feat: add pipefail handling and set command

src/shell/commands/mod.rs

@@ -12,6 +12,7 @@ mod head;
 mod mkdir;
 mod pwd;
 mod rm;
+mod set;
 mod sleep;
 mod unset;
 mod xargs;
@@ -76,6 +77,10 @@ pub fn builtin_commands() -> HashMap<String, Rc<dyn ShellCommand>> {
       "rm".to_string(),
       Rc::new(rm::RmCommand) as Rc<dyn ShellCommand>,
     ),
+    (
+      "set".to_string(),
+      Rc::new(set::SetCommand) as Rc<dyn ShellCommand>,
+    ),
     (
       "sleep".to_string(),
       Rc::new(sleep::SleepCommand) as Rc<dyn ShellCommand>,

src/shell/commands/set.rs

@@ -0,0 +1,62 @@
+// Copyright 2018-2025 the Deno authors. MIT license.
+
+use futures::future::LocalBoxFuture;
+
+use crate::shell::types::EnvChange;
+use crate::shell::types::ExecuteResult;
+
+use super::ShellCommand;
+use super::ShellCommandContext;
+
+pub struct SetCommand;
+
+impl ShellCommand for SetCommand {
+  fn execute(
+    &self,
+    mut context: ShellCommandContext,
+  ) -> LocalBoxFuture<'static, ExecuteResult> {
+    let result = execute_set(&mut context);
+    Box::pin(futures::future::ready(result))
+  }
+}
+
+fn execute_set(context: &mut ShellCommandContext) -> ExecuteResult {
+  let mut changes = Vec::new();
+  let args: Vec<String> = context
+    .args
+    .iter()
+    .filter_map(|a| a.to_str().map(|s| s.to_string()))
+    .collect();
+
+  let mut i = 0;
+  while i < args.len() {
+    let arg = &args[i];
+    if arg == "-o" || arg == "+o" {
+      let enable = arg == "-o";
+      if i + 1 < args.len() {
+        let option_name = &args[i + 1];
+        match option_name.as_str() {
+          "pipefail" => {
+            changes.push(EnvChange::SetOption("pipefail".to_string(), enable));
+          }
+          _ => {
+            let _ = context
+              .stderr
+              .write_line(&format!("set: unknown option: {}", option_name));
+            return ExecuteResult::from_exit_code(1);
+          }
+        }
+        i += 2;
+      } else {
+        // No option name provided - in bash this would list options
+        // For now, just return success
+        i += 1;
+      }
+    } else {
+      // Unknown argument
+      i += 1;
+    }
+  }
+
+  ExecuteResult::Continue(0, changes, Vec::new())
+}

src/shell/execute.rs

@@ -575,20 +575,33 @@ async fn execute_pipe_sequence(
   let output_handle = tokio::task::spawn_blocking(|| {
     last_output.unwrap().pipe_to_sender(stdout).unwrap();
   });
-  let mut results = futures::future::join_all(wait_tasks).await;
+  let results = futures::future::join_all(wait_tasks).await;
   output_handle.await.unwrap();
-  let last_result = results.pop().unwrap();
-  let all_handles = results.into_iter().flat_map(|r| r.into_handles());
-  match last_result {
-    ExecuteResult::Exit(code, mut handles) => {
-      handles.extend(all_handles);
-      ExecuteResult::Continue(code, Vec::new(), handles)
-    }
-    ExecuteResult::Continue(code, _, mut handles) => {
-      handles.extend(all_handles);
-      ExecuteResult::Continue(code, Vec::new(), handles)
+
+  // Determine exit code based on pipefail option
+  let exit_code = if state.options().pipefail {
+    // With pipefail: return the rightmost non-zero exit code, or 0 if all succeeded
+    results
+      .iter()
+      .rev()
+      .find_map(|r| {
+        let code = match r {
+          ExecuteResult::Exit(c, _) => *c,
+          ExecuteResult::Continue(c, _, _) => *c,
+        };
+        if code != 0 { Some(code) } else { None }
+      })
+      .unwrap_or(0)
+  } else {
+    // Without pipefail: return the last command's exit code
+    match results.last().unwrap() {
+      ExecuteResult::Exit(code, _) => *code,
+      ExecuteResult::Continue(code, _, _) => *code,
     }
-  }
+  };
+
+  let all_handles = results.into_iter().flat_map(|r| r.into_handles());
+  ExecuteResult::Continue(exit_code, Vec::new(), all_handles.collect())
 }
 
 async fn execute_subshell(

src/shell/types.rs

@@ -44,6 +44,13 @@ impl TreeExitCodeCell {
   }
 }
 
+/// Shell options that can be set via `set -o` / `set +o`.
+#[derive(Clone, Default)]
+pub struct ShellOptions {
+  /// When enabled, pipeline exit code is the rightmost non-zero exit code.
+  pub pipefail: bool,
+}
+
 #[derive(Clone)]
 pub struct ShellState {
   /// Environment variables that should be passed down to sub commands
@@ -54,6 +61,7 @@ pub struct ShellState {
   shell_vars: HashMap<OsString, OsString>,
   cwd: PathBuf,
   commands: Rc<HashMap<String, Rc<dyn ShellCommand>>>,
+  options: ShellOptions,
   kill_signal: KillSignal,
   process_tracker: ChildProcessTracker,
   tree_exit_code_cell: TreeExitCodeCell,
@@ -74,6 +82,7 @@ impl ShellState {
       shell_vars: Default::default(),
       cwd: PathBuf::new(),
       commands: Rc::new(commands),
+      options: Default::default(),
       kill_signal,
       process_tracker: ChildProcessTracker::new(),
       tree_exit_code_cell: Default::default(),
@@ -94,6 +103,17 @@ impl ShellState {
     &self.env_vars
   }
 
+  pub fn options(&self) -> &ShellOptions {
+    &self.options
+  }
+
+  pub fn set_option(&mut self, name: &str, value: bool) {
+    match name {
+      "pipefail" => self.options.pipefail = value,
+      _ => {} // ignore unknown options
+    }
+  }
+
   pub fn get_var(&self, name: &OsStr) -> Option<&OsString> {
     let name = if cfg!(windows) {
       Cow::Owned(name.to_ascii_uppercase())
@@ -138,6 +158,9 @@ impl ShellState {
       EnvChange::Cd(new_dir) => {
         self.set_cwd(new_dir.clone());
       }
+      EnvChange::SetOption(name, value) => {
+        self.set_option(name, *value);
+      }
     }
   }
 
@@ -222,6 +245,8 @@ pub enum EnvChange {
   // `unset ENV_VAR`
   UnsetVar(OsString),
   Cd(PathBuf),
+  // `set -o OPTION` or `set +o OPTION`
+  SetOption(String, bool),
 }
 
 pub type FutureExecuteResult = LocalBoxFuture<'static, ExecuteResult>;

tests/integration_test.rs

@@ -1677,3 +1677,53 @@ async fn sigpipe_from_pipeline() {
     .run()
     .await;
 }
+
+#[tokio::test]
+async fn pipefail_option() {
+  // Without pipefail: exit code is from last command (0)
+  TestBuilder::new()
+    .command("sh -c 'exit 1' | true")
+    .assert_exit_code(0)
+    .run()
+    .await;
+
+  // With pipefail: exit code is rightmost non-zero (1)
+  TestBuilder::new()
+    .command("set -o pipefail && sh -c 'exit 1' | true")
+    .assert_exit_code(1)
+    .run()
+    .await;
+
+  // Multiple failures - should return rightmost non-zero
+  TestBuilder::new()
+    .command("set -o pipefail && sh -c 'exit 2' | sh -c 'exit 3' | true")
+    .assert_exit_code(3)
+    .run()
+    .await;
+
+  // All succeed - should return 0
+  TestBuilder::new()
+    .command("set -o pipefail && true | true | true")
+    .assert_exit_code(0)
+    .run()
+    .await;
+
+  // Disable pipefail with +o
+  TestBuilder::new()
+    .command("set -o pipefail && set +o pipefail && sh -c 'exit 1' | true")
+    .assert_exit_code(0)
+    .run()
+    .await;
+}
+
+#[tokio::test]
+#[cfg(unix)]
+async fn pipefail_with_sigpipe() {
+  // With pipefail and SIGPIPE: should return 141 (128 + 13)
+  TestBuilder::new()
+    .command("set -o pipefail && yes | head -n 1")
+    .assert_stdout("y\n")
+    .assert_exit_code(141)
+    .run()
+    .await;
+}