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// 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 freebsd linux netbsd openbsd

package exec

import (

        "errors"

        "os"

        "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.EPERM

}

// 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.

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}

        }

        pathenv := os.Getenv("PATH")

        for _, dir := range strings.Split(pathenv, ":") {

                if dir == "" {

                        // Unix shell semantics: path element "" means "."

                        dir = "."

                }

                path := dir + "/" + file

                if err := findExecutable(path); err == nil {

                        return path, nil

                }

        }

        return "", &Error{file, ErrNotFound}

}