Added Commandf and Sprintf

command.go

@@ -0,0 +1,44 @@
+package shell
+
+import (
+	"fmt"
+	"io"
+	"os/exec"
+)
+
+// Commandf runs a shell command based on the format string
+func Commandf(format string, a ...interface{}) *exec.Cmd {
+	shellCmd := Sprintf(format, a...)
+	return exec.Command("/bin/sh", "-c", shellCmd)
+}
+
+// Sprintf generates a shell command with the format arguments escaped.
+func Sprintf(format string, a ...interface{}) string {
+	wrapped := make([]interface{}, len(a))
+	for i, v := range a {
+		wrapped[i] = escapable{v}
+	}
+	return fmt.Sprintf(format, wrapped...)
+}
+
+type escapable struct {
+	x interface{}
+}
+
+func (e escapable) Format(f fmt.State, c rune) {
+	s := "%"
+	for i := 0; i < 128; i++ {
+		if f.Flag(i) {
+			s += string(i)
+		}
+	}
+	if w, ok := f.Width(); ok {
+		s += fmt.Sprintf("%d", w)
+	}
+	if p, ok := f.Precision(); ok {
+		s += fmt.Sprintf(".%d", p)
+	}
+	s += string(c)
+	formatted := fmt.Sprintf(s, e.x)
+	io.WriteString(f, ReadableEscapeArg(formatted))
+}

command_test.go

@@ -0,0 +1,33 @@
+package shell
+
+import (
+	"bytes"
+	"testing"
+)
+
+func TestCommandf(t *testing.T) {
+	out, err := Commandf("echo %s  world   %s", "hello", "quote!me").Output()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(out) != "hello world quote!me\n" {
+		t.Fatalf("Unexpected hello world output: %#v", string(out))
+	}
+}
+
+func TestCommandf_Redirect(t *testing.T) {
+	var stdout, stderr bytes.Buffer
+	cmd := Commandf("echo %s; echo %s 1>&2", "hello from stdout", "bye from stderr")
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+	err := cmd.Run()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if stdout.String() != "hello from stdout\n" {
+		t.Errorf("Unexpected output from stdout: %v", stdout.String())
+	}
+	if stderr.String() != "bye from stderr\n" {
+		t.Errorf("Unexpected output from stderr: %v", stderr.String())
+	}
+}

escape.go

@@ -13,8 +13,8 @@ func EscapeArg(arg string) string {
 }
 
 // ReadableEscapeArg will not escape strings that do not requiring
-// escaping. Note that it is conservative in it's approach, so may escape
-// strings which do not require it.
+// escaping. Note that it is conservative, so may escape strings which do not
+// require it.
 func ReadableEscapeArg(arg string) string {
 	if readableRe.MatchString(arg) {
 		return arg