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Source file src/os/exec/lp_unix.go

  // Copyright 2010 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  // +build darwin dragonfly freebsd linux nacl netbsd openbsd solaris
  
  package exec
  
  import (
  	"errors"
  	"os"
  	"path/filepath"
  	"strings"
  )
  
  // ErrNotFound is the error resulting if a path search failed to find an executable file.
  var ErrNotFound = errors.New("executable file not found in $PATH")
  
  func findExecutable(file string) error {
  	d, err := os.Stat(file)
  	if err != nil {
  		return err
  	}
  	if m := d.Mode(); !m.IsDir() && m&0111 != 0 {
  		return nil
  	}
  	return os.ErrPermission
  }
  
  // LookPath searches for an executable binary named file
  // in the directories named by the PATH environment variable.
  // If file contains a slash, it is tried directly and the PATH is not consulted.
  // The result may be an absolute path or a path relative to the current directory.
  func LookPath(file string) (string, error) {
  	// NOTE(rsc): I wish we could use the Plan 9 behavior here
  	// (only bypass the path if file begins with / or ./ or ../)
  	// but that would not match all the Unix shells.
  
  	if strings.Contains(file, "/") {
  		err := findExecutable(file)
  		if err == nil {
  			return file, nil
  		}
  		return "", &Error{file, err}
  	}
  	path := os.Getenv("PATH")
  	for _, dir := range filepath.SplitList(path) {
  		if dir == "" {
  			// Unix shell semantics: path element "" means "."
  			dir = "."
  		}
  		path := filepath.Join(dir, file)
  		if err := findExecutable(path); err == nil {
  			return path, nil
  		}
  	}
  	return "", &Error{file, ErrNotFound}
  }
  

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