安装后Gulp命令未找到

我安装了 gulp（全局），看起来它已经成功运行了这段代码：

├── tildify@0.2.0
├── interpret@0.3.5
├── pretty-hrtime@0.2.1
├── deprecated@0.0.1
├── archy@0.0.2
├── minimist@0.2.0
├── semver@2.3.2
├── orchestrator@0.3.7 (stream-consume@0.1.0, sequencify@0.0.7, end-of-stream@0.1.5)
├── chalk@0.5.1 (escape-string-regexp@1.0.1, ansi-styles@1.1.0, supports-color@0.2.0, strip-ansi@0.3.0, has-ansi@0.1.0)
├── gulp-util@2.2.20 (lodash._reinterpolate@2.4.1, dateformat@1.0.8-1.2.3, vinyl@0.2.3, through2@0.5.1, multipipe@0.1.1, lodash.template@2.4.1)
├── liftoff@0.12.0 (extend@1.2.1, minimist@0.1.0, resolve@0.7.4, findup-sync@0.1.3)
└── vinyl-fs@0.3.5 (graceful-fs@3.0.2, lodash@2.4.1, mkdirp@0.5.0, strip-bom@0.3.1, vinyl@0.2.3, through2@0.5.1, glob-watcher@0.0.6, glob-stream@3.1.14)

但是当我输入gulp时，它会显示-bash：gulp：命令未找到

有任何想法是怎么回事吗？