feat: implement noclobber option (a.k.a. -C)

brush-core/src/interp.rs

@@ -1316,16 +1316,39 @@ pub(crate) async fn setup_redirect(
                 ast::IoFileRedirectTarget::Filename(f) => {
                     let mut options = std::fs::File::options();
 
+                    let mut expanded_fields =
+                        expansion::full_expand_and_split_word(shell, f).await?;
+
+                    if expanded_fields.len() != 1 {
+                        return Err(error::Error::InvalidRedirection);
+                    }
+
+                    let expanded_file_path: PathBuf =
+                        shell.get_absolute_path(Path::new(expanded_fields.remove(0).as_str()));
+
                     let default_fd_if_unspecified = get_default_fd_for_redirect_kind(kind);
                     match kind {
                         ast::IoFileRedirectKind::Read => {
                             options.read(true);
                         }
                         ast::IoFileRedirectKind::Write => {
-                            // TODO: honor noclobber options
-                            options.create(true);
-                            options.write(true);
-                            options.truncate(true);
+                            if shell
+                                .options
+                                .disallow_overwriting_regular_files_via_output_redirection
+                            {
+                                // First check to see if the path points to an existing regular
+                                // file.
+                                if !expanded_file_path.is_file() {
+                                    options.create(true);
+                                } else {
+                                    options.create_new(true);
+                                }
+                                options.write(true);
+                            } else {
+                                options.create(true);
+                                options.write(true);
+                                options.truncate(true);
+                            }
                         }
                         ast::IoFileRedirectKind::Append => {
                             options.create(true);
@@ -1352,16 +1375,6 @@ pub(crate) async fn setup_redirect(
 
                     fd_num = specified_fd_num.unwrap_or(default_fd_if_unspecified);
 
-                    let mut expanded_fields =
-                        expansion::full_expand_and_split_word(shell, f).await?;
-
-                    if expanded_fields.len() != 1 {
-                        return Err(error::Error::InvalidRedirection);
-                    }
-
-                    let expanded_file_path: PathBuf =
-                        shell.get_absolute_path(Path::new(expanded_fields.remove(0).as_str()));
-
                     let opened_file =
                         options.open(expanded_file_path.as_path()).map_err(|err| {
                             error::Error::RedirectionFailure(

brush-core/src/options.rs

@@ -191,6 +191,8 @@ impl RuntimeOptions {
         // There's a set of options enabled by default for all shells.
         let mut options = Self {
             interactive: create_options.interactive,
+            disallow_overwriting_regular_files_via_output_redirection: create_options
+                .disallow_overwriting_regular_files_via_output_redirection,
             do_not_execute_commands: create_options.do_not_execute_commands,
             enable_command_history: create_options.interactive,
             enable_job_control: create_options.interactive,

brush-core/src/shell.rs

@@ -123,6 +123,8 @@ pub struct CreateOptions {
     pub disabled_shopt_options: Vec<String>,
     /// Enabled shopt options.
     pub enabled_shopt_options: Vec<String>,
+    /// Disallow overwriting regular files via output redirection.
+    pub disallow_overwriting_regular_files_via_output_redirection: bool,
     /// Do not execute commands.
     pub do_not_execute_commands: bool,
     /// Whether the shell is interactive.

brush-shell/src/args.rs

@@ -45,6 +45,10 @@ pub struct CommandLineArgs {
     #[clap(long = "version", action = clap::ArgAction::Version)]
     pub version: Option<bool>,
 
+    /// Enable noclobber shell option.
+    #[arg(short = 'C')]
+    pub disallow_overwriting_regular_files_via_output_redirection: bool,
+
     /// Execute the provided command and then exit.
     #[arg(short = 'c', value_name = "COMMAND")]
     pub command: Option<String>,

brush-shell/src/main.rs

@@ -199,6 +199,8 @@ async fn instantiate_shell(
     let options = brush_interactive::Options {
         shell: brush_core::CreateOptions {
             disabled_shopt_options: args.disabled_shopt_options.clone(),
+            disallow_overwriting_regular_files_via_output_redirection: args
+                .disallow_overwriting_regular_files_via_output_redirection,
             enabled_shopt_options: args.enabled_shopt_options.clone(),
             do_not_execute_commands: args.do_not_execute_commands,
             login: args.login || argv0.as_ref().map_or(false, |a0| a0.starts_with('-')),

brush-shell/tests/cases/options.yaml

@@ -14,6 +14,32 @@ cases:
       env | grep newvar
       env | grep unexported
 
+  - name: "set -C"
+    ignore_stderr: true
+    stdin: |
+      touch existing-file
+
+      set -C
+
+      echo hi > non-existing-file
+      echo "Result (non existing): $?"
+      echo "File contents: $(cat non-existing-file)"
+      echo
+
+      echo hi > /dev/null
+      echo "Result (device file): $?"
+      echo
+
+      echo hi > existing-file
+      echo "Result (existing file): $?"
+      echo "File contents: $(cat existing-file)"
+      echo
+
+      echo hi >| existing-file
+      echo "Result (clobber): $?"
+      echo "File contents: $(cat existing-file)"
+      echo
+
   - name: "set -x"
     stdin: |
       set -x