shell腳本如何方便地處理JSON格式的數據呢，這里介紹一個工具：jq。

官方教程簡單翻譯如下。

我們以github上jq項目最新5條評論的JSON數據為例。獲取數據如下:

curl 'https://api.github.com/repos/stedolan/jq/commits?per_page=5'

結果如下：

[  {    "sha": "d25341478381063d1c76e81b3a52e0592a7c997f",    "commit": {      "author": {        "name": "Stephen Dolan",        "email": "mu@netsoc.tcd.ie",        "date": "2013-06-22T16:30:59Z"      },      "committer": {        "name": "Stephen Dolan",        "email": "mu@netsoc.tcd.ie",        "date": "2013-06-22T16:30:59Z"      },      "message": "Merge pull request #162 from stedolan/utf8-fixes/n/nUtf8 fixes. Closes #161",      "tree": {        "sha": "6ab697a8dfb5a96e124666bf6d6213822599fb40",        "url": "https://api.github.com/repos/stedolan/jq/git/trees/6ab697a8dfb5a96e124666bf6d6213822599fb40"      },      "url": "https://api.github.com/repos/stedolan/jq/git/commits/d25341478381063d1c76e81b3a52e0592a7c997f",      "comment_count": 0    },    "url": "https://api.github.com/repos/stedolan/jq/commits/d25341478381063d1c76e81b3a52e0592a7c997f",    "html_url": "https://github.com/stedolan/jq/commit/d25341478381063d1c76e81b3a52e0592a7c997f",    "comments_url": "https://api.github.com/repos/stedolan/jq/commits/d25341478381063d1c76e81b3a52e0592a7c997f/comments",    "author": {      "login": "stedolan",    ...

用 jq '.'即可：

curl 'https://api.github.com/repos/stedolan/jq/commits?per_page=5' | jq '.'

結果：

[  {    "parents": [      {        "html_url": "https://github.com/stedolan/jq/commit/54b9c9bdb225af5d886466d72f47eafc51acb4f7",        "url": "https://api.github.com/repos/stedolan/jq/commits/54b9c9bdb225af5d886466d72f47eafc51acb4f7",        "sha": "54b9c9bdb225af5d886466d72f47eafc51acb4f7"      },      {        "html_url": "https://github.com/stedolan/jq/commit/8b1b503609c161fea4b003a7179b3fbb2dd4345a",        "url": "https://api.github.com/repos/stedolan/jq/commits/8b1b503609c161fea4b003a7179b3fbb2dd4345a",        "sha": "8b1b503609c161fea4b003a7179b3fbb2dd4345a"      }    ],    "committer": {      "type": "User",      "received_events_url": "https://api.github.com/users/stedolan/received_events",      "events_url": "https://api.github.com/users/stedolan/events{/PRivacy}",      "repos_url": "https://api.github.com/users/stedolan/repos",      "organizations_url": "https://api.github.com/users/stedolan/orgs",...

這里的評論內容比較多，我們現在想拿第一個評論。

curl 'https://api.github.com/repos/stedolan/jq/commits?per_page=5' | jq '.[0]'

結果：

{  "parents": [    {      "html_url": "https://github.com/stedolan/jq/commit/54b9c9bdb225af5d886466d72f47eafc51acb4f7",      "url": "https://api.github.com/repos/stedolan/jq/commits/54b9c9bdb225af5d886466d72f47eafc51acb4f7",      "sha": "54b9c9bdb225af5d886466d72f47eafc51acb4f7"    },    {      "html_url": "https://github.com/stedolan/jq/commit/8b1b503609c161fea4b003a7179b3fbb2dd4345a",      "url": "https://api.github.com/repos/stedolan/jq/commits/8b1b503609c161fea4b003a7179b3fbb2dd4345a",      "sha": "8b1b503609c161fea4b003a7179b3fbb2dd4345a"    }  ],  "committer": {    "type": "User",    "received_events_url": "https://api.github.com/users/stedolan/received_events",    "events_url": "https://api.github.com/users/stedolan/events{/privacy}",    "repos_url": "https://api.github.com/users/stedolan/repos",    "organizations_url": "https://api.github.com/users/stedolan/orgs",    "subscriptions_url": "https://api.github.com/users/stedolan/subscriptions",    "starred_url": "https://api.github.com/users/stedolan/starred{/owner}{/repo}",    "gists_url": "https://api.github.com/users/stedolan/gists{/gist_id}",    "login": "stedolan",    "id": 79765,    "avatar_url": "https://1.gravatar.com/avatar/31de909d8e55dd07ed782d92ece59842?d=https%3A%2F%2Fidenticons.github.com%2Ffc5b6765b1c9cfaecea48ae71df4d279.png",    "gravatar_id": "31de909d8e55dd07ed782d92ece59842",    "url": "https://api.github.com/users/stedolan",    "html_url": "https://github.com/stedolan",    "followers_url": "https://api.github.com/users/stedolan/followers",    "following_url": "https://api.github.com/users/stedolan/following{/other_user}"  },  "author": {    "type": "User",    "received_events_url": "https://api.github.com/users/stedolan/received_events",    "events_url": "https://api.github.com/users/stedolan/events{/privacy}",    "repos_url": "https://api.github.com/users/stedolan/repos",    "organizations_url": "https://api.github.com/users/stedolan/orgs",    "subscriptions_url": "https://api.github.com/users/stedolan/subscriptions",    "starred_url": "https://api.github.com/users/stedolan/starred{/owner}{/repo}",    "gists_url": "https://api.github.com/users/stedolan/gists{/gist_id}",    "login": "stedolan",    "id": 79765,    "avatar_url": "https://1.gravatar.com/avatar/31de909d8e55dd07ed782d92ece59842?d=https%3A%2F%2Fidenticons.github.com%2Ffc5b6765b1c9cfaecea48ae71df4d279.png",    "gravatar_id": "31de909d8e55dd07ed782d92ece59842",    "url": "https://api.github.com/users/stedolan",    "html_url": "https://github.com/stedolan",    "followers_url": "https://api.github.com/users/stedolan/followers",    "following_url": "https://api.github.com/users/stedolan/following{/other_user}"  },  "comments_url": "https://api.github.com/repos/stedolan/jq/commits/d25341478381063d1c76e81b3a52e0592a7c997f/comments",  "html_url": "https://github.com/stedolan/jq/commit/d25341478381063d1c76e81b3a52e0592a7c997f",  "url": "https://api.github.com/repos/stedolan/jq/commits/d25341478381063d1c76e81b3a52e0592a7c997f",  "commit": {    "comment_count": 0,    "url": "https://api.github.com/repos/stedolan/jq/git/commits/d25341478381063d1c76e81b3a52e0592a7c997f",    "tree": {      "url": "https://api.github.com/repos/stedolan/jq/git/trees/6ab697a8dfb5a96e124666bf6d6213822599fb40",      "sha": "6ab697a8dfb5a96e124666bf6d6213822599fb40"    },    "message": "Merge pull request #162 from stedolan/utf8-fixes/n/nUtf8 fixes. Closes #161",    "committer": {      "date": "2013-06-22T16:30:59Z",      "email": "mu@netsoc.tcd.ie",      "name": "Stephen Dolan"    },    "author": {      "date": "2013-06-22T16:30:59Z",      "email": "mu@netsoc.tcd.ie",      "name": "Stephen Dolan"    }  },  "sha": "d25341478381063d1c76e81b3a52e0592a7c997f"}

可以看到，我們已經拿到了一條完整的評論內容。但我們真正關心的只是評論內容和用戶名，下面來獲取這兩項內容。

jq '.[0] | {message: .commit.message, name: .commit.committer.name}'

結果：

{  "name": "Stephen Dolan",  "message": "Merge pull request #162 from stedolan/utf8-fixes/n/nUtf8 fixes. Closes #161"}

我們可以看到，已經拿到了想要的內容，并且已經按我們自己定義的格式顯示了。

這里 | 后面的內容是以前面的內容為輸入的，.commit中的 . 就是指 .[0] 中的內容。

jq '.[] | {message: .commit.message, name: .commit.committer.name}'

結果：

{  "name": "Stephen Dolan",  "message": "Merge pull request #162 from stedolan/utf8-fixes/n/nUtf8 fixes. Closes #161"}{  "name": "Stephen Dolan",  "message": "Reject all overlong UTF8 sequences."}{  "name": "Stephen Dolan",  "message": "Fix various UTF8 parsing bugs./n/nIn particular, parse bad UTF8 by replacing the broken bits with U+FFFD/nand resychronise correctly after broken sequences."}{  "name": "Stephen Dolan",  "message": "Fix example in manual for `floor`. See #155."}{  "name": "Nicolas Williams",  "message": "Document floor"}

這里 .[] 獲取的是數組中的所有項。

我們看到，結果是一個個獨立的JSON對象，如何把結果組合成一個數組呢？

jq '[.[] | {message: .commit.message, name: .commit.committer.name}]'

結果：

[  {    "name": "Stephen Dolan",    "message": "Merge pull request #162 from stedolan/utf8-fixes/n/nUtf8 fixes. Closes #161"  },  {    "name": "Stephen Dolan",    "message": "Reject all overlong UTF8 sequences."  },  {    "name": "Stephen Dolan",    "message": "Fix various UTF8 parsing bugs./n/nIn particular, parse bad UTF8 by replacing the broken bits with U+FFFD/nand resychronise correctly after broken sequences."  },  {    "name": "Stephen Dolan",    "message": "Fix example in manual for `floor`. See #155."  },  {    "name": "Nicolas Williams",    "message": "Document floor"  }]

我們可以看到，只要在上一步的命令中內容的兩端加個中括號即可。

最后，我們如果想獲取每個評論的引用評論的url（在parents節點中，有一個或多個）呢？

jq '[.[] | {message: .commit.message, name: .commit.committer.name, parents: [.parents[].html_url]}]'

結果：

[  {    "parents": [      "https://github.com/stedolan/jq/commit/54b9c9bdb225af5d886466d72f47eafc51acb4f7",      "https://github.com/stedolan/jq/commit/8b1b503609c161fea4b003a7179b3fbb2dd4345a"    ],    "name": "Stephen Dolan",    "message": "Merge pull request #162 from stedolan/utf8-fixes/n/nUtf8 fixes. Closes #161"  },  {    "parents": [      "https://github.com/stedolan/jq/commit/ff48bd6ec538b01d1057be8e93b94eef6914e9ef"    ],    "name": "Stephen Dolan",    "message": "Reject all overlong UTF8 sequences."  },  {    "parents": [      "https://github.com/stedolan/jq/commit/54b9c9bdb225af5d886466d72f47eafc51acb4f7"    ],    "name": "Stephen Dolan",    "message": "Fix various UTF8 parsing bugs./n/nIn particular, parse bad UTF8 by replacing the broken bits with U+FFFD/nand resychronise correctly after broken sequences."  },  {    "parents": [      "https://github.com/stedolan/jq/commit/3dcdc582ea993afea3f5503a78a77675967ecdfa"    ],    "name": "Stephen Dolan",    "message": "Fix example in manual for `floor`. See #155."  },  {    "parents": [      "https://github.com/stedolan/jq/commit/7c4171d414f647ab08bcd20c76a4d8ed68d9c602"    ],    "name": "Nicolas Williams",    "message": "Document floor"  }]

這里用 .parents[].html_url 獲取當前項的 parents 節點中的所有項的 html_url 屬性的內容，然后兩邊加個中括號組裝成數組輸出。

怎么樣，經過這個例子可以看出，用jq處理JSON數據還是很方便強大的吧。

jq能處理的需要是嚴格的JSON格式數據，JSON對象和JSON字符串是不行的，如下面的兩種格式數據jq是不能處理的：

json對象：

{    a: 1,    b: {        c: "abc"    }}

json字符串：

'{"a":1,"b":{"c":"abc"}}'

正確的JSON格式：

{    "a": 1,    "b": {        "c": "abc"    }}

關于什么是JSON格式數據，請參考：http://www.json.org/

本文原文出自十年后的盧哥哥：http://www.CUOXin.com/lurenjiashuo/，轉載請注明出處。