---
title: Execution
description: Go SDK - Command execution API reference
---
Run commands inside a running sandbox. Non-zero exit codes are returned in [`ExecOutput`](#execoutput), not as Go errors. See [Commands](/sandboxes/commands) for usage examples.
## Sandbox
The exec entry points live on [`*Sandbox`](/sdk/go/sandbox#instance-methods).
#### sb.Exec()
```go
func (s *Sandbox) Exec(ctx context.Context, cmd string, args []string, opts ...ExecOption) (*ExecOutput, error)
```
```go
out, err := sb.Exec(ctx, "make", []string{"build"},
m.WithExecCwd("/app"),
m.WithExecEnv(map[string]string{"DEBUG": "1"}),
)
```
Run a command in the sandbox and return its collected output. Blocks until the command exits. The returned error is non-nil only on transport or runtime failures; a non-zero exit code is reported via [`ExecOutput.ExitCode`](#out-exitcode), not as an error.
Parameters
ctxcontext.Context
Cancels the wait. The guest process may continue in the background.
cmdstring
Program to run. Passed literally to the guest agent (the image ENTRYPOINT is not consulted).
args[]string
Command arguments. May be nil.
Per-command cwd, timeout, TTY allocation, user, and env.
Returns
Collected stdout, stderr, and exit code.
#### sb.Shell()
```go
func (s *Sandbox) Shell(ctx context.Context, command string, opts ...ExecOption) (*ExecOutput, error)
```
```go
out, err := sb.Shell(ctx, "echo $HOME && ls /tmp")
if err != nil {
return err
}
fmt.Print(out.Stdout())
```
Run `/bin/sh -c command` in the sandbox and collect its output. Blocks until the command exits. A convenience wrapper over [`Exec`](#sb-exec) for shell one-liners.
Parameters
ctxcontext.Context
Cancels the wait.
commandstring
Shell command line passed to /bin/sh -c.
Per-command cwd, timeout, TTY allocation, user, and env.
Returns
Collected stdout, stderr, and exit code.
#### sb.ExecStream()
```go
func (s *Sandbox) ExecStream(ctx context.Context, cmd string, args []string, opts ...ExecOption) (*ExecHandle, error)
```
```go
h, err := sb.ExecStream(ctx, "cat", nil, m.WithExecStdinPipe())
if err != nil {
return err
}
defer h.Close()
```
Start a streaming exec session and return an [`*ExecHandle`](#exechandle). The handle MUST be closed with [`Close`](#h-close) when the stream is no longer needed. Nonblocking: the handle returns immediately and the stream starts in the background.
`ctx` controls only the start handshake; individual [`Recv`](#h-recv) calls take their own `ctx`. Non-zero exit codes are not errors, inspect [`ExecEventExited`](#execeventkind).
Parameters
ctxcontext.Context
Controls the start handshake only.
cmdstring
Program to run.
args[]string
Command arguments. May be nil.
Returns
Live exec session. Close it when done.
#### sb.ShellStream()
```go
func (s *Sandbox) ShellStream(ctx context.Context, command string, opts ...ExecOption) (*ExecHandle, error)
```
```go
h, err := sb.ShellStream(ctx, "tail -f /var/log/app.log")
if err != nil {
return err
}
defer h.Close()
for {
ev, err := h.Recv(ctx)
if err != nil {
return err
}
switch ev.Kind {
case m.ExecEventStdout:
os.Stdout.Write(ev.Data)
case m.ExecEventDone:
return nil
}
}
```
Run `/bin/sh -c command` with streaming output. A convenience wrapper over [`ExecStream`](#sb-execstream). Nonblocking: the handle returns immediately and the stream starts in the background.
Parameters
ctxcontext.Context
Controls the start handshake only.
commandstring
Shell command line passed to /bin/sh -c.
Returns
Live exec session. Close it when done.
## ExecHandle
Returned by sb.ExecStream() · sb.ShellStream()
A handle to a running streaming execution and its events.
#### h.ID()
```go
func (h *ExecHandle) ID() (string, error)
```
Return the unique identifier for this exec session, assigned by the guest agent. Useful for correlating log entries or referencing the session from external tooling.
Returns
string
Session correlation id.
#### h.TakeStdin()
```go
func (h *ExecHandle) TakeStdin() *ExecSink
```
```go
sink := h.TakeStdin()
sink.Write([]byte("hello\n"))
sink.Close()
```
Return the stdin sink for this exec session. Single-take: returns `nil` if the session was not started with [`WithExecStdinPipe`](#withexecstdinpipe), or if `TakeStdin` was already called on this handle (matching the Node and Python SDKs). The caller is responsible for closing the sink when done writing; closing the sink without closing the exec handle is fine, they own different Rust-side resources.
Returns
Stdin writer, or nil if unavailable.
#### h.Recv()
```go
func (h *ExecHandle) Recv(ctx context.Context) (*ExecEvent, error)
```
```go
for {
ev, err := h.Recv(ctx)
if err != nil {
return err
}
switch ev.Kind {
case m.ExecEventStarted:
fmt.Printf("started pid=%d\n", ev.PID)
case m.ExecEventStdout:
os.Stdout.Write(ev.Data)
case m.ExecEventStderr:
os.Stderr.Write(ev.Data)
case m.ExecEventExited:
fmt.Printf("exited code=%d\n", ev.ExitCode)
case m.ExecEventDone:
return nil
}
}
```
Block until the next event arrives or the stream ends. Returns an event with `Kind == ExecEventDone` when all events have been consumed. `ctx` controls the wait; cancellation causes `Recv` to return `ctx.Err()` immediately. The underlying Rust call may continue to completion in the background.
Parameters
ctxcontext.Context
Cancels the wait for the next event.
Returns
#### h.Collect()
```go
func (h *ExecHandle) Collect(ctx context.Context) (*ExecOutput, error)
```
```go
out, err := h.Collect(ctx)
if err != nil {
return err
}
fmt.Print(out.Stdout())
```
Drain the stream, accumulate all output, and return it as an [`*ExecOutput`](#execoutput). Equivalent to calling [`Recv`](#h-recv) in a loop and assembling the result. The handle should be closed after `Collect` returns.
Parameters
ctxcontext.Context
Cancels the drain.
Returns
Collected stdout, stderr, and exit code.
#### h.Wait()
```go
func (h *ExecHandle) Wait(ctx context.Context) (int, error)
```
Block until the process exits and return its exit code. Unlike [`Collect`](#h-collect), stdout and stderr are discarded. The handle should be closed after `Wait` returns.
Parameters
ctxcontext.Context
Cancels the wait.
Returns
#### h.Kill()
```go
func (h *ExecHandle) Kill(ctx context.Context) error
```
Send SIGKILL to the running process.
Parameters
ctxcontext.Context
Cancels the call.
#### h.Signal()
```go
func (h *ExecHandle) Signal(ctx context.Context, signal int) error
```
```go
import "syscall"
if err := h.Signal(ctx, int(syscall.SIGTERM)); err != nil {
return err
}
```
Send a Unix signal to the running process. Pass values from `syscall` (e.g. `int(syscall.SIGTERM)`).
Parameters
ctxcontext.Context
Cancels the call.
signalint
Signal number, e.g. int(syscall.SIGTERM).
#### h.Resize()
```go
func (h *ExecHandle) Resize(ctx context.Context, rows, cols uint16) error
```
```go
if err := h.Resize(ctx, 40, 120); err != nil {
return err
}
```
Resize the pseudo-terminal for this exec session. Use with a session started with [`WithExecTTY(true)`](#withexectty), typically when relaying a terminal-size change from a remote client.
`Resize` may be called concurrently while another goroutine is blocked in [`Recv`](#h-recv).
Parameters
ctxcontext.Context
Cancels the resize call.
rowsuint16
New terminal height in character cells.
colsuint16
New terminal width in character cells.
#### h.Close()
```go
func (h *ExecHandle) Close() error
```
```go
defer h.Close()
```
Release the Rust-side exec handle. Does not kill the running process; call [`Signal`](#h-signal) or [`Kill`](#h-kill) first if you need to terminate it. Safe to call after `ExecEventDone` has been received.
## ExecOutput
Returned by sb.Exec() · sb.Shell() · h.Collect()
Collected output and exit status. Non-zero exit codes are results, not Go errors.
#### out.Stdout()
```go
func (e *ExecOutput) Stdout() string
```
Captured standard output as a string.
Returns
#### out.StdoutBytes()
```go
func (e *ExecOutput) StdoutBytes() []byte
```
Captured standard output as raw bytes. Use when the output may not be valid UTF-8.
Returns
#### out.Stderr()
```go
func (e *ExecOutput) Stderr() string
```
Captured standard error as a string.
Returns
#### out.StderrBytes()
```go
func (e *ExecOutput) StderrBytes() []byte
```
Captured standard error as raw bytes.
Returns
#### out.ExitCode()
```go
func (e *ExecOutput) ExitCode() int
```
The process's exit code, or `-1` if the guest did not report one (e.g. the process was killed by a signal).
Returns
#### out.Success()
```go
func (e *ExecOutput) Success() bool
```
Reports whether the command exited with code `0`.
Returns
bool
true if ExitCode() is 0.
## ExecSink
Returned by h.TakeStdin()
```go
type ExecSink = ffi.ExecSink
```
A write-only pipe to a running process's stdin. Implements `io.WriteCloser`.
#### sink.Write()
```go
func (sk *ExecSink) Write(p []byte) (int, error)
```
```go
h, err := sb.ExecStream(ctx, "cat", nil, m.WithExecStdinPipe())
if err != nil {
return err
}
defer h.Close()
sink := h.TakeStdin()
sink.Write([]byte("hello\n"))
sink.Close()
out, _ := h.Collect(ctx)
fmt.Print(out.Stdout()) // "hello\n"
```
Send data to the process stdin. Implements `io.Writer`. Uses `context.Background()` internally, there is no way to cancel a stuck write through this method alone.
Parameters
p[]byte
Bytes to write to stdin.
Returns
int
Number of bytes written.
#### sink.WriteCtx()
```go
func (sk *ExecSink) WriteCtx(ctx context.Context, p []byte) (int, error)
```
Like [`Write`](#sink-write), but with a caller-controlled context, so a stuck stdin write can be cancelled.
Parameters
ctxcontext.Context
Cancels the write.
p[]byte
Bytes to write to stdin.
Returns
int
Number of bytes written.
#### sink.Close()
```go
func (sk *ExecSink) Close() error
```
```go
sink.Close()
```
Close the stdin sink. In non-TTY pipe mode this sends EOF to the process. In TTY mode it prevents further writes through this sink, but the guest PTY remains open; send the terminal's EOF control character (usually `\x04` in canonical mode) when the interactive program needs one. Implements `io.Closer`.
## Options
#### WithExecCwd()
```go
func WithExecCwd(path string) ExecOption
```
Set the working directory for a single command.
Parameters
pathstring
Absolute path inside the guest.
#### WithExecTimeout()
```go
func WithExecTimeout(d time.Duration) ExecOption
```
```go
out, err := sb.Shell(ctx, "long-running-task",
m.WithExecTimeout(30*time.Second))
if m.IsKind(err, m.ErrExecTimeout) {
log.Println("timed out")
}
```
Set a per-command timeout. When exceeded, the guest terminates the process and the call returns an error with `Kind == ErrExecTimeout`. Sub-second precision rounds up to whole seconds; pass at least 1 second.
Parameters
dtime.Duration
Timeout duration, rounded up to whole seconds.
#### WithExecStdinPipe()
```go
func WithExecStdinPipe() ExecOption
```
Enable a stdin pipe for the exec session, allowing data to be written via [`ExecHandle.TakeStdin`](#h-takestdin).
#### WithExecTTY()
```go
func WithExecTTY(enabled bool) ExecOption
```
```go
h, err := sb.ExecStream(ctx, "/bin/bash", nil,
m.WithExecStdinPipe(),
m.WithExecTTY(true),
)
if err != nil {
return err
}
defer h.Close()
stdin := h.TakeStdin()
if stdin == nil {
return errors.New("stdin pipe is unavailable")
}
if err := h.Resize(ctx, 40, 120); err != nil {
return err
}
if _, err := stdin.Write([]byte("echo hello\n")); err != nil {
return err
}
```
Control whether the command runs inside a pseudo-terminal. Enable it for interactive programs such as shells, editors, REPLs, and `top`. Default: `false`.
When enabled, the guest process runs with its stdin, stdout, and stderr connected to the PTY. Streaming sessions expose the combined terminal output through [`ExecEventStdout`](#execeventkind); they do not emit a separately attributable stderr stream. Collected output similarly places the combined stream in [`Stdout`](#out-stdout) and leaves [`Stderr`](#out-stderr) empty. Add [`WithExecStdinPipe()`](#withexecstdinpipe) to write to the terminal programmatically, and use [`Resize`](#h-resize) to update its dimensions after the session starts.
Parameters
enabledbool
true to allocate a pseudo-terminal.
#### WithExecUser()
```go
func WithExecUser(user string) ExecOption
```
Run the command as the given guest user (UID or name).
Parameters
userstring
Guest user, as a UID or name.
#### WithExecEnv()
```go
func WithExecEnv(env map[string]string) ExecOption
```
```go
out, err := sb.Exec(ctx, "make", []string{"build"},
m.WithExecCwd("/app"),
m.WithExecEnv(map[string]string{"DEBUG": "1"}),
)
```
Add per-command environment variables. Called repeatedly, maps merge; later keys overwrite earlier ones.
Parameters
envmap[string]string
Environment variables for this command.
## Types
### ExecEvent
Returned by h.Recv()
One event from a streaming exec session. [`Kind`](#execeventkind) identifies which fields are populated.
| Field | Type | Description |
|-------|------|-------------|
| `Kind` | [`ExecEventKind`](#execeventkind) | Identifies which fields are populated |
| `PID` | `uint32` | Guest process id, set on `ExecEventStarted` |
| `Data` | `[]byte` | Chunk of stdout or stderr, set on `ExecEventStdout` / `ExecEventStderr` |
| `ExitCode` | `int` | Process exit code, set on `ExecEventExited` |
| `Failure` | [`*ExecFailure`](#execfailure) | Failure detail, set on `ExecEventFailed` and `ExecEventStdinError` |
### ExecEventKind
Field of ExecEvent
```go
type ExecEventKind = ffi.ExecEventKind
```
Identifies what an [`ExecEvent`](#execevent) carries.
| Constant | Description |
|----------|-------------|
| `ExecEventStarted` | Sent once when the guest process starts; `PID` is valid |
| `ExecEventStdout` | A chunk of stdout; in TTY mode, carries the combined terminal output stream. `Data` is valid |
| `ExecEventStderr` | A chunk of stderr; not emitted separately in TTY mode. `Data` is valid |
| `ExecEventExited` | The process exited; `ExitCode` is valid |
| `ExecEventFailed` | The user program never started (binary missing, permission denied, ...); `Failure` is valid and `ExitCode` is not meaningful |
| `ExecEventStdinError` | A stdin write failed; `Failure` is valid. Non-terminal: the process may still exit normally |
| `ExecEventDone` | All events have been consumed |
### ExecFailure
Field of ExecEvent
```go
type ExecFailure = ffi.ExecFailure
```
Structured detail about a failed-to-start exec, populated on `ExecEventFailed` and `ExecEventStdinError`. See [Error Handling](/sdk/errors#spawn-time-exec-failures) for the kinds it carries (`not_found`, `permission_denied`, etc.) and how to branch on them.
| Field | Type | Description |
|-------|------|-------------|
| `Kind` | `string` | Failure category, e.g. `not_found`, `permission_denied` |
| `Errno` | `*int` | Underlying errno, if known |
| `ErrnoName` | `string` | Symbolic errno name, if known |
| `Message` | `string` | Human-readable failure message |
| `Path` | `string` | Offending path, if applicable |
### ExecConfig
Populated by ExecOption
Configures a single [`Exec`](#sb-exec) or [`ExecStream`](#sb-execstream) call. Most callers set fields through the `WithExec*` functional options; `ExecConfig` is exported for parity with the other SDKs' config types.
| Field | Type | Description |
|-------|------|-------------|
| `Cwd` | `string` | Working directory inside the guest |
| `Timeout` | `time.Duration` | Kill the process after this duration; sub-second precision is rounded up |
| `StdinPipe` | `bool` | Enable a stdin pipe; required for [`TakeStdin`](#h-takestdin) |
| `TTY` | `bool` | Allocate a pseudo-terminal; default `false` |
| `User` | `string` | Guest user (UID or name) |
| `Env` | `map[string]string` | Per-command environment variables |
### ExecOption
Accepted by sb.Exec() · sb.Shell() · sb.ExecStream() · sb.ShellStream()
```go
type ExecOption func(*ExecConfig)
```
A functional option that mutates an [`ExecConfig`](#execconfig). Construct them with the `WithExec*` functions below.