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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}
}