インストール

brew install jq

jqは引数に様々なフィルタをパイプ（|）でつなげた形式で処理を指定します。

jq [オプション] 'フィルタ1 | フィルタ2 | フィルタ3 | ...' [入力ファイル]

とりあえず試す。apiからのjsonファイルを整形
'.'は入力データそのものを表す。

curl -s "http://tepco-usage-api.appspot.com/2014/2/3.json"|jq '.'

出力

[
  {
    "usage": 2849,
    "entryfor": "2014-02-02 15:00:00",
    "usage_updated": "2014-02-02 16:05:05",
    "forecast": 0,
    "forecast_peak_updated": "2012-02-02 23:30:00",
    "hour": 0,
    "capacity": 4756,
    "capacity_updated": "2012-02-02 23:30:00",
    "forecast_peak_usage": 3920,
    "month": 2,
    "forecast_peak_period": 18,
    "capacity_peak_period": 18,
    "year": 2014,
    "saving": false,
    "day": 3
  },
  # 以下略
]

配列の取り出し

curl -s "http://tepco-usage-api.appspot.com/2014/2/3.json"|jq '.[]'

出力

{
  "usage": 2849,
  "entryfor": "2014-02-02 15:00:00",
  "usage_updated": "2014-02-02 16:05:05",
  "forecast": 0,
  "forecast_peak_updated": "2012-02-02 23:30:00",
  "hour": 0,
  "capacity": 4756,
  "capacity_updated": "2012-02-02 23:30:00",
  "forecast_peak_usage": 3920,
  "month": 2,
  "forecast_peak_period": 18,
  "capacity_peak_period": 18,
  "year": 2014,
  "saving": false,
  "day": 3
}
{
# 以下略

ローカルjsonファイルを整形

(meibo.json)

{"name":"john","gender":"m","age":"18"}
{"name":"paul","gender":"m","age":"20"}
{"name":"alice","gender":"f","age":"15"}
{"name":"dabid","gender":"m","age":"17"}
{"name":"jasmin","gender":"f","age":"17"}

jsの引数にファイルを指定

$ jq "." meibo.json
[
  {
    "name": "john",
    "gender": "m",
    "age": "18"
  },
  {
    "name": "paul",
    "gender": "m",
    "age": "20"
  },
  {
    "name": "alice",
    "gender": "f",
    "age": "15"
  },
  {
    "name": "dabid",
    "gender": "m",
    "age": "17"
  },
  {
    "name": "jasmin",
    "gender": "f",
    "age": "17"
  }
]

catでjsonファイルを標準出力して、それをパイプでjqコマンド受け取る

(cat コマンド)
ファイルまたは標準入力の内容をそのまま標準出力に出力する。

$ cat meibo.json | jq .
[
  {
    "name": "john",
    "gender": "m",
    "age": "18"
  },
  {
    "name": "paul",
    "gender": "m",
    "age": "20"
  },
  {
    "name": "alice",
    "gender": "f",
    "age": "15"
  },
  {
    "name": "dabid",
    "gender": "m",
    "age": "17"
  },
  {
    "name": "jasmin",
    "gender": "f",
    "age": "17"
  }
]