Perl JSON arrays within a parent key - arrays

Question

I have created a script to get some information from various external sources, the results should then be in json format. There is a lot of data and I push everything to an array in a loop, then print the json array after everything has been completed, an extract of that loop part of the script:
#!/usr/bin/perl
use JSON -convert_blessed_universally;
use strict;
use warnings;
my #json_arr;
my #servers = ("SERVER1", "SERVER2");
my #details = ("SERVER1,10.1.2.3,Suse Linux",
"SERVER2,10.1.2.4,Windows 10",
"SERVER3,10.1.2.5,Windows XP");
my $json = JSON->new->convert_blessed;
foreach my $server(#servers) {
foreach (#details) {
my #detail = split(',',$_);
if ($server eq $detail[0]) {
push #json_arr, {name => "$server", ip => "$detail[1]", os => "$detail[2]"};
}
}
}
my $result = $json->encode(\#json_arr);
print $result;
This gives an output of:
[
{
"name" : "SERVER1",
"ip" : "10.1.2.3",
"os" : "Suse Linux",
},
{
"name" : "SERVER2",
"ip" : "10.1.2.4",
"os" : "Widows 10"
}
]
and a screenshot:
I am however trying to do it by setting a key element instead and having the additional data as children of the device name, i.e:
{
"instance" : [
{
"SERVER1" : {
"ip" : "10.1.2.3",
"os" : "Suse Linux"
},
"SERVER2" : {
"ip" : "10.1.2.4",
"os" : "Windows 10"
}
}
]
}
So I have tried a few things, including something like the below, then pushing to array, but I am getting funny results and just not getting the desired results.
my $json = '{
"instance" : [
$server => {
ip => "$detail[0]",
os => "$detail[1]"
}
]
}';
push #json_arr, $json;

Answer 1

It only takes a small re-arrangement
use warnings;
use strict;
use feature 'say';
use Data::Dumper;
use JSON::XS;
...
my #json_ary;
foreach my $server (#servers) {
foreach (#details) {
my #detail = split /,/;
if ($server eq $detail[0]) {
#push #json_ary, {name => "$server", ip => "$detail[1]" ...
push #json_ary,
{ $server => { ip => $detail[1], os => $detail[2] } }
}
}
}
print Dumper \#json_ary;
# Encode `{ instance => \#json_ary }` for the desired output
my $json = JSON->new->convert_blessed;
my $result = $json->pretty->encode( { instance => \#json_ary } );
say $result;
A few notes
No need for quotes around variables, since they get evaluated anyway ("$detail[0]" --> $detail[0] etc)
No need for quotes around hash keys, as a syntax convenience: key => 'value' is OK (and if the value is a variable it's just key => $var). That is, as long as there are no spaces in the key name
One way to pretty-print an existing JSON string:
print JSON::XS->new->ascii->pretty->encode(decode_json $json_str);
There may be a question of whether a hashref around each server entry (JSON objects) is needed or not; the above was confirmed in a comment after a discussion so I settled with it.
But if the output only needs a hashref with entries for servers in the array (and not an array of hashrefs for each server) then the code in the question can be modified to
my %server_details;
foreach my $server (#servers) {
foreach (#details) {
my #detail = split /,/;
if ($server eq $detail[0]) {
$server_details{$server} = { ip => $detail[1], os => $detail[2] }
}
}
}
Now this hash has details for all servers, and can be encoded with the key instance. Then it is not clear to me what the overall structure should be; one option is
my $result = JSON->pretty->encode( { instance => [ \%server_details ] } );
This would be suitable if there is more data in reality. If not then there may not be any need for an arrayref, but encode the usual
{ instance => \%server_details }

Answer 2

The problem is that you are adding hashes to an array (push #json_arr, ...) when you mean to add to a hash ($instance{ $server_name } = ...).
my %servers = map { $_ => 1 } #servers;
my %instance;
for ( #details ) {
my ( $name, $ip, $os ) = split /,/;
next if !$servers{ $name };
$instance{ $name } = {
ip => $ip,
os => $os,
};
}
my #instances = \%instance;
my $data = { instance => \#instances };
Or using map:
my %servers = map { $_ => 1 } #servers;
my %instance = (
map { $_->[0] => { ip => $_->[1], os => $_->[2] } }
grep $servers{ $_->[0] },
map [ split /,/ ],
#details
);
my #instances = \%instance;
my $data = { instance => \#instances };
This produces the following, as requested:
{
"instance" : [
{
"SERVER1" : {
"ip" : "10.1.2.3",
"os" : "Suse Linux"
},
"SERVER2" : {
"ip" : "10.1.2.4",
"os" : "Windows 10"
}
}
]
}
(This is different than zdim's first solution.)
Note that I got rid of the nested loops because they are nasty. For a few items, it's not a problem. But performance would suffer is #servers or #details would become large. So it's a bad idea, and a bad habit to get into.
Having an array which only even has a single element is weird. Did you perhaps want
{
"instance" : {
"SERVER1" : {
"ip" : "10.1.2.3",
"os" : "Suse Linux"
},
"SERVER2" : {
"ip" : "10.1.2.4",
"os" : "Windows 10"
}
}
}
This would be achieved by replacing
my $data = { instance => \#instances };
with
my $data = { instance => \%instance };