The DATA handle can be read using: <DATA> ...the point being that it's not <_DATA_>, it's <DATA>. Then at the end of your script, it is not _DATA_ (with a single underscore on either side), it's __DATA__, with two underscores on each side. At first I thought maybe you just made a typo, but I'm seeing you do it repeatedly, so it's worth mentioning.

As for decoding the JSON first, YES. It doesn't need to be a pattern matching problem (which is almost always much more difficult than people expect) when there are perfectly good JSON parsing modules that will return a structure that you can simply traverse, iterate over, or manipulate however you wish, easily.

Here's how I would start:

use strict;
use warnings;

use JSON;
use Data::Dumper;

my $j = JSON->new;
my $structure = $j->decode( do { local $/ = undef; <DATA> } );
print Dumper $structure;

__DATA__
JSON here.....
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Then after getting a look at how my data is structured, I could plan how I want to work with it.

If JSON and JSON::XS seem to heavy for you, try JSON::Tiny, in which case: my $structure = JSON::Tiny->new->decode( ..... );

Thankyou Dave for correcting me. Appreciate it.

I tried out and your structure after decoding looks like this:

$VAR1 = {
          'eNewConnec' => 0,
          'peakConnec' => 0,
          'eCompressed' => 15164826,
          'iUncompressed' => 639536,
          'bytesSeries' => [
                             [
                               '1390795661000',
                               1179,
                               4940,
                               1016,
                               3428
                             ],
                            
                                  [
                                    '1390792141000',
                                    0,
                                    0
                                  ],
                                  [
                                    '1390792121000',
                                    0,
                                    0
                                  ],
                                  [
                                    '1390792101000',
                                    0,
                                    0
                                  ],
                                  [
                                    '1390792081000',
                                    0,
                                    0
                                  ]
                                ],
          'earliestTime' => '1390792081000',
          'eClosedConn' => 0,
          'latestTime' => '1390795661000',
          'iNewConn' => 0,
          'eUncompressed' => 23533344,
          'iCompressed' => 228561
        };
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My data is incremental so the same content with different values get appended to __DATA__ over time. I need to grep all occurances of say earliestTime from this structure and get its value in a variable.

Thankyou Davio. I could extract the data from the structure now. But how can I iterate through this structure now. Assume that this structure will have multiple occurances of latestTime. And I want to print all the occurances I use this line to get the data:

my $time = $structure->{latestTime};
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My data is incremental so the same content with different values get appended to __DATA__ over time.

I'm guessing a bit here, but it sounds like you will wind up with an Array-of-Hashes structure (see perldsc). If so, and building on davido's JSON code, try something like (untested):

my @fields = qw(latestTime eCompressed eUncompressed iCompressed iUnco
+mpressed);

for my $i (0 .. $#$structure) {
    my $hr_record = $structure->[$i];
    print qq{record $i: };
    for my $field (@fields) {
        print qq{$field is $hr_record->{$field}, };
        }
    print qq{\n};
    }
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Unless the data file you're dealing with is (or is likely to become) quite large (many megabytes), I still think just decoding to a hash would be best.

But if you're committed to regexes (and assuming the entire file content has been slurped into $content), try something like (untested):
    my @latestTimes = $content =~ m{ "latestTime \s* : \s* \K \d+ }xmsg;
if you have Perl 5.10+ (for the  \K operator) or else
    my @latestTimes = $content =~ m{ "latestTime" \s* : \s* (\d+) }xmsg;

Then just repeat for your other fields:  eCompressed eUncompressed etc.

Update: But see davido's ++reply above.