: spanned_destination.span,
                     },
                     interactive,
+                    update_mode,
                 );
                 if let Err(error) = result {
                     Some(Value::Error {
@@ -244,6 +251,7 @@ fn move_file(
     spanned_from: Spanned<PathBuf>,
     spanned_to: Spanned<PathBuf>,
     interactive: bool,
+    update_mode: bool,
 ) -> Result<bool, ShellError> {
     let Spanned {
         item: from,
@@ -305,9 +313,13 @@ fn move_file(
         }
     }
 
-    match move_item(&from, from_span, &to) {
-        Ok(()) => Ok(true),
-        Err(e) => Err(e),
+    if update_mode && super::util::is_older(&from, &to) {
+        Ok(false)
+    } else {
+        match move_item(&from, from_span, &to) {
+            Ok(()) => Ok(true),
+            Err(e) => Err(e),
+        }
     }
 }
 

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

@@ -132,3 +132,31 @@ fn get_interactive_confirmation(prompt: String) -> Result<bool, Box<dyn Error>>
         Ok(false)
     }
 }
+
+pub fn is_older(src: &Path, dst: &Path) -> bool {
+    if !dst.exists() {
+        return true;
+    }
+    #[cfg(unix)]
+    {
+        use std::os::unix::fs::MetadataExt;
+        let src_ctime = std::fs::metadata(src)
+            .map(|m| m.ctime())
+            .unwrap_or(i64::MIN);
+        let dst_ctime = std::fs::metadata(dst)
+            .map(|m| m.ctime())
+            .unwrap_or(i64::MAX);
+        src_ctime <= dst_ctime
+    }
+    #[cfg(windows)]
+    {
+        use std::os::windows::fs::MetadataExt;
+        let src_ctime = std::fs::metadata(src)
+            .map(|m| m.last_write_time())
+            .unwrap_or(u64::MIN);
+        let dst_ctime = std::fs::metadata(dst)
+            .map(|m| m.last_write_time())
+            .unwrap_or(u64::MAX);
+        src_ctime <= dst_ctime
+    }
+}