1// Copyright 2010 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//go:build unix
6
7package exec
8
9import (
10	"errors"
11	"internal/syscall/unix"
12	"io/fs"
13	"os"
14	"path/filepath"
15	"strings"
16	"syscall"
17)
18
19// ErrNotFound is the error resulting if a path search failed to find an executable file.
20var ErrNotFound = errors.New("executable file not found in $PATH")
21
22func findExecutable(file string) error {
23	d, err := os.Stat(file)
24	if err != nil {
25		return err
26	}
27	m := d.Mode()
28	if m.IsDir() {
29		return syscall.EISDIR
30	}
31	err = unix.Eaccess(file, unix.X_OK)
32	// ENOSYS means Eaccess is not available or not implemented.
33	// EPERM can be returned by Linux containers employing seccomp.
34	// In both cases, fall back to checking the permission bits.
35	if err == nil || (err != syscall.ENOSYS && err != syscall.EPERM) {
36		return err
37	}
38	if m&0111 != 0 {
39		return nil
40	}
41	return fs.ErrPermission
42}
43
44// LookPath searches for an executable named file in the
45// directories named by the PATH environment variable.
46// If file contains a slash, it is tried directly and the PATH is not consulted.
47// Otherwise, on success, the result is an absolute path.
48//
49// In older versions of Go, LookPath could return a path relative to the current directory.
50// As of Go 1.19, LookPath will instead return that path along with an error satisfying
51// [errors.Is](err, [ErrDot]). See the package documentation for more details.
52func LookPath(file string) (string, error) {
53	// NOTE(rsc): I wish we could use the Plan 9 behavior here
54	// (only bypass the path if file begins with / or ./ or ../)
55	// but that would not match all the Unix shells.
56
57	if strings.Contains(file, "/") {
58		err := findExecutable(file)
59		if err == nil {
60			return file, nil
61		}
62		return "", &Error{file, err}
63	}
64	path := os.Getenv("PATH")
65	for _, dir := range filepath.SplitList(path) {
66		if dir == "" {
67			// Unix shell semantics: path element "" means "."
68			dir = "."
69		}
70		path := filepath.Join(dir, file)
71		if err := findExecutable(path); err == nil {
72			if !filepath.IsAbs(path) {
73				if execerrdot.Value() != "0" {
74					return path, &Error{file, ErrDot}
75				}
76				execerrdot.IncNonDefault()
77			}
78			return path, nil
79		}
80	}
81	return "", &Error{file, ErrNotFound}
82}
83
84// lookExtensions is a no-op on non-Windows platforms, since
85// they do not restrict executables to specific extensions.
86func lookExtensions(path, dir string) (string, error) {
87	return path, nil
88}
89