Embulk previewの便利オプション-G


Embulkで、カラムの数が多いデータをプレビューする場合は``-G``オプションを使いましょう。

## -Gを使わない出力

とても見にくいです。

```
embulk preview conf.yml 
2016-05-30 17:27:35.682 +0900: Embulk v0.8.9
2016-05-30 17:27:37.207 +0900 [INFO] (0001:preview): Loaded plugin embulk-input-apache-dummy-log (0.1.0)
+--------------------+-----------------------+-------------+-----------------------------+---------------+---------------------------------+-----------------+-------------+-----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| remote_host:string | identity_check:string | user:string |          datetime:timestamp | method:string |                     path:string | protocol:string | status:long | size:long |                                                                                                                                                                       referer:string |                                                                                                                                                                                    user_agent:string |
+--------------------+-----------------------+-------------+-----------------------------+---------------+---------------------------------+-----------------+-------------+-----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
|       80.180.78.98 |                     - |           - | 2016-05-30 08:27:37.346 UTC |           GET |                /category/sports |        HTTP/1.1 |         200 |        76 |                                                                                                                                                                                    - |                                                                                                                  Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:9.0.1) Gecko/20100101 Firefox/9.0.1 |
|      128.150.88.24 |                     - |           - | 2016-05-30 08:27:37.352 UTC |           GET |           /item/networking/1497 |        HTTP/1.1 |         200 |       104 |                                                                                                                                                                    /search/?c=Sports |                                                                                            Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.7 (KHTML, like Gecko) Chrome/16.0.912.77 Safari/535.7 |
```

## -Gオプションを使うと

データを1行、1カラムで表示するのでこのようなデータでは確認がしやすいです。

```
embulk preview -G /tmp/conf.yml 
*************************** 1 ***************************
   remote_host (   string) : 88.60.125.96
identity_check (   string) : -
          user (   string) : -
      datetime (timestamp) : 2016-05-30 08:27:48.244 UTC
        method (   string) : GET
          path (   string) : /item/cameras/183
      protocol (   string) : HTTP/1.1
        status (     long) : 200
          size (     long) : 73
       referer (   string) : -
    user_agent (   string) : Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; YTB730; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C)
*************************** 2 ***************************
   remote_host (   string) : 60.210.201.133
identity_check (   string) : -
          user (   string) : -
      datetime (timestamp) : 2016-05-30 08:27:48.250 UTC
        method (   string) : GET
          path (   string) : /category/software
      protocol (   string) : HTTP/1.1
        status (     long) : 200
          size (     long) : 135
       referer (   string) : -
    user_agent (   string) : Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:9.0.1) Gecko/20100101 Firefox/9.0.1
*************************** 3 ***************************
   remote_host (   string) : 144.78.182.90
identity_check (   string) : -
          user (   string) : -
      datetime (timestamp) : 2016-05-30 08:27:48.253 UTC
        method (   string) : GET
          path (   string) : /category/toys
      protocol (   string) : HTTP/1.1
        status (     long) : 200
          size (     long) : 133
       referer (   string) : /item/software/3978
    user_agent (   string) : Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:9.0.1) Gecko/20100101 Firefox/9.0.1
```

## 参考

* [Embulkのコマンドヘルプまとめ](http://qiita.com/hiroysato/items/86ad1cdfb1754440eed5)