Furkan has asked for the wisdom of the Perl Monks concerning the following question:

Hey Monks! I'm new here and I would like to ask you for help. So I've got a JSON File, may it be something like this: 

{
  "local": {
     "tomcat": {
          "general": {
               "catalina_home": "somewhere/tomcat/current",
               "install_dir": "somewhere/tomcat/8.5.20",
               "name": "Tomcat Web Application Server",
               "version": "1.8u131"
          }
          "instances" {
               "instance_name": {
                   "catalina_base": "somewhere/tomcat_instances/instan
+ce_name",
                   "port" {
                      "http": 18081,
                      "https": 19081
                   },
                   "unix_group": "tmcuser",
                   "unix_user": "tomcat1"
               },
               "instance_name2": {
                   "catalina_base": "somewhere/tomcat_instances/instan
+ce_name2",
                   "port" {
                      "http": 18082,
                      "https": 19082
                   },
                   "unix_group": "tmcuser",
                   "unix_user": "tomcat2",
               }
          }
     }
  }
}

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I want to read out certain information out of that JSON File and I already found out how to read informations which contains data (f.e. "catalina_base"), but I also would like to read out the instance names ("instance_name" and "instance_name2"). The way I read out the informations containing data is by for example: 
   (...)
   my $data = decode_json($json);
   my $Catalina_Base = $data->{'local'}->{'tomcat'}->{'instances'}->{'
+instance_name'}->{'catalina_base'};
   (...)

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How am I able to read out the instance name? If I try 
   (...)
   my $data = decode_json($json);
   my $Instance_Name = $data->{'local'}->{'tomcat'}->{'instances'}->{'
+instance_name'};
   (...)

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I get every single information instance_name contains like catalina_base, port etc. but I just want the name of the instance. Is there any way to do that? I would be really thankful if you could help me. Greetings Furkan

Replies are listed 'Best First'.
Re: reading special parts of a JSON File
by choroba (Cardinal) on Sep 18, 2017 at 09:29 UTC
    Use keys to get a list of keys. I had to fix the input JSON in several places (missing colons, trailing commas). 
    #! /usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

use JSON::XS;

my $json = '{
  "local": {
     "tomcat": {
          "general": {
               "catalina_home": "somewhere/tomcat/current",
               "install_dir": "somewhere/tomcat/8.5.20",
               "name": "Tomcat Web Application Server",
               "version": "1.8u131"
          },
          "instances": {
               "instance_name": {
                   "catalina_base": "somewhere/tomcat_instances/instan
+ce_name",
                   "port": {
                      "http": 18081,
                      "https": 19081
                   },
                   "unix_group": "tmcuser",
                   "unix_user": "tomcat1"
               },
               "instance_name2": {
                   "catalina_base": "somewhere/tomcat_instances/instan
+ce_name2",
                   "port": {
                      "http": 18082,
                      "https": 19082
                   },
                   "unix_group": "tmcuser",
                   "unix_user": "tomcat2"
               }
          }
     }
  }
}';

my $data = decode_json($json);
say for keys %{ $data->{local}{tomcat}{instances} };

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    ($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

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[reply]
[d/l]
[select]
Re: reading special parts of a JSON File
by Eily (Monsignor) on Sep 18, 2017 at 09:26 UTC

    Your question is a bit confusing, but from what I understand you want to use keys: 

    my $instances_hash = $data->{'local'}->{'tomcat'}->{'instances'};
my @names = keys %$instances_hash;
for my $name (@names)
{
  print "The name is $name\n";
}

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[reply]
[d/l]
      Thank you very much! Thanks to you I figured out how to solve my problem, thanks a lot!
[reply]
      I'm sorry that my question is confusing. I want to get the instance name (which is in "instance_name") and safe it into a variable for further uses. I'll try your idea, thank you!
[reply]

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