diff --git a/src/cmd/go/bug.go b/src/cmd/go/bug.go
index 8d55a09a2e..60279c6060 100644
--- a/src/cmd/go/bug.go
+++ b/src/cmd/go/bug.go
@@ -7,6 +7,7 @@ package main
 import (
 	"bytes"
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -18,7 +19,7 @@ import (
 	"strings"
 )
 
-var cmdBug = &Command{
+var cmdBug = &base.Command{
 	Run:       runBug,
 	UsageLine: "bug",
 	Short:     "start a bug report",
@@ -32,7 +33,7 @@ func init() {
 	cmdBug.Flag.BoolVar(&cfg.BuildV, "v", false, "")
 }
 
-func runBug(cmd *Command, args []string) {
+func runBug(cmd *base.Command, args []string) {
 	var buf bytes.Buffer
 	buf.WriteString(bugHeader)
 	inspectGoVersion(&buf)
diff --git a/src/cmd/go/build.go b/src/cmd/go/build.go
index 329e846518..caa876c4ae 100644
--- a/src/cmd/go/build.go
+++ b/src/cmd/go/build.go
@@ -28,10 +28,11 @@ import (
 	"time"
 
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"cmd/go/internal/str"
 )
 
-var cmdBuild = &Command{
+var cmdBuild = &base.Command{
 	UsageLine: "build [-o output] [-i] [build flags] [packages]",
 	Short:     "compile packages and dependencies",
 	Long: `
@@ -196,7 +197,7 @@ func init() {
 
 // addBuildFlags adds the flags common to the build, clean, get,
 // install, list, run, and test commands.
-func addBuildFlags(cmd *Command) {
+func addBuildFlags(cmd *base.Command) {
 	cmd.Flag.BoolVar(&cfg.BuildA, "a", false, "")
 	cmd.Flag.BoolVar(&cfg.BuildN, "n", false, "")
 	cmd.Flag.IntVar(&cfg.BuildP, "p", cfg.BuildP, "")
@@ -219,11 +220,6 @@ func addBuildFlags(cmd *Command) {
 	cmd.Flag.BoolVar(&cfg.BuildWork, "work", false, "")
 }
 
-func addBuildFlagsNX(cmd *Command) {
-	cmd.Flag.BoolVar(&cfg.BuildN, "n", false, "")
-	cmd.Flag.BoolVar(&cfg.BuildX, "x", false, "")
-}
-
 func isSpaceByte(c byte) bool {
 	return c == ' ' || c == '\t' || c == '\n' || c == '\r'
 }
@@ -321,7 +317,7 @@ func buildModeInit() {
 	case "c-archive":
 		pkgsFilter = func(p []*Package) []*Package {
 			if len(p) != 1 || p[0].Name != "main" {
-				fatalf("-buildmode=c-archive requires exactly one main package")
+				base.Fatalf("-buildmode=c-archive requires exactly one main package")
 			}
 			return p
 		}
@@ -350,7 +346,7 @@ func buildModeInit() {
 				codegenArg = "-shared"
 			case "darwin/amd64", "darwin/386":
 			default:
-				fatalf("-buildmode=c-shared not supported on %s\n", platform)
+				base.Fatalf("-buildmode=c-shared not supported on %s\n", platform)
 			}
 		}
 		ldBuildmode = "c-shared"
@@ -370,14 +366,14 @@ func buildModeInit() {
 		ldBuildmode = "exe"
 	case "pie":
 		if gccgo {
-			fatalf("-buildmode=pie not supported by gccgo")
+			base.Fatalf("-buildmode=pie not supported by gccgo")
 		} else {
 			switch platform {
 			case "linux/386", "linux/amd64", "linux/arm", "linux/arm64", "linux/ppc64le", "linux/s390x",
 				"android/amd64", "android/arm", "android/arm64", "android/386":
 				codegenArg = "-shared"
 			default:
-				fatalf("-buildmode=pie not supported on %s\n", platform)
+				base.Fatalf("-buildmode=pie not supported on %s\n", platform)
 			}
 		}
 		ldBuildmode = "pie"
@@ -389,12 +385,12 @@ func buildModeInit() {
 			switch platform {
 			case "linux/386", "linux/amd64", "linux/arm", "linux/arm64", "linux/ppc64le", "linux/s390x":
 			default:
-				fatalf("-buildmode=shared not supported on %s\n", platform)
+				base.Fatalf("-buildmode=shared not supported on %s\n", platform)
 			}
 			codegenArg = "-dynlink"
 		}
 		if cfg.BuildO != "" {
-			fatalf("-buildmode=shared and -o not supported together")
+			base.Fatalf("-buildmode=shared and -o not supported together")
 		}
 		ldBuildmode = "shared"
 	case "plugin":
@@ -406,14 +402,14 @@ func buildModeInit() {
 			case "linux/amd64", "linux/arm", "linux/arm64", "linux/386",
 				"android/amd64", "android/arm", "android/arm64", "android/386":
 			default:
-				fatalf("-buildmode=plugin not supported on %s\n", platform)
+				base.Fatalf("-buildmode=plugin not supported on %s\n", platform)
 			}
 			codegenArg = "-dynlink"
 		}
 		cfg.ExeSuffix = ".so"
 		ldBuildmode = "plugin"
 	default:
-		fatalf("buildmode=%s not supported", cfg.BuildBuildmode)
+		base.Fatalf("buildmode=%s not supported", cfg.BuildBuildmode)
 	}
 	if cfg.BuildLinkshared {
 		if gccgo {
@@ -423,7 +419,7 @@ func buildModeInit() {
 			case "linux/386", "linux/amd64", "linux/arm", "linux/arm64", "linux/ppc64le", "linux/s390x":
 				buildAsmflags = append(buildAsmflags, "-D=GOBUILDMODE_shared=1")
 			default:
-				fatalf("-linkshared not supported on %s\n", platform)
+				base.Fatalf("-linkshared not supported on %s\n", platform)
 			}
 			codegenArg = "-dynlink"
 			// TODO(mwhudson): remove -w when that gets fixed in linker.
@@ -447,7 +443,7 @@ func buildModeInit() {
 	}
 }
 
-func runBuild(cmd *Command, args []string) {
+func runBuild(cmd *base.Command, args []string) {
 	instrumentInit()
 	buildModeInit()
 	var b builder
@@ -487,9 +483,9 @@ func runBuild(cmd *Command, args []string) {
 
 	if cfg.BuildO != "" {
 		if len(pkgs) > 1 {
-			fatalf("go build: cannot use -o with multiple packages")
+			base.Fatalf("go build: cannot use -o with multiple packages")
 		} else if len(pkgs) == 0 {
-			fatalf("no packages to build")
+			base.Fatalf("no packages to build")
 		}
 		p := pkgs[0]
 		p.target = cfg.BuildO
@@ -504,7 +500,7 @@ func runBuild(cmd *Command, args []string) {
 	if cfg.BuildBuildmode == "shared" {
 		pkgs := pkgsFilter(packages(args))
 		if libName, err := libname(args, pkgs); err != nil {
-			fatalf("%s", err.Error())
+			base.Fatalf("%s", err.Error())
 		} else {
 			a = b.libaction(libName, pkgs, modeBuild, depMode)
 		}
@@ -517,7 +513,7 @@ func runBuild(cmd *Command, args []string) {
 	b.do(a)
 }
 
-var cmdInstall = &Command{
+var cmdInstall = &base.Command{
 	UsageLine: "install [build flags] [packages]",
 	Short:     "compile and install packages and dependencies",
 	Long: `
@@ -592,13 +588,13 @@ func libname(args []string, pkgs []*Package) (string, error) {
 	return "lib" + libname + ".so", nil
 }
 
-func runInstall(cmd *Command, args []string) {
+func runInstall(cmd *base.Command, args []string) {
 	installPackages(args, false)
 }
 
 func installPackages(args []string, forGet bool) {
 	if gobin != "" && !filepath.IsAbs(gobin) {
-		fatalf("cannot install, GOBIN must be an absolute path")
+		base.Fatalf("cannot install, GOBIN must be an absolute path")
 	}
 
 	instrumentInit()
@@ -609,18 +605,18 @@ func installPackages(args []string, forGet bool) {
 		if p.Target == "" && (!p.Standard || p.ImportPath != "unsafe") {
 			switch {
 			case p.gobinSubdir:
-				errorf("go install: cannot install cross-compiled binaries when GOBIN is set")
+				base.Errorf("go install: cannot install cross-compiled binaries when GOBIN is set")
 			case p.cmdline:
-				errorf("go install: no install location for .go files listed on command line (GOBIN not set)")
+				base.Errorf("go install: no install location for .go files listed on command line (GOBIN not set)")
 			case p.ConflictDir != "":
-				errorf("go install: no install location for %s: hidden by %s", p.Dir, p.ConflictDir)
+				base.Errorf("go install: no install location for %s: hidden by %s", p.Dir, p.ConflictDir)
 			default:
-				errorf("go install: no install location for directory %s outside GOPATH\n"+
+				base.Errorf("go install: no install location for directory %s outside GOPATH\n"+
 					"\tFor more details see: 'go help gopath'", p.Dir)
 			}
 		}
 	}
-	exitIfErrors()
+	base.ExitIfErrors()
 
 	var b builder
 	b.init()
@@ -629,7 +625,7 @@ func installPackages(args []string, forGet bool) {
 	var a *action
 	if cfg.BuildBuildmode == "shared" {
 		if libName, err := libname(args, pkgs); err != nil {
-			fatalf("%s", err.Error())
+			base.Fatalf("%s", err.Error())
 		} else {
 			a = b.libaction(libName, pkgs, modeInstall, modeInstall)
 		}
@@ -658,7 +654,7 @@ func installPackages(args []string, forGet bool) {
 		}
 	}
 	b.do(a)
-	exitIfErrors()
+	base.ExitIfErrors()
 
 	// Success. If this command is 'go install' with no arguments
 	// and the current directory (the implicit argument) is a command,
@@ -780,14 +776,14 @@ func (b *builder) init() {
 	} else {
 		b.work, err = ioutil.TempDir("", "go-build")
 		if err != nil {
-			fatalf("%s", err)
+			base.Fatalf("%s", err)
 		}
 		if cfg.BuildX || cfg.BuildWork {
 			fmt.Fprintf(os.Stderr, "WORK=%s\n", b.work)
 		}
 		if !cfg.BuildWork {
 			workdir := b.work
-			atexit(func() { os.RemoveAll(workdir) })
+			base.AtExit(func() { os.RemoveAll(workdir) })
 		}
 	}
 }
@@ -799,7 +795,7 @@ func goFilesPackage(gofiles []string) *Package {
 	// TODO: Remove this restriction.
 	for _, f := range gofiles {
 		if !strings.HasSuffix(f, ".go") {
-			fatalf("named files must be .go files")
+			base.Fatalf("named files must be .go files")
 		}
 	}
 
@@ -816,10 +812,10 @@ func goFilesPackage(gofiles []string) *Package {
 	for _, file := range gofiles {
 		fi, err := os.Stat(file)
 		if err != nil {
-			fatalf("%s", err)
+			base.Fatalf("%s", err)
 		}
 		if fi.IsDir() {
-			fatalf("%s is a directory, should be a Go file", file)
+			base.Fatalf("%s is a directory, should be a Go file", file)
 		}
 		dir1, _ := filepath.Split(file)
 		if dir1 == "" {
@@ -828,7 +824,7 @@ func goFilesPackage(gofiles []string) *Package {
 		if dir == "" {
 			dir = dir1
 		} else if dir != dir1 {
-			fatalf("named files must all be in one directory; have %s and %s", dir, dir1)
+			base.Fatalf("named files must all be in one directory; have %s and %s", dir, dir1)
 		}
 		dirent = append(dirent, fi)
 	}
@@ -836,11 +832,11 @@ func goFilesPackage(gofiles []string) *Package {
 
 	var err error
 	if dir == "" {
-		dir = cwd
+		dir = base.Cwd
 	}
 	dir, err = filepath.Abs(dir)
 	if err != nil {
-		fatalf("%s", err)
+		base.Fatalf("%s", err)
 	}
 
 	bp, err := ctxt.ImportDir(dir, 0)
@@ -895,7 +891,7 @@ func readpkglist(shlibpath string) (pkgs []*Package) {
 	} else {
 		pkglistbytes, err := readELFNote(shlibpath, "Go\x00\x00", 1)
 		if err != nil {
-			fatalf("readELFNote failed: %v", err)
+			base.Fatalf("readELFNote failed: %v", err)
 		}
 		scanner := bufio.NewScanner(bytes.NewBuffer(pkglistbytes))
 		for scanner.Scan() {
@@ -979,7 +975,7 @@ func (b *builder) action1(mode buildMode, depMode buildMode, p *Package, looksha
 			var stk importStack
 			p1 := loadPackage("cmd/cgo", &stk)
 			if p1.Error != nil {
-				fatalf("load cmd/cgo: %v", p1.Error)
+				base.Fatalf("load cmd/cgo: %v", p1.Error)
 			}
 			a.cgo = b.action(depMode, depMode, p1)
 			a.deps = append(a.deps, a.cgo)
@@ -1080,7 +1076,7 @@ func (b *builder) libaction(libname string, pkgs []*Package, mode, depMode build
 	a := &action{}
 	switch mode {
 	default:
-		fatalf("unrecognized mode %v", mode)
+		base.Fatalf("unrecognized mode %v", mode)
 
 	case modeBuild:
 		a.f = (*builder).linkShared
@@ -1107,7 +1103,7 @@ func (b *builder) libaction(libname string, pkgs []*Package, mode, depMode build
 				var stk importStack
 				p := loadPackage("runtime/cgo", &stk)
 				if p.Error != nil {
-					fatalf("load runtime/cgo: %v", p.Error)
+					base.Fatalf("load runtime/cgo: %v", p.Error)
 				}
 				computeStale(p)
 				// If runtime/cgo is in another shared library, then that's
@@ -1128,7 +1124,7 @@ func (b *builder) libaction(libname string, pkgs []*Package, mode, depMode build
 					var stk importStack
 					p := loadPackage("math", &stk)
 					if p.Error != nil {
-						fatalf("load math: %v", p.Error)
+						base.Fatalf("load math: %v", p.Error)
 					}
 					computeStale(p)
 					// If math is in another shared library, then that's
@@ -1153,7 +1149,7 @@ func (b *builder) libaction(libname string, pkgs []*Package, mode, depMode build
 			if libdir == "" {
 				libdir = plibdir
 			} else if libdir != plibdir {
-				fatalf("multiple roots %s & %s", libdir, plibdir)
+				base.Fatalf("multiple roots %s & %s", libdir, plibdir)
 			}
 		}
 		a.target = filepath.Join(libdir, libname)
@@ -1292,11 +1288,11 @@ func (b *builder) do(root *action) {
 
 		if err != nil {
 			if err == errPrintedOutput {
-				setExitStatus(2)
+				base.SetExitStatus(2)
 			} else if _, ok := err.(*build.NoGoError); ok && len(a.p.TestGoFiles) > 0 && b.testFilesOnlyOK {
 				// Ignore the "no buildable Go source files" error for a package with only test files.
 			} else {
-				errorf("%s", err)
+				base.Errorf("%s", err)
 			}
 			a.failed = true
 		}
@@ -1342,8 +1338,8 @@ func (b *builder) do(root *action) {
 					a := b.ready.pop()
 					b.exec.Unlock()
 					handle(a)
-				case <-interrupted:
-					setExitStatus(1)
+				case <-base.Interrupted:
+					base.SetExitStatus(1)
 					return
 				}
 			}
@@ -1465,7 +1461,7 @@ func (b *builder) build(a *action) (err error) {
 			sfiles = nil
 		}
 
-		cgoExe := tool("cgo")
+		cgoExe := base.Tool("cgo")
 		if a.cgo != nil && a.cgo.target != "" {
 			cgoExe = a.cgo.target
 		}
@@ -1857,7 +1853,7 @@ func (b *builder) copyFile(a *action, dst, src string, perm os.FileMode, force b
 	}
 
 	// On Windows, remove lingering ~ file from last attempt.
-	if toolIsWindows {
+	if base.ToolIsWindows {
 		if _, err := os.Stat(dst + "~"); err == nil {
 			os.Remove(dst + "~")
 		}
@@ -1865,7 +1861,7 @@ func (b *builder) copyFile(a *action, dst, src string, perm os.FileMode, force b
 
 	mayberemovefile(dst)
 	df, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
-	if err != nil && toolIsWindows {
+	if err != nil && base.ToolIsWindows {
 		// Windows does not allow deletion of a binary file
 		// while it is executing. Try to move it out of the way.
 		// If the move fails, which is likely, we'll try again the
@@ -1912,7 +1908,7 @@ func (b *builder) installHeader(a *action) error {
 func (b *builder) cover(a *action, dst, src string, perm os.FileMode, varName string) error {
 	return b.run(a.objdir, "cover "+a.p.ImportPath, nil,
 		cfg.BuildToolexec,
-		tool("cover"),
+		base.Tool("cover"),
 		"-mode", a.p.coverMode,
 		"-var", varName,
 		"-o", dst,
@@ -2018,7 +2014,7 @@ func (b *builder) showcmd(dir string, format string, args ...interface{}) {
 func (b *builder) showOutput(dir, desc, out string) {
 	prefix := "# " + desc
 	suffix := "\n" + out
-	if reldir := shortPath(dir); reldir != dir {
+	if reldir := base.ShortPath(dir); reldir != dir {
 		suffix = strings.Replace(suffix, " "+dir, " "+reldir, -1)
 		suffix = strings.Replace(suffix, "\n"+dir, "\n"+reldir, -1)
 	}
@@ -2029,29 +2025,6 @@ func (b *builder) showOutput(dir, desc, out string) {
 	b.print(prefix, suffix)
 }
 
-// shortPath returns an absolute or relative name for path, whatever is shorter.
-func shortPath(path string) string {
-	if rel, err := filepath.Rel(cwd, path); err == nil && len(rel) < len(path) {
-		return rel
-	}
-	return path
-}
-
-// relPaths returns a copy of paths with absolute paths
-// made relative to the current directory if they would be shorter.
-func relPaths(paths []string) []string {
-	var out []string
-	pwd, _ := os.Getwd()
-	for _, p := range paths {
-		rel, err := filepath.Rel(pwd, p)
-		if err == nil && len(rel) < len(p) {
-			p = rel
-		}
-		out = append(out, p)
-	}
-	return out
-}
-
 // errPrintedOutput is a special error indicating that a command failed
 // but that it generated output as well, and that output has already
 // been printed, so there's no point showing 'exit status 1' or whatever
@@ -2316,11 +2289,11 @@ func (noToolchain) cc(b *builder, p *Package, objdir, ofile, cfile string) error
 type gcToolchain struct{}
 
 func (gcToolchain) compiler() string {
-	return tool("compile")
+	return base.Tool("compile")
 }
 
 func (gcToolchain) linker() string {
-	return tool("link")
+	return base.Tool("link")
 }
 
 func (gcToolchain) gc(b *builder, p *Package, archive, obj string, asmhdr bool, importArgs []string, gofiles []string) (ofile string, output []byte, err error) {
@@ -2370,7 +2343,7 @@ func (gcToolchain) gc(b *builder, p *Package, archive, obj string, asmhdr bool,
 		}
 	}
 
-	args := []interface{}{cfg.BuildToolexec, tool("compile"), "-o", ofile, "-trimpath", b.work, buildGcflags, gcargs, "-D", p.localPrefix, importArgs}
+	args := []interface{}{cfg.BuildToolexec, base.Tool("compile"), "-o", ofile, "-trimpath", b.work, buildGcflags, gcargs, "-D", p.localPrefix, importArgs}
 	if ofile == archive {
 		args = append(args, "-pack")
 	}
@@ -2388,7 +2361,7 @@ func (gcToolchain) gc(b *builder, p *Package, archive, obj string, asmhdr bool,
 func (gcToolchain) asm(b *builder, p *Package, obj string, sfiles []string) ([]string, error) {
 	// Add -I pkg/GOOS_GOARCH so #include "textflag.h" works in .s files.
 	inc := filepath.Join(goroot, "pkg", "include")
-	args := []interface{}{cfg.BuildToolexec, tool("asm"), "-trimpath", b.work, "-I", obj, "-I", inc, "-D", "GOOS_" + cfg.Goos, "-D", "GOARCH_" + cfg.Goarch, buildAsmflags}
+	args := []interface{}{cfg.BuildToolexec, base.Tool("asm"), "-trimpath", b.work, "-I", obj, "-I", inc, "-D", "GOOS_" + cfg.Goos, "-D", "GOARCH_" + cfg.Goarch, buildAsmflags}
 	if p.ImportPath == "runtime" && cfg.Goarch == "386" {
 		for _, arg := range buildAsmflags {
 			if arg == "-dynlink" {
@@ -2414,7 +2387,7 @@ func (gcToolchain) asm(b *builder, p *Package, obj string, sfiles []string) ([]s
 func toolVerify(b *builder, p *Package, newTool string, ofile string, args []interface{}) error {
 	newArgs := make([]interface{}, len(args))
 	copy(newArgs, args)
-	newArgs[1] = tool(newTool)
+	newArgs[1] = base.Tool(newTool)
 	newArgs[3] = ofile + ".new" // x.6 becomes x.6.new
 	if err := b.run(p.Dir, p.ImportPath, nil, newArgs...); err != nil {
 		return err
@@ -2450,7 +2423,7 @@ func (gcToolchain) pack(b *builder, p *Package, objDir, afile string, ofiles []s
 	// Since it used to not work that way, verify.
 	if !cfg.BuildN {
 		if _, err := os.Stat(absAfile); err != nil {
-			fatalf("os.Stat of archive file failed: %v", err)
+			base.Fatalf("os.Stat of archive file failed: %v", err)
 		}
 	}
 
@@ -2600,7 +2573,7 @@ func (gcToolchain) ld(b *builder, root *action, out string, allactions []*action
 		dir, out = filepath.Split(out)
 	}
 
-	return b.run(dir, root.p.ImportPath, nil, cfg.BuildToolexec, tool("link"), "-o", out, importArgs, ldflags, mainpkg)
+	return b.run(dir, root.p.ImportPath, nil, cfg.BuildToolexec, base.Tool("link"), "-o", out, importArgs, ldflags, mainpkg)
 }
 
 func (gcToolchain) ldShared(b *builder, toplevelactions []*action, out string, allactions []*action) error {
@@ -2631,7 +2604,7 @@ func (gcToolchain) ldShared(b *builder, toplevelactions []*action, out string, a
 		}
 		ldflags = append(ldflags, d.p.ImportPath+"="+d.target)
 	}
-	return b.run(".", out, nil, cfg.BuildToolexec, tool("link"), "-o", out, importArgs, ldflags)
+	return b.run(".", out, nil, cfg.BuildToolexec, base.Tool("link"), "-o", out, importArgs, ldflags)
 }
 
 func (gcToolchain) cc(b *builder, p *Package, objdir, ofile, cfile string) error {
@@ -2943,7 +2916,7 @@ func (tools gccgoToolchain) link(b *builder, root *action, out string, allaction
 		ldflags = append(ldflags, "-zdefs", "-shared", "-nostdlib", "-lgo", "-lgcc_s", "-lgcc", "-lc")
 
 	default:
-		fatalf("-buildmode=%s not supported for gccgo", buildmode)
+		base.Fatalf("-buildmode=%s not supported for gccgo", buildmode)
 	}
 
 	switch buildmode {
diff --git a/src/cmd/go/clean.go b/src/cmd/go/clean.go
index f9f452d65d..4895eda4e3 100644
--- a/src/cmd/go/clean.go
+++ b/src/cmd/go/clean.go
@@ -6,6 +6,7 @@ package main
 
 import (
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -13,7 +14,7 @@ import (
 	"strings"
 )
 
-var cmdClean = &Command{
+var cmdClean = &base.Command{
 	UsageLine: "clean [-i] [-r] [-n] [-x] [build flags] [packages]",
 	Short:     "remove object files",
 	Long: `
@@ -75,7 +76,7 @@ func init() {
 	addBuildFlags(cmdClean)
 }
 
-func runClean(cmd *Command, args []string) {
+func runClean(cmd *base.Command, args []string) {
 	for _, pkg := range packagesAndErrors(args) {
 		clean(pkg)
 	}
@@ -113,12 +114,12 @@ func clean(p *Package) {
 	cleaned[p] = true
 
 	if p.Dir == "" {
-		errorf("can't load package: %v", p.Error)
+		base.Errorf("can't load package: %v", p.Error)
 		return
 	}
 	dirs, err := ioutil.ReadDir(p.Dir)
 	if err != nil {
-		errorf("go clean %s: %v", p.Dir, err)
+		base.Errorf("go clean %s: %v", p.Dir, err)
 		return
 	}
 
@@ -193,7 +194,7 @@ func clean(p *Package) {
 					}
 				}
 				if err := os.RemoveAll(filepath.Join(p.Dir, name)); err != nil {
-					errorf("go clean: %v", err)
+					base.Errorf("go clean: %v", err)
 				}
 			}
 			continue
@@ -232,7 +233,7 @@ func removeFile(f string) {
 		return
 	}
 	// Windows does not allow deletion of a binary file while it is executing.
-	if toolIsWindows {
+	if base.ToolIsWindows {
 		// Remove lingering ~ file from last attempt.
 		if _, err2 := os.Stat(f + "~"); err2 == nil {
 			os.Remove(f + "~")
@@ -245,5 +246,5 @@ func removeFile(f string) {
 			return
 		}
 	}
-	errorf("go clean: %v", err)
+	base.Errorf("go clean: %v", err)
 }
diff --git a/src/cmd/go/doc.go b/src/cmd/go/doc.go
index b9ecfc48bb..338fec14d3 100644
--- a/src/cmd/go/doc.go
+++ b/src/cmd/go/doc.go
@@ -6,9 +6,12 @@
 
 package main
 
-import "cmd/go/internal/cfg"
+import (
+	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
+)
 
-var cmdDoc = &Command{
+var cmdDoc = &base.Command{
 	Run:         runDoc,
 	UsageLine:   "doc [-u] [-c] [package|[package.]symbol[.method]]",
 	CustomFlags: true,
@@ -115,6 +118,6 @@ Flags:
 `,
 }
 
-func runDoc(cmd *Command, args []string) {
-	run(cfg.BuildToolexec, tool("doc"), args)
+func runDoc(cmd *base.Command, args []string) {
+	base.Run(cfg.BuildToolexec, base.Tool("doc"), args)
 }
diff --git a/src/cmd/go/env.go b/src/cmd/go/env.go
index 6db88f51ca..e143ddb357 100644
--- a/src/cmd/go/env.go
+++ b/src/cmd/go/env.go
@@ -6,13 +6,14 @@ package main
 
 import (
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"fmt"
 	"os"
 	"runtime"
 	"strings"
 )
 
-var cmdEnv = &Command{
+var cmdEnv = &base.Command{
 	Run:       runEnv,
 	UsageLine: "env [var ...]",
 	Short:     "print Go environment information",
@@ -40,7 +41,7 @@ func mkEnv() []cfg.EnvVar {
 		{"GOPATH", cfg.BuildContext.GOPATH},
 		{"GORACE", os.Getenv("GORACE")},
 		{"GOROOT", goroot},
-		{"GOTOOLDIR", toolDir},
+		{"GOTOOLDIR", base.ToolDir},
 
 		// disable escape codes in clang errors
 		{"TERM", "dumb"},
@@ -98,7 +99,7 @@ func extraEnvVars() []cfg.EnvVar {
 	}
 }
 
-func runEnv(cmd *Command, args []string) {
+func runEnv(cmd *base.Command, args []string) {
 	env := cfg.NewEnv
 	env = append(env, extraEnvVars()...)
 	if len(args) > 0 {
diff --git a/src/cmd/go/fix.go b/src/cmd/go/fix.go
index 9783226e36..bb8c34e14a 100644
--- a/src/cmd/go/fix.go
+++ b/src/cmd/go/fix.go
@@ -6,10 +6,11 @@ package main
 
 import (
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"cmd/go/internal/str"
 )
 
-var cmdFix = &Command{
+var cmdFix = &base.Command{
 	Run:       runFix,
 	UsageLine: "fix [packages]",
 	Short:     "run go tool fix on packages",
@@ -25,11 +26,11 @@ See also: go fmt, go vet.
 	`,
 }
 
-func runFix(cmd *Command, args []string) {
+func runFix(cmd *base.Command, args []string) {
 	for _, pkg := range packages(args) {
 		// Use pkg.gofiles instead of pkg.Dir so that
 		// the command only applies to this package,
 		// not to packages in subdirectories.
-		run(str.StringList(cfg.BuildToolexec, tool("fix"), relPaths(pkg.allgofiles)))
+		base.Run(str.StringList(cfg.BuildToolexec, base.Tool("fix"), base.RelPaths(pkg.allgofiles)))
 	}
 }
diff --git a/src/cmd/go/fmt.go b/src/cmd/go/fmt.go
index 4c40f9ab0b..e59f5cb919 100644
--- a/src/cmd/go/fmt.go
+++ b/src/cmd/go/fmt.go
@@ -5,16 +5,18 @@
 package main
 
 import (
+	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"cmd/go/internal/str"
 	"os"
 	"path/filepath"
 )
 
 func init() {
-	addBuildFlagsNX(cmdFmt)
+	cfg.AddBuildFlagsNX(&cmdFmt.Flag)
 }
 
-var cmdFmt = &Command{
+var cmdFmt = &base.Command{
 	Run:       runFmt,
 	UsageLine: "fmt [-n] [-x] [packages]",
 	Short:     "run gofmt on package sources",
@@ -34,20 +36,20 @@ See also: go fix, go vet.
 	`,
 }
 
-func runFmt(cmd *Command, args []string) {
+func runFmt(cmd *base.Command, args []string) {
 	gofmt := gofmtPath()
 	for _, pkg := range packages(args) {
 		// Use pkg.gofiles instead of pkg.Dir so that
 		// the command only applies to this package,
 		// not to packages in subdirectories.
-		run(str.StringList(gofmt, "-l", "-w", relPaths(pkg.allgofiles)))
+		base.Run(str.StringList(gofmt, "-l", "-w", base.RelPaths(pkg.allgofiles)))
 	}
 }
 
 func gofmtPath() string {
 	gofmt := "gofmt"
-	if toolIsWindows {
-		gofmt += toolWindowsExtension
+	if base.ToolIsWindows {
+		gofmt += base.ToolWindowsExtension
 	}
 
 	gofmtPath := filepath.Join(gobin, gofmt)
diff --git a/src/cmd/go/generate.go b/src/cmd/go/generate.go
index b4fd5a350b..b89fc95342 100644
--- a/src/cmd/go/generate.go
+++ b/src/cmd/go/generate.go
@@ -8,6 +8,7 @@ import (
 	"bufio"
 	"bytes"
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"fmt"
 	"io"
 	"log"
@@ -19,7 +20,7 @@ import (
 	"strings"
 )
 
-var cmdGenerate = &Command{
+var cmdGenerate = &base.Command{
 	Run:       runGenerate,
 	UsageLine: "generate [-run regexp] [-n] [-v] [-x] [build flags] [file.go... | packages]",
 	Short:     "generate Go files by processing source",
@@ -136,7 +137,7 @@ func init() {
 	cmdGenerate.Flag.StringVar(&generateRunFlag, "run", "", "")
 }
 
-func runGenerate(cmd *Command, args []string) {
+func runGenerate(cmd *base.Command, args []string) {
 	ignoreImports = true
 
 	if generateRunFlag != "" {
@@ -196,13 +197,13 @@ func (g *Generator) run() (ok bool) {
 			if e != stop {
 				panic(e)
 			}
-			setExitStatus(1)
+			base.SetExitStatus(1)
 		}
 	}()
 	g.dir, g.file = filepath.Split(g.path)
 	g.dir = filepath.Clean(g.dir) // No final separator please.
 	if cfg.BuildV {
-		fmt.Fprintf(os.Stderr, "%s\n", shortPath(g.path))
+		fmt.Fprintf(os.Stderr, "%s\n", base.ShortPath(g.path))
 	}
 
 	// Scan for lines that start "//go:generate".
@@ -265,7 +266,7 @@ func (g *Generator) run() (ok bool) {
 		g.exec(words)
 	}
 	if err != nil && err != io.EOF {
-		g.errorf("error reading %s: %s", shortPath(g.path), err)
+		g.errorf("error reading %s: %s", base.ShortPath(g.path), err)
 	}
 	return true
 }
@@ -355,7 +356,7 @@ var stop = fmt.Errorf("error in generation")
 // It then exits the program (with exit status 1) because generation stops
 // at the first error.
 func (g *Generator) errorf(format string, args ...interface{}) {
-	fmt.Fprintf(os.Stderr, "%s:%d: %s\n", shortPath(g.path), g.lineNum,
+	fmt.Fprintf(os.Stderr, "%s:%d: %s\n", base.ShortPath(g.path), g.lineNum,
 		fmt.Sprintf(format, args...))
 	panic(stop)
 }
diff --git a/src/cmd/go/get.go b/src/cmd/go/get.go
index cf8cc0817e..45c538d302 100644
--- a/src/cmd/go/get.go
+++ b/src/cmd/go/get.go
@@ -6,6 +6,7 @@ package main
 
 import (
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"cmd/go/internal/str"
 	"fmt"
 	"go/build"
@@ -17,7 +18,7 @@ import (
 	"strings"
 )
 
-var cmdGet = &Command{
+var cmdGet = &base.Command{
 	UsageLine: "get [-d] [-f] [-fix] [-insecure] [-t] [-u] [build flags] [packages]",
 	Short:     "download and install packages and dependencies",
 	Long: `
@@ -85,9 +86,9 @@ func init() {
 	cmdGet.Run = runGet // break init loop
 }
 
-func runGet(cmd *Command, args []string) {
+func runGet(cmd *base.Command, args []string) {
 	if *getF && !*getU {
-		fatalf("go get: cannot use -f flag without -u")
+		base.Fatalf("go get: cannot use -f flag without -u")
 	}
 
 	// Disable any prompting for passwords by Git.
@@ -127,7 +128,7 @@ func runGet(cmd *Command, args []string) {
 	for _, arg := range args {
 		download(arg, nil, &stk, mode)
 	}
-	exitIfErrors()
+	base.ExitIfErrors()
 
 	// Phase 2. Rescan packages and re-evaluate args list.
 
@@ -220,7 +221,7 @@ func download(arg string, parent *Package, stk *importStack, mode int) {
 
 	p := load(arg, mode)
 	if p.Error != nil && p.Error.hard {
-		errorf("%s", p.Error)
+		base.Errorf("%s", p.Error)
 		return
 	}
 
@@ -257,7 +258,7 @@ func download(arg string, parent *Package, stk *importStack, mode int) {
 		stk.push(arg)
 		err := downloadPackage(p)
 		if err != nil {
-			errorf("%s", &PackageError{ImportStack: stk.copy(), Err: err.Error()})
+			base.Errorf("%s", &PackageError{ImportStack: stk.copy(), Err: err.Error()})
 			stk.pop()
 			return
 		}
@@ -293,7 +294,7 @@ func download(arg string, parent *Package, stk *importStack, mode int) {
 			// Do not push here too, or else stk will say arg imports arg.
 			p := load(arg, mode)
 			if p.Error != nil {
-				errorf("%s", p.Error)
+				base.Errorf("%s", p.Error)
 				continue
 			}
 			pkgs = append(pkgs, p)
@@ -304,12 +305,12 @@ func download(arg string, parent *Package, stk *importStack, mode int) {
 	// due to wildcard expansion.
 	for _, p := range pkgs {
 		if *getFix {
-			run(cfg.BuildToolexec, str.StringList(tool("fix"), relPaths(p.allgofiles)))
+			base.Run(cfg.BuildToolexec, str.StringList(base.Tool("fix"), base.RelPaths(p.allgofiles)))
 
 			// The imports might have changed, so reload again.
 			p = reloadPackage(arg, stk)
 			if p.Error != nil {
-				errorf("%s", p.Error)
+				base.Errorf("%s", p.Error)
 				return
 			}
 		}
@@ -346,7 +347,7 @@ func download(arg string, parent *Package, stk *importStack, mode int) {
 					Err:         "must be imported as " + path[j+len("vendor/"):],
 				}
 				stk.pop()
-				errorf("%s", err)
+				base.Errorf("%s", err)
 				continue
 			}
 			// If this is a test import, apply vendor lookup now.
diff --git a/src/cmd/go/help.go b/src/cmd/go/help.go
index 0c663ad463..734916c453 100644
--- a/src/cmd/go/help.go
+++ b/src/cmd/go/help.go
@@ -4,7 +4,9 @@
 
 package main
 
-var helpC = &Command{
+import "cmd/go/internal/base"
+
+var helpC = &base.Command{
 	UsageLine: "c",
 	Short:     "calling between Go and C",
 	Long: `
@@ -26,7 +28,7 @@ the C or C++ compiler, respectively, to use.
 	`,
 }
 
-var helpPackages = &Command{
+var helpPackages = &base.Command{
 	UsageLine: "packages",
 	Short:     "description of package lists",
 	Long: `
@@ -100,7 +102,7 @@ by the go tool, as are directories named "testdata".
 	`,
 }
 
-var helpImportPath = &Command{
+var helpImportPath = &base.Command{
 	UsageLine: "importpath",
 	Short:     "import path syntax",
 	Long: `
@@ -277,7 +279,7 @@ See https://golang.org/s/go14customimport for details.
 	`,
 }
 
-var helpGopath = &Command{
+var helpGopath = &base.Command{
 	UsageLine: "gopath",
 	Short:     "GOPATH environment variable",
 	Long: `
@@ -429,7 +431,7 @@ See https://golang.org/s/go15vendor for details.
 	`,
 }
 
-var helpEnvironment = &Command{
+var helpEnvironment = &base.Command{
 	UsageLine: "environment",
 	Short:     "environment variables",
 	Long: `
@@ -511,7 +513,7 @@ Special-purpose environment variables:
 	`,
 }
 
-var helpFileType = &Command{
+var helpFileType = &base.Command{
 	UsageLine: "filetype",
 	Short:     "file types",
 	Long: `
@@ -557,7 +559,7 @@ for more details.
 	`,
 }
 
-var helpBuildmode = &Command{
+var helpBuildmode = &base.Command{
 	UsageLine: "buildmode",
 	Short:     "description of build modes",
 	Long: `
diff --git a/src/cmd/go/internal/base/base.go b/src/cmd/go/internal/base/base.go
new file mode 100644
index 0000000000..081c78b51e
--- /dev/null
+++ b/src/cmd/go/internal/base/base.go
@@ -0,0 +1,143 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package base defines shared basic pieces of the go command,
+// in particular logging and the Command structure.
+package base
+
+import (
+	"cmd/go/internal/cfg"
+	"cmd/go/internal/str"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"strings"
+	"sync"
+)
+
+// A Command is an implementation of a go command
+// like go build or go fix.
+type Command struct {
+	// Run runs the command.
+	// The args are the arguments after the command name.
+	Run func(cmd *Command, args []string)
+
+	// UsageLine is the one-line usage message.
+	// The first word in the line is taken to be the command name.
+	UsageLine string
+
+	// Short is the short description shown in the 'go help' output.
+	Short string
+
+	// Long is the long message shown in the 'go help <this-command>' output.
+	Long string
+
+	// Flag is a set of flags specific to this command.
+	Flag flag.FlagSet
+
+	// CustomFlags indicates that the command will do its own
+	// flag parsing.
+	CustomFlags bool
+}
+
+// Name returns the command's name: the first word in the usage line.
+func (c *Command) Name() string {
+	name := c.UsageLine
+	i := strings.Index(name, " ")
+	if i >= 0 {
+		name = name[:i]
+	}
+	return name
+}
+
+func (c *Command) Usage() {
+	fmt.Fprintf(os.Stderr, "usage: %s\n\n", c.UsageLine)
+	fmt.Fprintf(os.Stderr, "%s\n", strings.TrimSpace(c.Long))
+	os.Exit(2)
+}
+
+// Runnable reports whether the command can be run; otherwise
+// it is a documentation pseudo-command such as importpath.
+func (c *Command) Runnable() bool {
+	return c.Run != nil
+}
+
+var atExitFuncs []func()
+
+func AtExit(f func()) {
+	atExitFuncs = append(atExitFuncs, f)
+}
+
+func Exit() {
+	for _, f := range atExitFuncs {
+		f()
+	}
+	os.Exit(exitStatus)
+}
+
+func Fatalf(format string, args ...interface{}) {
+	Errorf(format, args...)
+	Exit()
+}
+
+func Errorf(format string, args ...interface{}) {
+	log.Printf(format, args...)
+	SetExitStatus(1)
+}
+
+func ExitIfErrors() {
+	if exitStatus != 0 {
+		Exit()
+	}
+}
+
+var exitStatus = 0
+var exitMu sync.Mutex
+
+func SetExitStatus(n int) {
+	exitMu.Lock()
+	if exitStatus < n {
+		exitStatus = n
+	}
+	exitMu.Unlock()
+}
+
+// Run runs the command, with stdout and stderr
+// connected to the go command's own stdout and stderr.
+// If the command fails, Run reports the error using Errorf.
+func Run(cmdargs ...interface{}) {
+	cmdline := str.StringList(cmdargs...)
+	if cfg.BuildN || cfg.BuildX {
+		fmt.Printf("%s\n", strings.Join(cmdline, " "))
+		if cfg.BuildN {
+			return
+		}
+	}
+
+	cmd := exec.Command(cmdline[0], cmdline[1:]...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	if err := cmd.Run(); err != nil {
+		Errorf("%v", err)
+	}
+}
+
+// RunStdin is like run but connects Stdin.
+func RunStdin(cmdline []string) {
+	cmd := exec.Command(cmdline[0], cmdline[1:]...)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	cmd.Env = cfg.OrigEnv
+	StartSigHandlers()
+	if err := cmd.Run(); err != nil {
+		Errorf("%v", err)
+	}
+}
+
+// Usage is the usage-reporting function, filled in by package main
+// but here for reference by other packages.
+var Usage func()
diff --git a/src/cmd/go/internal/base/path.go b/src/cmd/go/internal/base/path.go
new file mode 100644
index 0000000000..1e7f6222a5
--- /dev/null
+++ b/src/cmd/go/internal/base/path.go
@@ -0,0 +1,36 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package base
+
+import (
+	"os"
+	"path/filepath"
+)
+
+var Cwd, _ = os.Getwd()
+
+// ShortPath returns an absolute or relative name for path, whatever is shorter.
+func ShortPath(path string) string {
+	if rel, err := filepath.Rel(Cwd, path); err == nil && len(rel) < len(path) {
+		return rel
+	}
+	return path
+}
+
+// RelPaths returns a copy of paths with absolute paths
+// made relative to the current directory if they would be shorter.
+func RelPaths(paths []string) []string {
+	var out []string
+	// TODO(rsc): Can this use Cwd from above?
+	pwd, _ := os.Getwd()
+	for _, p := range paths {
+		rel, err := filepath.Rel(pwd, p)
+		if err == nil && len(rel) < len(p) {
+			p = rel
+		}
+		out = append(out, p)
+	}
+	return out
+}
diff --git a/src/cmd/go/signal.go b/src/cmd/go/internal/base/signal.go
similarity index 66%
rename from src/cmd/go/signal.go
rename to src/cmd/go/internal/base/signal.go
index e8ba0d3655..54d11876d0 100644
--- a/src/cmd/go/signal.go
+++ b/src/cmd/go/internal/base/signal.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package main
+package base
 
 import (
 	"os"
@@ -10,8 +10,8 @@ import (
 	"sync"
 )
 
-// interrupted is closed, if go process is interrupted.
-var interrupted = make(chan struct{})
+// Interrupted is closed when the go command receives an interrupt signal.
+var Interrupted = make(chan struct{})
 
 // processSignals setups signal handler.
 func processSignals() {
@@ -19,13 +19,13 @@ func processSignals() {
 	signal.Notify(sig, signalsToIgnore...)
 	go func() {
 		<-sig
-		close(interrupted)
+		close(Interrupted)
 	}()
 }
 
 var onceProcessSignals sync.Once
 
-// startSigHandlers start signal handlers.
-func startSigHandlers() {
+// StartSigHandlers starts the signal handlers.
+func StartSigHandlers() {
 	onceProcessSignals.Do(processSignals)
 }
diff --git a/src/cmd/go/signal_notunix.go b/src/cmd/go/internal/base/signal_notunix.go
similarity index 60%
rename from src/cmd/go/signal_notunix.go
rename to src/cmd/go/internal/base/signal_notunix.go
index 29aa9d8c20..9e869b03ea 100644
--- a/src/cmd/go/signal_notunix.go
+++ b/src/cmd/go/internal/base/signal_notunix.go
@@ -4,7 +4,7 @@
 
 // +build plan9 windows
 
-package main
+package base
 
 import (
 	"os"
@@ -12,6 +12,6 @@ import (
 
 var signalsToIgnore = []os.Signal{os.Interrupt}
 
-// signalTrace is the signal to send to make a Go program
-// crash with a stack trace.
-var signalTrace os.Signal = nil
+// SignalTrace is the signal to send to make a Go program
+// crash with a stack trace (no such signal in this case).
+var SignalTrace os.Signal = nil
diff --git a/src/cmd/go/signal_unix.go b/src/cmd/go/internal/base/signal_unix.go
similarity index 75%
rename from src/cmd/go/signal_unix.go
rename to src/cmd/go/internal/base/signal_unix.go
index e86cd46523..4ca3da9922 100644
--- a/src/cmd/go/signal_unix.go
+++ b/src/cmd/go/internal/base/signal_unix.go
@@ -4,7 +4,7 @@
 
 // +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
 
-package main
+package base
 
 import (
 	"os"
@@ -13,6 +13,6 @@ import (
 
 var signalsToIgnore = []os.Signal{os.Interrupt, syscall.SIGQUIT}
 
-// signalTrace is the signal to send to make a Go program
+// SignalTrace is the signal to send to make a Go program
 // crash with a stack trace.
-var signalTrace os.Signal = syscall.SIGQUIT
+var SignalTrace os.Signal = syscall.SIGQUIT
diff --git a/src/cmd/go/internal/base/tool.go b/src/cmd/go/internal/base/tool.go
new file mode 100644
index 0000000000..c907772c00
--- /dev/null
+++ b/src/cmd/go/internal/base/tool.go
@@ -0,0 +1,53 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package base
+
+import (
+	"fmt"
+	"go/build"
+	"os"
+	"path/filepath"
+	"runtime"
+
+	"cmd/go/internal/cfg"
+)
+
+// Configuration for finding tool binaries.
+var (
+	ToolGOOS      = runtime.GOOS
+	ToolGOARCH    = runtime.GOARCH
+	ToolIsWindows = ToolGOOS == "windows"
+	ToolDir       = build.ToolDir
+)
+
+const ToolWindowsExtension = ".exe"
+
+// Tool returns the path to the named tool (for example, "vet").
+// If the tool cannot be found, Tool exits the process.
+func Tool(toolName string) string {
+	toolPath := filepath.Join(ToolDir, toolName)
+	if ToolIsWindows {
+		toolPath += ToolWindowsExtension
+	}
+	if len(cfg.BuildToolexec) > 0 {
+		return toolPath
+	}
+	// Give a nice message if there is no tool with that name.
+	if _, err := os.Stat(toolPath); err != nil {
+		if isInGoToolsRepo(toolName) {
+			fmt.Fprintf(os.Stderr, "go tool: no such tool %q; to install:\n\tgo get golang.org/x/tools/cmd/%s\n", toolName, toolName)
+		} else {
+			fmt.Fprintf(os.Stderr, "go tool: no such tool %q\n", toolName)
+		}
+		SetExitStatus(2)
+		Exit()
+	}
+	return toolPath
+}
+
+// TODO: Delete.
+func isInGoToolsRepo(toolName string) bool {
+	return false
+}
diff --git a/src/cmd/go/internal/cfg/cfg.go b/src/cmd/go/internal/cfg/cfg.go
index 8a7942b877..c6cb2ce3db 100644
--- a/src/cmd/go/internal/cfg/cfg.go
+++ b/src/cmd/go/internal/cfg/cfg.go
@@ -7,6 +7,7 @@
 package cfg
 
 import (
+	"flag"
 	"go/build"
 	"runtime"
 )
@@ -57,3 +58,9 @@ var (
 	ExeSuffix string
 	Gopath    []string
 )
+
+// AddBuildFlagsNX adds the -n and -x build flags to the flag set.
+func AddBuildFlagsNX(flags *flag.FlagSet) {
+	flags.BoolVar(&BuildN, "n", false, "")
+	flags.BoolVar(&BuildX, "x", false, "")
+}
diff --git a/src/cmd/go/list.go b/src/cmd/go/list.go
index 1408502089..cb29ca75bb 100644
--- a/src/cmd/go/list.go
+++ b/src/cmd/go/list.go
@@ -7,6 +7,7 @@ package main
 import (
 	"bufio"
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"encoding/json"
 	"io"
 	"os"
@@ -14,7 +15,7 @@ import (
 	"text/template"
 )
 
-var cmdList = &Command{
+var cmdList = &base.Command{
 	UsageLine: "list [-e] [-f format] [-json] [build flags] [packages]",
 	Short:     "list packages",
 	Long: `
@@ -146,7 +147,7 @@ var listFmt = cmdList.Flag.String("f", "{{.ImportPath}}", "")
 var listJson = cmdList.Flag.Bool("json", false, "")
 var nl = []byte{'\n'}
 
-func runList(cmd *Command, args []string) {
+func runList(cmd *base.Command, args []string) {
 	buildModeInit()
 	out := newTrackingWriter(os.Stdout)
 	defer out.w.Flush()
@@ -157,7 +158,7 @@ func runList(cmd *Command, args []string) {
 			b, err := json.MarshalIndent(p, "", "\t")
 			if err != nil {
 				out.Flush()
-				fatalf("%s", err)
+				base.Fatalf("%s", err)
 			}
 			out.Write(b)
 			out.Write(nl)
@@ -176,12 +177,12 @@ func runList(cmd *Command, args []string) {
 		}
 		tmpl, err := template.New("main").Funcs(fm).Parse(*listFmt)
 		if err != nil {
-			fatalf("%s", err)
+			base.Fatalf("%s", err)
 		}
 		do = func(p *Package) {
 			if err := tmpl.Execute(out, p); err != nil {
 				out.Flush()
-				fatalf("%s", err)
+				base.Fatalf("%s", err)
 			}
 			if out.NeedNL() {
 				out.Write(nl)
diff --git a/src/cmd/go/main.go b/src/cmd/go/main.go
index 2925d1b359..aa019f2cea 100644
--- a/src/cmd/go/main.go
+++ b/src/cmd/go/main.go
@@ -8,78 +8,29 @@ import (
 	"bufio"
 	"bytes"
 	"cmd/go/internal/cfg"
-	"cmd/go/internal/str"
+	"cmd/go/internal/base"
 	"flag"
 	"fmt"
 	"go/build"
 	"io"
 	"log"
 	"os"
-	"os/exec"
 	"path"
 	"path/filepath"
 	"regexp"
 	"runtime"
 	"strings"
-	"sync"
 	"text/template"
 	"unicode"
 	"unicode/utf8"
 )
 
-// A Command is an implementation of a go command
-// like go build or go fix.
-type Command struct {
-	// Run runs the command.
-	// The args are the arguments after the command name.
-	Run func(cmd *Command, args []string)
-
-	// UsageLine is the one-line usage message.
-	// The first word in the line is taken to be the command name.
-	UsageLine string
-
-	// Short is the short description shown in the 'go help' output.
-	Short string
-
-	// Long is the long message shown in the 'go help <this-command>' output.
-	Long string
-
-	// Flag is a set of flags specific to this command.
-	Flag flag.FlagSet
-
-	// CustomFlags indicates that the command will do its own
-	// flag parsing.
-	CustomFlags bool
-}
-
-// Name returns the command's name: the first word in the usage line.
-func (c *Command) Name() string {
-	name := c.UsageLine
-	i := strings.Index(name, " ")
-	if i >= 0 {
-		name = name[:i]
-	}
-	return name
-}
-
-func (c *Command) Usage() {
-	fmt.Fprintf(os.Stderr, "usage: %s\n\n", c.UsageLine)
-	fmt.Fprintf(os.Stderr, "%s\n", strings.TrimSpace(c.Long))
-	os.Exit(2)
-}
-
-// Runnable reports whether the command can be run; otherwise
-// it is a documentation pseudo-command such as importpath.
-func (c *Command) Runnable() bool {
-	return c.Run != nil
-}
-
 // Commands lists the available commands and help topics.
 // The order here is the order in which they are printed by 'go help'.
-var commands []*Command
+var commands []*base.Command
 
 func init() {
-	commands = []*Command{
+	commands = []*base.Command{
 		cmdBuild,
 		cmdClean,
 		cmdDoc,
@@ -109,26 +60,15 @@ func init() {
 	}
 }
 
-var exitStatus = 0
-var exitMu sync.Mutex
-
-func setExitStatus(n int) {
-	exitMu.Lock()
-	if exitStatus < n {
-		exitStatus = n
-	}
-	exitMu.Unlock()
-}
-
 func main() {
 	_ = go11tag
-	flag.Usage = usage
+	flag.Usage = base.Usage
 	flag.Parse()
 	log.SetFlags(0)
 
 	args := flag.Args()
 	if len(args) < 1 {
-		usage()
+		base.Usage()
 	}
 
 	if args[0] == "help" {
@@ -185,14 +125,14 @@ func main() {
 				args = cmd.Flag.Args()
 			}
 			cmd.Run(cmd, args)
-			exit()
+			base.Exit()
 			return
 		}
 	}
 
 	fmt.Fprintf(os.Stderr, "go: unknown subcommand %q\nRun 'go help' for usage.\n", args[0])
-	setExitStatus(2)
-	exit()
+	base.SetExitStatus(2)
+	base.Exit()
 }
 
 var usageTemplate = `Go is a tool for managing Go source code.
@@ -289,7 +229,7 @@ func tmpl(w io.Writer, text string, data interface{}) {
 		if strings.Contains(ew.err.Error(), "pipe") {
 			os.Exit(1)
 		}
-		fatalf("writing output: %v", ew.err)
+		base.Fatalf("writing output: %v", ew.err)
 	}
 	if err != nil {
 		panic(err)
@@ -313,7 +253,7 @@ func printUsage(w io.Writer) {
 var usage func()
 
 func init() {
-	usage = mainUsage
+	base.Usage = mainUsage
 }
 
 func mainUsage() {
@@ -353,8 +293,8 @@ func help(args []string) {
 		fmt.Println()
 		buf := new(bytes.Buffer)
 		printUsage(buf)
-		usage := &Command{Long: buf.String()}
-		tmpl(&commentWriter{W: os.Stdout}, documentationTemplate, append([]*Command{usage}, commands...))
+		usage := &base.Command{Long: buf.String()}
+		tmpl(&commentWriter{W: os.Stdout}, documentationTemplate, append([]*base.Command{usage}, commands...))
 		fmt.Println("package main")
 		return
 	}
@@ -422,52 +362,6 @@ func importPaths(args []string) []string {
 	return out
 }
 
-var atexitFuncs []func()
-
-func atexit(f func()) {
-	atexitFuncs = append(atexitFuncs, f)
-}
-
-func exit() {
-	for _, f := range atexitFuncs {
-		f()
-	}
-	os.Exit(exitStatus)
-}
-
-func fatalf(format string, args ...interface{}) {
-	errorf(format, args...)
-	exit()
-}
-
-func errorf(format string, args ...interface{}) {
-	log.Printf(format, args...)
-	setExitStatus(1)
-}
-
-func exitIfErrors() {
-	if exitStatus != 0 {
-		exit()
-	}
-}
-
-func run(cmdargs ...interface{}) {
-	cmdline := str.StringList(cmdargs...)
-	if cfg.BuildN || cfg.BuildX {
-		fmt.Printf("%s\n", strings.Join(cmdline, " "))
-		if cfg.BuildN {
-			return
-		}
-	}
-
-	cmd := exec.Command(cmdline[0], cmdline[1:]...)
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	if err := cmd.Run(); err != nil {
-		errorf("%v", err)
-	}
-}
-
 // envForDir returns a copy of the environment
 // suitable for running in the given directory.
 // The environment is the current process's environment
diff --git a/src/cmd/go/pkg.go b/src/cmd/go/pkg.go
index ada30c8cec..69acbd3230 100644
--- a/src/cmd/go/pkg.go
+++ b/src/cmd/go/pkg.go
@@ -7,6 +7,7 @@ package main
 import (
 	"bytes"
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"cmd/go/internal/str"
 	"crypto/sha1"
 	"errors"
@@ -422,7 +423,7 @@ func loadImport(path, srcDir string, parent *Package, stk *importStack, importPo
 func setErrorPos(p *Package, importPos []token.Position) *Package {
 	if len(importPos) > 0 {
 		pos := importPos[0]
-		pos.Filename = shortPath(pos.Filename)
+		pos.Filename = base.ShortPath(pos.Filename)
 		p.Error.Pos = pos.String()
 	}
 	return p
@@ -469,7 +470,7 @@ func vendoredImportPath(parent *Package, path string) (found string) {
 	}
 
 	if !hasFilePathPrefix(dir, root) || len(dir) <= len(root) || dir[len(root)] != filepath.Separator || parent.ImportPath != "command-line-arguments" && !parent.local && filepath.Join(root, parent.ImportPath) != dir {
-		fatalf("unexpected directory layout:\n"+
+		base.Fatalf("unexpected directory layout:\n"+
 			"	import path: %s\n"+
 			"	root: %s\n"+
 			"	dir: %s\n"+
@@ -798,7 +799,7 @@ func expandScanner(err error) error {
 		// instead of just the first, as err.Error does.
 		var buf bytes.Buffer
 		for _, e := range err {
-			e.Pos.Filename = shortPath(e.Pos.Filename)
+			e.Pos.Filename = base.ShortPath(e.Pos.Filename)
 			buf.WriteString("\n")
 			buf.WriteString(e.Error())
 		}
@@ -863,7 +864,7 @@ func (p *Package) load(stk *importStack, bp *build.Package, err error) *Package
 		}
 		_, elem := filepath.Split(p.Dir)
 		full := cfg.BuildContext.GOOS + "_" + cfg.BuildContext.GOARCH + "/" + elem
-		if cfg.BuildContext.GOOS != toolGOOS || cfg.BuildContext.GOARCH != toolGOARCH {
+		if cfg.BuildContext.GOOS != base.ToolGOOS || cfg.BuildContext.GOARCH != base.ToolGOARCH {
 			// Install cross-compiled binaries to subdirectories of bin.
 			elem = full
 		}
@@ -902,7 +903,7 @@ func (p *Package) load(stk *importStack, bp *build.Package, err error) *Package
 
 				}
 			} else if !os.IsNotExist(err) {
-				fatalf("unexpected error reading %s: %v", shlibnamefile, err)
+				base.Fatalf("unexpected error reading %s: %v", shlibnamefile, err)
 			}
 		}
 	}
@@ -1647,7 +1648,7 @@ func computeBuildID(p *Package) {
 	if p.Standard && p.ImportPath == "runtime/internal/sys" && cfg.BuildContext.Compiler != "gccgo" {
 		data, err := ioutil.ReadFile(filepath.Join(p.Dir, "zversion.go"))
 		if err != nil {
-			fatalf("go: %s", err)
+			base.Fatalf("go: %s", err)
 		}
 		fmt.Fprintf(h, "zversion %q\n", string(data))
 	}
@@ -1667,8 +1668,6 @@ func computeBuildID(p *Package) {
 	p.buildID = fmt.Sprintf("%x", h.Sum(nil))
 }
 
-var cwd, _ = os.Getwd()
-
 var cmdCache = map[string]*Package{}
 
 // loadPackage is like loadImport but is used for command-line arguments,
@@ -1723,13 +1722,13 @@ func loadPackage(arg string, stk *importStack) *Package {
 	// referring to io/ioutil rather than a hypothetical import of
 	// "./ioutil".
 	if build.IsLocalImport(arg) {
-		bp, _ := cfg.BuildContext.ImportDir(filepath.Join(cwd, arg), build.FindOnly)
+		bp, _ := cfg.BuildContext.ImportDir(filepath.Join(base.Cwd, arg), build.FindOnly)
 		if bp.ImportPath != "" && bp.ImportPath != "." {
 			arg = bp.ImportPath
 		}
 	}
 
-	return loadImport(arg, cwd, nil, stk, nil, 0)
+	return loadImport(arg, base.Cwd, nil, stk, nil, 0)
 }
 
 // packages returns the packages named by the
@@ -1744,7 +1743,7 @@ func packages(args []string) []*Package {
 	var pkgs []*Package
 	for _, pkg := range packagesAndErrors(args) {
 		if pkg.Error != nil {
-			errorf("can't load package: %s", pkg.Error)
+			base.Errorf("can't load package: %s", pkg.Error)
 			continue
 		}
 		pkgs = append(pkgs, pkg)
@@ -1794,7 +1793,7 @@ func packagesForBuild(args []string) []*Package {
 	printed := map[*PackageError]bool{}
 	for _, pkg := range pkgs {
 		if pkg.Error != nil {
-			errorf("can't load package: %s", pkg.Error)
+			base.Errorf("can't load package: %s", pkg.Error)
 		}
 		for _, err := range pkg.DepsErrors {
 			// Since these are errors in dependencies,
@@ -1803,11 +1802,11 @@ func packagesForBuild(args []string) []*Package {
 			// Only print each once.
 			if !printed[err] {
 				printed[err] = true
-				errorf("%s", err)
+				base.Errorf("%s", err)
 			}
 		}
 	}
-	exitIfErrors()
+	base.ExitIfErrors()
 
 	// Check for duplicate loads of the same package.
 	// That should be impossible, but if it does happen then
@@ -1819,11 +1818,11 @@ func packagesForBuild(args []string) []*Package {
 	for _, pkg := range packageList(pkgs) {
 		if seen[pkg.ImportPath] && !reported[pkg.ImportPath] {
 			reported[pkg.ImportPath] = true
-			errorf("internal error: duplicate loads of %s", pkg.ImportPath)
+			base.Errorf("internal error: duplicate loads of %s", pkg.ImportPath)
 		}
 		seen[pkg.ImportPath] = true
 	}
-	exitIfErrors()
+	base.ExitIfErrors()
 
 	return pkgs
 }
diff --git a/src/cmd/go/pkg_test.go b/src/cmd/go/pkg_test.go
index 3988df8ce7..52d29ac9e8 100644
--- a/src/cmd/go/pkg_test.go
+++ b/src/cmd/go/pkg_test.go
@@ -6,6 +6,7 @@ package main
 
 import (
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"cmd/go/internal/str"
 	"io/ioutil"
 	"os"
@@ -164,7 +165,7 @@ func TestSharedLibName(t *testing.T) {
 				oldGopath := cfg.BuildContext.GOPATH
 				defer func() {
 					cfg.BuildContext.GOPATH = oldGopath
-					os.Chdir(cwd)
+					os.Chdir(base.Cwd)
 					err := os.RemoveAll(tmpGopath)
 					if err != nil {
 						t.Error(err)
diff --git a/src/cmd/go/run.go b/src/cmd/go/run.go
index 80d9919a5b..77a00541c1 100644
--- a/src/cmd/go/run.go
+++ b/src/cmd/go/run.go
@@ -6,6 +6,7 @@ package main
 
 import (
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"cmd/go/internal/str"
 	"fmt"
 	"os"
@@ -31,7 +32,7 @@ func findExecCmd() []string {
 	return execCmd
 }
 
-var cmdRun = &Command{
+var cmdRun = &base.Command{
 	UsageLine: "run [build flags] [-exec xprog] gofiles... [arguments...]",
 	Short:     "compile and run Go program",
 	Long: `
@@ -65,7 +66,7 @@ func printStderr(args ...interface{}) (int, error) {
 	return fmt.Fprint(os.Stderr, args...)
 }
 
-func runRun(cmd *Command, args []string) {
+func runRun(cmd *base.Command, args []string) {
 	instrumentInit()
 	buildModeInit()
 	var b builder
@@ -77,18 +78,18 @@ func runRun(cmd *Command, args []string) {
 	}
 	files, cmdArgs := args[:i], args[i:]
 	if len(files) == 0 {
-		fatalf("go run: no go files listed")
+		base.Fatalf("go run: no go files listed")
 	}
 	for _, file := range files {
 		if strings.HasSuffix(file, "_test.go") {
 			// goFilesPackage is going to assign this to TestGoFiles.
 			// Reject since it won't be part of the build.
-			fatalf("go run: cannot run *_test.go files (%s)", file)
+			base.Fatalf("go run: cannot run *_test.go files (%s)", file)
 		}
 	}
 	p := goFilesPackage(files)
 	if p.Error != nil {
-		fatalf("%s", p.Error)
+		base.Fatalf("%s", p.Error)
 	}
 	p.omitDWARF = true
 	if len(p.DepsErrors) > 0 {
@@ -100,13 +101,13 @@ func runRun(cmd *Command, args []string) {
 		for _, err := range p.DepsErrors {
 			if !printed[err] {
 				printed[err] = true
-				errorf("%s", err)
+				base.Errorf("%s", err)
 			}
 		}
 	}
-	exitIfErrors()
+	base.ExitIfErrors()
 	if p.Name != "main" {
-		fatalf("go run: cannot run non-main package")
+		base.Fatalf("go run: cannot run non-main package")
 	}
 	p.target = "" // must build - not up to date
 	var src string
@@ -121,7 +122,7 @@ func runRun(cmd *Command, args []string) {
 		if !cfg.BuildContext.CgoEnabled {
 			hint = " (cgo is disabled)"
 		}
-		fatalf("go run: no suitable source files%s", hint)
+		base.Fatalf("go run: no suitable source files%s", hint)
 	}
 	p.exeName = src[:len(src)-len(".go")] // name temporary executable for first go file
 	a1 := b.action(modeBuild, modeBuild, p)
@@ -140,19 +141,6 @@ func (b *builder) runProgram(a *action) error {
 		}
 	}
 
-	runStdin(cmdline)
+	base.RunStdin(cmdline)
 	return nil
 }
-
-// runStdin is like run, but connects Stdin.
-func runStdin(cmdline []string) {
-	cmd := exec.Command(cmdline[0], cmdline[1:]...)
-	cmd.Stdin = os.Stdin
-	cmd.Stdout = os.Stdout
-	cmd.Stderr = os.Stderr
-	cmd.Env = cfg.OrigEnv
-	startSigHandlers()
-	if err := cmd.Run(); err != nil {
-		errorf("%v", err)
-	}
-}
diff --git a/src/cmd/go/test.go b/src/cmd/go/test.go
index ac79d96dbc..04a2080fc4 100644
--- a/src/cmd/go/test.go
+++ b/src/cmd/go/test.go
@@ -7,6 +7,7 @@ package main
 import (
 	"bytes"
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"cmd/go/internal/str"
 	"errors"
 	"fmt"
@@ -36,7 +37,7 @@ func init() {
 
 const testUsage = "test [build/test flags] [packages] [build/test flags & test binary flags]"
 
-var cmdTest = &Command{
+var cmdTest = &base.Command{
 	CustomFlags: true,
 	UsageLine:   testUsage,
 	Short:       "test packages",
@@ -109,7 +110,7 @@ The test binary also accepts flags that control execution of the test; these
 flags are also accessible by 'go test'.
 `
 
-var helpTestflag = &Command{
+var helpTestflag = &base.Command{
 	UsageLine: "testflag",
 	Short:     "description of testing flags",
 	Long: `
@@ -314,7 +315,7 @@ In the second example, the argument math is passed through to the test
 binary, instead of being interpreted as the package list.
 `
 
-var helpTestfunc = &Command{
+var helpTestfunc = &base.Command{
 	UsageLine: "testfunc",
 	Short:     "description of testing functions",
 	Long: `
@@ -401,7 +402,7 @@ var testMainDeps = map[string]bool{
 	"os": true,
 }
 
-func runTest(cmd *Command, args []string) {
+func runTest(cmd *base.Command, args []string) {
 	var pkgArgs []string
 	pkgArgs, testArgs = testFlags(args)
 
@@ -411,17 +412,17 @@ func runTest(cmd *Command, args []string) {
 	buildModeInit()
 	pkgs := packagesForBuild(pkgArgs)
 	if len(pkgs) == 0 {
-		fatalf("no packages to test")
+		base.Fatalf("no packages to test")
 	}
 
 	if testC && len(pkgs) != 1 {
-		fatalf("cannot use -c flag with multiple packages")
+		base.Fatalf("cannot use -c flag with multiple packages")
 	}
 	if testO != "" && len(pkgs) != 1 {
-		fatalf("cannot use -o flag with multiple packages")
+		base.Fatalf("cannot use -o flag with multiple packages")
 	}
 	if testProfile && len(pkgs) != 1 {
-		fatalf("cannot use test profile flag with multiple packages")
+		base.Fatalf("cannot use test profile flag with multiple packages")
 	}
 
 	// If a test timeout was given and is parseable, set our kill timeout
@@ -556,9 +557,9 @@ func runTest(cmd *Command, args []string) {
 			failed := fmt.Sprintf("FAIL\t%s [setup failed]\n", p.ImportPath)
 
 			if p.ImportPath != "" {
-				errorf("# %s\n%s\n%s", p.ImportPath, str, failed)
+				base.Errorf("# %s\n%s\n%s", p.ImportPath, str, failed)
 			} else {
-				errorf("%s\n%s", str, failed)
+				base.Errorf("%s\n%s", str, failed)
 			}
 			continue
 		}
@@ -964,11 +965,11 @@ func builderTest(b *builder, p *Package) (buildAction, runAction, printAction *a
 
 	if testC || testNeedBinary {
 		// -c or profiling flag: create action to copy binary to ./test.out.
-		target := filepath.Join(cwd, testBinary+cfg.ExeSuffix)
+		target := filepath.Join(base.Cwd, testBinary+cfg.ExeSuffix)
 		if testO != "" {
 			target = testO
 			if !filepath.IsAbs(target) {
-				target = filepath.Join(cwd, target)
+				target = filepath.Join(base.Cwd, target)
 			}
 		}
 		buildAction = &action{
@@ -1110,7 +1111,7 @@ func builderRunTest(b *builder, a *action) error {
 		// We were unable to build the binary.
 		a.failed = false
 		fmt.Fprintf(a.testOutput, "FAIL\t%s [build failed]\n", a.p.ImportPath)
-		setExitStatus(1)
+		base.SetExitStatus(1)
 		return nil
 	}
 
@@ -1153,7 +1154,7 @@ func builderRunTest(b *builder, a *action) error {
 	// running.
 	if err == nil {
 		tick := time.NewTimer(testKillTimeout)
-		startSigHandlers()
+		base.StartSigHandlers()
 		done := make(chan error)
 		go func() {
 			done <- cmd.Wait()
@@ -1163,14 +1164,14 @@ func builderRunTest(b *builder, a *action) error {
 		case err = <-done:
 			// ok
 		case <-tick.C:
-			if signalTrace != nil {
+			if base.SignalTrace != nil {
 				// Send a quit signal in the hope that the program will print
 				// a stack trace and exit. Give it five seconds before resorting
 				// to Kill.
-				cmd.Process.Signal(signalTrace)
+				cmd.Process.Signal(base.SignalTrace)
 				select {
 				case err = <-done:
-					fmt.Fprintf(&buf, "*** Test killed with %v: ran too long (%v).\n", signalTrace, testKillTimeout)
+					fmt.Fprintf(&buf, "*** Test killed with %v: ran too long (%v).\n", base.SignalTrace, testKillTimeout)
 					break Outer
 				case <-time.After(5 * time.Second):
 				}
@@ -1195,7 +1196,7 @@ func builderRunTest(b *builder, a *action) error {
 		return nil
 	}
 
-	setExitStatus(1)
+	base.SetExitStatus(1)
 	if len(out) > 0 {
 		a.testOutput.Write(out)
 		// assume printing the test binary's exit status is superfluous
diff --git a/src/cmd/go/testflag.go b/src/cmd/go/testflag.go
index 749f1724c5..b2f63279d5 100644
--- a/src/cmd/go/testflag.go
+++ b/src/cmd/go/testflag.go
@@ -6,6 +6,7 @@ package main
 
 import (
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"flag"
 	"fmt"
 	"os"
@@ -64,7 +65,7 @@ var testFlagDefn = []*testFlagSpec{
 
 // add build flags to testFlagDefn
 func init() {
-	var cmd Command
+	var cmd base.Command
 	addBuildFlags(&cmd)
 	cmd.Flag.VisitAll(func(f *flag.Flag) {
 		if f.Name == "v" {
@@ -129,7 +130,7 @@ func testFlags(args []string) (packageNames, passToTest []string) {
 		}
 		if f.flagValue != nil {
 			if err := f.flagValue.Set(value); err != nil {
-				fatalf("invalid flag argument for -%s: %v", f.name, err)
+				base.Fatalf("invalid flag argument for -%s: %v", f.name, err)
 			}
 		} else {
 			// Test-only flags.
@@ -145,7 +146,7 @@ func testFlags(args []string) (packageNames, passToTest []string) {
 			case "exec":
 				execCmd, err = splitQuotedFields(value)
 				if err != nil {
-					fatalf("invalid flag argument for -%s: %v", f.name, err)
+					base.Fatalf("invalid flag argument for -%s: %v", f.name, err)
 				}
 			case "bench":
 				// record that we saw the flag; don't care about the value
@@ -172,7 +173,7 @@ func testFlags(args []string) (packageNames, passToTest []string) {
 				case "set", "count", "atomic":
 					cfg.TestCoverMode = value
 				default:
-					fatalf("invalid flag argument for -covermode: %q", value)
+					base.Fatalf("invalid flag argument for -covermode: %q", value)
 				}
 				testCover = true
 			case "outputdir":
@@ -199,7 +200,7 @@ func testFlags(args []string) (packageNames, passToTest []string) {
 	if testProfile && outputDir == "" {
 		dir, err := os.Getwd()
 		if err != nil {
-			fatalf("error from os.Getwd: %s", err)
+			base.Fatalf("error from os.Getwd: %s", err)
 		}
 		passToTest = append(passToTest, "-test.outputdir", dir)
 	}
@@ -216,7 +217,7 @@ func testFlag(args []string, i int) (f *testFlagSpec, value string, extra bool)
 	}
 	switch arg {
 	case "-?", "-h", "-help":
-		usage()
+		base.Usage()
 	}
 	if arg == "" || arg[0] != '-' {
 		return
diff --git a/src/cmd/go/tool.go b/src/cmd/go/tool.go
index 5f7b5a07e4..5f07e18c87 100644
--- a/src/cmd/go/tool.go
+++ b/src/cmd/go/tool.go
@@ -5,18 +5,17 @@
 package main
 
 import (
-	"cmd/go/internal/cfg"
 	"fmt"
-	"go/build"
 	"os"
 	"os/exec"
-	"path/filepath"
-	"runtime"
 	"sort"
 	"strings"
+
+	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 )
 
-var cmdTool = &Command{
+var cmdTool = &base.Command{
 	Run:       runTool,
 	UsageLine: "tool [-n] command [args...]",
 	Short:     "run specified go tool",
@@ -31,47 +30,13 @@ For more about each tool command, see 'go tool command -h'.
 `,
 }
 
-var (
-	toolGOOS      = runtime.GOOS
-	toolGOARCH    = runtime.GOARCH
-	toolIsWindows = toolGOOS == "windows"
-	toolDir       = build.ToolDir
-
-	toolN bool
-)
+var toolN bool
 
 func init() {
 	cmdTool.Flag.BoolVar(&toolN, "n", false, "")
 }
 
-const toolWindowsExtension = ".exe"
-
-func tool(toolName string) string {
-	toolPath := filepath.Join(toolDir, toolName)
-	if toolIsWindows {
-		toolPath += toolWindowsExtension
-	}
-	if len(cfg.BuildToolexec) > 0 {
-		return toolPath
-	}
-	// Give a nice message if there is no tool with that name.
-	if _, err := os.Stat(toolPath); err != nil {
-		if isInGoToolsRepo(toolName) {
-			fmt.Fprintf(os.Stderr, "go tool: no such tool %q; to install:\n\tgo get golang.org/x/tools/cmd/%s\n", toolName, toolName)
-		} else {
-			fmt.Fprintf(os.Stderr, "go tool: no such tool %q\n", toolName)
-		}
-		setExitStatus(2)
-		exit()
-	}
-	return toolPath
-}
-
-func isInGoToolsRepo(toolName string) bool {
-	return false
-}
-
-func runTool(cmd *Command, args []string) {
+func runTool(cmd *base.Command, args []string) {
 	if len(args) == 0 {
 		listTools()
 		return
@@ -83,11 +48,11 @@ func runTool(cmd *Command, args []string) {
 		case 'a' <= c && c <= 'z', '0' <= c && c <= '9', c == '_':
 		default:
 			fmt.Fprintf(os.Stderr, "go tool: bad tool name %q\n", toolName)
-			setExitStatus(2)
+			base.SetExitStatus(2)
 			return
 		}
 	}
-	toolPath := tool(toolName)
+	toolPath := base.Tool(toolName)
 	if toolPath == "" {
 		return
 	}
@@ -119,24 +84,24 @@ func runTool(cmd *Command, args []string) {
 		if e, ok := err.(*exec.ExitError); !ok || !e.Exited() || cfg.BuildX {
 			fmt.Fprintf(os.Stderr, "go tool %s: %s\n", toolName, err)
 		}
-		setExitStatus(1)
+		base.SetExitStatus(1)
 		return
 	}
 }
 
 // listTools prints a list of the available tools in the tools directory.
 func listTools() {
-	f, err := os.Open(toolDir)
+	f, err := os.Open(base.ToolDir)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "go tool: no tool directory: %s\n", err)
-		setExitStatus(2)
+		base.SetExitStatus(2)
 		return
 	}
 	defer f.Close()
 	names, err := f.Readdirnames(-1)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "go tool: can't read directory: %s\n", err)
-		setExitStatus(2)
+		base.SetExitStatus(2)
 		return
 	}
 
@@ -145,8 +110,8 @@ func listTools() {
 		// Unify presentation by going to lower case.
 		name = strings.ToLower(name)
 		// If it's windows, don't show the .exe suffix.
-		if toolIsWindows && strings.HasSuffix(name, toolWindowsExtension) {
-			name = name[:len(name)-len(toolWindowsExtension)]
+		if base.ToolIsWindows && strings.HasSuffix(name, base.ToolWindowsExtension) {
+			name = name[:len(name)-len(base.ToolWindowsExtension)]
 		}
 		fmt.Println(name)
 	}
diff --git a/src/cmd/go/version.go b/src/cmd/go/version.go
index 3045f350d7..7cc949569a 100644
--- a/src/cmd/go/version.go
+++ b/src/cmd/go/version.go
@@ -5,18 +5,19 @@
 package main
 
 import (
+	"cmd/go/internal/base"
 	"fmt"
 	"runtime"
 )
 
-var cmdVersion = &Command{
+var cmdVersion = &base.Command{
 	Run:       runVersion,
 	UsageLine: "version",
 	Short:     "print Go version",
 	Long:      `Version prints the Go version, as reported by runtime.Version.`,
 }
 
-func runVersion(cmd *Command, args []string) {
+func runVersion(cmd *base.Command, args []string) {
 	if len(args) != 0 {
 		cmd.Usage()
 	}
diff --git a/src/cmd/go/vet.go b/src/cmd/go/vet.go
index 8d6f26444e..98034ee585 100644
--- a/src/cmd/go/vet.go
+++ b/src/cmd/go/vet.go
@@ -8,6 +8,7 @@ import (
 	"path/filepath"
 
 	"cmd/go/internal/cfg"
+	"cmd/go/internal/base"
 	"cmd/go/internal/str"
 )
 
@@ -15,7 +16,7 @@ func init() {
 	addBuildFlags(cmdVet)
 }
 
-var cmdVet = &Command{
+var cmdVet = &base.Command{
 	Run:       runVet,
 	UsageLine: "vet [-n] [-x] [build flags] [packages]",
 	Short:     "run go tool vet on packages",
@@ -36,7 +37,7 @@ See also: go fmt, go fix.
 	`,
 }
 
-func runVet(cmd *Command, args []string) {
+func runVet(cmd *base.Command, args []string) {
 	for _, p := range packages(args) {
 		// Vet expects to be given a set of files all from the same package.
 		// Run once for package p and once for package p_test.
@@ -53,5 +54,5 @@ func runVetFiles(p *Package, files []string) {
 	for i := range files {
 		files[i] = filepath.Join(p.Dir, files[i])
 	}
-	run(cfg.BuildToolexec, tool("vet"), relPaths(files))
+	base.Run(cfg.BuildToolexec, base.Tool("vet"), base.RelPaths(files))
 }