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 // It is non-nil everywhere but Plan 9, which lacks EPIPE. See exec_posix.go. 242 var skipStdinCopyError func(error) bool 243 244 func (c *Cmd) stdin() (f *os.File, err error) { 245 if c.Stdin == nil { 246 f, err = os.Open(os.DevNull) 247 if err != nil { 248 return 249 } 250 c.closeAfterStart = append(c.closeAfterStart, f) 251 return 252 } 253 254 if f, ok := c.Stdin.(*os.File); ok { 255 return f, nil 256 } 257 258 pr, pw, err := os.Pipe() 259 if err != nil { 260 return 261 } 262 263 c.closeAfterStart = append(c.closeAfterStart, pr) 264 c.closeAfterWait = append(c.closeAfterWait, pw) 265 c.goroutine = append(c.goroutine, func() error { 266 _, err := io.Copy(pw, c.Stdin) 267 if skip := skipStdinCopyError; skip != nil && skip(err) { 268 err = nil 269 } 270 if err1 := pw.Close(); err == nil { 271 err = err1 272 } 273 return err 274 }) 275 return pr, nil 276 } 277 278 func (c *Cmd) stdout() (f *os.File, err error) { 279 return c.writerDescriptor(c.Stdout) 280 } 281 282 func (c *Cmd) stderr() (f *os.File, err error) { 283 if c.Stderr != nil && interfaceEqual(c.Stderr, c.Stdout) { 284 return c.childFiles[1], nil 285 } 286 return c.writerDescriptor(c.Stderr) 287 } 288 289 func (c *Cmd) writerDescriptor(w io.Writer) (f *os.File, err error) { 290 if w == nil { 291 f, err = os.OpenFile(os.DevNull, os.O_WRONLY, 0) 292 if err != nil { 293 return 294 } 295 c.closeAfterStart = append(c.closeAfterStart, f) 296 return 297 } 298 299 if f, ok := w.(*os.File); ok { 300 return f, nil 301 } 302 303 pr, pw, err := os.Pipe() 304 if err != nil { 305 return 306 } 307 308 c.closeAfterStart = append(c.closeAfterStart, pw) 309 c.closeAfterWait = append(c.closeAfterWait, pr) 310 c.goroutine = append(c.goroutine, func() error { 311 _, err := io.Copy(w, pr) 312 pr.Close() // in case io.Copy stopped due to write error 313 return err 314 }) 315 return pw, nil 316 } 317 318 func (c *Cmd) closeDescriptors(closers []io.Closer) { 319 for _, fd := range closers { 320 fd.Close() 321 } 322 } 323 324 // Run starts the specified command and waits for it to complete. 325 // 326 // The returned error is nil if the command runs, has no problems 327 // copying stdin, stdout, and stderr, and exits with a zero exit 328 // status. 329 // 330 // If the command starts but does not complete successfully, the error is of 331 // type *ExitError. Other error types may be returned for other situations. 332 // 333 // If the calling goroutine has locked the operating system thread 334 // with runtime.LockOSThread and modified any inheritable OS-level 335 // thread state (for example, Linux or Plan 9 name spaces), the new 336 // process will inherit the caller's thread state. 337 func (c *Cmd) Run() error { 338 if err := c.Start(); err != nil { 339 return err 340 } 341 return c.Wait() 342 } 343 344 // lookExtensions finds windows executable by its dir and path. 345 // It uses LookPath to try appropriate extensions. 346 // lookExtensions does not search PATH, instead it converts `prog` into `.\prog`. 347 func lookExtensions(path, dir string) (string, error) { 348 if filepath.Base(path) == path { 349 path = filepath.Join(".", path) 350 } 351 if dir == "" { 352 return LookPath(path) 353 } 354 if filepath.VolumeName(path) != "" { 355 return LookPath(path) 356 } 357 if len(path) > 1 && os.IsPathSeparator(path[0]) { 358 return LookPath(path) 359 } 360 dirandpath := filepath.Join(dir, path) 361 // We assume that LookPath will only add file extension. 362 lp, err := LookPath(dirandpath) 363 if err != nil { 364 return "", err 365 } 366 ext := strings.TrimPrefix(lp, dirandpath) 367 return path + ext, nil 368 } 369 370 // Start starts the specified command but does not wait for it to complete. 371 // 372 // The Wait method will return the exit code and release associated resources 373 // once the command exits. 374 func (c *Cmd) Start() error { 375 if c.lookPathErr != nil { 376 c.closeDescriptors(c.closeAfterStart) 377 c.closeDescriptors(c.closeAfterWait) 378 return c.lookPathErr 379 } 380 if runtime.GOOS == "windows" { 381 lp, err := lookExtensions(c.Path, c.Dir) 382 if err != nil { 383 c.closeDescriptors(c.closeAfterStart) 384 c.closeDescriptors(c.closeAfterWait) 385 return err 386 } 387 c.Path = lp 388 } 389 if c.Process != nil { 390 return errors.New("exec: already started") 391 } 392 if c.ctx != nil { 393 select { 394 case <-c.ctx.Done(): 395 c.closeDescriptors(c.closeAfterStart) 396 c.closeDescriptors(c.closeAfterWait) 397 return c.ctx.Err() 398 default: 399 } 400 } 401 402 c.childFiles = make([]*os.File, 0, 3+len(c.ExtraFiles)) 403 type F func(*Cmd) (*os.File, error) 404 for _, setupFd := range []F{(*Cmd).stdin, (*Cmd).stdout, (*Cmd).stderr} { 405 fd, err := setupFd(c) 406 if err != nil { 407 c.closeDescriptors(c.closeAfterStart) 408 c.closeDescriptors(c.closeAfterWait) 409 return err 410 } 411 c.childFiles = append(c.childFiles, fd) 412 } 413 c.childFiles = append(c.childFiles, c.ExtraFiles...) 414 415 var err error 416 c.Process, err = os.StartProcess(c.Path, c.argv(), &os.ProcAttr{ 417 Dir: c.Dir, 418 Files: c.childFiles, 419 Env: addCriticalEnv(dedupEnv(c.envv())), 420 Sys: c.SysProcAttr, 421 }) 422 if err != nil { 423 c.closeDescriptors(c.closeAfterStart) 424 c.closeDescriptors(c.closeAfterWait) 425 return err 426 } 427 428 c.closeDescriptors(c.closeAfterStart) 429 430 // Don't allocate the channel unless there are goroutines to fire. 431 if len(c.goroutine) > 0 { 432 c.errch = make(chan error, len(c.goroutine)) 433 for _, fn := range c.goroutine { 434 go func(fn func() error) { 435 c.errch <- fn() 436 }(fn) 437 } 438 } 439 440 if c.ctx != nil { 441 c.waitDone = make(chan struct{}) 442 go func() { 443 select { 444 case <-c.ctx.Done(): 445 c.Process.Kill() 446 case <-c.waitDone: 447 } 448 }() 449 } 450 451 return nil 452 } 453 454 // An ExitError reports an unsuccessful exit by a command. 455 type ExitError struct { 456 *os.ProcessState 457 458 // Stderr holds a subset of the standard error output from the 459 // Cmd.Output method if standard error was not otherwise being 460 // collected. 461 // 462 // If the error output is long, Stderr may contain only a prefix 463 // and suffix of the output, with the middle replaced with 464 // text about the number of omitted bytes. 465 // 466 // Stderr is provided for debugging, for inclusion in error messages. 467 // Users with other needs should redirect Cmd.Stderr as needed. 468 Stderr []byte 469 } 470 471 func (e *ExitError) Error() string { 472 return e.ProcessState.String() 473 } 474 475 // Wait waits for the command to exit and waits for any copying to 476 // stdin or copying from stdout or stderr to complete. 477 // 478 // The command must have been started by Start. 479 // 480 // The returned error is nil if the command runs, has no problems 481 // copying stdin, stdout, and stderr, and exits with a zero exit 482 // status. 483 // 484 // If the command fails to run or doesn't complete successfully, the 485 // error is of type *ExitError. Other error types may be 486 // returned for I/O problems. 487 // 488 // If any of c.Stdin, c.Stdout or c.Stderr are not an *os.File, Wait also waits 489 // for the respective I/O loop copying to or from the process to complete. 490 // 491 // Wait releases any resources associated with the Cmd. 492 func (c *Cmd) Wait() error { 493 if c.Process == nil { 494 return errors.New("exec: not started") 495 } 496 if c.finished { 497 return errors.New("exec: Wait was already called") 498 } 499 c.finished = true 500 501 state, err := c.Process.Wait() 502 if c.waitDone != nil { 503 close(c.waitDone) 504 } 505 c.ProcessState = state 506 507 var copyError error 508 for range c.goroutine { 509 if err := <-c.errch; err != nil && copyError == nil { 510 copyError = err 511 } 512 } 513 514 c.closeDescriptors(c.closeAfterWait) 515 516 if err != nil { 517 return err 518 } else if !state.Success() { 519 return &ExitError{ProcessState: state} 520 } 521 522 return copyError 523 } 524 525 // Output runs the command and returns its standard output. 526 // Any returned error will usually be of type *ExitError. 527 // If c.Stderr was nil, Output populates ExitError.Stderr. 528 func (c *Cmd) Output() ([]byte, error) { 529 if c.Stdout != nil { 530 return nil, errors.New("exec: Stdout already set") 531 } 532 var stdout bytes.Buffer 533 c.Stdout = &stdout 534 535 captureErr := c.Stderr == nil 536 if captureErr { 537 c.Stderr = &prefixSuffixSaver{N: 32 << 10} 538 } 539 540 err := c.Run() 541 if err != nil && captureErr { 542 if ee, ok := err.(*ExitError); ok { 543 ee.Stderr = c.Stderr.(*prefixSuffixSaver).Bytes() 544 } 545 } 546 return stdout.Bytes(), err 547 } 548 549 // CombinedOutput runs the command and returns its combined standard 550 // output and standard error. 551 func (c *Cmd) CombinedOutput() ([]byte, error) { 552 if c.Stdout != nil { 553 return nil, errors.New("exec: Stdout already set") 554 } 555 if c.Stderr != nil { 556 return nil, errors.New("exec: Stderr already set") 557 } 558 var b bytes.Buffer 559 c.Stdout = &b 560 c.Stderr = &b 561 err := c.Run() 562 return b.Bytes(), err 563 } 564 565 // StdinPipe returns a pipe that will be connected to the command's 566 // standard input when the command starts. 567 // The pipe will be closed automatically after Wait sees the command exit. 568 // A caller need only call Close to force the pipe to close sooner. 569 // For example, if the command being run will not exit until standard input 570 // is closed, the caller must close the pipe. 571 func (c *Cmd) StdinPipe() (io.WriteCloser, error) { 572 if c.Stdin != nil { 573 return nil, errors.New("exec: Stdin already set") 574 } 575 if c.Process != nil { 576 return nil, errors.New("exec: StdinPipe after process started") 577 } 578 pr, pw, err := os.Pipe() 579 if err != nil { 580 return nil, err 581 } 582 c.Stdin = pr 583 c.closeAfterStart = append(c.closeAfterStart, pr) 584 wc := &closeOnce{File: pw} 585 c.closeAfterWait = append(c.closeAfterWait, wc) 586 return wc, nil 587 } 588 589 type closeOnce struct { 590 *os.File 591 592 once sync.Once 593 err error 594 } 595 596 func (c *closeOnce) Close() error { 597 c.once.Do(c.close) 598 return c.err 599 } 600 601 func (c *closeOnce) close() { 602 c.err = c.File.Close() 603 } 604 605 // StdoutPipe returns a pipe that will be connected to the command's 606 // standard output when the command starts. 607 // 608 // Wait will close the pipe after seeing the command exit, so most callers 609 // need not close the pipe themselves; however, an implication is that 610 // it is incorrect to call Wait before all reads from the pipe have completed. 611 // For the same reason, it is incorrect to call Run when using StdoutPipe. 612 // See the example for idiomatic usage. 613 func (c *Cmd) StdoutPipe() (io.ReadCloser, error) { 614 if c.Stdout != nil { 615 return nil, errors.New("exec: Stdout already set") 616 } 617 if c.Process != nil { 618 return nil, errors.New("exec: StdoutPipe after process started") 619 } 620 pr, pw, err := os.Pipe() 621 if err != nil { 622 return nil, err 623 } 624 c.Stdout = pw 625 c.closeAfterStart = append(c.closeAfterStart, pw) 626 c.closeAfterWait = append(c.closeAfterWait, pr) 627 return pr, nil 628 } 629 630 // StderrPipe returns a pipe that will be connected to the command's 631 // standard error when the command starts. 632 // 633 // Wait will close the pipe after seeing the command exit, so most callers 634 // need not close the pipe themselves; however, an implication is that 635 // it is incorrect to call Wait before all reads from the pipe have completed. 636 // For the same reason, it is incorrect to use Run when using StderrPipe. 637 // See the StdoutPipe example for idiomatic usage. 638 func (c *Cmd) StderrPipe() (io.ReadCloser, error) { 639 if c.Stderr != nil { 640 return nil, errors.New("exec: Stderr already set") 641 } 642 if c.Process != nil { 643 return nil, errors.New("exec: StderrPipe after process started") 644 } 645 pr, pw, err := os.Pipe() 646 if err != nil { 647 return nil, err 648 } 649 c.Stderr = pw 650 c.closeAfterStart = append(c.closeAfterStart, pw) 651 c.closeAfterWait = append(c.closeAfterWait, pr) 652 return pr, nil 653 } 654 655 // prefixSuffixSaver is an io.Writer which retains the first N bytes 656 // and the last N bytes written to it. The Bytes() methods reconstructs 657 // it with a pretty error message. 658 type prefixSuffixSaver struct { 659 N int // max size of prefix or suffix 660 prefix []byte 661 suffix []byte // ring buffer once len(suffix) == N 662 suffixOff int // offset to write into suffix 663 skipped int64 664 665 // TODO(bradfitz): we could keep one large []byte and use part of it for 666 // the prefix, reserve space for the '... Omitting N bytes ...' message, 667 // then the ring buffer suffix, and just rearrange the ring buffer 668 // suffix when Bytes() is called, but it doesn't seem worth it for 669 // now just for error messages. It's only ~64KB anyway. 670 } 671 672 func (w *prefixSuffixSaver) Write(p []byte) (n int, err error) { 673 lenp := len(p) 674 p = w.fill(&w.prefix, p) 675 676 // Only keep the last w.N bytes of suffix data. 677 if overage := len(p) - w.N; overage > 0 { 678 p = p[overage:] 679 w.skipped += int64(overage) 680 } 681 p = w.fill(&w.suffix, p) 682 683 // w.suffix is full now if p is non-empty. Overwrite it in a circle. 684 for len(p) > 0 { // 0, 1, or 2 iterations. 685 n := copy(w.suffix[w.suffixOff:], p) 686 p = p[n:] 687 w.skipped += int64(n) 688 w.suffixOff += n 689 if w.suffixOff == w.N { 690 w.suffixOff = 0 691 } 692 } 693 return lenp, nil 694 } 695 696 // fill appends up to len(p) bytes of p to *dst, such that *dst does not 697 // grow larger than w.N. It returns the un-appended suffix of p. 698 func (w *prefixSuffixSaver) fill(dst *[]byte, p []byte) (pRemain []byte) { 699 if remain := w.N - len(*dst); remain > 0 { 700 add := minInt(len(p), remain) 701 *dst = append(*dst, p[:add]...) 702 p = p[add:] 703 } 704 return p 705 } 706 707 func (w *prefixSuffixSaver) Bytes() []byte { 708 if w.suffix == nil { 709 return w.prefix 710 } 711 if w.skipped == 0 { 712 return append(w.prefix, w.suffix...) 713 } 714 var buf bytes.Buffer 715 buf.Grow(len(w.prefix) + len(w.suffix) + 50) 716 buf.Write(w.prefix) 717 buf.WriteString("\n... omitting ") 718 buf.WriteString(strconv.FormatInt(w.skipped, 10)) 719 buf.WriteString(" bytes ...\n") 720 buf.Write(w.suffix[w.suffixOff:]) 721 buf.Write(w.suffix[:w.suffixOff]) 722 return buf.Bytes() 723 } 724 725 func minInt(a, b int) int { 726 if a < b { 727 return a 728 } 729 return b 730 } 731 732 // dedupEnv returns a copy of env with any duplicates removed, in favor of 733 // later values. 734 // Items not of the normal environment "key=value" form are preserved unchanged. 735 func dedupEnv(env []string) []string { 736 return dedupEnvCase(runtime.GOOS == "windows", env) 737 } 738 739 // dedupEnvCase is dedupEnv with a case option for testing. 740 // If caseInsensitive is true, the case of keys is ignored. 741 func dedupEnvCase(caseInsensitive bool, env []string) []string { 742 out := make([]string, 0, len(env)) 743 saw := make(map[string]int, len(env)) // key => index into out 744 for _, kv := range env { 745 eq := strings.Index(kv, "=") 746 if eq < 0 { 747 out = append(out, kv) 748 continue 749 } 750 k := kv[:eq] 751 if caseInsensitive { 752 k = strings.ToLower(k) 753 } 754 if dupIdx, isDup := saw[k]; isDup { 755 out[dupIdx] = kv 756 continue 757 } 758 saw[k] = len(out) 759 out = append(out, kv) 760 } 761 return out 762 } 763 764 // addCriticalEnv adds any critical environment variables that are required 765 // (or at least almost always required) on the operating system. 766 // Currently this is only used for Windows. 767 func addCriticalEnv(env []string) []string { 768 if runtime.GOOS != "windows" { 769 return env 770 } 771 for _, kv := range env { 772 eq := strings.Index(kv, "=") 773 if eq < 0 { 774 continue 775 } 776 k := kv[:eq] 777 if strings.EqualFold(k, "SYSTEMROOT") { 778 // We already have it. 779 return env 780 } 781 } 782 return append(env, "SYSTEMROOT="+os.Getenv("SYSTEMROOT")) 783 } 784
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