Let's say you are using the 'parse_json' module.

use JSON::Parse 'parse_json';

In this example, the JSON is stored in a variable named raw_json.

my $raw_json = '{"key1":"foo", "key2":true, "key3":false, "key4":null}';

The JSON is parsed into the $parsed_json variable.

my $parsed_json = parse_json($raw_json);

Dumper can be used to print the parsed json.

use Data::Dumper;
print Dumper $parsed_json;

Dumper should produce something like this.

$VAR1 = {
          'key1' => 'foo',
          'key2' => 1,
          'key3' => '',
          'key4' => undef
        };

Attempting to modify the value of key2, key3, or key4, like this . . .

$parsed_json->{key2} = "bar";

. . . will produce the following, because "true", "false", and "null" are literals, and the 'parse_json' module maps literals to read-only values.

Modification of a read-only value attempted

One option is to delete the key value pair.

delete $parsed_json->{key2};

And to then create the key with a value.

$parsed_json->{key2} = "bar";

parse_json_safe

Or, the parse_json_safe module can be used. With the 'parse_json_safe' module, "true", "false", and "null" are NOT mapped to read-only values.

use JSON::Parse 'parse_json_safe';

In this example, key2 is updated to contain a value of bar.

$parsed_json->{key2} = "bar";

Dumper should produce something like this.

$VAR1 = {
          'key1' => 'foo',
          'key2' => 'bar',
          'key3' => '',
          'key4' => undef
        };

New JSON object

Or, if you do not want to use parse_json_safe, you can create a new JSON object.

my $new_json_object = JSON::Parse->new ();

Then use the copy_literals module so that "true", "false", and "null" are NOT mapped to read-only values.

$new_json_object->copy_literals(1);

Then use the run module and store the output into the $parsed_json variable.

my $parsed_json = $new_json_object->run ($raw_json);

In this example, key2 is updated to contain a value of bar.

$parsed_json->{key2} = "bar";

Dumper should produce something like this.

$VAR1 = {
          'key1' => 'foo',
          'key2' => 'bar',
          'key3' => '',
          'key4' => undef
        };