From 5a5bddf900f33821ccfefdaf34e703e9c2c3819c Mon Sep 17 00:00:00 2001
From: Dave Cheney <dave@cheney.net>
Date: Thu, 11 Jun 2015 21:33:54 +1000
Subject: [PATCH] exec: initial import

---
 exec.go | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 exec.go

diff --git a/exec.go b/exec.go
new file mode 100644
index 0000000..9f6b848
--- /dev/null
+++ b/exec.go
@@ -0,0 +1,99 @@
+// package exec is a universal wrapper around the os/exec package.
+package exec
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"os/exec"
+)
+
+// Command returns a Cmd to execpute the named program with the given arguments.
+func Command(name string, args ...string) *Cmd {
+	return &Cmd{
+		Cmd:        exec.Command(name, args...),
+		initalised: true,
+	}
+}
+
+// Cmd represents a command to be run.
+// Cmd must be created by calling Command.
+// Cmd cannot be reused after calling its Run or Start methods.
+type Cmd struct {
+	*exec.Cmd
+	initalised bool
+}
+
+// Run starts the specified command and waits for it to complete.
+//
+// The returned error is nil if the command runs, has no problems
+// copying stdin, stdout, and stderr, and exits with a zero exit
+// status.
+//
+// If the command fails to run or doesn't complete successfully, the
+// error is of type *ExitError. Other error types may be
+// returned for I/O problems.
+func (c *Cmd) Run(opts ...func(*exec.Cmd) error) error {
+	if err := c.Start(opts...); err != nil {
+		return err
+	}
+	return c.Wait()
+}
+
+// Start starts the specified command but does not wait for it to complete.
+//
+// The Wait method will return the exit code and release associated resources
+// once the command exits.
+func (c *Cmd) Start(opts ...func(*exec.Cmd) error) error {
+	if !c.initalised {
+		return errors.New("exec: command not initalised")
+	}
+	if err := applyDefaultOptions(c.Cmd); err != nil {
+		return err
+	}
+	if err := applyOptions(c.Cmd, opts...); err != nil {
+		return err
+	}
+	return c.Cmd.Start()
+}
+
+// Stdout specifies the process's standard output.
+func Stdout(w io.Writer) func(*exec.Cmd) error {
+	return func(c *exec.Cmd) error {
+		if c.Stdout != nil {
+			return errors.New("exec: Stdout already set")
+		}
+		c.Stdout = w
+		return nil
+	}
+}
+
+// Output runs the command and returns its standard output.
+func (c *Cmd) Output(opts ...func(*exec.Cmd) error) ([]byte, error) {
+	var b bytes.Buffer
+	err := c.Run(append(opts, Stdout(&b))...)
+	return b.Bytes(), err
+}
+
+// Dir specifies the working directory of the command.
+// If Dir is empty, the command executes in the calling
+// process's current directory.
+func Dir(dir string) func(*exec.Cmd) error {
+	return func(c *exec.Cmd) error {
+		c.Dir = dir
+		return nil
+	}
+}
+
+func applyDefaultOptions(c *exec.Cmd) error {
+	return nil
+}
+
+func applyOptions(c *exec.Cmd, opts ...func(*exec.Cmd) error) error {
+	for _, opt := range opts {
+		if err := opt(c); err != nil {
+			return err
+		}
+	}
+	return nil
+}