diff --git a/lib/async.js b/lib/async.js
new file mode 100644
index 0000000..2f52b6c
--- /dev/null
+++ b/lib/async.js
@@ -0,0 +1,964 @@
+/*global setImmediate: false, setTimeout: false, console: false */
+
+/**
+ * https://raw.github.com/caolan/async/master/lib/async.js Feb 18, 2014
+ * Used under MIT - https://github.com/caolan/async/blob/master/LICENSE
+ */
+
+(function () {
+
+    var async = {};
+
+    // global on the server, window in the browser
+    var root, previous_async;
+
+    root = this;
+    if (root != null) {
+      previous_async = root.async;
+    }
+
+    async.noConflict = function () {
+        root.async = previous_async;
+        return async;
+    };
+
+    function only_once(fn) {
+        var called = false;
+        return function() {
+            if (called) throw new Error("Callback was already called.");
+            called = true;
+            fn.apply(root, arguments);
+        }
+    }
+
+    //// cross-browser compatiblity functions ////
+
+    var _each = function (arr, iterator) {
+        if (arr.forEach) {
+            return arr.forEach(iterator);
+        }
+        for (var i = 0; i < arr.length; i += 1) {
+            iterator(arr[i], i, arr);
+        }
+    };
+
+    var _map = function (arr, iterator) {
+        if (arr.map) {
+            return arr.map(iterator);
+        }
+        var results = [];
+        _each(arr, function (x, i, a) {
+            results.push(iterator(x, i, a));
+        });
+        return results;
+    };
+
+    var _reduce = function (arr, iterator, memo) {
+        if (arr.reduce) {
+            return arr.reduce(iterator, memo);
+        }
+        _each(arr, function (x, i, a) {
+            memo = iterator(memo, x, i, a);
+        });
+        return memo;
+    };
+
+    var _keys = function (obj) {
+        if (Object.keys) {
+            return Object.keys(obj);
+        }
+        var keys = [];
+        for (var k in obj) {
+            if (obj.hasOwnProperty(k)) {
+                keys.push(k);
+            }
+        }
+        return keys;
+    };
+
+    //// exported async module functions ////
+
+    //// nextTick implementation with browser-compatible fallback ////
+    if (typeof process === 'undefined' || !(process.nextTick)) {
+        if (typeof setImmediate === 'function') {
+            async.nextTick = function (fn) {
+                // not a direct alias for IE10 compatibility
+                setImmediate(fn);
+            };
+            async.setImmediate = async.nextTick;
+        }
+        else {
+            async.nextTick = function (fn) {
+                setTimeout(fn, 0);
+            };
+            async.setImmediate = async.nextTick;
+        }
+    }
+    else {
+        async.nextTick = process.nextTick;
+        if (typeof setImmediate !== 'undefined') {
+            async.setImmediate = function (fn) {
+              // not a direct alias for IE10 compatibility
+              setImmediate(fn);
+            };
+        }
+        else {
+            async.setImmediate = async.nextTick;
+        }
+    }
+
+    async.each = function (arr, iterator, callback) {
+        callback = callback || function () {};
+        if (!arr.length) {
+            return callback();
+        }
+        var completed = 0;
+        _each(arr, function (x) {
+            iterator(x, only_once(function (err) {
+                if (err) {
+                    callback(err);
+                    callback = function () {};
+                }
+                else {
+                    completed += 1;
+                    if (completed >= arr.length) {
+                        callback(null);
+                    }
+                }
+            }));
+        });
+    };
+    async.forEach = async.each;
+
+    async.eachSeries = function (arr, iterator, callback) {
+        callback = callback || function () {};
+        if (!arr.length) {
+            return callback();
+        }
+        var completed = 0;
+        var iterate = function () {
+            iterator(arr[completed], function (err) {
+                if (err) {
+                    callback(err);
+                    callback = function () {};
+                }
+                else {
+                    completed += 1;
+                    if (completed >= arr.length) {
+                        callback(null);
+                    }
+                    else {
+                        iterate();
+                    }
+                }
+            });
+        };
+        iterate();
+    };
+    async.forEachSeries = async.eachSeries;
+
+    async.eachLimit = function (arr, limit, iterator, callback) {
+        var fn = _eachLimit(limit);
+        fn.apply(null, [arr, iterator, callback]);
+    };
+    async.forEachLimit = async.eachLimit;
+
+    var _eachLimit = function (limit) {
+
+        return function (arr, iterator, callback) {
+            callback = callback || function () {};
+            if (!arr.length || limit <= 0) {
+                return callback();
+            }
+            var completed = 0;
+            var started = 0;
+            var running = 0;
+
+            (function replenish () {
+                if (completed >= arr.length) {
+                    return callback();
+                }
+
+                while (running < limit && started < arr.length) {
+                    started += 1;
+                    running += 1;
+                    iterator(arr[started - 1], function (err) {
+                        if (err) {
+                            callback(err);
+                            callback = function () {};
+                        }
+                        else {
+                            completed += 1;
+                            running -= 1;
+                            if (completed >= arr.length) {
+                                callback();
+                            }
+                            else {
+                                replenish();
+                            }
+                        }
+                    });
+                }
+            })();
+        };
+    };
+
+
+    var doParallel = function (fn) {
+        return function () {
+            var args = Array.prototype.slice.call(arguments);
+            return fn.apply(null, [async.each].concat(args));
+        };
+    };
+    var doParallelLimit = function(limit, fn) {
+        return function () {
+            var args = Array.prototype.slice.call(arguments);
+            return fn.apply(null, [_eachLimit(limit)].concat(args));
+        };
+    };
+    var doSeries = function (fn) {
+        return function () {
+            var args = Array.prototype.slice.call(arguments);
+            return fn.apply(null, [async.eachSeries].concat(args));
+        };
+    };
+
+
+    var _asyncMap = function (eachfn, arr, iterator, callback) {
+        var results = [];
+        arr = _map(arr, function (x, i) {
+            return {index: i, value: x};
+        });
+        eachfn(arr, function (x, callback) {
+            iterator(x.value, function (err, v) {
+                results[x.index] = v;
+                callback(err);
+            });
+        }, function (err) {
+            callback(err, results);
+        });
+    };
+    async.map = doParallel(_asyncMap);
+    async.mapSeries = doSeries(_asyncMap);
+    async.mapLimit = function (arr, limit, iterator, callback) {
+        return _mapLimit(limit)(arr, iterator, callback);
+    };
+
+    var _mapLimit = function(limit) {
+        return doParallelLimit(limit, _asyncMap);
+    };
+
+    // reduce only has a series version, as doing reduce in parallel won't
+    // work in many situations.
+    async.reduce = function (arr, memo, iterator, callback) {
+        async.eachSeries(arr, function (x, callback) {
+            iterator(memo, x, function (err, v) {
+                memo = v;
+                callback(err);
+            });
+        }, function (err) {
+            callback(err, memo);
+        });
+    };
+    // inject alias
+    async.inject = async.reduce;
+    // foldl alias
+    async.foldl = async.reduce;
+
+    async.reduceRight = function (arr, memo, iterator, callback) {
+        var reversed = _map(arr, function (x) {
+            return x;
+        }).reverse();
+        async.reduce(reversed, memo, iterator, callback);
+    };
+    // foldr alias
+    async.foldr = async.reduceRight;
+
+    var _filter = function (eachfn, arr, iterator, callback) {
+        var results = [];
+        arr = _map(arr, function (x, i) {
+            return {index: i, value: x};
+        });
+        eachfn(arr, function (x, callback) {
+            iterator(x.value, function (v) {
+                if (v) {
+                    results.push(x);
+                }
+                callback();
+            });
+        }, function (err) {
+            callback(_map(results.sort(function (a, b) {
+                return a.index - b.index;
+            }), function (x) {
+                return x.value;
+            }));
+        });
+    };
+    async.filter = doParallel(_filter);
+    async.filterSeries = doSeries(_filter);
+    // select alias
+    async.select = async.filter;
+    async.selectSeries = async.filterSeries;
+
+    var _reject = function (eachfn, arr, iterator, callback) {
+        var results = [];
+        arr = _map(arr, function (x, i) {
+            return {index: i, value: x};
+        });
+        eachfn(arr, function (x, callback) {
+            iterator(x.value, function (v) {
+                if (!v) {
+                    results.push(x);
+                }
+                callback();
+            });
+        }, function (err) {
+            callback(_map(results.sort(function (a, b) {
+                return a.index - b.index;
+            }), function (x) {
+                return x.value;
+            }));
+        });
+    };
+    async.reject = doParallel(_reject);
+    async.rejectSeries = doSeries(_reject);
+
+    var _detect = function (eachfn, arr, iterator, main_callback) {
+        eachfn(arr, function (x, callback) {
+            iterator(x, function (result) {
+                if (result) {
+                    main_callback(x);
+                    main_callback = function () {};
+                }
+                else {
+                    callback();
+                }
+            });
+        }, function (err) {
+            main_callback();
+        });
+    };
+    async.detect = doParallel(_detect);
+    async.detectSeries = doSeries(_detect);
+
+    async.some = function (arr, iterator, main_callback) {
+        async.each(arr, function (x, callback) {
+            iterator(x, function (v) {
+                if (v) {
+                    main_callback(true);
+                    main_callback = function () {};
+                }
+                callback();
+            });
+        }, function (err) {
+            main_callback(false);
+        });
+    };
+    // any alias
+    async.any = async.some;
+
+    async.every = function (arr, iterator, main_callback) {
+        async.each(arr, function (x, callback) {
+            iterator(x, function (v) {
+                if (!v) {
+                    main_callback(false);
+                    main_callback = function () {};
+                }
+                callback();
+            });
+        }, function (err) {
+            main_callback(true);
+        });
+    };
+    // all alias
+    async.all = async.every;
+
+    async.sortBy = function (arr, iterator, callback) {
+        async.map(arr, function (x, callback) {
+            iterator(x, function (err, criteria) {
+                if (err) {
+                    callback(err);
+                }
+                else {
+                    callback(null, {value: x, criteria: criteria});
+                }
+            });
+        }, function (err, results) {
+            if (err) {
+                return callback(err);
+            }
+            else {
+                var fn = function (left, right) {
+                    var a = left.criteria, b = right.criteria;
+                    return a < b ? -1 : a > b ? 1 : 0;
+                };
+                callback(null, _map(results.sort(fn), function (x) {
+                    return x.value;
+                }));
+            }
+        });
+    };
+
+    async.auto = function (tasks, callback) {
+        callback = callback || function () {};
+        var keys = _keys(tasks);
+        if (!keys.length) {
+            return callback(null);
+        }
+
+        var results = {};
+
+        var listeners = [];
+        var addListener = function (fn) {
+            listeners.unshift(fn);
+        };
+        var removeListener = function (fn) {
+            for (var i = 0; i < listeners.length; i += 1) {
+                if (listeners[i] === fn) {
+                    listeners.splice(i, 1);
+                    return;
+                }
+            }
+        };
+        var taskComplete = function () {
+            _each(listeners.slice(0), function (fn) {
+                fn();
+            });
+        };
+
+        addListener(function () {
+            if (_keys(results).length === keys.length) {
+                callback(null, results);
+                callback = function () {};
+            }
+        });
+
+        _each(keys, function (k) {
+            var task = (tasks[k] instanceof Function) ? [tasks[k]]: tasks[k];
+            var taskCallback = function (err) {
+                var args = Array.prototype.slice.call(arguments, 1);
+                if (args.length <= 1) {
+                    args = args[0];
+                }
+                if (err) {
+                    var safeResults = {};
+                    _each(_keys(results), function(rkey) {
+                        safeResults[rkey] = results[rkey];
+                    });
+                    safeResults[k] = args;
+                    callback(err, safeResults);
+                    // stop subsequent errors hitting callback multiple times
+                    callback = function () {};
+                }
+                else {
+                    results[k] = args;
+                    async.setImmediate(taskComplete);
+                }
+            };
+            var requires = task.slice(0, Math.abs(task.length - 1)) || [];
+            var ready = function () {
+                return _reduce(requires, function (a, x) {
+                    return (a && results.hasOwnProperty(x));
+                }, true) && !results.hasOwnProperty(k);
+            };
+            if (ready()) {
+                task[task.length - 1](taskCallback, results);
+            }
+            else {
+                var listener = function () {
+                    if (ready()) {
+                        removeListener(listener);
+                        task[task.length - 1](taskCallback, results);
+                    }
+                };
+                addListener(listener);
+            }
+        });
+    };
+
+    async.waterfall = function (tasks, callback) {
+        callback = callback || function () {};
+        if (tasks.constructor !== Array) {
+          var err = new Error('First argument to waterfall must be an array of functions');
+          return callback(err);
+        }
+        if (!tasks.length) {
+            return callback();
+        }
+        var wrapIterator = function (iterator) {
+            return function (err) {
+                if (err) {
+                    callback.apply(null, arguments);
+                    callback = function () {};
+                }
+                else {
+                    var args = Array.prototype.slice.call(arguments, 1);
+                    var next = iterator.next();
+                    if (next) {
+                        args.push(wrapIterator(next));
+                    }
+                    else {
+                        args.push(callback);
+                    }
+                    async.setImmediate(function () {
+                        iterator.apply(null, args);
+                    });
+                }
+            };
+        };
+        wrapIterator(async.iterator(tasks))();
+    };
+
+    var _parallel = function(eachfn, tasks, callback) {
+        callback = callback || function () {};
+        if (tasks.constructor === Array) {
+            eachfn.map(tasks, function (fn, callback) {
+                if (fn) {
+                    fn(function (err) {
+                        var args = Array.prototype.slice.call(arguments, 1);
+                        if (args.length <= 1) {
+                            args = args[0];
+                        }
+                        callback.call(null, err, args);
+                    });
+                }
+            }, callback);
+        }
+        else {
+            var results = {};
+            eachfn.each(_keys(tasks), function (k, callback) {
+                tasks[k](function (err) {
+                    var args = Array.prototype.slice.call(arguments, 1);
+                    if (args.length <= 1) {
+                        args = args[0];
+                    }
+                    results[k] = args;
+                    callback(err);
+                });
+            }, function (err) {
+                callback(err, results);
+            });
+        }
+    };
+
+    async.parallel = function (tasks, callback) {
+        _parallel({ map: async.map, each: async.each }, tasks, callback);
+    };
+
+    async.parallelLimit = function(tasks, limit, callback) {
+        _parallel({ map: _mapLimit(limit), each: _eachLimit(limit) }, tasks, callback);
+    };
+
+    async.series = function (tasks, callback) {
+        callback = callback || function () {};
+        if (tasks.constructor === Array) {
+            async.mapSeries(tasks, function (fn, callback) {
+                if (fn) {
+                    fn(function (err) {
+                        var args = Array.prototype.slice.call(arguments, 1);
+                        if (args.length <= 1) {
+                            args = args[0];
+                        }
+                        callback.call(null, err, args);
+                    });
+                }
+            }, callback);
+        }
+        else {
+            var results = {};
+            async.eachSeries(_keys(tasks), function (k, callback) {
+                tasks[k](function (err) {
+                    var args = Array.prototype.slice.call(arguments, 1);
+                    if (args.length <= 1) {
+                        args = args[0];
+                    }
+                    results[k] = args;
+                    callback(err);
+                });
+            }, function (err) {
+                callback(err, results);
+            });
+        }
+    };
+
+    async.iterator = function (tasks) {
+        var makeCallback = function (index) {
+            var fn = function () {
+                if (tasks.length) {
+                    tasks[index].apply(null, arguments);
+                }
+                return fn.next();
+            };
+            fn.next = function () {
+                return (index < tasks.length - 1) ? makeCallback(index + 1): null;
+            };
+            return fn;
+        };
+        return makeCallback(0);
+    };
+
+    async.apply = function (fn) {
+        var args = Array.prototype.slice.call(arguments, 1);
+        return function () {
+            return fn.apply(
+                null, args.concat(Array.prototype.slice.call(arguments))
+            );
+        };
+    };
+
+    var _concat = function (eachfn, arr, fn, callback) {
+        var r = [];
+        eachfn(arr, function (x, cb) {
+            fn(x, function (err, y) {
+                r = r.concat(y || []);
+                cb(err);
+            });
+        }, function (err) {
+            callback(err, r);
+        });
+    };
+    async.concat = doParallel(_concat);
+    async.concatSeries = doSeries(_concat);
+
+    async.whilst = function (test, iterator, callback) {
+        if (test()) {
+            iterator(function (err) {
+                if (err) {
+                    return callback(err);
+                }
+                async.whilst(test, iterator, callback);
+            });
+        }
+        else {
+            callback();
+        }
+    };
+
+    async.doWhilst = function (iterator, test, callback) {
+        iterator(function (err) {
+            if (err) {
+                return callback(err);
+            }
+            if (test()) {
+                async.doWhilst(iterator, test, callback);
+            }
+            else {
+                callback();
+            }
+        });
+    };
+
+    async.until = function (test, iterator, callback) {
+        if (!test()) {
+            iterator(function (err) {
+                if (err) {
+                    return callback(err);
+                }
+                async.until(test, iterator, callback);
+            });
+        }
+        else {
+            callback();
+        }
+    };
+
+    async.doUntil = function (iterator, test, callback) {
+        iterator(function (err) {
+            if (err) {
+                return callback(err);
+            }
+            if (!test()) {
+                async.doUntil(iterator, test, callback);
+            }
+            else {
+                callback();
+            }
+        });
+    };
+
+    async.queue = function (worker, concurrency) {
+        if (concurrency === undefined) {
+            concurrency = 1;
+        }
+        function _insert(q, data, pos, callback) {
+          if(data.constructor !== Array) {
+              data = [data];
+          }
+          _each(data, function(task) {
+              var item = {
+                  data: task,
+                  callback: typeof callback === 'function' ? callback : null
+              };
+
+              if (pos) {
+                q.tasks.unshift(item);
+              } else {
+                q.tasks.push(item);
+              }
+
+              if (q.saturated && q.tasks.length === concurrency) {
+                  q.saturated();
+              }
+              async.setImmediate(q.process);
+          });
+        }
+
+        var workers = 0;
+        var q = {
+            tasks: [],
+            concurrency: concurrency,
+            saturated: null,
+            empty: null,
+            drain: null,
+            push: function (data, callback) {
+              _insert(q, data, false, callback);
+            },
+            unshift: function (data, callback) {
+              _insert(q, data, true, callback);
+            },
+            process: function () {
+                if (workers < q.concurrency && q.tasks.length) {
+                    var task = q.tasks.shift();
+                    if (q.empty && q.tasks.length === 0) {
+                        q.empty();
+                    }
+                    workers += 1;
+                    var next = function () {
+                        workers -= 1;
+                        if (task.callback) {
+                            task.callback.apply(task, arguments);
+                        }
+                        if (q.drain && q.tasks.length + workers === 0) {
+                            q.drain();
+                        }
+                        q.process();
+                    };
+                    var cb = only_once(next);
+                    worker(task.data, cb);
+                }
+            },
+            length: function () {
+                return q.tasks.length;
+            },
+            running: function () {
+                return workers;
+            }
+        };
+        return q;
+    };
+
+    async.cargo = function (worker, payload) {
+        var working     = false,
+            tasks       = [];
+
+        var cargo = {
+            tasks: tasks,
+            payload: payload,
+            saturated: null,
+            empty: null,
+            drain: null,
+            push: function (data, callback) {
+                if(data.constructor !== Array) {
+                    data = [data];
+                }
+                _each(data, function(task) {
+                    tasks.push({
+                        data: task,
+                        callback: typeof callback === 'function' ? callback : null
+                    });
+                    if (cargo.saturated && tasks.length === payload) {
+                        cargo.saturated();
+                    }
+                });
+                async.setImmediate(cargo.process);
+            },
+            process: function process() {
+                if (working) return;
+                if (tasks.length === 0) {
+                    if(cargo.drain) cargo.drain();
+                    return;
+                }
+
+                var ts = typeof payload === 'number'
+                            ? tasks.splice(0, payload)
+                            : tasks.splice(0);
+
+                var ds = _map(ts, function (task) {
+                    return task.data;
+                });
+
+                if(cargo.empty) cargo.empty();
+                working = true;
+                worker(ds, function () {
+                    working = false;
+
+                    var args = arguments;
+                    _each(ts, function (data) {
+                        if (data.callback) {
+                            data.callback.apply(null, args);
+                        }
+                    });
+
+                    process();
+                });
+            },
+            length: function () {
+                return tasks.length;
+            },
+            running: function () {
+                return working;
+            }
+        };
+        return cargo;
+    };
+
+    var _console_fn = function (name) {
+        return function (fn) {
+            var args = Array.prototype.slice.call(arguments, 1);
+            fn.apply(null, args.concat([function (err) {
+                var args = Array.prototype.slice.call(arguments, 1);
+                if (typeof console !== 'undefined') {
+                    if (err) {
+                        if (console.error) {
+                            console.error(err);
+                        }
+                    }
+                    else if (console[name]) {
+                        _each(args, function (x) {
+                            console[name](x);
+                        });
+                    }
+                }
+            }]));
+        };
+    };
+    async.log = _console_fn('log');
+    async.dir = _console_fn('dir');
+    /*async.info = _console_fn('info');
+    async.warn = _console_fn('warn');
+    async.error = _console_fn('error');*/
+
+    async.memoize = function (fn, hasher) {
+        var memo = {};
+        var queues = {};
+        hasher = hasher || function (x) {
+            return x;
+        };
+        var memoized = function () {
+            var args = Array.prototype.slice.call(arguments);
+            var callback = args.pop();
+            var key = hasher.apply(null, args);
+            if (key in memo) {
+                callback.apply(null, memo[key]);
+            }
+            else if (key in queues) {
+                queues[key].push(callback);
+            }
+            else {
+                queues[key] = [callback];
+                fn.apply(null, args.concat([function () {
+                    memo[key] = arguments;
+                    var q = queues[key];
+                    delete queues[key];
+                    for (var i = 0, l = q.length; i < l; i++) {
+                      q[i].apply(null, arguments);
+                    }
+                }]));
+            }
+        };
+        memoized.memo = memo;
+        memoized.unmemoized = fn;
+        return memoized;
+    };
+
+    async.unmemoize = function (fn) {
+      return function () {
+        return (fn.unmemoized || fn).apply(null, arguments);
+      };
+    };
+
+    async.times = function (count, iterator, callback) {
+        var counter = [];
+        for (var i = 0; i < count; i++) {
+            counter.push(i);
+        }
+        return async.map(counter, iterator, callback);
+    };
+
+    async.timesSeries = function (count, iterator, callback) {
+        var counter = [];
+        for (var i = 0; i < count; i++) {
+            counter.push(i);
+        }
+        return async.mapSeries(counter, iterator, callback);
+    };
+
+    async.compose = function (/* functions... */) {
+        var fns = Array.prototype.reverse.call(arguments);
+        return function () {
+            var that = this;
+            var args = Array.prototype.slice.call(arguments);
+            var callback = args.pop();
+            async.reduce(fns, args, function (newargs, fn, cb) {
+                fn.apply(that, newargs.concat([function () {
+                    var err = arguments[0];
+                    var nextargs = Array.prototype.slice.call(arguments, 1);
+                    cb(err, nextargs);
+                }]))
+            },
+            function (err, results) {
+                callback.apply(that, [err].concat(results));
+            });
+        };
+    };
+
+    var _applyEach = function (eachfn, fns /*args...*/) {
+        var go = function () {
+            var that = this;
+            var args = Array.prototype.slice.call(arguments);
+            var callback = args.pop();
+            return eachfn(fns, function (fn, cb) {
+                fn.apply(that, args.concat([cb]));
+            },
+            callback);
+        };
+        if (arguments.length > 2) {
+            var args = Array.prototype.slice.call(arguments, 2);
+            return go.apply(this, args);
+        }
+        else {
+            return go;
+        }
+    };
+    async.applyEach = doParallel(_applyEach);
+    async.applyEachSeries = doSeries(_applyEach);
+
+    async.forever = function (fn, callback) {
+        function next(err) {
+            if (err) {
+                if (callback) {
+                    return callback(err);
+                }
+                throw err;
+            }
+            fn(next);
+        }
+        next();
+    };
+
+    // AMD / RequireJS
+    if (typeof define !== 'undefined' && define.amd) {
+        define([], function () {
+            return async;
+        });
+    }
+    // Node.js
+    else if (typeof module !== 'undefined' && module.exports) {
+        module.exports = async;
+    }
+    // included directly via <script> tag
+    else {
+        root.async = async;
+    }
+
+}());
diff --git a/src/shell.js b/src/shell.js
index 4b31b81..6a386e4 100644
--- a/src/shell.js
+++ b/src/shell.js
@@ -2,7 +2,8 @@
 define(function(require) {
 
   var Path = require('src/path');
-  var Error = require('src/error');
+  var FilerError = require('src/error');
+  var async = require('async');
 
   function Shell(fs, options) {
     options = options || {};
@@ -26,14 +27,14 @@ define(function(require) {
       // Make sure the path actually exists, and is a dir
       fs.stat(path, function(err, stats) {
         if(err) {
-          callback(new Error.ENotDirectory());
+          callback(new FilerError.ENotDirectory());
           return;
         }
         if(stats.type === 'DIRECTORY') {
           cwd = path;
           callback();
         } else {
-          callback(new Error.ENotDirectory());
+          callback(new FilerError.ENotDirectory());
         }
       });
     };
@@ -120,6 +121,44 @@ define(function(require) {
     });
   };
 
+  /**
+   * Concatenate multiple files into a single String, with each
+   * file separated by a newline. The `files` argument should
+   * be a String (path to single file) or an Array of Strings
+   * (multiple file paths).
+   */
+  Shell.prototype.cat = function(files, callback) {
+    if(!files) {
+      callback(new Error("Missing files argument"));
+      return;
+    }
+
+    var fs = this.fs;
+    var all = '';
+    files = typeof files === 'string' ? [ files ] : files;
+    callback = callback || function(){};
+
+    function append(item, callback) {
+      var filename = Path.resolve(this.cwd, item);
+      fs.readFile(filename, 'utf8', function(error, data) {
+        if(error) {
+          callback(error);
+          return;
+        }
+        all += data + '\n';
+        callback();
+      });
+    }
+
+    async.eachSeries(files, append, function(error) {
+      if(error) {
+        callback(error);
+      } else {
+        callback(null, all.replace(/\n$/, ''));
+      }
+    });
+  };
+
   return Shell;
 
 });
diff --git a/tests/spec/shell/cat.spec.js b/tests/spec/shell/cat.spec.js
new file mode 100644
index 0000000..5464e2d
--- /dev/null
+++ b/tests/spec/shell/cat.spec.js
@@ -0,0 +1,82 @@
+define(["Filer", "util"], function(Filer, util) {
+
+  describe('FileSystemShell.cat', function() {
+    beforeEach(util.setup);
+    afterEach(util.cleanup);
+
+    it('should be a function', function() {
+      var shell = util.shell();
+      expect(shell.cat).to.be.a('function');
+    });
+
+    it('should fail when files argument is absent', function(done) {
+      var fs = util.fs();
+      var shell = fs.Shell();
+
+      shell.cat(null, function(error, data) {
+        expect(error).to.exist;
+        expect(data).not.to.exist;
+        done();
+      });
+    });
+
+    it('should return the contents of a single file', function(done) {
+      var fs = util.fs();
+      var shell = fs.Shell();
+      var contents = "file contents";
+
+      fs.writeFile('/file', contents, function(err) {
+        if(err) throw err;
+
+        shell.cat('/file', function(err, data) {
+          expect(err).not.to.exist;
+          expect(data).to.equal(contents);
+          done();
+        });
+      });
+    });
+
+    it('should return the contents of multiple files', function(done) {
+      var fs = util.fs();
+      var shell = fs.Shell();
+      var contents = "file contents";
+      var contents2 = contents + '\n' + contents;
+
+      fs.writeFile('/file', contents, function(err) {
+        if(err) throw err;
+
+        fs.writeFile('/file2', contents2, function(err) {
+          if(err) throw err;
+
+          shell.cat(['/file', '/file2'], function(err, data) {
+            expect(err).not.to.exist;
+            expect(data).to.equal(contents + '\n' + contents2);
+            done();
+          });
+        });
+      });
+    });
+
+    it('should fail if any of multiple file paths is invalid', function(done) {
+      var fs = util.fs();
+      var shell = fs.Shell();
+      var contents = "file contents";
+      var contents2 = contents + '\n' + contents;
+
+      fs.writeFile('/file', contents, function(err) {
+        if(err) throw err;
+
+        fs.writeFile('/file2', contents2, function(err) {
+          if(err) throw err;
+
+          shell.cat(['/file', '/nofile'], function(err, data) {
+            expect(err).to.exist;
+            expect(data).not.to.exist;
+            done();
+          });
+        });
+      });
+    });
+
+  });
+});
diff --git a/tests/test-manifest.js b/tests/test-manifest.js
index 2fa4f63..32758c0 100644
--- a/tests/test-manifest.js
+++ b/tests/test-manifest.js
@@ -46,6 +46,7 @@ define([
   "spec/shell/cd.spec",
   "spec/shell/touch.spec",
   "spec/shell/exec.spec",
+  "spec/shell/cat.spec",
 
   // Ported node.js tests (filenames match names in https://github.com/joyent/node/tree/master/test)
   "spec/node-js/simple/test-fs-mkdir",