node/lib/path.js

var isWindows = process.platform === 'win32';


// resolves . and .. elements in a path array with directory names there
// must be no slashes, empty elements, or device names (c:\) in the array
// (so also no leading and trailing slashes - it does not distinguish
// relative and absolute paths)
function normalizeArray(parts, allowAboveRoot) {
  // if the path tries to go above the root, `up` ends up > 0
  var up = 0;
  for (var i = parts.length; i >= 0; i--) {
    var last = parts[i];
    if (last == '.') {
      parts.splice(i, 1);
    } else if (last === '..') {
      parts.splice(i, 1);
      up++;
    } else if (up) {
      parts.splice(i, 1);
      up--;
    }
  }

  // if the path is allowed to go above the root, restore leading ..s
  if (allowAboveRoot) {
    for (; up--; up) {
      parts.unshift('..');
    }
  }

  return parts;
}


if (isWindows) {

  // Regex to split a filename into [*, dir, basename, ext]
  // windows version
  var splitPathRe = /^(.+(?:[\\\/](?!$)|:)|[\\\/])?((?:.+?)?(\.[^.]*)?)$/;

  // Regex to split a windows path into three parts: [*, device, slash,
  // tail] windows-only
  var splitDeviceRe =
      /^([a-zA-Z]:|[\\\/]{2}[^\\\/]+[\\\/][^\\\/]+)?([\\\/])?(.*?)$/;

  // path.resolve([from ...], to)
  // windows version
  exports.resolve = function() {
    // Prepend cwd to provided paths
    var paths = [process.cwd()].concat(
        Array.prototype.slice.call(arguments, 0));

    var resolvedDevice = '',
        resolvedTail = '',
        resolvedAbsolute = false;

    for (var i = paths.length; i >= 0; i--) {
      var path = paths[i];

      // Skip empty and invalid entries
      if (typeof path !== 'string' || !path) {
        continue;
      }

      var result = splitDeviceRe.exec(path),
          device = result[1] || '',
          isUnc = device && device.charAt(1) !== ':',
          isAbsolute = !!result[2] || isUnc, // UNC paths are always absolute
          tail = result[3];

      if (device &&
          resolvedDevice &&
          device.toLowerCase() !== resolvedDevice.toLowerCase()) {
        // This path points to another device so it is not applicable
        continue;
      }

      if (!resolvedDevice) {
        resolvedDevice = device;
      }
      if (!resolvedAbsolute) {
        resolvedTail = tail + '\\' + resolvedTail;
        resolvedAbsolute = isAbsolute;
      }

      if (resolvedDevice && resolvedAbsolute) {
        break;
      }
    }

    if (!resolvedAbsolute && resolvedDevice) {
      // If we still don't have an absolute path,
      // prepend the current path for the device found.

      // TODO
      // Windows stores the current directories for 'other' drives
      // as hidden environment variables like =C:=c:\windows (literally)
      // var deviceCwd = os.getCwdForDrive(resolvedDevice);
      var deviceCwd = '';

      // If there is no cwd set for the drive, it is at root
      resolvedTail = deviceCwd + '\\' + resolvedTail;
      resolvedAbsolute = true;
    }

    // Replace slashes (in UNC share name) by backslashes
    resolvedDevice = resolvedDevice.replace(/\//g, '\\');

    // At this point the path should be resolved to a full absolute path,
    // but handle relative paths to be safe (might happen when process.cwd()
    // fails)

    // Normalize the tail path

    function f(p) {
      return !!p;
    }

    resolvedTail = normalizeArray(resolvedTail.split(/[\\\/]+/).filter(f),
                                  !resolvedAbsolute).join('\\');

    return (resolvedDevice + (resolvedAbsolute ? '\\' : '') + resolvedTail) ||
           '.';
  };

  // windows version
  exports.normalize = function(path) {
    var result = splitDeviceRe.exec(path),
        device = result[1] || '',
        isUnc = device && device.charAt(1) !== ':',
        isAbsolute = !!result[2] || isUnc, // UNC paths are always absolute
        tail = result[3],
        trailingSlash = /[\\\/]$/.test(tail);

    // Normalize the tail path
    tail = normalizeArray(tail.split(/[\\\/]+/).filter(function(p) {
      return !!p;
    }), !isAbsolute).join('\\');

    if (!tail && !isAbsolute) {
      tail = '.';
    }
    if (tail && trailingSlash) {
      tail += '\\';
    }

    return device + (isAbsolute ? '\\' : '') + tail;
  };

  // windows version
  exports.join = function() {
    function f(p) {
      return p && typeof p === 'string';
    }

    var paths = Array.prototype.slice.call(arguments, 0).filter(f);
    var joined = paths.join('\\');

    // Make sure that the joined path doesn't start with two slashes
    // - it will be mistaken for an unc path by normalize() -
    // unless the paths[0] also starts with two slashes
    if (/^[\\\/]{2}/.test(joined) && !/^[\\\/]{2}/.test(paths[0])) {
      joined = joined.slice(1);
    }

    return exports.normalize(joined);
  };


} else /* posix */ {

  // Regex to split a filename into [*, dir, basename, ext]
  // posix version
  var splitPathRe = /^(.+\/(?!$)|\/)?((?:.+?)?(\.[^.]*)?)$/;

  // path.resolve([from ...], to)
  // posix version
  exports.resolve = function() {
    // Prepend cwd to provided paths
    var paths = [process.cwd()].concat(
        Array.prototype.slice.call(arguments, 0));

    var resolvedPath = '',
        resolvedAbsolute = false;

    for (var i = paths.length; i >= 0 && !resolvedAbsolute; i--) {
      var path = paths[i];
      // Skip empty and invalid entries
      if (typeof path !== 'string' || !path) {
        continue;
      }
      resolvedPath = path + '/' + resolvedPath;
      resolvedAbsolute = path.charAt(0) === '/';
    }

    // At this point the path should be resolved to a full absolute path, but
    // handle relative paths to be safe (might happen when process.cwd() fails)

    // Normalize the path
    resolvedPath = normalizeArray(resolvedPath.split('/').filter(function(p) {
      return !!p;
    }), !resolvedAbsolute).join('/');

    return ((resolvedAbsolute ? '/' : '') + resolvedPath) || '.';
  };

  // path.normalize(path)
  // posix version
  exports.normalize = function(path) {
    var isAbsolute = path.charAt(0) === '/',
        trailingSlash = path.slice(-1) === '/';

    // Normalize the path
    path = normalizeArray(path.split('/').filter(function(p) {
      return !!p;
    }), !isAbsolute).join('/');

    if (!path && !isAbsolute) {
      path = '.';
    }
    if (path && trailingSlash) {
      path += '/';
    }

    return (isAbsolute ? '/' : '') + path;
  };


  // posix version
  exports.join = function() {
    var paths = Array.prototype.slice.call(arguments, 0);
    return exports.normalize(paths.filter(function(p, index) {
      return p && typeof p === 'string';
    }).join('/'));
  };
}


exports.dirname = function(path) {
  var dir = splitPathRe.exec(path)[1] || '';
  if (!dir) {
    // No dirname
    return '.';
  } else if (dir.length === 1 ||
      (isWindows && dir.length <= 3 && dir.charAt(1) === ':')) {
    // It is just a slash or a drive letter with a slash
    return dir;
  } else {
    // It is a full dirname, strip trailing slash
    return dir.substring(0, dir.length - 1);
  }
};


exports.basename = function(path, ext) {
  var f = splitPathRe.exec(path)[2] || '';
  // TODO: make this comparison case-insensitive on windows?
  if (ext && f.substr(-1 * ext.length) === ext) {
    f = f.substr(0, f.length - ext.length);
  }
  return f;
};


exports.extname = function(path) {
  return splitPathRe.exec(path)[3] || '';
};


exports.exists = function(path, callback) {
  process.binding('fs').stat(path, function(err, stats) {
    if (callback) callback(err ? false : true);
  });
};


exports.existsSync = function(path) {
  try {
    process.binding('fs').stat(path);
    return true;
  } catch (e) {
    return false;
  }
};