// Copyright 2010 The Go Authors. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//    * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//    * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
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// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

package subprocess

import (
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strings"
)

// LookPath searches for an executable 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) {
	sep := string([]rune{os.PathSeparator})
	exts := findPathExtensions()
	if strings.Contains(file, sep) {
		path, err := findExecutable(file, exts)
		if err == nil {
			return path, nil
		}
		return "", exec.ErrNotFound
	}
	path := os.Getenv("PATH")
	for _, dir := range filepath.SplitList(path) {
		if dir == "" {
			// Windows often has empty components in the PATH and
			// treating them as "." is not expected.
			if runtime.GOOS == "windows" {
				continue
			}
			// Unix shell semantics: path element "" means "."
			dir = "."
		}
		path := filepath.Join(dir, file)
		if resolved, err := findExecutable(path, exts); err == nil {
			return resolved, nil
		}
	}
	return "", exec.ErrNotFound
}
