github.com/c12o16h1/go/src@v0.0.0-20200114212001-5a151c0f00ed/os/exec/exec.go (about) 1 // Copyright 2009 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 exec runs external commands. It wraps os.StartProcess to make it 6 // easier to remap stdin and stdout, connect I/O with pipes, and do other 7 // adjustments. 8 // 9 // Unlike the "system" library call from C and other languages, the 10 // os/exec package intentionally does not invoke the system shell and 11 // does not expand any glob patterns or handle other expansions, 12 // pipelines, or redirections typically done by shells. The package 13 // behaves more like C's "exec" family of functions. To expand glob 14 // patterns, either call the shell directly, taking care to escape any 15 // dangerous input, or use the path/filepath package's Glob function. 16 // To expand environment variables, use package os's ExpandEnv. 17 // 18 // Note that the examples in this package assume a Unix system. 19 // They may not run on Windows, and they do not run in the Go Playground 20 // used by golang.org and godoc.org. 21 package exec 22 23 import ( 24 "bytes" 25 "context" 26 "errors" 27 "io" 28 "os" 29 "path/filepath" 30 "runtime" 31 "strconv" 32 "strings" 33 "sync" 34 "syscall" 35 ) 36 37 // Error is returned by LookPath when it fails to classify a file as an 38 // executable. 39 type Error struct { 40 // Name is the file name for which the error occurred. 41 Name string 42 // Err is the underlying error. 43 Err error 44 } 45 46 func (e *Error) Error() string { 47 return "exec: " + strconv.Quote(e.Name) + ": " + e.Err.Error() 48 } 49 50 func (e *Error) Unwrap() error { return e.Err } 51 52 // Cmd represents an external command being prepared or run. 53 // 54 // A Cmd cannot be reused after calling its Run, Output or CombinedOutput 55 // methods. 56 type Cmd struct { 57 // Path is the path of the command to run. 58 // 59 // This is the only field that must be set to a non-zero 60 // value. If Path is relative, it is evaluated relative 61 // to Dir. 62 Path string 63 64 // Args holds command line arguments, including the command as Args[0]. 65 // If the Args field is empty or nil, Run uses {Path}. 66 // 67 // In typical use, both Path and Args are set by calling Command. 68 Args []string 69 70 // Env specifies the environment of the process. 71 // Each entry is of the form "key=value". 72 // If Env is nil, the new process uses the current process's 73 // environment. 74 // If Env contains duplicate environment keys, only the last 75 // value in the slice for each duplicate key is used. 76 // As a special case on Windows, SYSTEMROOT is always added if 77 // missing and not explicitly set to the empty string. 78 Env []string 79 80 // Dir specifies the working directory of the command. 81 // If Dir is the empty string, Run runs the command in the 82 // calling process's current directory. 83 Dir string 84 85 // Stdin specifies the process's standard input. 86 // 87 // If Stdin is nil, the process reads from the null device (os.DevNull). 88 // 89 // If Stdin is an *os.File, the process's standard input is connected 90 // directly to that file. 91 // 92 // Otherwise, during the execution of the command a separate 93 // goroutine reads from Stdin and delivers that data to the command 94 // over a pipe. In this case, Wait does not complete until the goroutine 95 // stops copying, either because it has reached the end of Stdin 96 // (EOF or a read error) or because writing to the pipe returned an error. 97 Stdin io.Reader 98 99 // Stdout and Stderr specify the process's standard output and error. 100 // 101 // If either is nil, Run connects the corresponding file descriptor 102 // to the null device (os.DevNull). 103 // 104 // If either is an *os.File, the corresponding output from the process 105 // is connected directly to that file. 106 // 107 // Otherwise, during the execution of the command a separate goroutine 108 // reads from the process over a pipe and delivers that data to the 109 // corresponding Writer. In this case, Wait does not complete until the 110 // goroutine reaches EOF or encounters an error. 111 // 112 // If Stdout and Stderr are the same writer, and have a type that can 113 // be compared with ==, at most one goroutine at a time will call Write. 114 Stdout io.Writer 115 Stderr io.Writer 116 117 // ExtraFiles specifies additional open files to be inherited by the 118 // new process. It does not include standard input, standard output, or 119 // standard error. If non-nil, entry i becomes file descriptor 3+i. 120 // 121 // ExtraFiles is not supported on Windows. 122 ExtraFiles []*os.File 123 124 // SysProcAttr holds optional, operating system-specific attributes. 125 // Run passes it to os.StartProcess as the os.ProcAttr's Sys field. 126 SysProcAttr *syscall.SysProcAttr 127 128 // Process is the underlying process, once started. 129 Process *os.Process 130 131 // ProcessState contains information about an exited process, 132 // available after a call to Wait or Run. 133 ProcessState *os.ProcessState 134 135 ctx context.Context // nil means none 136 lookPathErr error // LookPath error, if any. 137 finished bool // when Wait was called 138 childFiles []*os.File 139 closeAfterStart []io.Closer 140 closeAfterWait []io.Closer 141 goroutine []func() error 142 errch chan error // one send per goroutine 143 waitDone chan struct{} 144 } 145 146 // Command returns the Cmd struct to execute the named program with 147 // the given arguments. 148 // 149 // It sets only the Path and Args in the returned structure. 150 // 151 // If name contains no path separators, Command uses LookPath to 152 // resolve name to a complete path if possible. Otherwise it uses name 153 // directly as Path. 154 // 155 // The returned Cmd's Args field is constructed from the command name 156 // followed by the elements of arg, so arg should not include the 157 // command name itself. For example, Command("echo", "hello"). 158 // Args[0] is always name, not the possibly resolved Path. 159 // 160 // On Windows, processes receive the whole command line as a single string 161 // and do their own parsing. Command combines and quotes Args into a command 162 // line string with an algorithm compatible with applications using 163 // CommandLineToArgvW (which is the most common way). Notable exceptions are 164 // msiexec.exe and cmd.exe (and thus, all batch files), which have a different 165 // unquoting algorithm. In these or other similar cases, you can do the 166 // quoting yourself and provide the full command line in SysProcAttr.CmdLine, 167 // leaving Args empty. 168 func Command(name string, arg ...string) *Cmd { 169 cmd := &Cmd{ 170 Path: name, 171 Args: append([]string{name}, arg...), 172 } 173 if filepath.Base(name) == name { 174 if lp, err := LookPath(name); err != nil { 175 cmd.lookPathErr = err 176 } else { 177 cmd.Path = lp 178 } 179 } 180 return cmd 181 } 182 183 // CommandContext is like Command but includes a context. 184 // 185 // The provided context is used to kill the process (by calling 186 // os.Process.Kill) if the context becomes done before the command 187 // completes on its own. 188 func CommandContext(ctx context.Context, name string, arg ...string) *Cmd { 189 if ctx == nil { 190 panic("nil Context") 191 } 192 cmd := Command(name, arg...) 193 cmd.ctx = ctx 194 return cmd 195 } 196 197 // String returns a human-readable description of c. 198 // It is intended only for debugging. 199 // In particular, it is not suitable for use as input to a shell. 200 // The output of String may vary across Go releases. 201 func (c *Cmd) String() string { 202 if c.lookPathErr != nil { 203 // failed to resolve path; report the original requested path (plus args) 204 return strings.Join(c.Args, " ") 205 } 206 // report the exact executable path (plus args) 207 b := new(strings.Builder) 208 b.WriteString(c.Path) 209 for _, a := range c.Args[1:] { 210 b.WriteByte(' ') 211 b.WriteString(a) 212 } 213 return b.String() 214 } 215 216 // interfaceEqual protects against panics from doing equality tests on 217 // two interfaces with non-comparable underlying types. 218 func interfaceEqual(a, b interface{}) bool { 219 defer func() { 220 recover() 221 }() 222 return a == b 223 } 224 225 func (c *Cmd) envv() []string { 226 if c.Env != nil { 227 return c.Env 228 } 229 return os.Environ() 230 } 231 232 func (c *Cmd) argv() []string { 233 if len(c.Args) > 0 { 234 return c.Args 235 } 236 return []string{c.Path} 237 } 238 239 // skipStdinCopyError optionally specifies a function which reports 240 // whether the provided stdin copy error should be ignored. 241 var skipStdinCopyError func(error) bool 242 243 func (c *Cmd) stdin() (f *os.File, err error) { 244 if c.Stdin == nil { 245 f, err = os.Open(os.DevNull) 246 if err != nil { 247 return 248 } 249 c.closeAfterStart = append(c.closeAfterStart, f) 250 return 251 } 252 253 if f, ok := c.Stdin.(*os.File); ok { 254 return f, nil 255 } 256 257 pr, pw, err := os.Pipe() 258 if err != nil { 259 return 260 } 261 262 c.closeAfterStart = append(c.closeAfterStart, pr) 263 c.closeAfterWait = append(c.closeAfterWait, pw) 264 c.goroutine = append(c.goroutine, func() error { 265 _, err := io.Copy(pw, c.Stdin) 266 if skip := skipStdinCopyError; skip != nil && skip(err) { 267 err = nil 268 } 269 if err1 := pw.Close(); err == nil { 270 err = err1 271 } 272 return err 273 }) 274 return pr, nil 275 } 276 277 func (c *Cmd) stdout() (f *os.File, err error) { 278 return c.writerDescriptor(c.Stdout) 279 } 280 281 func (c *Cmd) stderr() (f *os.File, err error) { 282 if c.Stderr != nil && interfaceEqual(c.Stderr, c.Stdout) { 283 return c.childFiles[1], nil 284 } 285 return c.writerDescriptor(c.Stderr) 286 } 287 288 func (c *Cmd) writerDescriptor(w io.Writer) (f *os.File, err error) { 289 if w == nil { 290 f, err = os.OpenFile(os.DevNull, os.O_WRONLY, 0) 291 if err != nil { 292 return 293 } 294 c.closeAfterStart = append(c.closeAfterStart, f) 295 return 296 } 297 298 if f, ok := w.(*os.File); ok { 299 return f, nil 300 } 301 302 pr, pw, err := os.Pipe() 303 if err != nil { 304 return 305 } 306 307 c.closeAfterStart = append(c.closeAfterStart, pw) 308 c.closeAfterWait = append(c.closeAfterWait, pr) 309 c.goroutine = append(c.goroutine, func() error { 310 _, err := io.Copy(w, pr) 311 pr.Close() // in case io.Copy stopped due to write error 312 return err 313 }) 314 return pw, nil 315 } 316 317 func (c *Cmd) closeDescriptors(closers []io.Closer) { 318 for _, fd := range closers { 319 fd.Close() 320 } 321 } 322 323 // Run starts the specified command and waits for it to complete. 324 // 325 // The returned error is nil if the command runs, has no problems 326 // copying stdin, stdout, and stderr, and exits with a zero exit 327 // status. 328 // 329 // If the command starts but does not complete successfully, the error is of 330 // type *ExitError. Other error types may be returned for other situations. 331 // 332 // If the calling goroutine has locked the operating system thread 333 // with runtime.LockOSThread and modified any inheritable OS-level 334 // thread state (for example, Linux or Plan 9 name spaces), the new 335 // process will inherit the caller's thread state. 336 func (c *Cmd) Run() error { 337 if err := c.Start(); err != nil { 338 return err 339 } 340 return c.Wait() 341 } 342 343 // lookExtensions finds windows executable by its dir and path. 344 // It uses LookPath to try appropriate extensions. 345 // lookExtensions does not search PATH, instead it converts `prog` into `.\prog`. 346 func lookExtensions(path, dir string) (string, error) { 347 if filepath.Base(path) == path { 348 path = filepath.Join(".", path) 349 } 350 if dir == "" { 351 return LookPath(path) 352 } 353 if filepath.VolumeName(path) != "" { 354 return LookPath(path) 355 } 356 if len(path) > 1 && os.IsPathSeparator(path[0]) { 357 return LookPath(path) 358 } 359 dirandpath := filepath.Join(dir, path) 360 // We assume that LookPath will only add file extension. 361 lp, err := LookPath(dirandpath) 362 if err != nil { 363 return "", err 364 } 365 ext := strings.TrimPrefix(lp, dirandpath) 366 return path + ext, nil 367 } 368 369 // Start starts the specified command but does not wait for it to complete. 370 // 371 // If Start returns successfully, the c.Process field will be set. 372 // 373 // The Wait method will return the exit code and release associated resources 374 // once the command exits. 375 func (c *Cmd) Start() error { 376 if c.lookPathErr != nil { 377 c.closeDescriptors(c.closeAfterStart) 378 c.closeDescriptors(c.closeAfterWait) 379 return c.lookPathErr 380 } 381 if runtime.GOOS == "windows" { 382 lp, err := lookExtensions(c.Path, c.Dir) 383 if err != nil { 384 c.closeDescriptors(c.closeAfterStart) 385 c.closeDescriptors(c.closeAfterWait) 386 return err 387 } 388 c.Path = lp 389 } 390 if c.Process != nil { 391 return errors.New("exec: already started") 392 } 393 if c.ctx != nil { 394 select { 395 case <-c.ctx.Done(): 396 c.closeDescriptors(c.closeAfterStart) 397 c.closeDescriptors(c.closeAfterWait) 398 return c.ctx.Err() 399 default: 400 } 401 } 402 403 c.childFiles = make([]*os.File, 0, 3+len(c.ExtraFiles)) 404 type F func(*Cmd) (*os.File, error) 405 for _, setupFd := range []F{(*Cmd).stdin, (*Cmd).stdout, (*Cmd).stderr} { 406 fd, err := setupFd(c) 407 if err != nil { 408 c.closeDescriptors(c.closeAfterStart) 409 c.closeDescriptors(c.closeAfterWait) 410 return err 411 } 412 c.childFiles = append(c.childFiles, fd) 413 } 414 c.childFiles = append(c.childFiles, c.ExtraFiles...) 415 416 var err error 417 c.Process, err = os.StartProcess(c.Path, c.argv(), &os.ProcAttr{ 418 Dir: c.Dir, 419 Files: c.childFiles, 420 Env: addCriticalEnv(dedupEnv(c.envv())), 421 Sys: c.SysProcAttr, 422 }) 423 if err != nil { 424 c.closeDescriptors(c.closeAfterStart) 425 c.closeDescriptors(c.closeAfterWait) 426 return err 427 } 428 429 c.closeDescriptors(c.closeAfterStart) 430 431 // Don't allocate the channel unless there are goroutines to fire. 432 if len(c.goroutine) > 0 { 433 c.errch = make(chan error, len(c.goroutine)) 434 for _, fn := range c.goroutine { 435 go func(fn func() error) { 436 c.errch <- fn() 437 }(fn) 438 } 439 } 440 441 if c.ctx != nil { 442 c.waitDone = make(chan struct{}) 443 go func() { 444 select { 445 case <-c.ctx.Done(): 446 c.Process.Kill() 447 case <-c.waitDone: 448 } 449 }() 450 } 451 452 return nil 453 } 454 455 // An ExitError reports an unsuccessful exit by a command. 456 type ExitError struct { 457 *os.ProcessState 458 459 // Stderr holds a subset of the standard error output from the 460 // Cmd.Output method if standard error was not otherwise being 461 // collected. 462 // 463 // If the error output is long, Stderr may contain only a prefix 464 // and suffix of the output, with the middle replaced with 465 // text about the number of omitted bytes. 466 // 467 // Stderr is provided for debugging, for inclusion in error messages. 468 // Users with other needs should redirect Cmd.Stderr as needed. 469 Stderr []byte 470 } 471 472 func (e *ExitError) Error() string { 473 return e.ProcessState.String() 474 } 475 476 // Wait waits for the command to exit and waits for any copying to 477 // stdin or copying from stdout or stderr to complete. 478 // 479 // The command must have been started by Start. 480 // 481 // The returned error is nil if the command runs, has no problems 482 // copying stdin, stdout, and stderr, and exits with a zero exit 483 // status. 484 // 485 // If the command fails to run or doesn't complete successfully, the 486 // error is of type *ExitError. Other error types may be 487 // returned for I/O problems. 488 // 489 // If any of c.Stdin, c.Stdout or c.Stderr are not an *os.File, Wait also waits 490 // for the respective I/O loop copying to or from the process to complete. 491 // 492 // Wait releases any resources associated with the Cmd. 493 func (c *Cmd) Wait() error { 494 if c.Process == nil { 495 return errors.New("exec: not started") 496 } 497 if c.finished { 498 return errors.New("exec: Wait was already called") 499 } 500 c.finished = true 501 502 state, err := c.Process.Wait() 503 if c.waitDone != nil { 504 close(c.waitDone) 505 } 506 c.ProcessState = state 507 508 var copyError error 509 for range c.goroutine { 510 if err := <-c.errch; err != nil && copyError == nil { 511 copyError = err 512 } 513 } 514 515 c.closeDescriptors(c.closeAfterWait) 516 517 if err != nil { 518 return err 519 } else if !state.Success() { 520 return &ExitError{ProcessState: state} 521 } 522 523 return copyError 524 } 525 526 // Output runs the command and returns its standard output. 527 // Any returned error will usually be of type *ExitError. 528 // If c.Stderr was nil, Output populates ExitError.Stderr. 529 func (c *Cmd) Output() ([]byte, error) { 530 if c.Stdout != nil { 531 return nil, errors.New("exec: Stdout already set") 532 } 533 var stdout bytes.Buffer 534 c.Stdout = &stdout 535 536 captureErr := c.Stderr == nil 537 if captureErr { 538 c.Stderr = &prefixSuffixSaver{N: 32 << 10} 539 } 540 541 err := c.Run() 542 if err != nil && captureErr { 543 if ee, ok := err.(*ExitError); ok { 544 ee.Stderr = c.Stderr.(*prefixSuffixSaver).Bytes() 545 } 546 } 547 return stdout.Bytes(), err 548 } 549 550 // CombinedOutput runs the command and returns its combined standard 551 // output and standard error. 552 func (c *Cmd) CombinedOutput() ([]byte, error) { 553 if c.Stdout != nil { 554 return nil, errors.New("exec: Stdout already set") 555 } 556 if c.Stderr != nil { 557 return nil, errors.New("exec: Stderr already set") 558 } 559 var b bytes.Buffer 560 c.Stdout = &b 561 c.Stderr = &b 562 err := c.Run() 563 return b.Bytes(), err 564 } 565 566 // StdinPipe returns a pipe that will be connected to the command's 567 // standard input when the command starts. 568 // The pipe will be closed automatically after Wait sees the command exit. 569 // A caller need only call Close to force the pipe to close sooner. 570 // For example, if the command being run will not exit until standard input 571 // is closed, the caller must close the pipe. 572 func (c *Cmd) StdinPipe() (io.WriteCloser, error) { 573 if c.Stdin != nil { 574 return nil, errors.New("exec: Stdin already set") 575 } 576 if c.Process != nil { 577 return nil, errors.New("exec: StdinPipe after process started") 578 } 579 pr, pw, err := os.Pipe() 580 if err != nil { 581 return nil, err 582 } 583 c.Stdin = pr 584 c.closeAfterStart = append(c.closeAfterStart, pr) 585 wc := &closeOnce{File: pw} 586 c.closeAfterWait = append(c.closeAfterWait, wc) 587 return wc, nil 588 } 589 590 type closeOnce struct { 591 *os.File 592 593 once sync.Once 594 err error 595 } 596 597 func (c *closeOnce) Close() error { 598 c.once.Do(c.close) 599 return c.err 600 } 601 602 func (c *closeOnce) close() { 603 c.err = c.File.Close() 604 } 605 606 // StdoutPipe returns a pipe that will be connected to the command's 607 // standard output when the command starts. 608 // 609 // Wait will close the pipe after seeing the command exit, so most callers 610 // need not close the pipe themselves. It is thus incorrect to call Wait 611 // before all reads from the pipe have completed. 612 // For the same reason, it is incorrect to call Run when using StdoutPipe. 613 // See the example for idiomatic usage. 614 func (c *Cmd) StdoutPipe() (io.ReadCloser, error) { 615 if c.Stdout != nil { 616 return nil, errors.New("exec: Stdout already set") 617 } 618 if c.Process != nil { 619 return nil, errors.New("exec: StdoutPipe after process started") 620 } 621 pr, pw, err := os.Pipe() 622 if err != nil { 623 return nil, err 624 } 625 c.Stdout = pw 626 c.closeAfterStart = append(c.closeAfterStart, pw) 627 c.closeAfterWait = append(c.closeAfterWait, pr) 628 return pr, nil 629 } 630 631 // StderrPipe returns a pipe that will be connected to the command's 632 // standard error when the command starts. 633 // 634 // Wait will close the pipe after seeing the command exit, so most callers 635 // need not close the pipe themselves. It is thus incorrect to call Wait 636 // before all reads from the pipe have completed. 637 // For the same reason, it is incorrect to use Run when using StderrPipe. 638 // See the StdoutPipe example for idiomatic usage. 639 func (c *Cmd) StderrPipe() (io.ReadCloser, error) { 640 if c.Stderr != nil { 641 return nil, errors.New("exec: Stderr already set") 642 } 643 if c.Process != nil { 644 return nil, errors.New("exec: StderrPipe after process started") 645 } 646 pr, pw, err := os.Pipe() 647 if err != nil { 648 return nil, err 649 } 650 c.Stderr = pw 651 c.closeAfterStart = append(c.closeAfterStart, pw) 652 c.closeAfterWait = append(c.closeAfterWait, pr) 653 return pr, nil 654 } 655 656 // prefixSuffixSaver is an io.Writer which retains the first N bytes 657 // and the last N bytes written to it. The Bytes() methods reconstructs 658 // it with a pretty error message. 659 type prefixSuffixSaver struct { 660 N int // max size of prefix or suffix 661 prefix []byte 662 suffix []byte // ring buffer once len(suffix) == N 663 suffixOff int // offset to write into suffix 664 skipped int64 665 666 // TODO(bradfitz): we could keep one large []byte and use part of it for 667 // the prefix, reserve space for the '... Omitting N bytes ...' message, 668 // then the ring buffer suffix, and just rearrange the ring buffer 669 // suffix when Bytes() is called, but it doesn't seem worth it for 670 // now just for error messages. It's only ~64KB anyway. 671 } 672 673 func (w *prefixSuffixSaver) Write(p []byte) (n int, err error) { 674 lenp := len(p) 675 p = w.fill(&w.prefix, p) 676 677 // Only keep the last w.N bytes of suffix data. 678 if overage := len(p) - w.N; overage > 0 { 679 p = p[overage:] 680 w.skipped += int64(overage) 681 } 682 p = w.fill(&w.suffix, p) 683 684 // w.suffix is full now if p is non-empty. Overwrite it in a circle. 685 for len(p) > 0 { // 0, 1, or 2 iterations. 686 n := copy(w.suffix[w.suffixOff:], p) 687 p = p[n:] 688 w.skipped += int64(n) 689 w.suffixOff += n 690 if w.suffixOff == w.N { 691 w.suffixOff = 0 692 } 693 } 694 return lenp, nil 695 } 696 697 // fill appends up to len(p) bytes of p to *dst, such that *dst does not 698 // grow larger than w.N. It returns the un-appended suffix of p. 699 func (w *prefixSuffixSaver) fill(dst *[]byte, p []byte) (pRemain []byte) { 700 if remain := w.N - len(*dst); remain > 0 { 701 add := minInt(len(p), remain) 702 *dst = append(*dst, p[:add]...) 703 p = p[add:] 704 } 705 return p 706 } 707 708 func (w *prefixSuffixSaver) Bytes() []byte { 709 if w.suffix == nil { 710 return w.prefix 711 } 712 if w.skipped == 0 { 713 return append(w.prefix, w.suffix...) 714 } 715 var buf bytes.Buffer 716 buf.Grow(len(w.prefix) + len(w.suffix) + 50) 717 buf.Write(w.prefix) 718 buf.WriteString("\n... omitting ") 719 buf.WriteString(strconv.FormatInt(w.skipped, 10)) 720 buf.WriteString(" bytes ...\n") 721 buf.Write(w.suffix[w.suffixOff:]) 722 buf.Write(w.suffix[:w.suffixOff]) 723 return buf.Bytes() 724 } 725 726 func minInt(a, b int) int { 727 if a < b { 728 return a 729 } 730 return b 731 } 732 733 // dedupEnv returns a copy of env with any duplicates removed, in favor of 734 // later values. 735 // Items not of the normal environment "key=value" form are preserved unchanged. 736 func dedupEnv(env []string) []string { 737 return dedupEnvCase(runtime.GOOS == "windows", env) 738 } 739 740 // dedupEnvCase is dedupEnv with a case option for testing. 741 // If caseInsensitive is true, the case of keys is ignored. 742 func dedupEnvCase(caseInsensitive bool, env []string) []string { 743 out := make([]string, 0, len(env)) 744 saw := make(map[string]int, len(env)) // key => index into out 745 for _, kv := range env { 746 eq := strings.Index(kv, "=") 747 if eq < 0 { 748 out = append(out, kv) 749 continue 750 } 751 k := kv[:eq] 752 if caseInsensitive { 753 k = strings.ToLower(k) 754 } 755 if dupIdx, isDup := saw[k]; isDup { 756 out[dupIdx] = kv 757 continue 758 } 759 saw[k] = len(out) 760 out = append(out, kv) 761 } 762 return out 763 } 764 765 // addCriticalEnv adds any critical environment variables that are required 766 // (or at least almost always required) on the operating system. 767 // Currently this is only used for Windows. 768 func addCriticalEnv(env []string) []string { 769 if runtime.GOOS != "windows" { 770 return env 771 } 772 for _, kv := range env { 773 eq := strings.Index(kv, "=") 774 if eq < 0 { 775 continue 776 } 777 k := kv[:eq] 778 if strings.EqualFold(k, "SYSTEMROOT") { 779 // We already have it. 780 return env 781 } 782 } 783 return append(env, "SYSTEMROOT="+os.Getenv("SYSTEMROOT")) 784 }