Win8 Strawberry 5.8.9.5 (32)  Wed 09/07/2022  7:13:21
C:\@Work\Perl\monks
>perl

use strict;
use warnings;

use Data::Dump qw(dd);  # for debug

my $j = <<'EOJ';
"device": [{"host_info"  :  { "engine_id":null   ,
"name": null   ,"host_group_info" :{"name":null,"remarks":null
,
    "id" : 0 } }}
  ]
EOJ
print ">>\n$j<< \n";

my $dent   = '    ';
my $n_dent = 0;

my %pretty = (
    '{' => sub { my $d = $dent x ++$n_dent;  return qq{$_[0]\n$d}; },
    '}' => sub { my $d = $dent x --$n_dent;  return qq{\n$d$_[0]}; },
    ',' => sub { my $d = $dent x   $n_dent;  return qq{$_[0]\n$d}; },
    ':' => sub { my $d = $dent x   $n_dent;  return qq{$_[0] };    },
    );

$j =~ s{ \s* ([{},:]) \s* }
       { $pretty{$1}->($1) }xmsge;
print ">>\n$j<< \n";

^Z
>>
"device": [{"host_info"  :  { "engine_id":null   ,
"name": null   ,"host_group_info" :{"name":null,"remarks":null
,
    "id" : 0 } }}
  ]
<<
>>
"device": [{
    "host_info": {
        "engine_id": null,
        "name": null,
        "host_group_info": {
            "name": null,
            "remarks": null,
            "id": 0
        }
    }
}]
<<