add tasks

updatefile.js

@@ -15,12 +15,31 @@ module.exports = function(app) {
     return updateExample(app, 'bar');
   });
 
-  // register a "sub-updater"
+  app.task('baz', function() {
+    return updateExample(app, 'baz');
+  });
+
+  app.task('undo', function() {
+  var cwd = app.options.dest || app.cwd;
+  return app.src('example.txt', {cwd: cwd})
+    .pipe(erase(app.options.n))
+    .pipe(app.dest(cwd));
+  });
+
+  /**
+   * "Sub-updater"
+   */
+
   app.register('abc', function(abc) {
     this.task('default', function() {
       return updateExample(app, 'abc:default');
     });
+
+    this.task('xyz', function() {
+      return updateExample(app, 'abc:xyz');
+    });
   });
+
   app.task('default', ['foo']);
 };
 
@@ -57,3 +76,20 @@ function append(str) {
     next(null, file);
   });
 }
+
+/**
+ * Erase the given number of lines from the end of a string
+ *
+ * @param {String} `str`
+ * @return {Stream} vinyl stream
+ * @api public
+ */
+
+function erase(num) {
+  var n = typeof num === 'number' ? num : 1;
+  return through.obj(function(file, enc, next) {
+    var lines = file.contents.toString().trim().split('\n');
+    file.contents = new Buffer(lines.slice(0, -n).join('\n') + '\n');
+    next(null, file);
+  });
+}