github.com/code-reading/golang@v0.0.0-20220303082512-ba5bc0e589a3/go/src/os/exec/lp_unix.go (about)

     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 aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
     6  // +build aix darwin dragonfly freebsd linux netbsd openbsd solaris
     7  
     8  package exec
     9  
    10  import (
    11  	"errors"
    12  	"io/fs"
    13  	"os"
    14  	"path/filepath"
    15  	"strings"
    16  )
    17  
    18  // ErrNotFound is the error resulting if a path search failed to find an executable file.
    19  var ErrNotFound = errors.New("executable file not found in $PATH")
    20  
    21  func findExecutable(file string) error {
    22  	d, err := os.Stat(file)
    23  	if err != nil {
    24  		return err
    25  	}
    26  	if m := d.Mode(); !m.IsDir() && m&0111 != 0 {
    27  		return nil
    28  	}
    29  	return fs.ErrPermission
    30  }
    31  
    32  // LookPath searches for an executable named file in the
    33  // directories named by the PATH environment variable.
    34  // If file contains a slash, it is tried directly and the PATH is not consulted.
    35  // The result may be an absolute path or a path relative to the current directory.
    36  func LookPath(file string) (string, error) {
    37  	// NOTE(rsc): I wish we could use the Plan 9 behavior here
    38  	// (only bypass the path if file begins with / or ./ or ../)
    39  	// but that would not match all the Unix shells.
    40  
    41  	if strings.Contains(file, "/") {
    42  		err := findExecutable(file)
    43  		if err == nil {
    44  			return file, nil
    45  		}
    46  		return "", &Error{file, err}
    47  	}
    48  	path := os.Getenv("PATH")
    49  	for _, dir := range filepath.SplitList(path) {
    50  		if dir == "" {
    51  			// Unix shell semantics: path element "" means "."
    52  			dir = "."
    53  		}
    54  		path := filepath.Join(dir, file)
    55  		if err := findExecutable(path); err == nil {
    56  			return path, nil
    57  		}
    58  	}
    59  	return "", &Error{file, ErrNotFound}
    60  }