egrep 特殊表达式，如括号表达式 [] 中的 \w

Question

我正在尝试使用扩展的 grep 从 JSON 中提取数据。我使用的正则表达式在我的regexr instance 上是有效的，但由于某种原因它在 bash 中不起作用。

我尝试了很多东西，特别是 bare double dash 以及对正则表达式的各种小修改以进行转义。

#!/bin/bash
networks='{ "networks": [ { "admin_state_up": true, "availability_zone_hints": [], "availability_zones": [], "created_at": "2019-03-12T23:45:13Z", "description": "", "id": "7188504a-72cb-4590-a9b0-414732017837", "ipv4_address_scope": null, "ipv6_address_scope": null, "is_default": false, "mtu": 1450, "name": "BLUE", "port_security_enabled": true, "project_id": "187d635aec4c43fe8e8918afb3a5c82e", "provider:network_type": "vxlan", "provider:physical_network": null, "provider:segmentation_id": 86, "revision_number": 2, "router:external": false, "shared": false, "status": "ACTIVE", "subnets": [], "tags": [], "tenant_id": "187d635aec4c43fe8e8918afb3a5c82e", "updated_at": "2019-03-12T23:45:13Z" }, { "admin_state_up": true, "availability_zone_hints": [], "availability_zones": [], "created_at": "2019-03-12T23:45:13Z", "description": "", "id": "ed82083f-0a7c-4322-a4fb-de8db23e2bae", "ipv4_address_scope": null, "ipv6_address_scope": null, "is_default": false, "mtu": 1450, "name": "RED", "port_security_enabled": true, "project_id": "187d635aec4c43fe8e8918afb3a5c82e", "provider:network_type": "vxlan", "provider:physical_network": null, "provider:segmentation_id": 108, "revision_number": 2, "router:external": false, "shared": false, "status": "ACTIVE", "subnets": [], "tags": [], "tenant_id": "187d635aec4c43fe8e8918afb3a5c82e", "updated_at": "2019-03-12T23:45:13Z" }, { "admin_state_up": true, "availability_zone_hints": [], "availability_zones": [], "created_at": "2019-03-12T23:45:13Z", "description": "", "id": "1eb6647e-869e-4e83-9468-43e2c320bccc", "ipv4_address_scope": null, "ipv6_address_scope": null, "is_default": false, "mtu": 1450, "name": "public", "port_security_enabled": true, "project_id": "187d635aec4c43fe8e8918afb3a5c82e", "provider:network_type": "vxlan", "provider:physical_network": null, "provider:segmentation_id": 32, "revision_number": 2, "router:external": false, "shared": false, "status": "ACTIVE", "subnets": [], "tags": [], "tenant_id": "187d635aec4c43fe8e8918afb3a5c82e", "updated_at": "2019-03-12T23:45:13Z" } ] }'
result=`echo $networks | grep -oE '"(id|name)": "([\w+-]+)"'`
echo $result

上述代码不起作用，但如果我切换到以下正则表达式，它就会起作用。我也只需要为 id 字段添加提取，以便能够使用 \2 反向引用（第 2 组）提取 id 和名称

grep -oE '"(id|name)": "(\w+)"'

你能帮我理解为什么脚本不起作用吗？

全格式 JSON

{
  "networks": [{
    "admin_state_up": true,
    "availability_zone_hints": [],
    "availability_zones": [],
    "created_at": "2019-03-12T23:45:13Z",
    "description": "",
    "id": "7188504a-72cb-4590-a9b0-414732017837",
    "ipv4_address_scope": null,
    "ipv6_address_scope": null,
    "is_default": false,
    "mtu": 1450,
    "name": "BLUE",
    "port_security_enabled": true,
    "project_id": "187d635aec4c43fe8e8918afb3a5c82e",
    "provider:network_type": "vxlan",
    "provider:physical_network": null,
    "provider:segmentation_id": 86,
    "revision_number": 2,
    "router:external": false,
    "shared": false,
    "status": "ACTIVE",
    "subnets": [],
    "tags": [],
    "tenant_id": "187d635aec4c43fe8e8918afb3a5c82e",
    "updated_at": "2019-03-12T23:45:13Z"
  }, {
    "admin_state_up": true,
    "availability_zone_hints": [],
    "availability_zones": [],
    "created_at": "2019-03-12T23:45:13Z",
    "description": "",
    "id": "ed82083f-0a7c-4322-a4fb-de8db23e2bae",
    "ipv4_address_scope": null,
    "ipv6_address_scope": null,
    "is_default": false,
    "mtu": 1450,
    "name": "RED",
    "port_security_enabled": true,
    "project_id": "187d635aec4c43fe8e8918afb3a5c82e",
    "provider:network_type": "vxlan",
    "provider:physical_network": null,
    "provider:segmentation_id": 108,
    "revision_number": 2,
    "router:external": false,
    "shared": false,
    "status": "ACTIVE",
    "subnets": [],
    "tags": [],
    "tenant_id": "187d635aec4c43fe8e8918afb3a5c82e",
    "updated_at": "2019-03-12T23:45:13Z"
  }, {
    "admin_state_up": true,
    "availability_zone_hints": [],
    "availability_zones": [],
    "created_at": "2019-03-12T23:45:13Z",
    "description": "",
    "id": "1eb6647e-869e-4e83-9468-43e2c320bccc",
    "ipv4_address_scope": null,
    "ipv6_address_scope": null,
    "is_default": false,
    "mtu": 1450,
    "name": "public",
    "port_security_enabled": true,
    "project_id": "187d635aec4c43fe8e8918afb3a5c82e",
    "provider:network_type": "vxlan",
    "provider:physical_network": null,
    "provider:segmentation_id": 32,
    "revision_number": 2,
    "router:external": false,
    "shared": false,
    "status": "ACTIVE",
    "subnets": [],
    "tags": [],
    "tenant_id": "187d635aec4c43fe8e8918afb3a5c82e",
    "updated_at": "2019-03-12T23:45:13Z"
  }]
}

Answer 1

根据man grep：

反斜杠字符和特殊表达式

符号\w 是[[:alnum:]] 的同义词，\W 是[^[:alnum:]] 的同义词。 ... 括号表达式是由 [ 和 ] 括起来的字符列表。 ... 要包含文字 ] 将其放在列表的首位。类似地，要包含文字 ^，请将其放在除第一个之外的任何位置。最后，要包含文字 - 将其放在最后。

基本上，\w 在评估时字面意思被替换为这些字符，给你"([[[:alnum:]]+-]+)"，在美国标准语言环境中给你"([[a-zA-Z0-9]+-]+)"。

由于括号表达式被它看到的第一个] 截断（除非它是括号表达式的第一个元素），所以该组只有[[[:alnum:]]+，或“一个或多个数字、字母和[。这个表达式后面跟着-]+，意思是“正好一个连字符和一个或多个]”。这显然很糟糕。

如果你尝试

echo $networks | grep -oE '"(id|name)": "([[:alnum:]+-]+)"'

即\w不带外括号表达式，相关部分表示“由一个或多个数字、字母、连字符和加号组成的一组（由"包围）”，其输出：

"id": "7188504a-72cb-4590-a9b0-414732017837"
"name": "BLUE"
"id": "ed82083f-0a7c-4322-a4fb-de8db23e2bae"
"name": "RED"
"id": "1eb6647e-869e-4e83-9468-43e2c320bccc"
"name": "public"

Answer 2

使用 PERL (-P) 而不是扩展 (-E) 正则表达式，看起来 \w 被解释为预期的那样，没有转义问题：注意 -oP

result=$( echo $networks | grep -oP '"(id|name)": "([\w+-]+)"' ) ; 
echo $result
"id": "7188504a-72cb-4590-a9b0-414732017837" "name": "BLUE" "id": "ed82083f-0a7c-4322-a4fb-de8db23e2bae" "name": "RED" "id": "1eb6647e-869e-4e83-9468-43e2c320bccc" "name": "public"

Answer 3

作为一种解决方法（它不能解决“转义\w 问题）

result=$( echo $networks | grep -oE '"(id|name)": "([a-zA-Z_+-]+)"' ) ; 
echo $result

打印我：

"name": "BLUE" "name": "RED" "name": "public"

注意：更喜欢使用$( ) 语法来执行子shell，而不是反引号。