common: add interface for executing external programs

Add 'CommandExecutor' interfaced type for executing arbitrary commands
('git', 'launchctl', etc.).

Signed-off-by: Victoria Dye <[email protected]>

Author: vdye

internal/common/command.go

@@ -0,0 +1,41 @@
+package common
+
+import (
+	"fmt"
+	"os/exec"
+)
+
+type CommandExecutor interface {
+	Run(command string, args ...string) (int, error)
+}
+
+type commandExecutor struct{}
+
+func NewCommandExecutor() *commandExecutor {
+	return &commandExecutor{}
+}
+
+func (c *commandExecutor) Run(command string, args ...string) (int, error) {
+	exe, err := exec.LookPath(command)
+	if err != nil {
+		return -1, fmt.Errorf("failed to find '%s' on the path: %w", command, err)
+	}
+
+	cmd := exec.Command(exe, args...)
+
+	err = cmd.Start()
+	if err != nil {
+		return -1, fmt.Errorf("command failed to start: %w", err)
+	}
+
+	err = cmd.Wait()
+	_, isExitError := err.(*exec.ExitError)
+
+	// If the command succeeded, or ran to completion but returned a nonzero
+	// exit code, return non-erroneous result
+	if err == nil || isExitError {
+		return cmd.ProcessState.ExitCode(), nil
+	} else {
+		return -1, err
+	}
+}