lp_unix.go

     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  
     7  package exec
     8  
     9  import (
    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.
    20  var ErrNotFound = errors.New("executable file not found in $PATH")
    21  
    22  func 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  func lookPath(file string) (string, error) {
    45  	// NOTE(rsc): I wish we could use the Plan 9 behavior here
    46  	// (only bypass the path if file begins with / or ./ or ../)
    47  	// but that would not match all the Unix shells.
    48  
    49  	if err := validateLookPath(file); err != nil {
    50  		return "", &Error{file, err}
    51  	}
    52  
    53  	if strings.Contains(file, "/") {
    54  		err := findExecutable(file)
    55  		if err == nil {
    56  			return file, nil
    57  		}
    58  		return "", &Error{file, err}
    59  	}
    60  	path := os.Getenv("PATH")
    61  	for _, dir := range filepath.SplitList(path) {
    62  		if dir == "" {
    63  			// Unix shell semantics: path element "" means "."
    64  			dir = "."
    65  		}
    66  		path := filepath.Join(dir, file)
    67  		if err := findExecutable(path); err == nil {
    68  			if !filepath.IsAbs(path) {
    69  				if execerrdot.Value() != "0" {
    70  					return path, &Error{file, ErrDot}
    71  				}
    72  				execerrdot.IncNonDefault()
    73  			}
    74  			return path, nil
    75  		}
    76  	}
    77  	return "", &Error{file, ErrNotFound}
    78  }
    79  
    80  // lookExtensions is a no-op on non-Windows platforms, since
    81  // they do not restrict executables to specific extensions.
    82  func lookExtensions(path, dir string) (string, error) {
    83  	return path, nil
    84  }
    85
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