exechelper

exechelper is a simple wrapper around standard go 'exec' that tries to follow the spirit of its API closely

Its main features are:

1. It allows you to pass strings containing the command you want executed instead of an array of args.
2. It's Start() returns an errCh that will get zero or one errors, and be closed after the command has finished running
3. You can use the WithXYZ pattern to do things like customize things like Stdout, Stdin, StdError, Dir, and Env variables

Run Examples:

if err := exechelper.Run("go list -m");err != nil {...}

if err := exechelper.Run("go list -m",WithEnv(os.Environs()));err != nil {...}

if err := exechelper.Run("go list -m",WithDir(dir)); err != nil {...}

outputBuffer := bytes.NewBuffer([]byte{})
errBuffer := bytes.NewBuffer([]bytes{})
if err := exechelper.Run("go list -m",WithStdout(outputBuffer),WithStderr(errBuffer));err != nil {...}

Start Examples

ctx,cancel := context.WithCancel(context.Background())
errCh := exechelper.Start(startContext,"spire-server run",WithContext(ctx))

// cancel() - will stop the running cmd if its still running
// <-errCh - provides any error from the Start.  Will always have zero or one err, so <-errCh will block until Start has finished
//           For non-zero Exit code will return a exec.ExitError
//           Note: cancel() will almost always result in a non-zero exit code

Similarly, exechelper.Output(...), exechelper.CombinedOutput(...) are provided.

Multiplexing Stdout/Stderr

WithStdout and WithStderr can be used multiple times, with each provided io.Writer provided getting a copy of the stdout/stderr. As many WithStdout or WithStderr options may be used on the same Run/Start/Output/CombinedOutput as you wish

Example:

outputBuffer := bytes.NewBuffer([]byte{})
errBuffer := bytes.NewBuffer([]bytes{})
if err := exechelper.Run("go list -m",WithStdout(outputBuffer),WithStderr(errBuffer),WithStdout(os.Stdout),WithStderr(os.Stderr));err != nil {...}
// stdout of "go list -m" is written to both outputBuffer and os.Stdout.  stderr is written to both errBuffer and os.Stdout

Terminating with SIGTERM and a grace period

By default, canceling the context on a Start will result in SIGKILL being sent to the child process (this is how exec.Cmd works). It is often useful to send SIGTERM first, and allow a grace period before sending SIGKILL to allow processes the opportunity to clean themselves up.

Example:

ctx,cancel := context.WithCancel(context.Background())
errCh := exechelper.Start(startContext,"spire-server run",WithContext(ctx),WithGracePeriod(30*time.Second))
cancel()
<-errCh
// Calling cancel will send SIGTERM to the spire-server and wait up to 30 seconds for it to exit before sending SIGKILL
// errCh will receive any errors from the exit of spire-server immediately after spire-server exiting, whether that
// is immediately, any time during the 30 second grace period, or after the SIGKILL is sent