env.go

     1  // Copyright 2012 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package envcmd implements the “go env” command.
     6  package envcmd
     7  
     8  import (
     9  	"bytes"
    10  	"context"
    11  	"encoding/json"
    12  	"fmt"
    13  	"go/build"
    14  	"internal/buildcfg"
    15  	"io"
    16  	"os"
    17  	"path/filepath"
    18  	"runtime"
    19  	"slices"
    20  	"sort"
    21  	"strings"
    22  	"unicode"
    23  	"unicode/utf8"
    24  
    25  	"cmd/go/internal/base"
    26  	"cmd/go/internal/cache"
    27  	"cmd/go/internal/cfg"
    28  	"cmd/go/internal/fsys"
    29  	"cmd/go/internal/load"
    30  	"cmd/go/internal/modload"
    31  	"cmd/go/internal/work"
    32  	"cmd/internal/quoted"
    33  	"cmd/internal/telemetry"
    34  )
    35  
    36  var CmdEnv = &base.Command{
    37  	UsageLine: "go env [-json] [-changed] [-u] [-w] [var ...]",
    38  	Short:     "print Go environment information",
    39  	Long: `
    40  Env prints Go environment information.
    41  
    42  By default env prints information as a shell script
    43  (on Windows, a batch file). If one or more variable
    44  names is given as arguments, env prints the value of
    45  each named variable on its own line.
    46  
    47  The -json flag prints the environment in JSON format
    48  instead of as a shell script.
    49  
    50  The -u flag requires one or more arguments and unsets
    51  the default setting for the named environment variables,
    52  if one has been set with 'go env -w'.
    53  
    54  The -w flag requires one or more arguments of the
    55  form NAME=VALUE and changes the default settings
    56  of the named environment variables to the given values.
    57  
    58  The -changed flag prints only those settings whose effective
    59  value differs from the default value that would be obtained in
    60  an empty environment with no prior uses of the -w flag.
    61  
    62  For more about environment variables, see 'go help environment'.
    63  	`,
    64  }
    65  
    66  func init() {
    67  	CmdEnv.Run = runEnv // break init cycle
    68  	base.AddChdirFlag(&CmdEnv.Flag)
    69  	base.AddBuildFlagsNX(&CmdEnv.Flag)
    70  }
    71  
    72  var (
    73  	envJson    = CmdEnv.Flag.Bool("json", false, "")
    74  	envU       = CmdEnv.Flag.Bool("u", false, "")
    75  	envW       = CmdEnv.Flag.Bool("w", false, "")
    76  	envChanged = CmdEnv.Flag.Bool("changed", false, "")
    77  )
    78  
    79  func MkEnv() []cfg.EnvVar {
    80  	envFile, envFileChanged, _ := cfg.EnvFile()
    81  	env := []cfg.EnvVar{
    82  		// NOTE: Keep this list (and in general, all lists in source code) sorted by name.
    83  		{Name: "GO111MODULE", Value: cfg.Getenv("GO111MODULE")},
    84  		{Name: "GOARCH", Value: cfg.Goarch, Changed: cfg.Goarch != runtime.GOARCH},
    85  		{Name: "GOAUTH", Value: cfg.GOAUTH, Changed: cfg.GOAUTHChanged},
    86  		{Name: "GOBIN", Value: cfg.GOBIN},
    87  		{Name: "GOCACHE"},
    88  		{Name: "GODEBUG", Value: os.Getenv("GODEBUG")},
    89  		{Name: "GOENV", Value: envFile, Changed: envFileChanged},
    90  		{Name: "GOEXE", Value: cfg.ExeSuffix},
    91  
    92  		// List the raw value of GOEXPERIMENT, not the cleaned one.
    93  		// The set of default experiments may change from one release
    94  		// to the next, so a GOEXPERIMENT setting that is redundant
    95  		// with the current toolchain might actually be relevant with
    96  		// a different version (for example, when bisecting a regression).
    97  		{Name: "GOEXPERIMENT", Value: cfg.RawGOEXPERIMENT},
    98  
    99  		{Name: "GOFLAGS", Value: cfg.Getenv("GOFLAGS")},
   100  		{Name: "GOHOSTARCH", Value: runtime.GOARCH},
   101  		{Name: "GOHOSTOS", Value: runtime.GOOS},
   102  		{Name: "GOINSECURE", Value: cfg.GOINSECURE},
   103  		{Name: "GOMODCACHE", Value: cfg.GOMODCACHE, Changed: cfg.GOMODCACHEChanged},
   104  		{Name: "GONOPROXY", Value: cfg.GONOPROXY, Changed: cfg.GONOPROXYChanged},
   105  		{Name: "GONOSUMDB", Value: cfg.GONOSUMDB, Changed: cfg.GONOSUMDBChanged},
   106  		{Name: "GOOS", Value: cfg.Goos, Changed: cfg.Goos != runtime.GOOS},
   107  		{Name: "GOPATH", Value: cfg.BuildContext.GOPATH, Changed: cfg.GOPATHChanged},
   108  		{Name: "GOPRIVATE", Value: cfg.GOPRIVATE},
   109  		{Name: "GOPROXY", Value: cfg.GOPROXY, Changed: cfg.GOPROXYChanged},
   110  		{Name: "GOROOT", Value: cfg.GOROOT},
   111  		{Name: "GOSUMDB", Value: cfg.GOSUMDB, Changed: cfg.GOSUMDBChanged},
   112  		{Name: "GOTELEMETRY", Value: telemetry.Mode()},
   113  		{Name: "GOTELEMETRYDIR", Value: telemetry.Dir()},
   114  		{Name: "GOTMPDIR", Value: cfg.Getenv("GOTMPDIR")},
   115  		{Name: "GOTOOLCHAIN"},
   116  		{Name: "GOTOOLDIR", Value: build.ToolDir},
   117  		{Name: "GOVCS", Value: cfg.GOVCS},
   118  		{Name: "GOVERSION", Value: runtime.Version()},
   119  	}
   120  
   121  	for i := range env {
   122  		switch env[i].Name {
   123  		case "GO111MODULE":
   124  			if env[i].Value != "on" && env[i].Value != "" {
   125  				env[i].Changed = true
   126  			}
   127  		case "GOBIN", "GOEXPERIMENT", "GOFLAGS", "GOINSECURE", "GOPRIVATE", "GOTMPDIR", "GOVCS":
   128  			if env[i].Value != "" {
   129  				env[i].Changed = true
   130  			}
   131  		case "GOCACHE":
   132  			env[i].Value, env[i].Changed = cache.DefaultDir()
   133  		case "GOTOOLCHAIN":
   134  			env[i].Value, env[i].Changed = cfg.EnvOrAndChanged("GOTOOLCHAIN", "")
   135  		case "GODEBUG":
   136  			env[i].Changed = env[i].Value != ""
   137  		}
   138  	}
   139  
   140  	if work.GccgoBin != "" {
   141  		env = append(env, cfg.EnvVar{Name: "GCCGO", Value: work.GccgoBin, Changed: true})
   142  	} else {
   143  		env = append(env, cfg.EnvVar{Name: "GCCGO", Value: work.GccgoName})
   144  	}
   145  
   146  	goarch, val, changed := cfg.GetArchEnv()
   147  	if goarch != "" {
   148  		env = append(env, cfg.EnvVar{Name: goarch, Value: val, Changed: changed})
   149  	}
   150  
   151  	cc := cfg.Getenv("CC")
   152  	ccChanged := true
   153  	if cc == "" {
   154  		ccChanged = false
   155  		cc = cfg.DefaultCC(cfg.Goos, cfg.Goarch)
   156  	}
   157  	cxx := cfg.Getenv("CXX")
   158  	cxxChanged := true
   159  	if cxx == "" {
   160  		cxxChanged = false
   161  		cxx = cfg.DefaultCXX(cfg.Goos, cfg.Goarch)
   162  	}
   163  	ar, arChanged := cfg.EnvOrAndChanged("AR", "ar")
   164  	env = append(env, cfg.EnvVar{Name: "AR", Value: ar, Changed: arChanged})
   165  	env = append(env, cfg.EnvVar{Name: "CC", Value: cc, Changed: ccChanged})
   166  	env = append(env, cfg.EnvVar{Name: "CXX", Value: cxx, Changed: cxxChanged})
   167  
   168  	if cfg.BuildContext.CgoEnabled {
   169  		env = append(env, cfg.EnvVar{Name: "CGO_ENABLED", Value: "1", Changed: cfg.CGOChanged})
   170  	} else {
   171  		env = append(env, cfg.EnvVar{Name: "CGO_ENABLED", Value: "0", Changed: cfg.CGOChanged})
   172  	}
   173  
   174  	return env
   175  }
   176  
   177  func findEnv(env []cfg.EnvVar, name string) string {
   178  	for _, e := range env {
   179  		if e.Name == name {
   180  			return e.Value
   181  		}
   182  	}
   183  	if cfg.CanGetenv(name) {
   184  		return cfg.Getenv(name)
   185  	}
   186  	return ""
   187  }
   188  
   189  // ExtraEnvVars returns environment variables that should not leak into child processes.
   190  func ExtraEnvVars() []cfg.EnvVar {
   191  	gomod := ""
   192  	modload.Init()
   193  	if modload.HasModRoot() {
   194  		gomod = modload.ModFilePath()
   195  	} else if modload.Enabled() {
   196  		gomod = os.DevNull
   197  	}
   198  	modload.InitWorkfile()
   199  	gowork := modload.WorkFilePath()
   200  	// As a special case, if a user set off explicitly, report that in GOWORK.
   201  	if cfg.Getenv("GOWORK") == "off" {
   202  		gowork = "off"
   203  	}
   204  	return []cfg.EnvVar{
   205  		{Name: "GOMOD", Value: gomod},
   206  		{Name: "GOWORK", Value: gowork},
   207  	}
   208  }
   209  
   210  // ExtraEnvVarsCostly returns environment variables that should not leak into child processes
   211  // but are costly to evaluate.
   212  func ExtraEnvVarsCostly() []cfg.EnvVar {
   213  	b := work.NewBuilder("")
   214  	defer func() {
   215  		if err := b.Close(); err != nil {
   216  			base.Fatal(err)
   217  		}
   218  	}()
   219  
   220  	cppflags, cflags, cxxflags, fflags, ldflags, err := b.CFlags(&load.Package{})
   221  	if err != nil {
   222  		// Should not happen - b.CFlags was given an empty package.
   223  		fmt.Fprintf(os.Stderr, "go: invalid cflags: %v\n", err)
   224  		return nil
   225  	}
   226  	cmd := b.GccCmd(".", "")
   227  
   228  	join := func(s []string) string {
   229  		q, err := quoted.Join(s)
   230  		if err != nil {
   231  			return strings.Join(s, " ")
   232  		}
   233  		return q
   234  	}
   235  
   236  	ret := []cfg.EnvVar{
   237  		// Note: Update the switch in runEnv below when adding to this list.
   238  		{Name: "CGO_CFLAGS", Value: join(cflags)},
   239  		{Name: "CGO_CPPFLAGS", Value: join(cppflags)},
   240  		{Name: "CGO_CXXFLAGS", Value: join(cxxflags)},
   241  		{Name: "CGO_FFLAGS", Value: join(fflags)},
   242  		{Name: "CGO_LDFLAGS", Value: join(ldflags)},
   243  		{Name: "PKG_CONFIG", Value: b.PkgconfigCmd()},
   244  		{Name: "GOGCCFLAGS", Value: join(cmd[3:])},
   245  	}
   246  
   247  	for i := range ret {
   248  		ev := &ret[i]
   249  		switch ev.Name {
   250  		case "GOGCCFLAGS": // GOGCCFLAGS cannot be modified
   251  		case "CGO_CPPFLAGS":
   252  			ev.Changed = ev.Value != ""
   253  		case "PKG_CONFIG":
   254  			ev.Changed = ev.Value != cfg.DefaultPkgConfig
   255  		case "CGO_CXXFLAGS", "CGO_CFLAGS", "CGO_FFLAGS", "CGO_LDFLAGS":
   256  			ev.Changed = ev.Value != work.DefaultCFlags
   257  		}
   258  	}
   259  
   260  	return ret
   261  }
   262  
   263  // argKey returns the KEY part of the arg KEY=VAL, or else arg itself.
   264  func argKey(arg string) string {
   265  	i := strings.Index(arg, "=")
   266  	if i < 0 {
   267  		return arg
   268  	}
   269  	return arg[:i]
   270  }
   271  
   272  func runEnv(ctx context.Context, cmd *base.Command, args []string) {
   273  	if *envJson && *envU {
   274  		base.Fatalf("go: cannot use -json with -u")
   275  	}
   276  	if *envJson && *envW {
   277  		base.Fatalf("go: cannot use -json with -w")
   278  	}
   279  	if *envU && *envW {
   280  		base.Fatalf("go: cannot use -u with -w")
   281  	}
   282  
   283  	// Handle 'go env -w' and 'go env -u' before calling buildcfg.Check,
   284  	// so they can be used to recover from an invalid configuration.
   285  	if *envW {
   286  		runEnvW(args)
   287  		return
   288  	}
   289  
   290  	if *envU {
   291  		runEnvU(args)
   292  		return
   293  	}
   294  
   295  	buildcfg.Check()
   296  	if cfg.ExperimentErr != nil {
   297  		base.Fatal(cfg.ExperimentErr)
   298  	}
   299  
   300  	for _, arg := range args {
   301  		if strings.Contains(arg, "=") {
   302  			base.Fatalf("go: invalid variable name %q (use -w to set variable)", arg)
   303  		}
   304  	}
   305  
   306  	env := cfg.CmdEnv
   307  	env = append(env, ExtraEnvVars()...)
   308  
   309  	if err := fsys.Init(base.Cwd()); err != nil {
   310  		base.Fatal(err)
   311  	}
   312  
   313  	// Do we need to call ExtraEnvVarsCostly, which is a bit expensive?
   314  	needCostly := false
   315  	if len(args) == 0 {
   316  		// We're listing all environment variables ("go env"),
   317  		// including the expensive ones.
   318  		needCostly = true
   319  	} else {
   320  		needCostly = false
   321  	checkCostly:
   322  		for _, arg := range args {
   323  			switch argKey(arg) {
   324  			case "CGO_CFLAGS",
   325  				"CGO_CPPFLAGS",
   326  				"CGO_CXXFLAGS",
   327  				"CGO_FFLAGS",
   328  				"CGO_LDFLAGS",
   329  				"PKG_CONFIG",
   330  				"GOGCCFLAGS":
   331  				needCostly = true
   332  				break checkCostly
   333  			}
   334  		}
   335  	}
   336  	if needCostly {
   337  		work.BuildInit()
   338  		env = append(env, ExtraEnvVarsCostly()...)
   339  	}
   340  
   341  	if len(args) > 0 {
   342  		// Show only the named vars.
   343  		if !*envChanged {
   344  			if *envJson {
   345  				es := make([]cfg.EnvVar, 0, len(args))
   346  				for _, name := range args {
   347  					e := cfg.EnvVar{Name: name, Value: findEnv(env, name)}
   348  					es = append(es, e)
   349  				}
   350  				env = es
   351  			} else {
   352  				// Print just the values, without names.
   353  				for _, name := range args {
   354  					fmt.Printf("%s\n", findEnv(env, name))
   355  				}
   356  				return
   357  			}
   358  		} else {
   359  			// Show only the changed, named vars.
   360  			var es []cfg.EnvVar
   361  			for _, name := range args {
   362  				for _, e := range env {
   363  					if e.Name == name {
   364  						es = append(es, e)
   365  						break
   366  					}
   367  				}
   368  			}
   369  			env = es
   370  		}
   371  	}
   372  
   373  	// print
   374  	if *envJson {
   375  		printEnvAsJSON(env, *envChanged)
   376  	} else {
   377  		PrintEnv(os.Stdout, env, *envChanged)
   378  	}
   379  }
   380  
   381  func runEnvW(args []string) {
   382  	// Process and sanity-check command line.
   383  	if len(args) == 0 {
   384  		base.Fatalf("go: no KEY=VALUE arguments given")
   385  	}
   386  	osEnv := make(map[string]string)
   387  	for _, e := range cfg.OrigEnv {
   388  		if i := strings.Index(e, "="); i >= 0 {
   389  			osEnv[e[:i]] = e[i+1:]
   390  		}
   391  	}
   392  	add := make(map[string]string)
   393  	for _, arg := range args {
   394  		key, val, found := strings.Cut(arg, "=")
   395  		if !found {
   396  			base.Fatalf("go: arguments must be KEY=VALUE: invalid argument: %s", arg)
   397  		}
   398  		if err := checkEnvWrite(key, val); err != nil {
   399  			base.Fatal(err)
   400  		}
   401  		if _, ok := add[key]; ok {
   402  			base.Fatalf("go: multiple values for key: %s", key)
   403  		}
   404  		add[key] = val
   405  		if osVal := osEnv[key]; osVal != "" && osVal != val {
   406  			fmt.Fprintf(os.Stderr, "warning: go env -w %s=... does not override conflicting OS environment variable\n", key)
   407  		}
   408  	}
   409  
   410  	if err := checkBuildConfig(add, nil); err != nil {
   411  		base.Fatal(err)
   412  	}
   413  
   414  	gotmp, okGOTMP := add["GOTMPDIR"]
   415  	if okGOTMP {
   416  		if !filepath.IsAbs(gotmp) && gotmp != "" {
   417  			base.Fatalf("go: GOTMPDIR must be an absolute path")
   418  		}
   419  	}
   420  
   421  	updateEnvFile(add, nil)
   422  }
   423  
   424  func runEnvU(args []string) {
   425  	// Process and sanity-check command line.
   426  	if len(args) == 0 {
   427  		base.Fatalf("go: 'go env -u' requires an argument")
   428  	}
   429  	del := make(map[string]bool)
   430  	for _, arg := range args {
   431  		if err := checkEnvWrite(arg, ""); err != nil {
   432  			base.Fatal(err)
   433  		}
   434  		del[arg] = true
   435  	}
   436  
   437  	if err := checkBuildConfig(nil, del); err != nil {
   438  		base.Fatal(err)
   439  	}
   440  
   441  	updateEnvFile(nil, del)
   442  }
   443  
   444  // checkBuildConfig checks whether the build configuration is valid
   445  // after the specified configuration environment changes are applied.
   446  func checkBuildConfig(add map[string]string, del map[string]bool) error {
   447  	// get returns the value for key after applying add and del and
   448  	// reports whether it changed. cur should be the current value
   449  	// (i.e., before applying changes) and def should be the default
   450  	// value (i.e., when no environment variables are provided at all).
   451  	get := func(key, cur, def string) (string, bool) {
   452  		if val, ok := add[key]; ok {
   453  			return val, true
   454  		}
   455  		if del[key] {
   456  			val := getOrigEnv(key)
   457  			if val == "" {
   458  				val = def
   459  			}
   460  			return val, true
   461  		}
   462  		return cur, false
   463  	}
   464  
   465  	goos, okGOOS := get("GOOS", cfg.Goos, build.Default.GOOS)
   466  	goarch, okGOARCH := get("GOARCH", cfg.Goarch, build.Default.GOARCH)
   467  	if okGOOS || okGOARCH {
   468  		if err := work.CheckGOOSARCHPair(goos, goarch); err != nil {
   469  			return err
   470  		}
   471  	}
   472  
   473  	goexperiment, okGOEXPERIMENT := get("GOEXPERIMENT", cfg.RawGOEXPERIMENT, buildcfg.DefaultGOEXPERIMENT)
   474  	if okGOEXPERIMENT {
   475  		if _, err := buildcfg.ParseGOEXPERIMENT(goos, goarch, goexperiment); err != nil {
   476  			return err
   477  		}
   478  	}
   479  
   480  	return nil
   481  }
   482  
   483  // PrintEnv prints the environment variables to w.
   484  func PrintEnv(w io.Writer, env []cfg.EnvVar, onlyChanged bool) {
   485  	env = slices.Clone(env)
   486  	slices.SortFunc(env, func(x, y cfg.EnvVar) int { return strings.Compare(x.Name, y.Name) })
   487  
   488  	for _, e := range env {
   489  		if e.Name != "TERM" {
   490  			if runtime.GOOS != "plan9" && bytes.Contains([]byte(e.Value), []byte{0}) {
   491  				base.Fatalf("go: internal error: encountered null byte in environment variable %s on non-plan9 platform", e.Name)
   492  			}
   493  			if onlyChanged && !e.Changed {
   494  				continue
   495  			}
   496  			switch runtime.GOOS {
   497  			default:
   498  				fmt.Fprintf(w, "%s=%s\n", e.Name, shellQuote(e.Value))
   499  			case "plan9":
   500  				if strings.IndexByte(e.Value, '\x00') < 0 {
   501  					fmt.Fprintf(w, "%s='%s'\n", e.Name, strings.ReplaceAll(e.Value, "'", "''"))
   502  				} else {
   503  					v := strings.Split(e.Value, "\x00")
   504  					fmt.Fprintf(w, "%s=(", e.Name)
   505  					for x, s := range v {
   506  						if x > 0 {
   507  							fmt.Fprintf(w, " ")
   508  						}
   509  						fmt.Fprintf(w, "'%s'", strings.ReplaceAll(s, "'", "''"))
   510  					}
   511  					fmt.Fprintf(w, ")\n")
   512  				}
   513  			case "windows":
   514  				if hasNonGraphic(e.Value) {
   515  					base.Errorf("go: stripping unprintable or unescapable characters from %%%q%%", e.Name)
   516  				}
   517  				fmt.Fprintf(w, "set %s=%s\n", e.Name, batchEscape(e.Value))
   518  			}
   519  		}
   520  	}
   521  }
   522  
   523  func hasNonGraphic(s string) bool {
   524  	for _, c := range []byte(s) {
   525  		if c == '\r' || c == '\n' || (!unicode.IsGraphic(rune(c)) && !unicode.IsSpace(rune(c))) {
   526  			return true
   527  		}
   528  	}
   529  	return false
   530  }
   531  
   532  func shellQuote(s string) string {
   533  	var b bytes.Buffer
   534  	b.WriteByte('\'')
   535  	for _, x := range []byte(s) {
   536  		if x == '\'' {
   537  			// Close the single quoted string, add an escaped single quote,
   538  			// and start another single quoted string.
   539  			b.WriteString(`'\''`)
   540  		} else {
   541  			b.WriteByte(x)
   542  		}
   543  	}
   544  	b.WriteByte('\'')
   545  	return b.String()
   546  }
   547  
   548  func batchEscape(s string) string {
   549  	var b bytes.Buffer
   550  	for _, x := range []byte(s) {
   551  		if x == '\r' || x == '\n' || (!unicode.IsGraphic(rune(x)) && !unicode.IsSpace(rune(x))) {
   552  			b.WriteRune(unicode.ReplacementChar)
   553  			continue
   554  		}
   555  		switch x {
   556  		case '%':
   557  			b.WriteString("%%")
   558  		case '<', '>', '|', '&', '^':
   559  			// These are special characters that need to be escaped with ^. See
   560  			// https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/set_1.
   561  			b.WriteByte('^')
   562  			b.WriteByte(x)
   563  		default:
   564  			b.WriteByte(x)
   565  		}
   566  	}
   567  	return b.String()
   568  }
   569  
   570  func printEnvAsJSON(env []cfg.EnvVar, onlyChanged bool) {
   571  	m := make(map[string]string)
   572  	for _, e := range env {
   573  		if e.Name == "TERM" {
   574  			continue
   575  		}
   576  		if onlyChanged && !e.Changed {
   577  			continue
   578  		}
   579  		m[e.Name] = e.Value
   580  	}
   581  	enc := json.NewEncoder(os.Stdout)
   582  	enc.SetIndent("", "\t")
   583  	if err := enc.Encode(m); err != nil {
   584  		base.Fatalf("go: %s", err)
   585  	}
   586  }
   587  
   588  func getOrigEnv(key string) string {
   589  	for _, v := range cfg.OrigEnv {
   590  		if v, found := strings.CutPrefix(v, key+"="); found {
   591  			return v
   592  		}
   593  	}
   594  	return ""
   595  }
   596  
   597  func checkEnvWrite(key, val string) error {
   598  	switch key {
   599  	case "GOEXE", "GOGCCFLAGS", "GOHOSTARCH", "GOHOSTOS", "GOMOD", "GOWORK", "GOTOOLDIR", "GOVERSION", "GOTELEMETRY", "GOTELEMETRYDIR":
   600  		return fmt.Errorf("%s cannot be modified", key)
   601  	case "GOENV", "GODEBUG":
   602  		return fmt.Errorf("%s can only be set using the OS environment", key)
   603  	}
   604  
   605  	// To catch typos and the like, check that we know the variable.
   606  	// If it's already in the env file, we assume it's known.
   607  	if !cfg.CanGetenv(key) {
   608  		return fmt.Errorf("unknown go command variable %s", key)
   609  	}
   610  
   611  	// Some variables can only have one of a few valid values. If set to an
   612  	// invalid value, the next cmd/go invocation might fail immediately,
   613  	// even 'go env -w' itself.
   614  	switch key {
   615  	case "GO111MODULE":
   616  		switch val {
   617  		case "", "auto", "on", "off":
   618  		default:
   619  			return fmt.Errorf("invalid %s value %q", key, val)
   620  		}
   621  	case "GOPATH":
   622  		if strings.HasPrefix(val, "~") {
   623  			return fmt.Errorf("GOPATH entry cannot start with shell metacharacter '~': %q", val)
   624  		}
   625  		if !filepath.IsAbs(val) && val != "" {
   626  			return fmt.Errorf("GOPATH entry is relative; must be absolute path: %q", val)
   627  		}
   628  	case "GOMODCACHE":
   629  		if !filepath.IsAbs(val) && val != "" {
   630  			return fmt.Errorf("GOMODCACHE entry is relative; must be absolute path: %q", val)
   631  		}
   632  	case "CC", "CXX":
   633  		if val == "" {
   634  			break
   635  		}
   636  		args, err := quoted.Split(val)
   637  		if err != nil {
   638  			return fmt.Errorf("invalid %s: %v", key, err)
   639  		}
   640  		if len(args) == 0 {
   641  			return fmt.Errorf("%s entry cannot contain only space", key)
   642  		}
   643  		if !filepath.IsAbs(args[0]) && args[0] != filepath.Base(args[0]) {
   644  			return fmt.Errorf("%s entry is relative; must be absolute path: %q", key, args[0])
   645  		}
   646  	}
   647  
   648  	if !utf8.ValidString(val) {
   649  		return fmt.Errorf("invalid UTF-8 in %s=... value", key)
   650  	}
   651  	if strings.Contains(val, "\x00") {
   652  		return fmt.Errorf("invalid NUL in %s=... value", key)
   653  	}
   654  	if strings.ContainsAny(val, "\v\r\n") {
   655  		return fmt.Errorf("invalid newline in %s=... value", key)
   656  	}
   657  	return nil
   658  }
   659  
   660  func readEnvFileLines(mustExist bool) []string {
   661  	file, _, err := cfg.EnvFile()
   662  	if file == "" {
   663  		if mustExist {
   664  			base.Fatalf("go: cannot find go env config: %v", err)
   665  		}
   666  		return nil
   667  	}
   668  	data, err := os.ReadFile(file)
   669  	if err != nil && (!os.IsNotExist(err) || mustExist) {
   670  		base.Fatalf("go: reading go env config: %v", err)
   671  	}
   672  	lines := strings.SplitAfter(string(data), "\n")
   673  	if lines[len(lines)-1] == "" {
   674  		lines = lines[:len(lines)-1]
   675  	} else {
   676  		lines[len(lines)-1] += "\n"
   677  	}
   678  	return lines
   679  }
   680  
   681  func updateEnvFile(add map[string]string, del map[string]bool) {
   682  	lines := readEnvFileLines(len(add) == 0)
   683  
   684  	// Delete all but last copy of any duplicated variables,
   685  	// since the last copy is the one that takes effect.
   686  	prev := make(map[string]int)
   687  	for l, line := range lines {
   688  		if key := lineToKey(line); key != "" {
   689  			if p, ok := prev[key]; ok {
   690  				lines[p] = ""
   691  			}
   692  			prev[key] = l
   693  		}
   694  	}
   695  
   696  	// Add variables (go env -w). Update existing lines in file if present, add to end otherwise.
   697  	for key, val := range add {
   698  		if p, ok := prev[key]; ok {
   699  			lines[p] = key + "=" + val + "\n"
   700  			delete(add, key)
   701  		}
   702  	}
   703  	for key, val := range add {
   704  		lines = append(lines, key+"="+val+"\n")
   705  	}
   706  
   707  	// Delete requested variables (go env -u).
   708  	for key := range del {
   709  		if p, ok := prev[key]; ok {
   710  			lines[p] = ""
   711  		}
   712  	}
   713  
   714  	// Sort runs of KEY=VALUE lines
   715  	// (that is, blocks of lines where blocks are separated
   716  	// by comments, blank lines, or invalid lines).
   717  	start := 0
   718  	for i := 0; i <= len(lines); i++ {
   719  		if i == len(lines) || lineToKey(lines[i]) == "" {
   720  			sortKeyValues(lines[start:i])
   721  			start = i + 1
   722  		}
   723  	}
   724  
   725  	file, _, err := cfg.EnvFile()
   726  	if file == "" {
   727  		base.Fatalf("go: cannot find go env config: %v", err)
   728  	}
   729  	data := []byte(strings.Join(lines, ""))
   730  	err = os.WriteFile(file, data, 0666)
   731  	if err != nil {
   732  		// Try creating directory.
   733  		os.MkdirAll(filepath.Dir(file), 0777)
   734  		err = os.WriteFile(file, data, 0666)
   735  		if err != nil {
   736  			base.Fatalf("go: writing go env config: %v", err)
   737  		}
   738  	}
   739  }
   740  
   741  // lineToKey returns the KEY part of the line KEY=VALUE or else an empty string.
   742  func lineToKey(line string) string {
   743  	i := strings.Index(line, "=")
   744  	if i < 0 || strings.Contains(line[:i], "#") {
   745  		return ""
   746  	}
   747  	return line[:i]
   748  }
   749  
   750  // sortKeyValues sorts a sequence of lines by key.
   751  // It differs from sort.Strings in that GO386= sorts after GO=.
   752  func sortKeyValues(lines []string) {
   753  	sort.Slice(lines, func(i, j int) bool {
   754  		return lineToKey(lines[i]) < lineToKey(lines[j])
   755  	})
   756  }
   757
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