How to access JSON data from perl?

Question

I have a JSON file as below.

{
    "card":{
      "cardName":"10AN10G",
      "portSignalRates":[
         "10AN10G-1-OTU2",
         "10AN10G-1-OTU2E",
         "10AN10G-1-TENGIGE",
         "10AN10G-1-STM64"
      ],
      "listOfPort":{
         "10AN10G-1-OTU2":{
            "portAid":"10AN10G-1-OTU2",
            "signalType":"OTU2",
            "tabNames":[
               "PortDetails"
            ],
            "requestType":{
               "PortDetails":"PTP"
            },
            "paramDetailsMap":{
               "PortDetails":[
                  {
                     "type":"dijit.form.TextBox",
                     "name":"signalType",
                     "title":"Signal Rate",
                     "id":"",
                     "options":[

                     ],
                     "label":"",
                     "value":"OTU2",
                     "checked":"",
                     "enabled":"false",
                     "selected":""
                  },
                  {
                     "type":"dijit.form.TextBox",
                     "name":"userLabel",
                     "title":"Description",
                     "id":"",
                     "options":[

                     ],
                     "label":"",
                     "value":"",
                     "checked":"",
                     "enabled":"true",
                     "selected":""
                  },
                  {
                     "type":"dijit.form.Select",
                     "name":"Frequency",
                     "title":"Transmit Frequency"
                  }
               ]
            }
         }
      }
   }
}

I require the output to be:

signalType:"Signal Rate",
userLabel:"Description",
Frequency:"Transmit Frequency",.. ,.....

I tried with:

grep -oP '(?<=\"title\":\")[^"]*' file > outfile

but this just splits the value of title and returns.

Can I use perl to access elements of the JSON data that I want?

I don't think this is the problem but, just to let you know, your JSON you posted is invalid. — djikay
– djikay, Commented Jul 3, 2014 at 23:37
jq is a nifty command line filter for json of the sed/awk sort. stedolan.github.io/jq — daotoad
– daotoad, Commented Jul 4, 2014 at 1:33
I edited the post to make the JSON "valid". I used an online service and jq, json_verify to check the work. My thinking was a basic question like this might be useful to answer (even repeatedly), but that it needed proper data to be useful. I would not be surprised if it was a duplicate of another SO post (e.g. see this one on JSON and perl). But I think that is OK :-) — G. Cito
– G. Cito, Commented Jul 4, 2014 at 13:56

Gergo Erdosi · Accepted Answer · 2014-07-03 23:39:58Z

4

I suggest to use decode_json instead of a regex. First, install the JSON module from CPAN:

sudo perl -MCPAN -e 'install JSON'

Alternatively you can use apt-get on Ubuntu:

sudo apt-get install libjson-pp-perl

Once it is installed, you can use this code:

my $json = '{... your json string ...}';
my $decoded = decode_json($json);

$decoded->{'card'}{'listOfPort'}{'10AN10G-1-OTU2'}{'signalType'}

You can find more details in this article.

answered Jul 3, 2014 at 23:39

Gergo Erdosi

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G. Cito · Accepted Answer · 2014-07-16 00:49:49Z

Yes you can use the JSON perl module. Of course it meeds to be installed via cpan, cpanm or your system's packaging system. Parse the JSON into a hash and then use that in the normal way from Perl. Here's a quick example:

use JSON;
use IO::All;
use strict;
use warnings;

my $data < io '/tmp/data.json';
my $j = decode_json($data);

use DDP; # for quick debug printing

p $j->{card}{listOfPort}{"10AN10G-1-OTU2"}{paramDetailsMap}{PortDetails}[0]{title}
"Signal Rate"

You might want to use some deep diving techniques to get at the inner values more easily/programmatically (take a look at the Data::Diver module for that) - my example is meant to show only that it is possible and a bit of the mechanics of mapping JSON into a perl hash with the excellent JSON module. The documentation has lots of useful examples.

bloodyKnuckles · Accepted Answer · 2014-07-04 00:33:54Z

0

Perl on the command line:

perl -pe 's/"name":"([^"]+)","title":/"$1":/g' file > outfile

Output (pertinent part):

{"card": ... "signalType":"Signal Rate", ... "userLabel":"Description", ... "Frequency":"Transmit Frequency" ... }

edited Jul 4, 2014 at 0:33

answered Jul 3, 2014 at 23:47

bloodyKnuckles

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1 Comment

bloodyKnuckles Over a year ago

Ah, okay. Updated response to execute with Perl on the command line.

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