Extract string from JSON using grep

Question

I have a JSON input:

{
  "policyItems": [
    {
      "accesses": [
        {
          "type": "submit-app",
          "isAllowed": true
        }
      ],
      "users": [],
      "groups": [
        "Application_Team_1",
        "team2"
      ],
      "conditions": [],
      "delegateAdmin": false
    }
  ]
}

I did a command line curl to dispaly the queue policy yarn:

curl  -u "login:password" http://myHost:6080/service/public/v2/api/service/YARN_Cluster/policy/YARN%20NameQueue/

It works fine.

Then I added grep to extract all the list of groups items:

curl  -u "login:password" http://myHost:6080/service/public/v2/api/service/YARN_Cluster/policy/YARN%20NameQueue/ | 
grep -oP '(?<="groups": ")[^"]*'

This following is the result:

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   579    0   579    0     0   4384      0 --:--:-- --:--:-- --:--:--  4419

It is not working. How can I do it using grep and not jq ?

@WiktorStribiżew Os is Linux and grep (GNU grep) 2.20 Copyright (C) 2014 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later . — vero, Jun 21 '18 at 12:55
Possible duplicate of [How to recover the hdp](https://stackoverflow.com/questions/50966502/how-to-recover-the-hdp) — oliv, Jun 21 '18 at 13:01
@oliv, the requirement said no use of jq so, it is not a possible duplicate — papigee, Jun 21 '18 at 13:04
@WiktorStribiżewyes Exactly I need to get Application_team_1 and team2 — vero, Jun 21 '18 at 13:05
Possible duplicate of [How can I search for a multiline pattern in a file?](https://stackoverflow.com/questions/152708/how-can-i-search-for-a-multiline-pattern-in-a-file) — Benjamin W., Jun 21 '18 at 13:08
@WiktorStribiżew Good , Can you write it in answer to mark it resolve please ? Thank you — vero, Jun 21 '18 at 13:08
Thank you , I posted another question is related to this one https://stackoverflow.com/questions/50983265/bad-request-curl-with-grep?noredirect=1#comment88961456_50983265 — vero, Jun 22 '18 at 07:58

score 1 · Accepted Answer · answered Jun 22 '18 at 08:09

You may use

grep -Poza '(?:\G(?!^)",|"groups":\s*\[)\s*"\K[^"]+'

Options

P - use PCRE engine to parse the pattern
o - output matches found
z - slurp the whole file, treat the file as a whole single string
a - treat the file as a text file (it should be used because when the -z switch may trigger grep binary data behaviour that changes the return values).

Pattern

(?:\G(?!^)",|"groups":\s*\[) - either the end of the previous match (\G(?!^)) and then ", substring, or (|) a literal text "groups":, 0+ whitespaces (\s*) and a [ char (\[)
\s*" - 0+ whitespaces and " char
\K - match reset operator discarding the whole text matched so far
[^"]+ - 1+ chars other than "

As you see, this expression finds "group": [", omits that text and matches each value inside "s only after that text.

See the PCRE regex demo.

Can you help me on this question is related to regex https://stackoverflow.com/questions/51065117/find-string-in-substring-regex — vero, Jun 27 '18 at 14:23

Extract string from JSON using grep

1 Answers1